Tesi sul tema "Acid mine drainage"

Integrons are a two-part gene capture and expression system found in a wide diversity of bacterial lineages. The Integron is implicated in the spread and development of multiple-antibiotic resistance in clinical and animal production environments. In addition to their importance to human health, Integrons are a particularly suitable model for how bacteria adapt to selective pressure, as they combine an ability to collect and express genes of complementary function with the potential to participate in HGT. In this study, integrons are used as a model to examine how bacteria respond to selective pressures, other than those found in a clinical context. A series of locations along a river system that are contaminated with differential levels of heavy metals was selected as a study site. Investigations into the structure of the bacterial community at the sites, and the incidence and diversity of integrons within the populations were performed.

The waste products acid mine drainage formed during coal mining and fly ash from coal burning power generation, pose substantial environmental and economic problems for South Africa. Eskom has developed a remediation system employing alkaline fly ash to neutralize and precipitate heavy metals from toxic acidic acid mine drainage streams. The aim of this study was to assess the microbial diversity in and microbial impact on this remediation system.

Thesis (M.S.)--West Virginia University, 1999.
Title from document title page. Document formatted into pages; contains ix, 130 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 128-130).

This research focuses on the removal of Fe, Cu, Zn and Mn from synthetic metal solutions and real AMD from Wheal Jane mine using natural zeolite. Laboratory experiments were performed to investigate the effectiveness of natural zeolite as a potential low cost material for the removal of these heavy metals from AMD. These include, equilibrium tests, batch kinetic studies, column studies and desorption studies. Equilibrium studies showed that the capacity of natural zeolite for heavy metals increased with an increase in initial solution pH. Fitting of the Langmuir and Freundlich isotherms to experimental data gave good fits, R\(^2\) values ranging from 0.9 – 0.99. The selectivity series of natural zeolite was: Fe\(^{3+}\)>Zn\(^{2+}\)>Cu\(^{2+}\)>Mn\(^{2+}\). The amount of exchangeable cations increased at equilibrium, indicating that ion exchange had taken place. Higher metal uptakes were achieved by increasing agitation speed, initial solution pH, particle size reduction, and thermal pre-treatment. The rate limiting step for this process was intraparticle diffusion. Column studies showed that natural zeolite was capable of removing heavy metals from a continuously flowing solution. The breakthrough time increased with a longer bed height and slower flow rate. The bed depth service time model (BDST) was used to simulate experimental data and deviated from these by 12 – 14%. The treatment of actual Wheal Jane mine AMD showed that about 71-99% Fe and 97-99% Cu were removed from solution. Results from the treatment of actual AMD revealed that natural zeolite was best suited for treating dilute metal solutions, and hence should be used downstream of other AMD treatment technologies.

The treatment of acid mine drainage (AMD) by sulfate-reducing bacteria (SRB) has been reported in the literature as a possible alternative to chemical treatment. The overall objective of this study was to implement such a treatment process at the mine site and specifically within the open mine pit itself. The first step of this study was to characterize process parameters. To accomplish this, a reactor was designed and built to simulate hydrodynamic conditions found in the mine pit. This reactor contained a 6$ sp{ prime prime}$ deep gravel bed in which a mixed population of SRB was inoculated. The operation of this reactor demonstrated that treatment of a continuous flow of AMD by SRB was possible, however, the response to changes in the composition of the AMD and to flow conditions was limited. The results indicated that further studies should be directed at the gravel bed itself since this was where the SRB are located and is the active site within the system.
The role of various physical parameters of a gravel bed in the biological treatment of AMD by SRB was examined. This was accomplished by using gravel of different sizes (0.25$ sp{ prime prime}$ vs. 0.5$ sp{ prime prime})$ and composition (granite vs limestone) to form 12$ sp{ prime prime}$ beds in a series of column reactors. The difference in size results in variations in the total surface area, the void volume and various volume ratios within the system. The effect of potential geological buffering by limestone was examined by using and comparing with beds composed of granite.
The gravel beds were inoculated with a mixed culture of SRB and overlaid with 6 L of AMD. After the SRB were established, a series of experiments were performed in which 16.7%, 25%, 75% and 100% of the water column was replaced with an equivalent quantity of fresh AMD. Changes in pH, ORP, electric conductivity, and concentrations of metal and sulfate were monitored for at least 28 days. Sulfate and metal removal at days 7 and 28 of each experiment were compared. The SRB can tolerate a wide range of disturbances, however, an increase in the load of fresh AMD decreased the performance of the system. The results indicated that the total surface area is of greater importance than the void volume in the overall treatment process by SRB.
A dimensionless number was constructed to describe the relationships between the physical parameters of the gravel bed. A plot of the proportion of sulfate removed and this dimensionless number could provide essential information for the sizing of a gravel bed for the purposes of sulfate reduction. This was done for each type of gravel and comparison of the two curves indicated that there was no significant difference between the two gravels.
The importance of the physical substrate for the SRB has been reported in the literature. However, no known attempt has been made to quantify the relationships between the physical parameters and the biological activity. Such information would be useful for the sizing of wetlands and other passive treatment system that uses SRB activity for the purposes of treating AMD. This study is a step towards filling this void.

Thesis (Ph. D.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains ix, 112 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 56-57).

Thesis (Ph. D.)--Ohio State University, 2004.
Title from first page of PDF file. Document formatted into pages; contains xiii, 123 p. : ill. (some col.). Advisor: Jerry M. Bigham, Soil Science. Includes bibliographical references (p. 113-123).

Acid mine drainage (AMD) at Stockton Coal Mine, located near Westport, New Zealand, is generated from the oxidation of pyrite within sedimentary overburden exposed during surface mining. The pyrite oxidation releases significant acidity, Fe, and sulphate together with trace metals to the receiving environment. Aluminium is also elevated in drainage waters due to acid leaching from overburden materials. Thirteen AMD seeps emanating from waste rock dumps, and associated sediment ponds were monitored at Stockton Coal Mine to characterise water chemistry, delineate their spatial and temporal variability, and quantify metal loads. Dissolved metal concentrations ranged from 0.05-1430 mg/L Fe, 0.200-627 mg/L Al, 0.0024-0.594 mg/L Cu, 0.0052-4.21 mg/L Ni, 0.019- 18.8 mg/L Zn, <0.00005-0.0232 mg/L Cd, 0.0007-0.0028 mg/L Pb, <0.001-0.154 mg/L As and 0.103- 29.3 mg/L Mn and the pH ranged from 2.04-4.31. Currently this AMD is treated further downstream by a number of water treatment plants employing a combination of ultra fine limestone and calcium hydroxide; however, in the interest of assessing more cost-effective technologies, passive treatment systems were investigated for their treatment and hydraulic efficacy and as potential cost-effective options. Biogeochemical reactors (BGCRs) were selected as the most appropriate passive treatment system for ameliorating AMD at Stockton Coal Mine. Results of mesocosm-scale treatability tests showed that BGCRs incorporating mussel shells, Pinus radiata bark, wood fragments (post peel), and compost increased pH to ≥6.7 and sequestered ≥98.2% of the metal load from the Manchester Seep located within the Mangatini Stream catchment. The following design criteria were recommended for BGCRs incorporating 20-30 vol. % mussel shells as an alkalinity amendment: 1) 0.3 mol sulphate /m3 substrate/day for sulphate removal (mean of 94.1% removal (range of 87.6-98.0%)); 2) 0.4 mol metals/m3/day for metal (mean of 99.0% removal (range of 98.5-99.9%)) and partial sulphate (mean of 46.0% removal (range of 39.6-57.8%)) removal; and 3) 0.8 mol metals/m3/day for metal (mean of 98.4% removal (range of 98.2-98.6%) and minimal sulphate (mean of 16.6% removal (range of 11.9- 19.2%)) removal. At the maximum recommended loading rate of 0.8 mol total metals/m3/day an average of 20.0 kg/day (7.30 tonnes/year) of metals and 85.2 kg acidity as CaCO3/day could be removed from the Manchester Seep AMD by employing BGCRs. The design hydraulic residence time (HRT) would be 3.64 days. On an acidity areal loading basis, a design criterion of 65 g/m2/day was recommended. Tracer studies conducted on the BGCRs indicated ideal flow characteristics for cylindrical drumshaped reactors and non-ideal flow conditions for trapezoidal-shaped reactors indicative of shortcircuiting, channelised flow paths and internal recirculation. Consequently, this resulted in compromised treatment performance in the trapezoidal-shaped reactors. The relaxed tanks in series (TIS) model could be successfully applied to model the treatment performance of drum-shaped reactors; however, the model was unsuccessful for trapezoidal-shaped reactors. Because most pilot and full-scaled vertical flow wetlands (VFWs) have consisted of trapezoidal-prism basins excavated into the ground, the rate-removal methods previously recommended (e.g. mol metals/m3/day) should be applied to BGCR design, evaluation and operation rather than results of hydraulic and reactor modelling. Overall, a staged passive treatment approach is recommended. The first stage should consist of a sedimentation basin to remove sediment, the second stage a BGCR to remove acidity and metals and the third an aerobic wetland to provide oxygenation and tertiary treatment of metals (primarily Fe) from BGCR effluent. Preliminary analysis indicates that BGCRs are potentially a more cost-effective means of treating AMD at Stockton Coal Mine compared with the current active lime-dosing plant by over $125/tonne of acidity ($197/tonne for BGCRs versus $324/tonne for lime dosing (60% efficient)); however, their successful implementation would need to recognise current treatment goals, required areal footprint and inherent maintenance requirements.

The sorption of heavy metals from Acid Mine Drainage (AMD) by using clinoptilolite, a natural zeolite, was studied in this thesis. The behavior of clinoptilolite, as an ion exchanger, was studied to see if the concentration of iron, copper, zinc, and manganese could be reduced to acceptable environmental standards. Folldal works, Løkken works, and Røros copper works were the mines investigated during this study. However, experiments were conducted on the AMD from Folldal and Løkken works. From the kinetic experiments, the percent adsorption and distribution ratio (Kd) were determined as a function of heavy metal concentration. The percent adsorption showed that the ion exchange process followed three stages; (1) surface exchange with a high adsorption rate, (2) the inversion stage, and (3) moderate adsorption. Higher concentrations of clinoptilolite had a better treatment effect on iron, copper and zinc. The results also indicated competition between iron and manganese, where iron ions occupied the adsorption sites of manganese ions when all the surface sites are taken. The amount of manganese, unlike the other metals, increased with time during the experiment. The distribution ratio showed different results for each metal. In general for iron, copper, and zinc there was an increase in the distribution ratio as the heavy metal concentration decreased. This indicated that all the metals were to some extent exchanged with the cations of the clinoptilolite. The AMD from both areas contained large concentrations of total organic carbon (TOC), and it is assumed that fouling of the clinoptilolite could occur. Equilibrium isotherms were determined and the results showed that neither the Langmuir nor the Freundlich isotherm have a good fit to the experimental data. The results showed that the adsorption capacity of clinoptilolite decreased as a result of surface coverage, and the selectivity sequence was determined to be Fe3+ > Cu2+ > Zn2+ > Mn2+ for both Folldal and Løkken. Ion exchange with clinoptilolite reduced the amount of heavy metals from the AMD, although the final concentrations were considerably higher than the set requirement of 10 µg Cu/L. Precipitation as an initial step before ion exchange was therefore tested. The results showed a better removal of iron, copper and zinc with 99.6, 97.3, and 37.7 % from Folldal, and 98.3, 98.7, and 59.9 % from Løkken, respectively. Even though the use of precipitation gave much better results, the final concentrations of the heavy metals were still above the acceptable environmental standard.

1. В. Бузило, А. Павличенко, С. Кулина, В. Кіященко. Шляхи забезпечення екологічної безпеки при ліквідації вуглевидобувних підприємств. Розробка родовищ. 2013. С. 437-440. 2. Costa M.-C., Duarte J.-C. Bioremediation of acid mine drainage using acidic soil and organic wastes for promoting sulphate-reducing bacteria activity on a column reactor. Water, Air, and Soil Pollution. 2005. Vol. 165. P. 325-345. 3. Bhupinder D. Biotechnological Tools for Remediation of Acid Mine Drainage. Bio-Geotechnologies for Mine Site Rehabilitation / eds. MNV Prasad Paulo Jorge de Campos Favas Subodh Kumar Maiti. Elsevier. 2018. 730 p. 4. Ford K.L. Passive treatment systems for acid mine drainage. U.S. Bureau of Land Management Papers. 2003. 19 p.
As a result of restructuring in 1990-2000 and occupation in 2014 the coal-rich Donetsk Basin saw massive mine closures. Leaving behind acid mine drainage, dam failures, non-remediated areas and cases of direct discharges into waterways that could lead to serious and long-term environmental impacts. The elimination of mines leads to changes in natural conditions for the living organisms and the formation of unfavorable environmental situations, such as. Acidic mine drainage occurs naturally in some environments as part of rock weathering, but is enhanced by large-scale soil disturbances common in mining. Acid mine drainage neutralization depends on its chemistry, electron donors / receptors, temperature, and pH. Iron-reducing bacteria and sulfate-reducing bacteria form the root component of these bioreactors. Acidophilic heterotrophic bacteria promote the oxidation of ferrous to ferric iron in acidic waters.
В результаті реструктуризації в 1990-2000 рр. та окупації в 2014 р. багатого вугіллям Донецький басейн побачив масове закриття шахт. Залишаючи за собою дренаж кислотних шахт, аварії дамб, не відновлювані ділянки та випадки прямих скидів у водні шляхи, які можуть призвести до серйозних і довгострокових впливів на навколишнє середовище. Ліквідація шахт призводить до змін природних умов для живих організмів та формування несприятливих екологічних ситуацій. Кислотний дренаж шахт природним чином відбувається в деяких середовищах як частина вивітрювання гірських порід, але посилюється широкомасштабними ґрунтовими порушеннями, характерними для гірничодобувних робіт. Нейтралізація дренажу кислотних шахт залежить від його хімії, донорів / акцепторів електронів, температури та рН. Основним компонентом цих біореакторів є залізоредукуючі бактерії та сульфатредукуючі бактерії. Ацидофільні гетеротрофні бактерії сприяють окисленню заліза(ІІ) до заліза(ІІІ) в кислих водах.

Environmental art: Art relating to the individual’s response, understanding and interest towards the land, including art forms such as Land/Earth art as well as more sensitive art forms such as Eco-art, focussed more on the earth’s natural processes. Exploitation: The exploitation of mineral resources is closely associated with progress and success, but also that of benefiting from something at the cost of something else, in this case exploiting gold at the cost of the ecology of the natural environment. Gold mining industry: The labour-intensive activity of removing gold from ore, mined from deep within the earth’s crust through a system of shafts and stopes. Installation art: Refers to what is contested as being a medium or process of art, whereby three-dimensional works are designed to influence the perception of a space, often site-specific, within an enclosed space or the outside environment, temporary or permanent. The found object or existing object is often used in installation art for its intellectual value. Inter-and-trans-disciplinary approach: The utilisation and collaboration of different disciplines as a means to find a solution to a (environmental) problem. Landscape: A cultural construct, referring not to physical topography, but to an aesthetically processed vision of the environment, mostly arranged and framed by an artist. Post-industrial environment: Referring to an environment, man-made or natural in a state preceded by industry. Often these environments are characterised as polluted and derelicts sites left behind by large mining industries. The gold-mining industry on the Witwatersrand, is characterised by massive tailings dumps and slimes dams. Resource curse: A term coined by artist Jeannette Unite, describing the phenomenon of extreme poverty co-existing with valuable minerals in the same region, especially prevalent in Africa. Technospasm: A term conceptualised by archeo-metallurgist Duncan Miller, as the unsustainable rate of non-renewable mineral resources extraction. South Africa is known to the world for its vast deposits of valuable minerals, of which gold has played a seminal role in the development of the country’s economy. What is left after more than 120 years of mining for this precious metal is a landscape, better described as a derelict post-industrial environment, characterised by pollution and impoverished communities. Environmental degradation caused by mining industries is not unique to the African continent, but is a worldwide phenomenon. Due to the rapid deterioration of environments caused by mining and industry, new environmentalist attitudes became prevalent by the 1970s in the West, seeking change in attitudes towards the land. Along with earth activists, artists also started to question humankind’s destructive relationship towards the land. Apart from the early developments of Land/Earth art during the 1960s, artists have taken on roles of activists, interventionists and collaborators of multi- and interdisciplinary projects since then, in order to remediate and re-cultivate post-industrial sites. Environmental artists find value in what art holistically contributes to society, as opposed to the commodity value of art. While artists in the West significantly progressed in environmentally orientated art, South African artists focused more on responding to the socio-economic conditions induced by the long-standing Apartheid era. Few South African artists have attempted to engage in environmentally-concerned art, especially related to the mining industry. However, Western attitudes towards the land can be derived from South Africa’s landscape depictions since its colonisation by Europeans up to contemporary versions of the South African landscape environment today. This study provides a historic overview of South Africa’s aesthetic relationship with the mining landscape, specifically of the post-industrial sites situated in the Witwatersrand. The aim is to determine the South African artists’ contribution towards developing an environmental awareness, and to call for more artists to take part in visual art forms concerning the disruption of the environment, caused by the mining industry. The study determines the relevance of art as a means to raise environmental issues and whether art may be utilised for post-industrial remediation projects. International examples of Reclamation art projects and its incorporation of science are investigated to find solutions towards contaminated post-industrial sites. These examples are compared to the work of a small number of South African artists who have attempted to engage in the post-industrial mining environment through Earthworks and science The researcher’s own work is discussed to raise awareness of the adverse effects of Acid Mine Drainage (AMD) caused by the gold-mining industry in the Witwatersrand. A body of installation art produced for this degree was displayed in a gallery space, which presented a platform for audience engagement. Through this body of work and through the examples discussed in this dissertation, the researcher urges South African artists to take up the task of moral responsibility towards the environment for the survival of future generations of life on earth.
Dissertation (MA)--University of Pretoria, 2012.
Visual Arts
unrestricted

Thesis (M.S.)--West Virginia University, 2000.
Title from document title page. Document formatted into pages; contains vii, 38 p. : ill. Includes abstract. Includes bibliographical references (p. 29-30).

This thesis has assessed the viability of using Bayer precipitates, formed by the seawater neutralization of Bayer liquor residues, as an alternative neutralization reagent to treat acid mine drainage (AMD) water. Bayer precipitates were found to out-performed commercially used alkali in the removal of heavy metals and as a pH neutralizing reagent for AMD waters. The robustness and versatility of Bayer precipitates for the treatment of different AMD waters makes them an attractive alternative to commercial materials, especially as they have the potential to reduce the footprint of both mining industries.

Acid Mine Drainage (AMD) is characterized by high metal concentrations and an extremely low pH, primarily generated by the microbial oxidation of iron sulfides from mine tailings. Research on the microbial AMD community has largely focused on Bacteria, while little information is known about the Archaeal and Eukaryote members or the seasonal patterns within the communities. Here I examined the Bacterial, Archaeal, and eukaryotic AMD seasonal microbial community, using direct sequencing techniques on AMD samples from the Copper Cliff Tailings AMD site in Sudbury, Ontario, Canada. I found large variation in the community profile and species composition between sampling times of both the Bacterial and Eukaryote communities, suggesting a dynamic community, both between and within seasons. Bacterial diversity was highest during the winter, with Acidithiobacillus dominating, while during the summer, Acidiphilium was the dominant genus. The winter Eukaryote community was dominated by classes of algae and fungi, while the majority of summer sequencing could not be classified to the class level. Few reads were obtained for the Archaeal domain, with low and similar biodiversity between seasons. Overall, the AMD community variation and abundance were found to largely correlate with drainage water and seasonal temperature.

[Truncated abstract] The influence of environmental conditions and properties of pyritic shale in the mining waste from Mt. Whaleback in Western Australia, in particular the inclusions and encapsulation of pyrite on the oxidation of pyritic shale and its subsequent acid mine drainage, was studied by employing an isothermal batch reactor system and QEMSCAN technique. The experimental technique was validated by comparing the experimental results obtained in this study with the literature data. It was found that the presence of water significantly accelerates the rate of shale oxidation. Weathering of the shale samples was found to influence the O2 consumption rate. It was also found that shale properties have a major effect on the oxidation rate and thereby affect the acid generation. Static test methods (Sobek and Lawrence) were employed to test the Neutralisation Potential (NP) of more than 100 actual and composite samples including pyritic shale samples, rock samples, mineral samples, various pyrite-mineral, pyrite-shale, and pseudo-shale blends. The influence of sample properties (bulk elemental composition, and mineralogy), test technique (Sobek and Lawrence) and associated variables (acid strength and volume) on the acid neutralisation potential of the samples was studied. It was found that the Sobek method produced consistently higher NP results under comparable acid conditions to those obtained with the Lawrence method. The theoretical NP values of individual minerals were calculated based on the mineral composition combined with the acid neutralising equations and ideal chemical formula. ... To experimentally model the major mineral phases, 11 minerals were used to produce pyrite-mineral blends and pseudo-shales, whose compositions mimic those of the actual shales studied. Mineral blends were employed to evaluate and contrast their individual acid generation or neutralisation behaviour with binary and higher order interactions. Blends of pyrite with some selected shales were also employed in this study. It was found that interactions can occur between the multiple mineral components which can enhance the rate of acid generation beyond that of the individual behaviour. It was found that the products from the pre-oxidation of shales, the properties and morphology of a sample such as the surface area, encapsulation, the mineralogy and pH all play a significant role in the acid generation and neutralisation rates. However, the absolute rate of acid generation appears to be most sensitive to the components such as Fe3+, which contribute to its reaction mechanisms. This investigation has provided a scientific insight into the acid generation and neutralisation behaviour of pyritic shale in relation to its mineralogy. It was found that the relative instantaneous rates of acid generation and consumption for individual minerals can be significantly different to that of their total potentials for acid generation and neutralisation. The significantly different behaviour of the actual and pseudo shales suggests that at low pH, there may be other mechanisms underlying the net capacity and rates of shales to generate or consume acid than bulk mineralogy. These findings have significant implications to the mining industry operating in reactive grounds.

Rare earth elements (REE) are known as the lanthanide series (La-Lu) plus yttrium (Y) and scandium (Sc). REE are essential materials for modern industries and especially for green technologies (wind turbines, batteries, lasers, catalysts, etc.). However, despite their high global demand, their supply is limited such that the EU has cataloged it as critical raw materials. In order to ensure the supply of REE in the future, the search for alternative sources of these elements worldwide has been promoted in recent years. Acid mine drainage (AMD) produced by the Fe-sulphide weathering can effectively leach Fe, Al, SO4, and REE from the host rock. This can lead to high concentrations of these liberated species in the affected waters. Thus, the REE concentrations in AMD can be between two and three orders of magnitude higher than natural waters, as such it can be considered as a complementary source of REE recovery. The increase of pH in AMD by mixing neutral waters results in the precipitation of iron oxy-hydroxysulfate (schwertmannite) from pH 3-3.5, and aluminum (basaluminite) from pH 4-4.5 in the river channels. This process may be accompanied by REE scavenging. Due to its acidity and high metal load, acid mine drainage presents a major environmental problem worldwide, therefore, different treatment systems have been developed to minimize its impact. Disperse Alkaline Substrate (DAS) passive remediation system neutralizes AMD by dissolving calcite, and allowing the sequential precipitation of schwertmannite and basaluminite in separated layers, where REE are preferably retained in the basaluminite-enriched waste. Despite this, there are still no studies describing the adsorption of REE on both basaluminite and schwertmannite in these environments. The REE scavenging mechanism is studied by adsorption on synthetic minerals of basaluminite and schwertmannite as a result of variation to the both the pH and sulfate concentration. A thermodynamic adsorption model is proposed based on experimental results in order to predict and explain the REE mobility in AMD mixtures with neutral waters and in a passive treatment system. Basaluminite and schwertmannite have a nanocrystalline character. Further, schwertmannite has been observed to transform into goethite on weekly timescales, resulting in sulfate release. However, there is a gap of knowledge about basaluminite stability at variable sulfate concentration and pH and its possible transformation to other more crystalline Al-minerals. In this study, basaluminite local order at different pH values and dissolved sulfate concentrations was characterized. Results demonstrate that basaluminite can transform to nanoboehmite in weeks under circumneutral pH. However, the presence of sulfate can inhibit this transformation. Separate adsorption experiments on both basaluminite and schwertmannite were performed with two different concentrations of SO4 while varying the pH (3-7). Results show that the adsorption is strongly dependent on pH, and to a lesser extent on sulfate concentration. Lanthanide and yttrium adsorption is most effective near pH 5 and higher, while that of scandium begins around pH 4. Due to the high concentrations of sulfate in acidic waters, the predominant aqueous REE species are sulfate complexes (MSO4+). Notably, Sc(OH)2+ represents a significant proportion of aqueous Sc. , A surface complexation model is proposed in which predominant aqueous species (Mz+) adsorb on the mineral surface, XOH, following the reaction: The adsorption of the lanthanides and yttrium occurs through the exchange of one and two protons from the basaluminite and schwertmannite surface, respectively, with the aqueous sulfate complexes. The sorbed species form monodentate surface complexes with the aluminum mineral and bidentate with the iron mineral. In the case of Sc, the aqueous species ScSO4+ and Sc(OH)2+ form bidentate surface complexes with both minerals. EXAFS analysis of the YSO4+ complex adsorbed on the basaluminite surface suggests the formation of a monodentate inner sphere complex, in agreement with the proposed thermodynamic model. Once the surface complexation model was validated, it was used to asses and predict the REE mobility in passive remediation systems and acidic water mixing zones with alkaline inputs from the field. The REE are preferentially retained in basaluminite-rich waste during passive remediation due to its sorption capacity between pH 5-6. In contrast, schwertmannite waste contains very little REE because the formation of this mineral occurs at pH lower than 4, which prevents REE adsorption. Further, Sc may be scavenged during schwertmannite precipitation as a result of this low pH The model correctly predicts the absence of REE in schwertmannite precipitates and the enrichment of the heavy and intermediate REE with respect to the light REE in basaluminite precipitates collected in the water mixing zones. However, there is a systematic overestimation of the fractionation of rare earths in basaluminite precipitate. This inaccuracy is mainly due to the fact that the mineral precipitation and adsorption are not synchronous process, while basaluminite precipitates from pH 4, REE adsorption occurs at higher pH values, between 5 and 7, when the water mixture reaches these values and a fraction of the particles have been dispersed.
Las tierras raras (en inglés rare earth elements, REE) son conocidas como el conjunto de la serie de los lantánidos (La-Lu), itrio (Y) y escandio(Sc). Las tierras raras son materiales indispensables para las industrias modernas y en especial para las tecnologías verdes (aerogeneradores, baterías, láseres, catalizadores, etc.). Sin embargo a pesar de su gran demanda mundial, su abastecimiento es limitado, por lo que han sido catalogadas por la UE como materias primas críticas (Critical Raw Materials). Con el objetivo de asegurar el abastecimiento de REE en el futuro, en los últimos años se ha promovido la búsqueda de fuentes alternativas de estos elementos en todo el mundo. El drenaje ácido de mina (en inglés acid mine drainage, AMD) producido por la meteorización de sulfuros de Fe, tiene un alto poder de lixiviación de las rocas, por lo que las aguas afectadas adquieren elevadas concentraciones en disolución de Fe, Al, SO4 y otros metales, como las REE. Así, las concentraciones de REE en AMD son entre dos y tres órdenes de magnitud superiores al resto de las aguas naturales y pueden suponer una fuente complementaria de recuperación de REE. El aumento de pH del AMD por mezcla con aguas neutras da lugar a la precipitación en los cauces de los ríos de oxy-hidroxisulfatos de hierro (schwertmannita), a partir de pH 3-3.5, y de aluminio (basaluminita), a partir de pH 4-4.5; acompañado de la eliminación de las tierras raras. Debido a su acidez y carga metálica, el drenaje ácido de mina presenta un problema medioambiental de primera magnitud, por lo que se han desarrollado diferentes sistemas de tratamiento para minimizar su impacto. El sistema de tratamiento pasivo Disperse Alkaline Substrate (DAS) produce la neutralización de las aguas ácidas por la disolución de la calcita presente en el sistema, permitiendo la precipitación secuencial, de schwertmannita y basaluminita. Las tierras raras quedan retenidas preferentemente en el residuo enriquecido en basaluminita. A pesar de ello, aún no existen estudios que describan la adsorción de tierras raras tanto en basaluminita como schwertmannita en estos ambientes. En esta tesis se estudia el mecanismo de retención de las tierras raras mediante adsorción en minerales sintéticos de basaluminita y schwertmannita, en función del pH y del contenido de sulfato disuelto. Con los resultados experimentales obtenidos, se propone un modelo termodinámico de adsorción para predecir y explicar la movilidad de las tierras raras observada en mezclas de AMD con aguas neutras y en un sistema de tratamiento pasivo. La basaluminita y la schwertmannita presentan un carácter nanocristalino. Es conocido que la schwertmannita se transforma en goethita en semanas, liberando sulfato. Sin embargo, nada se sabe de la basaluminita y su posible transformación a otros minerales de Al más cristalinos. De este modo, la caracterización del orden local de la basaluminita a diferentes valores de pH y sulfato se expone en primer lugar. Dependiendo del pH y el sulfato en disolución, la basaluminita se transforma en diferentes grados a nanoboehmita en semanas, pero tiende a estabilizarse con la presencia de sulfato en solución. Los experimentos de adsorción en basaluminita y schwertmannita con diferentes concentraciones de SO4 realizados para cada mineral y en rangos de 3-7 de pH han demostrado que la adsorción es fuertemente dependiente del pH, y en menor medida del sulfato. La adsorción de los lantánidos y del itrio es efectiva a pH 5, mientras que la del escandio comienza a pH 4. Debido a las altas concentraciones de sulfato en aguas ácidas, las especies acuosas predominantes de las tierras raras son los complejos con sulfato, MSO4+. Además del complejo sulfato, el Sc presenta importantes proporciones de Sc(OH)2+ en solución. En función de la dependencia del pH y de la importancia de la especiación acuosa, se propone un modelo de complejación superficial donde la especie acuosa predominante (Mz+) se adsorbe a la superficie libre el mineral, XOH, cumpliendo la siguiente reacción: La adsorción de los lantánidos y del itrio se produce a través del intercambio de uno o dos protones de la superficie de la basaluminita o de la schwertmannita, respectivamente, con los complejos sulfato acuoso, formando complejos superficiales monodentados con el mineral de aluminio y bidentados con el de hierro. En el caso del Sc, las especies acuosas ScSO4+ y Sc(OH)2+ forman complejos superficiales bidentados con ambos minerales. Complementando el modelo propuesto, el análisis de EXAFS del complejo YSO4+ adsorbido en la superficie basaluminita sugiere la formación de un complejo monodentado de esfera interna, coincidiendo con el modelo termodinámico propuesto. El modelo de complejación superficial, una vez validado, ha permitido evaluar y predecir la movilidad de REE en los sistemas de tratamiento pasivos y en zonas de mezcla de aguas ácidas con aportes alcalinos estudiados en el campo. La preferente retención de las tierras raras en la zona de la basaluminita precipitada en los sistemas de tratamiento pasivo ocurre por adsorción de las mismas a pH entre 5-6. La ausencia de tierras raras en la zona de schwertmannita se debe al bajo pH de su formación, inferior a 4, que impide la adsorción de las mismas. Sin embargo, debido a su menor pH de adsorción, una fracción de Sc puede quedar retenida en la schwertmannita. El modelo también predice correctamente la ausencia de REE en los precipitados de schwertmannita y el enriquecimiento de las tierras raras pesadas e intermedias respecto a las ligeras en los precipitados de basaluminita recogidos en el campo en las zonas de mezcla de aguas. Sin embargo, se ha observado una sistemática sobreestimación del fraccionamiento de las tierras raras en los precipitados de basaluminita. Este hecho se debe principalmente a que la precipitación del mineral no ocurre de forma síncrona con la adsorción, precipitando la basaluminita a partir de pH 4 y adsorbiendo tierras raras a pH más altos, entre 5 y 7, cuando las partículas sólidas han sido parcialmente dispersadas.

Addition of alkalinity to acid mine drainage (AMD) results in the neutralisation of acidity and precipitation of dissolved metals as insoluble hydroxides. Two aspects of the current AMD treatment practice at the Stockton Mine could be enhanced. Firstly, residual water quality may be poor due to unreacted alkalinity reagents, particularly CaCO3, resulting in poor water clarity and elevated suspended solids (SS). Secondly, neutralisation to circum-neutral pH may not avoid the discharge of residual metals (Ni and Zn) due to incomplete adsorption and hydroxide precipitation. The aim of this project was to enhance the conventional neutralisation of AMD through addition of humic substances (HS) to reduce residual SS and trace metal concentrations. Humic substances are organically derived and have a high molecular weight. Functional groups on the surface of HS are capable of binding dissolved metals, forming HS-metal complexes. Incorporation of HS complexed metals into settling floc could result in increased metal removal from the dissolved phase. Modified jar testing was used to investigate the effects of HS addition before, after and during (pH 4.5) neutralisation of AMD in two treatment scenarios at the Stockton Mine; the Blackwater Treatment Plant (BTP) using NaOH and Ca(OH)2 and the Mangatini Stream-sump System (MSS) using CaCO3. Supernatant samples collected during the sedimentation period were analysed for basic water quality parameters (turbidity and suspended solids) and dissolved (< 0.45 µm) metal concentrations. The addition of HS to the BTP process before (pH 2.8) and during (pH 4.5) neutralisation resulted in HS precipitation. Precipitated HS subsequently acted as a nucleation site, triggering flocculation of precipitating metal hydroxides, resulting in low turbidity and suspended solids (SS) of less than 2 NTU and 5 mg/L, respectively. The addition of HS after neutralisation (pH 7) did not result in HS precipitation. Intermolecular bridging of HS by the divalent Ca resulted in incorporation of HS into floc when neutralised by Ca(OH)2, resulting in low turbidity and SS. However, in NaOH neutralised conditions, the monovalent Na was unable to bridge HS molecules, resulting in HS remaining dissolved and contributing to elevated turbidity and SS of up to 24.4 NTU and 18.4, respectively. The neutralisation efficiency of CaCO3 is relatively low, thus approximately 1000 mg/L CaCO3 remained unreacted in MSS scenarios, resulting in elevated turbidity and SS. When added after neutralisation, dissolved Solid Energy Humic Acid (SEHA) facilitated flocculation of residual CaCO3 SS, resulting in an up to 75% lower suspended solids than CaCO3 neutralisation alone conditions. Although the results are good, the efficiency of SEHA as a polymer compared unfavorably in a cost: benefit analysis to two commercially available polymers for the removal of residual CaCO3. Neutralisation of AMD in control samples resulted in decreased concentrations of the target metal group (Ni, Zn, Cu, Cd, and Pb) by hydroxide precipitation, co-precipitation, and adsorption. Equilibrium speciation modeling showed that the HS-metal binding affinity controlled the effectiveness of HS addition for metal removal. The low HS complexation affinity of Ni and Zn resulted in no additional metal removal by HS dosing. The removal of Cu was enhanced by over 50% for SEHA 20 during-neutralisation conditions neutralised by both NaOH and Ca(OH)2. Up to 80% lower Cd concentrations were observed for all HS dose conditions when neutralised by Ca(OH)2. Data for CaCO3 HS dosed metal removal was statistically indeterminate. The high detection limit for Pb made any HS dosed removal enhancement difficult to identify, which was unfortunate as Pb has a high HS complexation affinity (Čežı́ková, Kozler et al. 2001; Milne, Kinniburgh et al. 2003). A simple cost: benefit analysis showed that the additional removal of metals by HS dosing was less efficient than conventional neutralisation alone, on a cost basis. Overall, incorporation of HS into AMD treatment results in improved water quality for CaCO3 neutralisation and lower concentrations of metals with a high HS binding affinity, for some conditions. However, further investigation is required to improve the feasibility of HS incorporation into the AMD neutralisation process.

Includes bibliographical references.
Acid mine drainage (AMD) is one of the major environmental challenges facing the South African mining sector. Acid mine drainage has received significant public attention in recent years. South Africa's long mining history has led to a growing concern that coal-related AMD from these mines (both operational and defunct) will continue for centuries to come. Pyrite bearing fine waste, generated during coal preparation and beneficiation, is thought to carry a significant amount of AMD pollution risk. Coal-related AMD generation has not been afforded the same exposure as AMD generation from high sulphide minerals such as gold and copper ores. This is exacerbated by the growing concern over water quality degradation in the Mpumalanga region of South Africa. The development of integrated solutions to address the management of coal-related AMD requires an understanding of the principle causes behind coal-related AMD. To date, most of the prediction methods described in literature have been derived for the prediction of AMD in metal bearing ores. Furthermore, some of these methods are based on assumptions and do not take into consideration the various sulphur species present. Additionally, some of these methods have limited applicability to coal due to the high total organic carbon content (TOC) of the material. This research project attempts to address these short comings and uncertainties by developing a systematic and meaningful framework for the characterisation of South African coal and coal waste. The research project contributes to the knowledge of coal-related AMD with particular emphasis on the characterisation methods responsible for sulphur speciation and mineralogy for coal. The approach entails carrying out a case study assessment aimed at empirically assessing a coal tailings sample according to: particle size distribution, textural reference, mineralogical characteristics, and how the aforementioned factors influence the acid potential in coal. The approach intends to address key factors which include: identifying the sulphur bearing organic and inorganic constituents related AMD generation in coal, assessing how the mineralogy, texture and particle size distribution contribute to AMD potential in coal tailings, and then identifying suitable analytical techniques and test methods which can provide data. The combination of these key outcomes will seek to provide a systematic and meaningful framework for the characterisation of coal and coal waste streams. The characterisation methods used in this case study outlined a framework focusing on four main areas of acid mine drainage characterisation for coal wastes, these included: chemical characterisation, mineralogical characterisation, sulphur speciation and AMD prediction. This comprehensive approach employed a suite of techniques, including: petrography, quantitative x-ray diffraction (QXRD) and quantitative evaluation of minerals by scanning electron spectrometry (QEMSCAN).

Hydrated lime, Ca(OH)₂, has been rediscovered as an environmentally sustainable product, which could be of help in the remediation of acid mine drainage (AMD), especially in the AMD neutralization process. This is due to its ease of acquisition, affordable price and unique versatile properties such as reactivity and neutralization efficiency. AMD is an acidic wastewater containing high concentrations of sulphates and dissolved heavy metals mainly ferrous iron. The dissolution of Ca(OH)₂ in aqueous solution is complex, which make its kinetics in AMD neutralization difficult to understand. The aim of this study was therefore to understand the Ca(OH)₂ kinetics in simplified solutions such as de-ionized water and CH₃COOH. The neutralization process is an acid-base reaction; therefore, pH was used as a critical parameter in determining Ca(OH)₂ dissolution rate. The determination of the dissolution rate was attempted in two ways – measurement of dissolved calcium and determining change of particle size distribution. There were two methods of determining calcium assays investigated, that is EDTA-EBT titration method and OCPC spectrophotometric method. Both methods worked successfully for a Ca(OH)₂-H₂O system. The EDTA-EBT titration method worked better even at higher concentrations of calcium (up to 100 ppm) while the complexometric spectrophotometric method was consistent with Beer-Lambert Law for a narrow calcium concentration range of 1 to 2 ppm, when a small amount of magnesium was introduced. However, both methods failed in the presence of appreciable quantities of magnesium, sulphates and ferric ion. The investigation for particle characterization found that image analysis of SEM images was a better particle-size characterization option than laser diffraction measurement, which tended to cause blinding of the instrument window, but still yielded only qualitative results. There were four reactor configurations used, that is batch reactor for determining the effect of the hydrodynamics (stirring rate and powder addition) and three types of slurry CSTRs. The jacketed chemostat was found to be the optimal reactor configuration while the other two were used as base cases. The Ca(OH)₂ dissolution rate in de-ionized water decreased from 4.0×10⁻⁵ to 1.6×10⁻⁵ mol‧L⁻¹‧s⁻¹ when the temperature was increased from 26 °C to 42 °C. Correspondingly, the pH decreased with Ca(OH)₂ dissolution rate from 11.89 to 11.6. The dissolution rate expression was first order and consistent with the Nernst-Brunner Equation, with the dissolution rate constant of 2.34×10⁻³ s⁻¹ and the activation energy of 18.1 kJ mol ⁻¹ respectively. The overall Ca(OH)₂ dissolution rate in CH₃COOH solution decreased from 2.6×10⁻⁴ to 1.7×10⁻⁴ mol‧L⁻¹‧s⁻¹ when the temperature was increased from 25 °C to 44 °C. At constant ambient temperature (22°C), the Ca(OH)₂ dissolution rate increased with the decrease in pH from 12.1 to 4.38, then decreased with the decrease in pH from 4.38 to 3.5. Using pH to correlate dissolved calcium data and then to determine the rate of reaction, it was found that the dissolution rate is zeroth-order to hydrogen proton and first-order with respect to calcium concentration with the dissolution rate constant of 1.2×10⁻² s⁻¹ and the activation energy of 5.7kJ mol ⁻¹ respectively. These results confirmed that the dissolution of Ca(OH)₂ in DI water and the acetic acid solution is complex. The lower values of the activation energies (5.7 – 18.1 kJ mol ⁻¹), signifies that the kinetics of the Ca(OH)₂ dissolution are mass transfer controlled. Furthermore, these results were confirmed by the weak dependence of the dissolution rate to temperature. However, it was found that slurry CSTR is an efficient reactor system to study the effect of pH on the kinetics of hydrated lime at steady-state conditions.

Thesis (M.S.)--West Virginia University, 2008.
Title from document title page. Document formatted into pages; contains x, 81 p. : ill. (some col.), col. map. Includes abstract. Includes bibliographical references.

The changes that have taken place in the British Coal Industry over the last five years have meant that in many coalfileds the last deep mines have closed. When a coalfield is abandoned and dewatering ceases, groundwater levels rebound, threatening surface waters with polluting discharges. However, the sparse data sets available limit modelling with existing techniques. A lumped parameter model GRAM (Groundater Rebound in Abandoned Mineworkings) has been developed. This model conceptualises a coalfield as a group of 'ponds'. Each pond is an area of the coalfield that has been extensively worked and can be considered as a single hydraulic unit. The ponds are connected by pipes which represent major inter-connecting roadways along which flow is assumed to be turbulent. Discharge to the surface is also represented using pipes. Flow through the pipes can be calculated using the Prandtl and Nikuradse of the Colebrook-White pipeflow equations. The storage coefficient can vary vertically to represent both worked Coal Measures and the intervening unworked strata. GRAM is able to predict the timing and volume of discahrges. An iron component gives an indication of the water quality evolution of the discahrges. Monte Carlo simulation allows the variables that have most error in their estimation to be represented by probability distributions. The Dysart-Leven Coalfield in eastern Fife, Scotland has not been mined since 1985. However, dewatering has continued to protect the workings in the Frances Colliery. In 1994 British Coal decided the Frances would never reopen, there is therfore no longer a need to continue dewatering. GRAM has been used to produce estimates of the quantity, timing and location of dischargges from the Dysart-Leven Coalfield should pumping cease. MODFLOW has also been applied to the coalfield with less success. Water quality modelling was also attempted using GRAM's iron component, however, conclusive results will not be obtained until the three variables over which ther is most uncertainty have been calibrated against existing discharges.

Acid mine drainage is of growing concern for both developing and developed economies. Thus there is increasing pressure to develop alternative remediation strategies. Biological sulphidogenic mechanisms have long since been studied but, very few have been implemented on a large scale. Limitations are due to the inability to acquire a suitable, low cost, environmentally friendly, renewable carbon source. The present study investigated the use of an algae biomass generated by the HRAOP of an IAPS as a carbon source for the EBRU 00AB/06 SRB consortium. The algae biomass and consortium were utilized together to remediate simulated AMD. Remediation involved decreasing the sulphate and metal concentrations in solution and decreasing the acidity of a simulated AMD. Experiments were carried out to investigate the capability of the EBRU 00AB/06 SRB consortium for sulphate reduction and sulphide generation. The consortium produced colonies when grown under anaerobic conditions in Petri dishes containing modified lactate SRB medium. The SRB consortium reduced the sulphate concentration of modified Postgates medium B and generated sulphide. Further analysis of the EBRU 00AB/06 SRB consortium revealed that the consortium was minimally impacted at pH 5 and by sulphate and iron at 3 g.L-1 and 0.5 g.L-1 respectively. The EBRU 00AB/06 SRB consortium was exposed to Actinomycin D and Ethidium Bromide to determine whether transcription and translation of proteins was required for sulphate reduction. Results indicated that sulphide generation and sulphate reduction were inducible. Analysis of the algae biomass used in this study revealed the empirical formula C1.0H1.91N0.084S0.003O0.36 indicating a carbon source rich in the nutrients required to sustain microbial development. Light microscopy revealed that algae cell walls and in particular those of Pediastrum were susceptible to acid hydrolysis. Dinitrosalicylic acid, Nile red, Bradford and Ninhydrin assays were used to determine the reducing sugar, lipid, protein and amino acid content respectively, of the mixed algae biomass. Results showed that upon exposure of the biomass to simulated AMD at pH 1 and pH 3, the concentration of reducing sugars and amino acids in solution increased. Whereas levels of lipids remained unchanged while the protein concentration decreased, indicating that, upon exposure of algae biomass to AMD, simulated or otherwise, cells ruptured, proteins were hydrolyzed and polysaccharides were broken down to sugars which are immediately available for SRB utilization. Exposure of biomass to simulated AMD revealed further that the presence of algae biomass increased the pH of simulated AMD (pH 3) to pH 7.67 after 4 d. Likewise, the pH of simulated AMD at 1 increased to 1.77 after 2 d while pH of the neutral control increased to 8.1 after 4 d. A direct comparison between lactate and algae biomass revealed 94 % sulphate removal after 23 d in the presence of algae biomass while 82 % sulphate removal was measured in the presence of lactate. Thus the EBRU 00AB/06 SRB consortium successfully utilized algae biomass for sulphate reduction and sulphide generation. In another experiment to establish if the consortium could remediate simulated AMD (pH 5) containing 0.5 g.L-1 iron and 3 g.L-1 sulphate while utilizing an algae biomass as the carbon source no residual iron was detected after 14 d and by day 23, an 89.07 % reduction in sulphate was measured. The results of this investigation are discussed in terms of utilizing a readily available and renewable biomass in the form of microalgae produced in HRAOPs as an effective carbon source in the SRB catalysed remediation of AMD.

Many countries around the world use coal as fuel for the purpose of power generation. The extraction of coal produces large volumes of waste rock (WR) that are sometimes sulphide rich (principally containing iron sulphides such as pyrite (FeS2) and pyrrhotite (Fe1-xS)), with varying quantities of trace elements such as As, Si, Cu, Zn, Ni, Co, Mo and Cr etc). Such waste is environmentally sensitive due to the risk of oxidation in presence of atmospheric oxygen and water. Sulphide oxidation may result in acidic waters (acid mine drainage, AMD), which often contains high loads of dissolved metals. Coal combustion results in large amounts of fly ash (FA), which also is of environmental concern. However, FA is alkaline and may potentially be used for neutralisation of AMD. Therefore, the AMD producing potential of WR from coal mining and the neutralisation potential of FAs from coal and biomass combustion was studied with the ultimate goal to develop a methodology to decrease the environmental problems related to these materials.WR was sampled form the Lakhra coal field in Pakistan, which has an estimated coal reserve of 1.3 Bton, from lignite to sub-bituminous in quality. The WR samples were characterised by mineralogical and geochemical methods and the acid producing potential was determined by static (Acid Base Accounting) and kinetic (modified humidity cells test) methods. Besides organic material, the WRs are composed of quartz, pyrite, kaolinite, hematite and gypsum with varying amounts of calcite, lime, malladerite, spangolite, franklinite and birnessite. The Lakhra WR has strong potential to generate AMD (-70 to -492 kg CaCO3/ton) and pollute natural waters by leaching of elements such as Cd, Co, Cr, Cu, Ni, Pb, Zn, Fe and SO42-. Three different FAs based on the origin, fuel type and storage methods were studied. They were characterised by mineralogical and geochemical methods, the leachability was studied by batch leaching tests and the potential for buffering acids and neutralisation of AMD was quantified. Fly ash from burning i) brown coal (lignite) in Pakistan (PK), ii) black (bituminous) coal from Finland (FI) and iii) biomass FA provided by a sulphate pulp and paper mill in Sweden (SE) were studied. All ashes contained quarts, PK also iron oxide, anhydrite, and magnesioferrite, FI also mullite and lime, and SE also calcite and anorthite. All ashes were enriched in As, Cd, Co, Cr, Cu, Hg, Ni, Pb and Zn compared to continental crust, and all ashes had a strong neutralisation potential, the bioash, SE, in particular. The results are encouraging and suggest that it is possible to use FA to mitigate the environmental problems with coal mine WR. Methods for that will be the focus for the continued research.
Godkänd; 2014; 20141013 (asiqur); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Asif Qureshi Ämne: Tillämpad geologi/Applied Geology Uppsats: Potential of Fly Ashes for Neutralisation of Acid Mine Drainage from Coal Mine Waste Rock Examinator: Professor Björn Öhlander Institutionen för samhällsbyggnad och naturresurser Luleå tekniska universitet Diskutant: Dr Josef Mácsik Ecoloop AB Stockholm Tid: Torsdag den 18 december 2014 kl 13.00 Plats: E246, Luleå tekniska universitet

L’anomenat drenatge àcid de mina (AMD) ve generat per l’oxidació de sulfurs i és causa major de contaminació d’aigües a nivell mundial. L’arsènic és un del princiapls contaminants laconcentració del qual pot assolir centenars de mgL-1, és a dir, de 5 a 6 ordres de magnitud més gran que el límit de potabilitat per a l’aigua (10μg L-1) establert per la UE en 1998. En aquesta tesi, s’estudia l’impacte de la mobilització de l’arsènic al llarg de descàrregues de drenatge àcid de mina. L’oxidació de sulfurs que contenen arsènic (tal com l’arsenopirita (AsFeS), la pirita rica en arsènic (FeS2) o la marcassita (FeS2) és una de les principals fonts d’alliberament d’arsènic a l’aigua. En la primera part de la tesi, s’ha estudiat la cinètica de dissolució de l’arsenopirita i de la marcassita a pHs àcids i neutre, utilitzant reactors de flux continu, i s’han valorat els efectes del pH, de l’oxigen dissolt i de la temperatura en la dissolució d’ambdós sulfurs. A partir de les velocitats en estat estacionari establertes, es proposen les respectives lleis de dissolució que tenen en compte el lleu i el fort efecte del pH i de l’oxigen dissolt, respectivament, en llur dissolució. La incorporació d’aquestes lleis cinètiques en les bases de dades del codis geoquímics i de transport reactitu permeten fer prediccions molt més realistes. L’impacte mediambiental causat per l’arsènic alliberat a les aigües depèn de la seva atenuació natural. El principal procés que controla el destí i la mobilitat de l’arsènic aquós és l’adsorció de l’arsenat en fases de ferro precipitades. Per tant, cal tenir en compte el paper que juga l’estat d’oxidació de l’arsènic. En la segona part de la tesi, shan estudiat tant l’oxidació de l’arsènic com l’adsorció de l’arsènic. L’oxidació s’estudia en condicions abiòtiques i biòtiques a pH i composició típics d’aigües àcides de mina, fent servir experiments de tipus batch. S’hi mostra com en condicions biòtiques tenen lloc simultàniament l’oxidació de Fe(II) a Fe (III) i d’arsenit a arsenat, de manera que mentre els bacteris governen la primera, el contingut de Fe(III) domina la segona. En condicions abiòtiques, l’oxidació d’arsenit a arsenat en presència de Fe(III) és lenta, tot i que augmenta augmentant la presència de Fe(III) i de clorur amb llum de dia. L’adsorció d’arsènic en llocs d’AMD, i per tant l’atenuació d’arsènic, ocorre mitjançant l’adsorció d’arsenat en precipitats formats per oxi-hidròxids i oxi-hidròxid-sulfats de ferro (principalment schwertmannita (Fe8O8(OH)5.5(SO4)1.25), K-jarosita (KFe3(SO4)2(OH)6) i goetita (FeOOH)). S’han estudiat les capacitats d’adsorció de la jarosita i de la goetita i s’han comparat amb la de la schwertmannita. Amb aquest propòsit es van fer experiments de tipus batch a pH molt àcid i amb mostres sintetitzades de K-jarosita i de goetita. Sense la competència d’altres anions, la capacitat de la jarosita per eliminar arsenat és més alta que la de la goetita. També s’ha vist que la força iònica té un escàs efecte en l’adsorció d’ambdós minerals, però que la presència de sulfat, que és l’anió més abundant en aigües àcides de mina, minva llurs capacitas d’adsorció. Cal conèixer bé els mecanismes dominants que controlen el contingut d’arsènic en les aigües, no només en condicions de laboratori, sinó també en les condicions de camp. Per tant, en la tercera part de la tesi s’han estudiat el processos d’atenuació de l’arsènic en un sistema natural. Amb aquest objetiu s’han caracterizat exhaustivament l’aigua i els sediments del rieron provinent de la mina abandonada Tinto Santa Rosa, situada a la Faixa Pirítica Ibèrica (IPB). La característica dominant de l’aigua del rierol és un descens del pH aigües avall que va acompanyat d’un decreixement sistemàtic de les concentracions de ferro ferrós i de ferro total, d’arsenit i d’arsenat, així com d’arsènic total. A més a més, els sediments de llit mostren contiguts alts d’arsènic. Els principals mecanismes que dominen el destí i la mobilitat de l’arsènic en aquestes aigües de camp són l’oxidació del ferro i de l’arsènic i la precipitatió de compostos de Fe(III) que adsorbeixen l’arsenat. S’ha proposat un model unidimensional de trasnport reactiu, utilitzant el codi PHREEQC, per explicar i quantificar els processos mencionats que han estat estudiats en condicions de laboratori.
Acid mine drainage (AMD) generated by sulfide oxidative dissolution is a major cause of water contamination world-wide. Arsenic is one of the main AMD pollutants whose concentration can reach up to hundreds of mg L-1, i.e. 5-6 orders of magnitude higher than the limit of 10 μg L-1 for potable water established by the European Union in 1998. This thesis is concerned with the impact of arsenic mobilization along AMD discharges. Oxidation of As-bearing sulfides such as arsenopyrite (AsFeS), As-rich pyrite (FeS2) or marcasite (FeS2) is one of the main sources of arsenic release. The first part of this thesis is focused on the dissolution kinetics of arsenopyrite and marcasite at acidic to neutral pH using long term flow-through experiments. The effects of pH, dissolved oxygen and temperature on their dissolution were assessed. The respective dissolution rate laws were proposed on the basis of the steady-state rates, taking into consideration the slight pH effect and the strong dissolved oxygen effect on dissolution. The incorporation of these rate laws into the kinetic databases of geochemical and reactive transport codes allows us to obtain better realistic simulations. The environmental impact of released arsenic into waters depends on its natural attenuation. The arsenic oxidation state is considered given that the main process that controls the fate and mobility of aqueous arsenic is arsenate sorption onto precipitated Fe-phases. The second part of the thesis discusses arsenic oxidation and arsenic sorption. Oxidation was studied by means of batch experiments under abiotic and biotic conditions at typical AMD water pH and water composition. Simultaneous oxidation of Fe(II) to Fe(III) and arsenite to arsenate occurs under biotic conditions, the former mediated by bacteria, and the latter by the presence of Fe(III). Under abiotic conditions, oxidation of arsenite to arsenate in the presence of Fe(III) is slow, but is enhanced by increasing dissolved Fe(III) and chloride concentrations in the presence of light. Arsenic sorption at AMD sites, and hence arsenic attenuation, occurs via arsenate sorption on new iron-oxyhydroxide and iron-oxyhydroxide-sulphate precipitates (mainly, schwertmannite (Fe8O8(OH)5.5(SO4)1.25), jarosite (KFe3(SO4)2(OH)6) and goethite (FeOOH)). The sorption capacity of goethite and jarosite was studied and compared with the one reported for schwertmannite. To this end, batch experiments were conducted using synthetic powders of K-jarosite and goethite at highly acidic pH. In the absence of competitive effects of other anions, K-jarosite presented better removal efficiency for arsenate, and ionic strength and pH had little effect on the sorption capacity of the two minerals. In contrast, these sorption capacities diminished considerably in the presence of sulfate, which is the main anion in AMD waters. A deeper understanding of the dominant mechanisms controlling arsenic content in waters demands the study of the processes not only under laboratory but also under natural conditions. Accordingly, the third part of this thesis deals with the arsenic attenuation processes in a natural system. To this end, the acidic water and sediments of the abandoned Tinto Santa Rosa mine discharge, located in the Iberian Pyritic Belt, were studied. The most striking feature of the water was a pH decrease accompanied by a systematic decrease in ferrous iron, total iron, arsenite, arsenate and total arsenic concentration. Additionally, bed-stream sediments showed high arsenic contents. The main processes that control the fate and mobility of arsenic in waters in the field were iron and arsenic oxidation, precipitation of Fe(III)- minerals and sorption of As(V) onto them. A 1-D reactive transport model using the PHREEQC code was used to explain and quantify the aforementioned processes that had been studied previously under laboratory conditions.

Fly ash and AMD samples were characterised by standard analytical methods for selection of the test materials. Active treatment by means of mixing fly ash with AMD in beakers and a large tank at pre-determined ratios have shown that fly ash is capable of neutralising AMD and increasing the pH beyond neutral values, which optimises the removal of heavy metals and ions. The trend was: the more fly ash added the quicker was the reaction time and higher the pH values achieved. Iron was reduced by as much 99 % in beaker scale experiments via Fe(OH)3 precipitation at pH values >
4.0. A 99 % decrease in aluminium concentration was observed which was attributed to the precipitation of primarily gibbsite and various other mineral phases at pH values >
5.5. As the pH increases, sulphate is adsorbed via Fe(OH)3 and gypsum precipitation at elevated pH. Sulphate attenuation with fly ash was excellent, achieving 98 % attenuation with beaker scale experiments and 1:1 fly ash:AMD ratio. Sulphate attenuation with fly ash was comparable to membrane and ion exchange systems and exceeded the performance of limestone treatment. Except for the larger volumes of fly ash needed to neutralise the AMD, fly ash proved to be a feasible and cost efficient alternative to limestone treatment. Fly ash produced competing results to limestone concerning acidity removal and sulphate attenuation. The comparison highlighted the advantages of utilising fly ash in comparison to limestone and demonstrated its cost effectiveness. The results of this study have shown that fly ash could be successfully applied for the neutralisation of acid mine drainage (AMD) and effectively attenuate the sulphate load in the treated water. The critical parameters to this technology are the variations of chemical composition and mineralogy of fly ash, which could influence the pH, contact time of the neutralisation reaction, and the same is true if the AMD quality varies.

Acid mine drainage (AMD) is a significant environmental issue worldwide, which often causes severe contamination and marked species losses in receiving streams. However, little is known about how this stress alters food webs and ecosystem function. I conducted a literature review, which revealed that AMD-impacted streams generally had depauperate benthic communities dominated by a few tolerant species and impaired ecosystem processes. Next, using survey and experimental-based approaches, I investigated food web structure and energy flow in these highly stressed streams, which typically have low pH (< 3), high concentrations of dissolved metals (Al, Fe), and substrata coated with metal hydroxide precipitates, on the South Island, New Zealand. Inputs of AMD caused substantial loss of consumers and reduced the overall number of links between species generating small and simplified food webs, with few invertebrates and no fish. Comparative analysis of food webs from a survey of 20 streams with either anthropogenic or natural sources of acidity and metals, indicated that anthropogenic sources had a stronger negative effect on food web properties (size, food chain length, number of links); an effect driven primarily by differences in consumer diversity and diet. However, the presence of fewer trophic levels and reduced trophic diversity (detected using isotopic metrics), were common structural attributes in AMD-impacted webs along a pH gradient, regardless of impact level. Furthermore, complementary dietary analyses of consumer gut contents and stable isotope signatures (δ13C and 15N) confirmed that primary consumers fed generally on basal resources and that there were few predatory interactions, which reflected low densities of small-bodied chironomids. This suggests that food quantity was unlikely to limit primary consumers but that reduced prey availability may be an additional stressor for predators. In these radically re-structured food webs, trophic bottlenecks were generated at the primary consumer level and energy flow to higher consumers was disrupted. However, streams still retained some limited function, including slow leaf litter breakdown, which provided detrital resources and supported the small food webs. Overall, my findings have furthered our understanding of these highly stressed stream ecosystems by providing new insights into interactions among species and trophic levels that structure food webs and enable function.

CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A drenagem ácida de minas (DAM) é um problema ambiental capaz de comprometer a qualidade dos recursos hídricos, que decorre da oxidação de sulfetos. A adoção de medidas corretivas e/ou preventivas dependerá do programa de predição escolhido, este geralmente inclui testes do potencial de geração de acidez (método estático), e da velocidade com que ocorre o processo (método cinético). No presente trabalho avaliou-se o potencial de geração de DAM usando o teste de Balanço Ácido Base Modificada (BABM), e monitorou-se a qualidade da água da drenagem dos rejeitos, durante 23 semanas, usando o método das colunas de lixiviação segundo a Acid Drainage Technology Initiative, para amostras de rejeitos provenientes da Carbonífera Criciúma e da Carbonífera Metropolitana. As duas amostras da Carbonífera Criciúma (SRA e SRB) apresentaram potencial de geração de acidez e as amostras da Metropolitana apresentam um pequeno risco de gerar acidez, segundo os resultados do BABM. Porém os resultados do método cinético, para todos os casos, mostram valores de pH menores que 4 e valores crescentes para a concentração do SO4 -2, acidez e o Eh, que mostra que são geradoras de DAM. Deve se ter em conta que o teste de BABM não leva em consideração a cinética das reações para a produção de acidez e sua neutralização. Os valores de concentração para o Zn, Mn e Al excedem os padrões de qualidade de água (segundo a Resolução No 357, CONAMA). No caso do Pb, os resultados não foram conclusivos devido ao alto limite de detecção do equipamento. Utilizando o modelo do núcleo não reagido, a etapa controladora da taxa de oxidação para a pirita (de FeS2 a SO4 -2) para as amostras SRA e SRB foi transferência de massa através da camada limite, com tempos teóricos para conversão completa (t) de 2,7 e 1,6 anos respectivamente, para as condições ensaiadas. A outra amostra da Carbonífera Criciúma (VR) apresentou como etapa controladora nas semanas iniciais a transferência de massa através da camada cinza e nas semanas finais a reação química propriamente dita, sendo t estimado em 3,4 anos para as condições ensaiadas.
The acid rock mine drainage (ARD) arising from sulfides oxidation in mining areas is a serious environmental problem that markedly affects the quality of the surrounding water. Choosing the measure for remediation and/or preventing pollution effect depends on a suitable evaluation through a prediction program, it has principally tests of the acid generation potential (static method), and rate of the corresponding chemical reactions (kinetic methods). The present study aimed to evaluate the potential of ARD of wastes from two coal mines Criciúma and Metropolitana, using a Modified Acid Base Accounting (MABA) and evaluated the drainage water quality during 23 weeks using leaching columns test according Acid Drainage Technology Initiative protocol. According MABA results two coal mine Criciúma Samples (SRA e SRB) indicated an acid generation potential, and Metropolitana samples present a small risk to generate acidity. However the kinetic method results, for all the samples present pH < 4 and increasing concentrations values for SO4 -2, acidity and Eh that indicate acid generation potential. The MABA test does not consider the reaction rate of acid production and its neutralizations reactions. The concentrations values of Zn, Mn and Al exceeds water quality standard (Resolução No 357, CONAMA). In the case of Pb the results were inconclusives due to the equipment high detection limit for this element. Shrinking Core Model was used to determinate rate control to pyrite oxidation kinetic (de FeS2 a SO4 -2). SRA and SRB samples the layer diffusion control was the control rate, with complete conversion theoretical time (t) of 2.7 and 1.6 years, respectively, for the test conditions. The Criciúma Coal Mine sample (VR) presents product layer diffusion as control rate at the beginning weeks and then the chemical reaction was the control rate at the final weeks of the test and for this control the calculated t was 3.4 years for the test conditions.

Acid mine drainage (AMD) and increasing salinity of freshwater ecosystems pose serious threats to water quality in water-stressed South Africa. These threats are exacerbated by mining activities, mainly gold and coal from both active and abandoned mines that continue to release acidic water that is rich in toxic metals and high sulphate concentrations. Therefore, the overarching hypothesis for this study was that “the combination of AMD and sulphate salts confers high ecological risk to the aquatic biota”. The study employed both laboratory and field investigations to test this hypothesis and provide appropriate tools to protect freshwater ecosystems from increasing anthropogenic impacts. Firstly, a laboratory investigation was carried out to develop risk-based water quality guidelines (WQGs) for sulphates and treated AMD (TAMD) using the species sensitivity distributions (SSDs) technique. Five South African freshwater species belonging to five different taxonomic groupings, including Adenophlebia auriculata (insect), Burnupia stenochorias (mollusc), Caridina nilotica (crustacea), Pseudokirchneriella subcapitata (algae) and Oreochromis mossambicus (fish) were exposed to varying concentrations of sodium sulphate (Na2SO4), magnesium sulphate (MgSO4) and calcium sulphate (CaSO4), as well as TAMD in separate ecotoxicological experiments, applying short-term (96 h) non-renewal and long-term (240 h) renewal exposure test methods. Secondly, a novel trait-based approach (TBA) was also used to predict the vulnerability of taxa to treated acid mine drainage (TAMD). The TBA used a combination of carefully selected traits of organisms that are mechanistically linked to TAMD for their potential vulnerability predictions. Leptoceridae (caddisflies) and Leptophlebiidae (mayflies) were selected taxa for evaluation of the trait-based vulnerability predictions to TAMD for laboratory toxicity exposures. This was followed by a field investigation to assess macroinvertebrates assemblage responses, abundance and richness to a TAMD-impacted stream using the South African Scoring System version 5 (SASS5) protocol. Outcomes form the above three sources were combined in a multi-criteria analysis (MCA) to develop an appropriate water quality management strategy in a form of a trait-based decision-making support tool. Results of the risk-based WQGs revealed that Na2SO4 was the most toxic of the tested salts. A concentration of 0.020 g/L Na2SO4, 0.055 g/L CaSO4, and 0.108 g/L MgSO4 or a combined sulphate salts limit of 0.067 g/L were derived as long-term WQGs to protect over 95% of the population species in a natural environment considered as relatively pristine. This means that the generic 0.25 g/L sulphate compliance limit for South African freshwater systems is under-protective. Burnupia stenochorias was the most sensitive to AMD after long-term exposures, and it was adjudged as a good indicator of AMD along with P. subcapitata. Long-term scenario-specific WQG for AMD for the protection of over 95% of the population species was derived as 0.014%. Results of the TBA revealed that the relative abundance and diversity of taxa at a site that received direct impact from TAMD generally corresponded to trait-based predictions. The site that received direct TAMD was largely dominated by members of the Corixidae and Naucoridae families. However, Leptoceridae was more vulnerable to TAMD than Leptophlebidae contrary to predictions. Its assemblage did not match the predictions although Leptophlebiidae corresponded to predictions in terms of its assemblage and diversity. As water quality improved further downstream of the TAMD source, macroinvertebrates assemblage and diversity also improved as predicted. However, it is important to note that other equally important traits that were not studied might influence the response of organisms during toxicity test exposures. The MCA findings suggest that the trait-based decision-making support tool is a useful management strategy for the predicting vulnerability of taxa aquatic stressors including AMD and increasing salinity. Overall, the outcome of this study suggests that AMD poses an ecological risk to aquatic biota, but this becomes riskier in the presence of excess sulphate salts. Albeit, the WQGs for sulphate salts and AMD as well as the developed trait-based decision support tool all contribute novel sound scientific knowledge basis for managing the AMD and increasing salinity in freshwater ecosystems. The study recommends incorporating different life stages of indigenous species tested to determine if their sensitivity to AMD and sulphate would correspond to current findings because early life stages could be more sensitive to aquatic stressors than juveniles or adults. This is important for the derivation of strong and relevant WQGs. The TBA requires further refinement for its incorporation in ecotoxicology on a wide scale.

This dissertation includes theoretical and applied components that address the effect of coatings on rates of mineral reactions that occur in acid mine drainage (AMD) environments. The two major projects investigated how diffusion-limited transport of reactants through pore spaces in coatings on mineral grains affects the reaction rate of the underlying mineral. The first project considered the growth of gypsum coatings on the surface of dissolving limestone in anoxic limestone drains (ALD), which reduces the neutralization rate of the dissolving limestone and the subsequent effectiveness of this treatment. The second project investigated the conditions where iron oxyhydroxide coatings form on oxidizing pyrite and the potential strategies to prevent "runaway" AMD by reducing the rate of acid production to the point that the acid can be neutralized by the surrounding rocks. In both studies, experiments were conducted to measure reaction rates for the underlying minerals, as coatings grew thicker. These experimental data were fit to a diffusion model to estimate diffusion coefficients of reactants through pore spaces in coatings. These models are extrapolated to longer times to predict the behavior of the coated grains under field conditions. The experimental results indicate that management practices can be improved for ALDs and mine waste piles. For example, supersaturation with respect to gypsum, leading to coating formation, can be avoided by diluting the ALD feed solution or by replacing limestone with dolomite. AMD can be prevented if the rate of alkalinity addition to mine waste piles is faster than acid is produced by pyrite oxidation. The diffusion model developed in this study predicts when iron oxyhydroxide coatings will become thick enough that alkalinity from the surroundings is sufficient to neutralize acid produced by coated pyrite oxidation and additional alkalinity is no longer required.
Ph. D.