Academic literature on the topic 'Tailings (Metallurgy) – Environmental aspects – Vermont'

The article is devoted to the conversion of mining enterprises from open way of development of ore deposits into underground method of development. The aim is regulation of the main preparation stages of the mining industry to diversifi mining and ore processing. The research methodology includes a critical analysis of the theory and practice of production processes, development of recommendations and justifi of effi of modernization of the existing situation. The results of the research . The paper features a characteristic of mining methods and an analysis of their advantages and disadvantages. It formulates the present state of the mining industry in Russia in conditions of the market and toughening of requirements to environmental management. The article explains the environmental and resource essence of the technology of fi the mined-out space with hardening fi mixtures. It offers a description of the technology with the solvent extraction of metals from ore with a focus on underground solvent extraction of off-balance ore in the frame of the combined criterion of completeness of metal extraction technology. The model presented in the article is based on the effectiveness of mechanochemical activation of raw materials for the preparation of hardening fi mixtures. It defi the profi from the involvement of off-balance ore into the manufacture. The paper features the concept of state management of ore-bearing massifs on the basis of the regulation of natural and technogenic stress levels by fi the technological voids with hardening mixtures. Another concept described in the article is the production of metals by solvent extraction and aspects of its implementation, including that by disintegrator. The scope of the results implementation includes mining and processing enterprises, mainly non-ferrous ore exploiting metallurgy. Conclusions . Conversion to underground deposit development requires development of technologies of fi the technological voids with hardening mixtures. These technologies are based on utilization of tailings processing benefi and metallurgy after extracting from them the residual metals by, for example, mechanochemical activation. Comprehensive modernization of technology development increases the completeness of the use of sub-soil resources, contributes to the improvement of the economy of mining enterprises and to improvement of the environment.

A geochemical study of the composition of natural sediments and contaminating mine tailings in Hastings and Alice Arms has been carried out. Apart from the geochemical investigation on the solid fraction, pore waters from six sediment cores have been analyzed to evaluate the diagenetic processes in the sediments of these two inlets. Differences in the mineralogy as well as in the chemical composition of the sediments were used to distinguish the natural sediments from contaminated sediments and pure tailings. In Alice Arm, two types of tailings could be differentiated with these methods. The first tailings type originated from the Kitsault Mo-deposit, which was mined in the past two decades by the B.C. Molybdenum Corporation and AMAX/Canada. These tailings are characterized by a number of features which make them distinguishable from natural sediments. The K-feldspar content of the tailings is significantly increased, mainly at the expense of plagioclase, which is the main characteristic for the mineralogical identification of this tailings type. The enhanced K-feldspar content is the cause for increased K and Rb values in the Mo-mine tailings. Another indicator specific to these recent tailings is an increased Mo content. The second tailings type is derived from an older mining operation in the Kitsault Valley, most likely the Dolly Varden Silver Mine. A specific indicator for these tailings is their high Ba content which is due to large amounts of barite. This mineral phase could be identified by X-ray diffraction methods in a heavy mineral fraction of the relevant sediment layers. Both tailings types show enrichment in their Pb, Zn and S concentrations, caused by an increased amount of metal-sulphides in the ore materials. In this area, these elements can therefore serve as a general indicator for the contamination of natural sediment with either tailings type. The interstitial water analyses indicated that the sediments in both inlets become reducing at a fairly shallow depth (10-15 cm), resulting in the mobilization of Mn, Fe and Mo from the solid phase. In the deeper parts of the cores, consumption of these metals could usually be observed which is likely due to precipitation of authigenic components. The dissolved Mo concentrations in the sediments contaminated with the modern tailings were much higher than in the natural sediments. In the pore water of the pure tailings the concentration reaches some 300 times that of the overlying water, which is the highest value ever reported for saline pore waters. These high Mo concentrations must support a flux of Mo from the sediment into the overlying water, and it is shown that such a flux could increase the inventory of naturally occurring dissolved Mo in the deep waters of Alice Arm by up to 4%.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

[Truncated abstract] As mineral deposits continue to be mined, the non economic gangue materials such as sulphides (e.g. pyrite) that are extracted as part of the ore body or overburden are deposited within the waste rock and/or milled tailings. As a result of natural weathering processes, these reactive materials represent a potential hazard to surrounding environments. A major consequence, resulting from mine-waste impoundments containing sulphidic materials, relates to the offsite movement of low pH leachates containing elevated concentrations of metal ions posing a contamination threat. The processes and mechanisms acting in the formation of acid mine drainage (AMD) are highly variable and, to a high extent, controlled by climatic conditions as the main driver of water flow and wetness of the system which in turn determines the availability of oxygen as well as water for pyrite weathering. In particular, this thesis is based on the hypothesis that in semiarid and arid climates the acid production may be water … The experiments were repeated at different water contents ranging from 0.24 to 0.33 cm3 cm-3. Breakthrough curves (BTC) of Li+, K+, Ca2+, Mg2+, Na+ and pH were measured and described with models of different complexities. This included the use of a simple linear and non-linear isotherms for Li+ alone, a binary Li+ - K+ ion exchange, and a complete multicomponent chemical equilibrium description of ion transport. The latter, by including dissolution of primary minerals which released base cations such as Mg2+, Ca2+ and K+ explained some of the elution patterns of base cations for which the Li+ - K+ exchange was the dominant process. Furthermore, under unsaturated water flow conditions, retardation of Li+ increased with decreasing water content. Thus solute mobility in mafic rock tailings appears to decrease under strongly unsaturated water flow conditions.

One hundred surface sediment samples and two 30 cm cores were collected from Howe Sound, British Columbia, a deep (≈280 m) fjord with a restricted inner basin into which mine tailings had been dumped for 75 years. The abundances of major elements Si, Al, Ti, Fe, Mg, Ca, Na, K, C, N, and P, and minor elements Ba, Co, Cr, Cu, Mn, Ni, Pb, Rb, Sr, V, Y, Zn, and Zr were determined as well as nutrient and trace metal concentrations in porewater from the two cores. The solid-phase data suggest that the inner basin sediments are dominated by Squamish River-derived feldspars, while the outer basin is characterized more by quartz and Fe and Mg minerals, which enter the southernmost portion of the fjord via estuarine circulation from Georgia Strait. Although Fe, Cu, Pb, Zn, and Ba are still enriched in sediments near the tailings outfall, the lapse of 13 years since cessation of tailings deposition has apparently resulted in reduced metal levels throughout much of the rest of the inlet due to ongoing dilution by natural sedimentation. Profiles of these metals with depth show that the tailings deposit proper is buried by ≈14 cm of natural sediment in the deep central portion of the inner basin. Porewater analysis of the two cores revealed that active bacterial remobilization of organic matter is occurring at both locations; although the organic carbon content of the outer basin is greater than that in the inner basin, sulphate-reduction is more intense in the latter due to the higher sedimentation rate. Despite this, dissolved sulphides were nearly absent in porewaters, leading to the conclusion that authigenic pyrite precipitation is removing some of the dissolved Fe. Dissolved Cu and Zn are enriched in surficial porewaters of both the outer and inner basins (i.e. Cu = 215 and 132 nmol/L, respectively, and Zn = 32 µmol/L and 1.6 /µmol/L), but decrease rapidly within the top 2-3 cm, suggestive of active removal by some mechanism. Dissolved Pb concentrations were low (<3 nmol/L) in both cores, and did not show any surface enrichment. These data suggest that a strongly reducing environment such as is found at depth in natural sediments inhibits the release of some labile metals which may be contained within them.
Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate

The commercial mining of asbestos occurred in four Provinces of South Africa (Northern Cape, North West, Limpopo and Mpumalanga). It was initiated in the late 1800's and lasted for over a hundred years into the beginning of this century. As a producer of amphibole asbestos, South Africa far outpaced every other country being responsible for 97% of global production. The last crocidolite mine closed in 1996 and chrysotile in 2002. Anecdotal information concerning environmental contamination as a result of the former mining activities and the improper disposal of mine waste tailings has been reported by a variety of authors. Few comprehensive or systematic surveys have been conducted to date to document this issue and very little quantifiable research has been completed on the communities located in close proximity to the former mine sites to determine the extent of contamination. In 2004-2006 communities were surveyed within the Northern Cape and North West Provinces to determine the extent and severity of environmental contamination. This research developed and applied a methodology to select those communities suspected of environmental contamination, a targeted survey methodology, and a protocol for rapid sample laboratory analysis. A total of 41 communities were initially predicted by the model to be suspected for environmental asbestos contamination. Based on the inclusion of local knowledge, a final 36 communities were selected for a screening-level field assessment, 34 of which were found to contain environmental asbestos contamination at rates ranging from 20 to 100% of the surveyed locations. A total of 1 843 samples of soil and building material were collected in the screening level assessment. One community (Ga-Mopedi) was selected as being representative of the total cohort and a more detailed house to house survey was completed. A total of 1 486 samples were collected during the detailed survey. Results of the detailed survey revealed 26.2% of the homes were contaminated with asbestos containing soil and/or building material. A theoretical quantitative cumulative exposure assessment was developed to estimate the disease burden within the study area population of 126,130 individuals within the surveyed communities resulting in a predicted range of 25-52.4 excess deaths per year from lung cancer and mesothelioma due solely to environmental exposures to asbestos pollution.

The subject of this thesis is the development of alternative approaches to environmental management and mine closure plans using case examples of the Big Bell/Cue Mining District and as a working example, an area of unconfined washout of historical gold-mine process tailings located in this arid inland region of Western Australia. This is considered appropriate in the light of the social and political thrust for industry to develop simultaneously positive economic, social and environmental outcomes from their activities. The Big Bell mining operation ceased mining in June 2003 and the Mine Closure Plan reflected a classical approach of minimization of public liability and strict compliance with legislative requirements. During the life of the modern mine the approach to rehabilitation was similarly classical in its approach It is intended for this document to inform the mining industry using the case example of the now closed Big Bell Mine as to how greater long-term outcomes may have been achieved for the State and the region for the future. This thesis specifically investigates alternative ways to approach rehabilitation in arid areas of Western Australia using the washout area as an example and trial area. This thesis has approached the issue by addressing the quantification of what has occurred through the gathering of baseline data of the case study area and then by the implementation of a series of relevant trials to identify appropriate eco-functional process-sensitive methods for rehabilitation as an alternative to current industry practice. Trials investigating the use of "retention banks" and "clay/seed balls" and the use of ex-mine milling waste carbon were conducted to investigate relevant possible techniques suitable for arid mine-site waste dump rehabilitation. Data analysis indicated that the main reason for the high level of degradation within the case study area is due to the smothering effect of the fine clayey tails cover and due to acidity of the tailings. A detailed examination of 92 soil samples found water infiltration of tails-washed areas as half that of control areas. Acidity of alluvium has declined from pH 5.2 to 3.8. The acidity has penetrated at depth to hardpan. Trials were commenced to rehabilitate the area using a combination of earthworks (retention banks and· scarification), pH- adjustment (using ex-mill carbon and crushed lime), and the use of native seed pelletised into clay-balls. The introduction of ex-mill carbon was shown to be effective in ameliorating pH in the tails wash area and improving its capacity to regenerate. Considering it is a widely available waste product with the gold mining industry it should be seriously considered in its application for rehabilitation purposes, and specifically in areas affected by severe acidification and desertification particularly by mismanaged tailings with pyrite content. The use of clay balls should also be subjected to further investigation. It is at least equal to the traditional use of raw seed and fertilizer with immediate and abundant rainfall. As this almost never occurs, it should prove to be superior, in delivering higher rates of viability for seed used. The thesis then attempts to integrate this study within the context of the wider issues of environmental management, specifically the best practice of mine closure plans and the adoption of sustainable economic, social and environmental outcomes from mining as an integral part of responsible operational environmental management plans. The thesis argues that the environmental management planning and specifically the Mine Closure Plan should not waste the myriad of opportunities that are the by-product of mining for the long-term sustainable benefit of the wider region. It is argued that if mining companies are serious about sustainability, then they cannot continue with short-term cycles of mining and closure. However to be realistic it will take concerted willingness from all stakeholders to pursue these outcomes. While a given mining operation can offer extensive resources and assets to support this approach the commercial and legislative pressures of core mining activities necessarily mean that mines are in fact encouraged to simply return the environment back to as natural state after operations are complete. Invariably this means hundreds of millions of dollars of infrastructure are levelled and scrapped to avoid all future liability, whilst the potential for sustainable outcomes is essentially ignored. The same Government that enforces the Mining Act and has a State Sustainability Strategy imposes the conditions which create unimaginative classical mine closure plans. Government, industry and the residents of regions must work together to seriously develop sustainable outcomes to mining.

The mining industry produces vast quantities of overburden and mill tailings. In many instances the disposal of these wastes on the Earth's surface have caused local, and occasionally even regional, water resources to become contaminated. Contamination typically arises from the oxidation of metal sulfide minerals contained within these wastes. Upon oxidation these minerals release sulfate, their associated metal cations and acidity into solution. This study investigated the potential for groundwater contamination arising from a Pb/Zn tailings impoundment in the North West Province of South Africa (Pering Mine). The tailings is composed predominantly of dolomite, which imparts to the material an alkaline pH and a high acid buffering capacity. Acid-base accounting (ABA) established that the capacity of the tailings to buffer acidity surpasses any acid producing potential that could arise from pyrite (FeS2), galena (PbS) and sphalerite (ZnS) oxidation. These minerals account for about 3 to 6% of the tailings by mass. Total elemental analysis (XRF) showed that the material has high total concentrations of Fe (19083 mg kg-I), Zn (5481 mg kg-I), Pb (398 mg kg-I), S (15400 mg kg-I), Al (9152 mg kg-I) and Mn (29102 mg kg-I). Only a very small fraction of this, however, was soluble under saturated conditions. An estimation of potentially available concentrations, using the DTPA extraction method, indicated that high concentrations of Zn (1056 mg kg-I), and moderate concentrations of Pb (27.3 mg kg-I) and Cu (6.01 mg kg-I) could potentially be available to cause contamination. A number of leaching experiments were undertaken to accurately quantify the release of elements from the tailings material. These experiments were aimed at determining the potential for groundwater contamination and also provided a means whereby the long-term release of contaminants could be modelled using the convection-dispersion equation for solute transport. Four leaching treatments were investigated. Two consisted of using distilled water under intermittent and continuous flow, while a third used intermittent flow of deoxygenated distilled water to assess leaching under conditions of reduced oxygen. The.mobilisation of potential contaminants under a worst case scenario was assessed by means of leaching with an acetic acid solution at pH 2.88 (after the US Environmental Protection Agency's toxicity characteristic leaching procedure). The acid buffering potential of the tailings was considerable. Even after 8 months of weekly leaching with 1 pore volume of acetic acid solution the pH of the effluent was maintained above pH 5.90. The protracted acidity caused very high concentrations of Pb, Zn, Mu, Ca, Mg, Hg and S to be released into solution. Leaching the tailings with distilled water also caused the effluent to have noticeable traces of contamination, most importantly from S, Mg, Mu and Zn. In many instances concentrations significantly exceeded guideline values for South African drinking water. Modelling solute transport with the convectiondispersion equation predicted that sol- and Mu contamination could persist for a very long period of time. (±700 years under continuous saturated leaching), while Mg and Zn concentrations would most likely exceed recommended limits for a much shorter period of time (±300 years under the same conditions). In light of the various column leaching experiments it was concluded that seepage from the Pering tailings impoundment could cause groundwater contamination. A drill-rig and coring system were used to collect both tailings and pore-water samples from eight boreholes spread out across the tailings impoundment. These investigations showed that most of the impoundment was aerobic (Eh ranged from +323 to +454 mY) and alkaline (pH 8.0 to 9.5). This chemical environment favours sulfide oxidation and as a consequence high concentrations of S have been released into the pore-water of the impoundment (S concentrations ranged from 211 to 1221 mg r l ). The acidity released as a by-product of sulfide oxidation was being buffered by dolomite dissolution, which in turn was releasing high concentrations of Mg (175 to 917 mg r l ) and Ca (62.6 to 247 mg r l ) into solution. Metal concentrations in the pore-water were low as a result of the strong metal sorbing capacity of the tailings and possible secondary precipitation. The only metal which significantly exceeded recommended limits throughout the impoundment was Hg (concentrations were between 100 and 6000 times the recommended limit of 0.001 mg r l ). Under the current geochemical conditions it is expected that Hg, S and Mg will likely pose the greatest threat to groundwater. The main concerns associated with mine tailings are that of mine drainage and dust blow off..In order to eradicate the latter problem, the tailings impoundment at Pering Mine was covered with a layer of rocks. Modelling the water balance of the impoundment using the computer model HYDRUS-2D showed that the rock cladding has potentially increased the volume of drainage water seeping from the impoundment. In light of the leaching experiments and field work, which proved that water passing through the tailings became enriched with various potentially toxic elements, it is expected that the problem of groundwater contamination around Pering Mine has been further exacerbated by the rock cladding. It was therefore concluded that there would be a strong likelihood of groundwater contamination in the vicinity of the mine.
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.

The original aims of this project were to investigate the potential for phytoremediation, with emphasis on metal accumulation, of three contrasting industrial processing wastes. These were tailings material (PT) from the decommissioned Pering Pb/Zn Mine (Reivilo, North West Province, South Africa (SA)), smelter slag (SS) from the Samancor Mnsmelter (Meyerton, Gauteng, SA) and electro-winning waste (EW) from MMC (Nelspruit, Mpumalanga, SA). It became evident, however, early in the project, that the use of metal hyperaccumulating plants was not a viable technology for these wastes. The project objectives were thus adapted to investigate alternative remedial technologies. The use of endemic and adapted grass species was investigated to revegetate the PT. In addition, chemically-enhanced phytoremediation was investigated to induce metal hyperaccumulation by grasses grown in the PT (Part 1). Revegetation of the SS and EW were not considered feasible, thus land disposal of these two Mn-rich processing wastes was investigated (Part 2). Part 1 - Revegetation of tailings from Pering Mine The PT was found to be alkaline (pH > 8.0), and consisted mainly of finely crushed dolomite. It was generally nutrient poor with high amounts of readily extractable Zn. It also had a very high P-sorption capacity. Seven grass species (Andropogon eucomus Nees; Cenchrus ciliaris L.; Cymbopogon plurinodis Stapf ex Burtt Davy; Digitaria eriantha Steud; Eragrostis superba Peyr; Eragrostis tef (Zucc.) Trotter and Fingeruthia africana Lehm) were grown in PT treated with different rates of inorganic fertiliser under glasshouse conditions. The fertiliser was applied at rates equivalent to 100 kg N, 150 kg P and 100 kg K ha-1 (full), half the full rate (half) and no fertiliser (0). Seed of C. ciliaris, C. plurinodis, D. eriantha, E. superba and F. africana were collected from Pering Mine. Seed of A. eucomus was collected from the tailings dam of an abandoned chrysotile asbestos mine. These were germinated in seedling trays and replanted into the pots. A commercial variety of E. tef was tested, but due to poor survival this species was subsequently excluded. The foliage and root biomass of the grasses and concentrations of Ca, Cu, Fe, K, Mg, Mn, Pb and Zn in the foliage were determined. The yield of all the grasses increased with an increase in fertiliser rate, with a significant species by fertiliser interaction (p = 0.002). The highest yield was measured for C ciliaris, followed by D. eriantha (4.02 and 3.43 g porI, respectively), at the full fertiliser application rate. Cymbopogon plurinodis was the third highest yielding species, while the yields of E. superba and F. africana were similar. There were positive linear correlations between foliage yield and fertiliser application rate for all grasses. The root biomass of the grasses also increased with an increase in fertiliser application rate. The interaction between grass species and fertiliser level had a non-significant (p = 0.085) effect on the yield of grasses, though there were significant individual effects of species (p < 0.001) and fertiliser (p < 0.001). Digitaria eriantha had the highest root biomass at each fertiliser application rate, followed by C plurinodis and C ciliaris. Similarly to foliage yield, there were positive linear correlations between root biomass and fertiliser application level. Positive, linear correlations were found between foliage yield and root biomass, though the strength of these varied. The weakest correlation was found for D. eriantha (R2 = 0.42) but this was attributed to a moderately high variance in foliage yield and roots becoming potbound. Generally, nutrient concentrations were within adequacy ranges reported in the literature, except for P concentrations. This was attributed to the high P-sorption capacity of the PT. Zinc concentrations were higher than the recommended range for grasses, and also increased with an increase in fertiliser application rate. This was attributed to the high available Zn concentrations in the PT and improved growth of the grasses at higher fertiliser application rates. It was recommended that C ciliaris and D. eriantha be used for revegetation due to high biomass production and that E. superba be used because of rapid growth rate and high self-propagation potential. Both C plurinodis and F. africana can also be used but are slower to establish, while A. eucomus was not a suitable species for revegetation of the PT. Inorganic fertiliser improved the growth of all these species and is recommended for the initial establishment of the grasses. An experiment was conducted to investigate the potential of inducing metal hyperaccumulation in three grass species (C ciliaris, D. eriantha and E. superba) grown in the PT. Grasses were grown in fertilised tailings for six weeks, then either ethylenediaminetetraacetic acid (EDTA) or diethylentriaminepentaacetic acid (DTPA) was added to the pots at rates of 0, 0.25, 0.5, 1 and 2 g kg-I. Grasses were allowed to grow for an additional week before harvesting. The concentrations of Cu, Pb and Zn were determined in the foliage. The interactive effect of species and chelating agent on the uptake of Cu was marginally significant (p = 0.042) and non-significant for Pb and Zn (p = 0.14 and 0.73, respectively). While the addition of the chelating agents resulted in an increase in Pb uptake by the grasses, it did not induce metal hyperaccumulation in the grasses. This was attributed to the ineffectiveness of the chelating agents in the PT in the presence of competing base cations (mainly Ca). The use of this technology was not recommended. Part 2 - Land disposal of Mn-rich processing wastes Chemical characterisation of the SS showed that it was an alkaline (pH > 9.5), Mn-rich silicate (glaucochroite), that generally·had low amounts of soluble and readily extractable metals. Acidic extractants removed high amounts of Mn, Ca and Mg, attributed to the dissolution of the silicate mineral. The EW was highly saline (saturated paste EC = 6 780 mS m,l) with a near-neutral pH. It had high amounts of soluble Mu, NHt+, S, Mg, Ca and Co. The primary minerals were magnetite, jacobsite (MnFe204) and gypsum. The effect of SS and EW on selected chemical properties of six soils was investigated by means of an incubation experiment, and their effect on the yield and element uptake by ryegrass was investigated in selected soils under glasshouse conditions. Five A-horizons (Bonheim (Ba), Hutton (Hu), lnanda (la), Shortlands (Sd) and Valsrivier (Va» and an Ehorizon (Longlands (Lo» were treated with SS at rates of 30, 60, 120,240 and 480 g kg'l and EW at rates of20, 40,80,160 and 320 g kg'l. Soils were incubated at field capacity at 24 QC and sampled periodically over 252 days. The soil pH, both immediately and over time, increased, while exchangeable acidity decreased after the addition of SS to the soils. The pH at the high rates of SS tended to be very high (about 8). The electrical conductivity (EC) of the soils also increased with an increase in SS application rates and over time. The most marked changes tended to occur in the more acidic soils (e.g. la). In the soils treated with EW, there was generally an increase in the pH of the acid soils (e.g. la) while in the more alkaline soils the pH tended to decrease (e.g. Va), immediately after waste application. There was a general decrease in pH over time, with a concurrent increase in exchangeable acidity, due to nitrification processes. The EC of all the soils increased sharply with an increase in EW application rate, attributed to the very saline nature of the EW. Water-soluble Mn concentrations in the soils treated with SS tended to be below measurable limits, except in the acid la. Iron concentrations decreased with an increase in SS application rate and over time for all soils. The water-soluble concentrations of Mn, Ca, Mg and S increased sharply with an increase in EW application rate in all soils. There was also a general increase in Mn concentrations over time. Iron concentrations tended to be low in the EW-treated soils, while Co concentrations increased as EW application rate increased. Exchangeable (EX, 0.05 M CaCh-extractable) concentrations of Fe, Co, Cu, Zn and Ni were low in the SS-treated soils. The concentrations of EX-Mn tended to increase with an increase in SS application rate in the la soil, but generally decreased in the other soils. There was also a decrease over time, attributed to the high pH leading to immobilisation of Mn. The EX-metal concentrations of the EW-treated soils were generally low, except for Mn. The concentrations of EX-Mn increased sharply as EW application rate increased. The contribution of EX-Mn was calculated to range from 209 to 3 340 mg Mn for EW rates of 20 to 320 g kg-I, respectively. In the Lo soil the expected amount of Mn was extracted at the different EW application rates. In the other soils the EX-Mn concentrations were typically higher than expected. This was attributed primarily to the dissolution ofMn from the EW due to the interaction between soil organic matter and the EW. There was generally an increase in EX-Mn concentrations over time, attributed to the decrease in pH of the soils treated with EW. The above-ground biomass production of ryegrass grown in Lo and Hu soils treated with SS increased at low application rates, but decreased again at the highest rates. The reduction in yield was attributed to an increase in soil pH leading to trace nutrient deficiencies. At the lower SS application rates, nutrient concentrations of the ryegrass tended to be within typical adequate ranges reported in the literature. Of concern was the elevated Mn concentration in the ryegrass foliage, though no toxicity symptoms were seen. This was attributed to the dissolution of the silicate mineral due to soil acidification processes and the possible ameliorating effect of high Ca and Si concentrations on Mn toxicity. The growth of ryegrass was generally poor in the Hu soil treated with EW and it did not survive beyond germination in the Lo soil treated with EW. In the Hu soil plants grew well in the 20 and 40 g kg-I EW treatments, but died at the higher rates. In both cases mortality was thought to be due to the high salinity that resulted in toxicity and osmotic stress in the newly germinated seedlings. The improved growth at the lower rates ofEW, in the Hu soil, was attributed mainly to increased N availability. The concentrations of Mn in the foliage were elevated in the soils treated with EW. A pot experiment was conducted to test the effect of applying either humic acid (HA) or compost (at a rate of 20 g kg-I) with lime (at rates of 0, 5 and 10 Mg ha-I) on the growth and nutrient uptake of ryegrass grown in the Hu soil treated with EW at rates of 0, 10, 20 and 40 g kg-I. A basal P-fertiliser was also applied in this experiment. The highest yields were measured in the treatments receiving either HA or compost at the highest application rate ofEW. The addition oflime did not improve the yield of the HA treatments, but did in the compost treatments. Generally, nutrient concentrations were adequate. The Mn concentrations were markedly lower than expected, and this was attributed to the formation of insoluble Mn-P compounds due to the addition of fertiliser. The effect of either HA or compost on Mn concentrations was not marked, but lime reduced Mn uptake. A leaching column experiment showed that, generally, the Mn was not readily leached through a simulated soil profile, though the addition of compost may enhance mobility. There was also evidence to indicate an increase in salinity and that Co concentrations of the leachate may be a problem. These data suggest that soil organic matter may be a very important factor in determining the release of Mn from the wastes, notably the EW. The land disposal of the SS and EW was not recommended at the rates investigated here, as both showed the potential for Mn accumulation in above-ground foliage, even at low application rates, while high application rates negatively impacted on plant growth. It appears that P-compounds may be beneficial in reducing Mn availability in the EW, but further testing is required.
Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.