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1
Ekström, Tomas. "Leaching of concrete : the leaching process and its effects /". Lund : Univ, 2003. http://www.byggnadsmaterial.lth.se/.
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2
Barbosa, Filho Olavo. "Thiocyanate leaching of gold". Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46663.
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3
Trejo-Gallardo, Jaime. "Modeling chalcopyrite leaching kinetics". Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/240.
Testo completoAbstract (sommario):
Chalcopyrite (CuFeS2) is the most abundant of the copper sulfides and also one of the
most refractory for leaching. Several processing routes have been proposed to
overcome drawbacks associated with environmental problems related to copper
extraction from this mineral. Atmospheric leaching in acidic ferric sulfate is regarded as
being particularly attractive over other hydrometallurgical systems. However, the
challenge has been to overcome the problem of slow extraction rates due to passivity
encountered at high solution potentials in this system. This highlights the need to
investigate better operating conditions to optimize copper extraction and prevent the
problem of passivation, and to develop suitable modeling tools to assess and diagnose
leaching performance.
In this work, a dissolution rate expression for chalcopyrite leaching in acidic ferric sulfate
media is proposed accounting for effects in the active and passive regions under
potentials from 415 to 550 mV (Ag/AgCl). A model of chemical speciation in the bulk
solution elucidates the idea of passivation caused by precipitation of ferric species and
their consequent adsorption onto the chalcopyrite surface. Electrochemical studies on
massive samples of chalcopyrite involving characterization and modeling of the anodic
and cathodic half-cell reactions of chalcopyrite leaching together with mixed potential
considerations lead to the development of the mathematical expression for dissolution rate.
The mathematical model was calibrated with electrochemical parameters and results
are in good agreement with real leaching data from batch tests for solution potential
regions where passivity is not observed. On the other hand, the passive region was
modeled by means of adjusting parameters related to adsorption energies of the
passivating species. Results of the model for this region deviate from real data as
potential becomes higher probably due to diffusion resistance through a layer
composed of ferric complexes.
4
Munkondya, Ferguson Mukozoke. "Kinetic modelling of leaching". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47583.
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5
Sililo, Bernard Liswani. "Modelling uranium leaching kinetics". Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/61336.
Testo completoAbstract (sommario):
The uranium price decline has negatively impacted on the uranium mining industry. This
decline in price requires that uranium metallurgical processes be made to operate more
efficiently. Some key parameters that influence the dissolution and kinetics of leaching
uraninite (one of the main minerals from which uranium can be extracted) are pH, oxidationreduction
potential and iron concentration. A good understanding of the effect these
parameters have on the leach kinetics would lead to an efficient operation of metallurgical
processes. The objective of this work was therefore to investigate the effects of these key
drivers on leach kinetics of Rӧssing Uranium ore. Added to this, was an attempt to come up
with a mathematical model which can successfully replicate the leach kinetics. A series of
laboratory leach experiments were performed on Rӧssing ore where the pH, oxidationreduction
potential and total iron were varied, one at a time, to establish the effects they
have on the leach kinetics and on the uranium extraction.
Analysis of the data collected from this study showed that the leach kinetics are more
dependent on the oxidation-reduction potential, followed by the iron concentration and least
affected by the pH. It was further shown that oxidation-reduction potential is a function of
total iron. An integral method was used to analyse the kinetic data. A literature study reveals
that uraninite dissolution follows first order kinetics, but of interest in these results was that
the uranium dissolution was found to closely follow the second order. Further research is
recommended to look at ascertaining these results. Two models were developed, one using regression and the other by curve fitting method. Both models could fit the
experimental data well enough.Dissertation (MSc)--University of Pretoria, 2016.
Materials Science and Metallurgical Engineering
MSc
Unrestricted
6
Watson, Jack. "Leaching for Maintenance: Factors to Consider for Determining the Leaching Requirement for Crops (AZ". College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 1999. http://hdl.handle.net/10150/146964.
Testo completoAbstract (sommario):
3 pp.As a result of the application of irrigation water containing soluble salts, a salt load is continually added to the soil. Soil salts have to be removed on an ongoing basis through maintenance leaching to prevent yield losses from a salinity buildup. This publication provides factors to consider for determining the leaching requirement for crops.
7
Tavakolikhaledi, Mohammadreza. "Vanadium : leaching and solvent extraction". Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/46814.
Testo completoAbstract (sommario):
The fundamental understanding of vanadium hydrometallurgy was developed in three phases: vanadium (V) leaching, vanadium (III) oxidative leaching, and solvent extraction of vanadium (V&IV).
In the first section, V₂O₅ leaching was studied in three steps. First, vanadium leaching and solubility of VO₂⁺ at different pH’s and temperatures were investigated in sulfuric acid. Secondly, the kinetics of vanadium leaching in pH 5 and pH 8 solutions, and the reductive leaching of vanadium pentoxide using sodium sulfite were studied. It was shown that the kinetics of acid leaching is rapid but suffers from low solubility of VO₂⁺ in solution. Thirdly, the shrinking sphere model was employed to analyze the kinetics of reductive leaching.
In the second step, V₂O₃ oxidative leaching was studied from 30°C to 90°C in sulfuric acid. This study has also been done in three different sections. First, the kinetics of oxidative leaching using oxygen was investigated. It was shown that this oxidative leaching is chemical reaction rate controlled with an activation energy of 69 kJ/mol. In the next step, it was shown that the presence of ferric enhanced kinetics significantly. Finally, oxidative leaching using a constant ferric-ferrous ratio from 1 to 300 was studied. The addition of KMnO₄ solution to the leach reactor was found to be a suitable oxidant for controlling solution potential. The oxidation rate using the constant ferric-ferrous ratio was very sensitive to temperature, with a large activation energy (38 kJ/mol) and the rate was proportional to the Fe(III)/Fe(II) concentration to the power of 0.47.
In the third part, purification of synthetic vanadium-containing solutions using the solvent extraction technique was investigated. Various solvent extractants have been tested for vanadium recovery from acid leachates. One of the biggest problems for purification of the vanadium solution is iron separation. Therefore, this research assesses selectivity of vanadium over iron. The extraction of vanadium (V&IV), iron (III&II) with phosphinic acid (CYANEX 272), phosphonic acid (IONQUEST 801), phosphoric acid (D2EHPA) and phosphine oxide (CYANEX 923) extractants is reported. In addition, the extraction reactions for vanadium (V) and (IV) extraction using CYANEX 923 and D2EHPA were also studied.
8
Hill, Annette Rosemary. "Leaching of alternative pavement materials". Thesis, University of Nottingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410354.
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9
Dubus, Igor G. "Calibration of pesticide leaching models". Thesis, Cranfield University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.269528.
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10
May, Noelene. "The ferric leaching of pyrite". Master's thesis, University of Cape Town, 1997. http://hdl.handle.net/11427/17952.
Testo completoAbstract (sommario):
Bibliography: pages 82-90.The bioleaching of pyrite has been found to occur via an indirect mechanism. Ferric iron leaches the pyrite, and is reduced to ferrous iron. Bacteria such as Thiobacillus ferrooxidans oxidise the ferrous iron to ferric iron, thus maintaining a high redox potential. In this thesis, the effect of the redox potential on the ferric leach rate was investigated by examining previously published data and by developing an experimental technique where dynamic redox potential measurements were used to study the kinetics of the sub-process. The ferric leach rate of pyrite was found to be of the order of 5 x 10⁻⁷ moles pyrite per mole pyrite per second, which is of the same order of magnitude as rates reported for the bioleaching of pyrite over similar ranges of redox potential. The rate decreased as the redox potential decreased, in what appeared to be a Butler-Volmer-like manner. This, along with the observation that there was no significant effect of the total iron concentration, suggested the likelihood of an electrochemical mechanism being operative, with charge transfer at the pyrite surface being rate limiting.
11
Albertani, Bryce Martin. "The leaching of α-spodumene". Thesis, Albertani, Bryce Martin (2018) The leaching of α-spodumene. Honours thesis, Murdoch University, 2018. https://researchrepository.murdoch.edu.au/id/eprint/44868/.
Testo completoAbstract (sommario):
An investigation into the direct leaching of α-spodumene has being warranted due to increasing societal interest in lithium-ion battery technology. The direct leaching of α-spodumene utilising a caustic autoclave process was investigated, in aspirations of leaching significant quantities of lithium from the silicate matrix of α-spodumene. The influence of reagent dosage, temperature, reaction time and particle size on the extraction efficiency of lithium were investigated. From the investigations conducted it became evident that the leaching efficiency of α-spodumene was consistently greater than 40.00% under the optimal conditions. The optimal conditions evaluated throughout the investigation were found to occur at 573.15 kelvin, 14 molar NaOH, a 6 hour residence time and a P80 of 325 μm.
The lithium recovered to solution is present as a hydroxide species, of which is in significant demand within the lithium-ion battery production industry. Sodium silicate or ‘water glass’ was also found to be present within the leach products adding a potential valuable by-product to the process investigated.
12
Parker, Gretel Kristen. "Spectroelectrochemical investigation of chalcopyrite leaching". Thesis, Griffith University, 2006. http://hdl.handle.net/10072/365971.
Testo completoAbstract (sommario):
This thesis describes an experimental investigation, utilising primarily spectroelectrochemical techniques, into the mechanism of chalcopyrite leaching and the properties of the metal-deficient product layer. A systematic comparison of the leaching behaviour and products in chloride and sulfate lixiviants was undertaken, and variation of leach conditions was also considered. The product layer distribution, structure and morphology was examined, and various model systems and compounds investigated to aid in identifying the product layer composition and properties. A range of chalcopyrites, and other pertinent sulfide-minerals, were investigated. The behaviour of chalcopyrite in both chloride and sulfate electrolytes was investigated in situ and ex situ. Electrochemical experiments demonstrated similar initial behaviour in both chloride and sulfate systems. Potentiostatic techniques combined with normal Raman interrogation of the mineral surface showed much thicker product layers formed on the chalcopyrite leached in chloride electrolytes, over the entire surface. The product layer formed on chalcopyrite leached in chloride solutions consisted of octasulfur and/or a Raman-inactive product phase that could be activated under 442 nm laser irradiation to form polymeric sulfur. The parent phase could not be positively identified but is probably an amorphous metal-deficient remnant lattice on the oxidised mineral surface, which can be restructured under specific conditions to polymeric sulfur. Model compound investigations demonstrated that the induced phase converted to elemental sulfur at ~70°C. Polymeric sulfur was present on leached surfaces even in the absence of laser-inducement but was generally overwhelmed by the octasulfur signal (but identified on samples kept under ultrahigh vacuum conditions). Similar product was rarely observed over the sulfate-leached chalcopyrite surface, as the product layer was too thin to be detectable. However, at 'active' sites (cracks, fissures and grain boundaries) product with a lower ?(SS) Raman shift was encountered, indicating longer sulfur bonds and probably less metal-deficiency. Polysulfides, polysulfanes, jarosite and sulfoxy anions were not detected on acid-leached samples. Model sulfide compounds, and proposed intermediates in chalcopyrite oxidation, were investigated using spectroelectrochemical and neutron reflectometry techniques. The same laser-induced polymeric sulfur phase was identified on high-Fe sphalerite and pyrite surfaces during acid-chloride leaching, though not on covellite surfaces. Sulfoxy anion intermediates were observed on pyrite oxidation in acid solution, confirming a different mechanism to that observed for chalcopyrite oxidation. CuS showed distinctly different spectroelectrochemical behaviour to chalcopyrite and thus is not an intermediate in chalcopyrite oxidation. More aggressive leaching of chalcopyrite was investigated at circumneutral pH. Raman, Environmental Scanning Electron Microscopy (ESEM) and X-ray Photoelectron Spectroscopy (XPS) indicated the presence of highly soluble sulfate salts on the sample surface, though the majority of the product consisted of ferric oxyhydroxides and elemental sulfur. Optical and electron microscopy revealed that the product layer thickness and properties varied as a function of grain orientation. Dynamic Secondary Ion - Mass Spectroscopy (SIMS) and XPS were used to yield elemental composition and valence-state information of oxidation products, and how these varied with depth. Oxidation appeared to be incongruent in the early stages of oxidation, with iron more deficient on the surface than copper. The metal-deficiency extended to some depth (up to hundreds of nanometres) on both chloride and sulfate leached samples. Copper maintained a formal univalent oxidation state on the corroding chalcopyrite surface, while iron was present as ferric ion and sulfur present in oxidation states intermediate between sulfide and elemental sulfur. Submonolayer in situ investigations of chalcopyrite oxidation in acid chloride and sulfate solutions were undertaken via development of a technique to facilitate surface-enhanced Raman scattering (SERS) from the chalcopyrite surface. Both ex situ and in situ investigations were undertaken and showed an amorphous product containing sulfur bonds but distinct from polysulfides, polythionates or elemental sulfur allotropes. The product spectrum was similar in sulfate and chloride solutions, in good agreement with electrochemical observations. Normal Raman and SERS investigations indicate that chalcopyrite oxidation proceeds via a mechanism of cation removal and concomitant oxidation of the remnant sulfide lattice. Sulfur bonding does not appear to commence immediately, and when it does occur, an amorphous structure is formed. This amorphous leached layer is stable for relatively long periods of time at room temperature and extends to some depth. In the case of the chloride, the leached layer ages to sulfur, though of a somewhat amorphous nature that does not volatilise extensively under vacuum. The greater aging of the leached layer on chloride-leached samples is probably facilitated by the ability of copper to leave the lattice as a cuprous complex.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Science
Full Text
13
Dyson, Devy Alexander William. "Modeling the kinetics of the zinc pressure leaching process - oxidative sphalerite leaching in sulphuric acid media". Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63409.
Testo completoAbstract (sommario):
In the field of hydrometallurgy, the industrial uptake of leaching models has been overlooked partially due to the lack of universal models. A model developed for one plant cannot easily be transferred for the application of a different plant without redesigning the leaching kinetics in the code. The Multiple Convolution Integral (MCI)-based model developed in this thesis has the ability to be universally applied by user-controlled inputs. Chemical reactions can be selected while the modeling software calculates the mass and energy balances. Residence times, operating conditions, and the rate-limiting reagents can also be defined to calculate a precise fraction reacted (leach extent) for sulphide minerals. The ability of the using the MCI model for predicting sphalerite leaching is examined in comparison to hydrometallurgical plant data collected from a Canadian pressure leach operation. The results are promising, showing that the model can predict plant Zn extraction data to within an error of 1.5 %. The model is further verified through bench scale pressure leaching experiments where 94 % of the zinc is extracted within 90 minutes using a concentrate sample from the same industrial plant. The effect of temperature is analyzed and the activation energy is calculated to be 40.8 kJ/mol. Interesting discoveries with respect to the reagent concentrations and their effect on the overall fraction reacted are also explored from the model results. In addition, the limitations of the MCI model are explained along with suggestions for improvement.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
14
Marshall, Miles Ramsvik. "Spatial variablity and pesticide leaching : measurement and modelling the hydrodynamic aspects of pesticide leaching in soils". Thesis, University of Reading, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402812.
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15
Gashier, Wail. "Accelerated leaching methods for cementitious nuclear wasteforms and the impact of superplasticisers on the leaching behaviour". Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/12266/.
Testo completoAbstract (sommario):
The Intermediate Level Wastes (ILW), produced during the reprocessing of spent nuclear fuel, are commonly encapsulated in a blast furnace slag (BFS) and Portland cement (PC) composite and stored in repositories. These cements are required to safely immobilise these wastes for long durations of time. Additives are used in the cementitious wastes to further enhance them for example superplasticisers are used in general cement industry to increase fluidity, resulting in large reductions of water required for mixing, giving high early strength development, a decrease in permeability and ultimately significant reduction in costs. However superplasticisers contain molecules that can complex insoluble radioelements such as plutonium and uranium increasing their solubility and in turn mobility. This can be problematic while the cementitious wastes are stored. The standard storage conditions in the UK are that a cement is stored in a steel canister, then a backfill cement such as NRVB (Nirex Reference Vault Backfill cement) is poured over this cement, allowed to set after which the container is sealed. These conditions expose the waste forms to potential contact with ground water in the event of damage to the container. It is therefore important to study the leaching behaviour of these cementitious waste forms and simulate any resultant degradation that would occur over the very long durations they are expected to be stored. The impact of superplasticisers on these leaching behaviours is also investigated to understand the impact these additives have. The project investigated the leaching behaviour of caesium (Cs) and strontium (Sr) within a 90wt% blast furnace slag (BFS) and 10wt% Portland cement (PC) system (9:1 BFS:PC). A static leaching method was used to monitor the behaviour of Cs and Sr in solution without changing it. Three accelerated leaching methods were then used, semi-static wherein the solution (deionised water) was changed at regular intervals, acidic using ammonium nitrate (NH4NO3) solution and electrical using a current of 5A/m2 and 25 A/m2. If successful these methods can help characterise the suitability of cement formulations for distant future use. The semi-static method showed small increases in leaching, replacing the solution reset the concentration gradient and kept the pH near neutral. The acidic leaching method increased leaching rates significantly however caused the formation of phases that would not occur naturally and also suppressed Al leaching. The electrical methods caused the largest increase in leaching rates, with the closest similarity to the non-accelerated leaching conditions, the crystal structure was similar to that in static leaching and the hydrate phases formed were similar. A current of 25 A/m2 over a 1-3 day period would leach the same amount of Cs and Sr elements as static leaching for 2 years. The leaching behaviour of Cs and Sr is dependent on how they are retained within the cement. The project found that Cs remains as CsNO3. Sr(NO3)2, however, was not present in the hardened cement and retained within the hydrogarnet and a nitrated AFm phase. Secondly the impact of superplasticisers on the leaching behaviour of the cement matrix containing cerium was also explored using ADVA cast 551. Cerium was chosen as opposed to caesium or strontium as the main concerns in industry due to superplasticisers is regarding the complexion of uranium and plutonium, and Ce is a good simulant for plutonium. It was found that the introduction of ADVA cast 551 increased the fluidity and workability of the cement, did not alter the cement crystal structure however did increase the leached amounts of Ce by approximately 30%. In storage conditions this complexed Ce would come into contact with the cement backfill. A flow through leaching test was used on an NRVB cement sample and synthesised solutions of the leached Ce including the ADVA cast 551 to monitor how much Ce would pass through. It was found that similar amounts of Ce had passed through the NRVB whether the solution contained superplasticiser or not. This project found that the leaching behaviour of ions was dependent on how the ion is present and in which phase. Due to Cs and Sr being incorporated differently the Cs leaches much faster than the Sr, as it is not incorporated into any phase. The Sr is associated with several phases, however is mainly found to be associated with AFm type phases. The most efficient leaching accelerant method is the electrical method; therefore with further investigation this could potentially be used to explore the optimal cement compositions for cementitious waste immobilisation. This could also be used in cement samples containing superplasticiser, given that this increases mobility over short durations, the next step would be to investigate the long-term impacts, via simulation using electrical leaching.
16
Garlapalli, Ravinder Kumar. "Leaching of chalcopyrite with sodium hypochlorite". Morgantown, W. Va. : [West Virginia University Libraries], 2010. http://hdl.handle.net/10450/11213.
Testo completoAbstract (sommario):
Thesis (M.S.)--West Virginia University, 2010.Title from document title page. Document formatted into pages; contains vii, 47 p. : ill. Includes abstract. Includes bibliographical references (p. 46-47).
17
Lázaro-Báez, María Isabel. "Electrochemistry of the leaching of chalcopyrite". Murdoch University, 2001. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20060817.125248.
Testo completoAbstract (sommario):
The potential region in which chalcopyrite dissolves during
the oxidative leaching of the mineral in ferric sulphate solutions
has been established. These results have been modelled using an
extended mixed-potential description of the system. The initial
stages of the dissolution process have been studied using a
chalcopyrite disk and a platinum ring electrode held at appropriate
potentials for the detection of ferrous and cupric ions. These
experiments have shown that the initial stages of oxidation of the
mineral involve the formation of soluble sulphur species in addition
to elemental sulphur. The ring-disk experiments are generally
consistent with thiosulphate as this species. The effectof potential
and various ratios of ferric to ferrous ions on the rate has been
investigated by both electrochemical and chemical analysis
techniques. The role of non-oxidative dissolution in the leaching
of chalcopyrite has been explored and it has been shown that the
initial rate of non-oxidative dissolution is significant and could
exceed the oxidative rate at long leach times.
18
Xia, Chen. "Thiosulphate stability in gold leaching process". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ59414.pdf.
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19
Lázaro-Báez, María Isabel. "Electrochemistry of the leaching of chalcopyrite /". Access via Murdoch University Digital Theses Project, 2001. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20060817.125248.
Testo completo
20
Ndlovu, Sehliselo. "Bacterial leaching of pyrite single crystals". Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.401694.
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21
Andac, M. "Leaching of cement-stabilised solid waste". Thesis, University of Aberdeen, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.592062.
Testo completoAbstract (sommario):
The physical, chemical and leaching properties of municipal solid waste incinerator (abbreviated MSWI) fly ash itself and the long term leaching properties and leaching mechanisms of stabilised MSWI-fly ash in cement systems were analysed. MSWI-fly ash is a complex material which consists of crystalline phases including NaCl, KCl, CaSO4, SiO2, glassy silicates and also an amorphous organic phase. The MSWI-fly ash has a relatively high content of toxic metals, mainly Zn and Pb. The leaching properties of these elements from the ash depends on leachate pH as well as the leach test method. The most leachable major elements are alkali metals and calcium. The toxic metals are also liable to be leached in disposal situations. Ordinary Portland Cement (OPC) and Calcium Sulfoaluminate Cement (CSA) were used for stabilisation of MSWI-fly ash. The ash is partly pozzolanic in the cement systems and affects each type of cement differently. Inclusion of 10% ash in OPC matrices reduces the formation of Ca(OH)2. In a CSA matrix, formation of AFm and AFt reduced and also new compound or compounds form after 60 days curing. In CO2 bubbled water, the leaching rate of elements from 10% MSWI-fly ash containing cements, especially Zn and Pb, change with time as well as with ongoing hydration. The extension of curing time for CSA + 10% ash paste degrades the matrix retention of Pb: the leached percent of Pb increases from 0.0009 to 0.0023% with extension of curing from 7 to 60 days. But the percent of Zn leached decreases with extension of curing time: 0.087 to 0.0157%. On the other hand the leaching percent of Zn and Pb from OPC + 10% ash decreases with curing time. Generally in short term curing, the leached percent of elements from an OPC + 10% ash paste is higher than from a CSA + 10% ash paste.
22
Al-Omeiri, Saeed S. "Leaching of copper-refined anode slime". Thesis, University of Strathclyde, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435125.
Testo completo
23
Cai, Liping. "CFD modelling of chalcopyrite heap leaching". Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/44559.
Testo completoAbstract (sommario):
Heap leaching is widely applied to recover metals from ore. The behaviour of the fluid and chemical species inside heaps, which involves many coupled physico-chemical phenomena, are highly variable and complex. Computational Fluid Dynamics (CFD) simulation can provide an efficient approach to investigate these phenomena and offer guidelines to improve heap design. Stagnant zones exist in the packed bed with multiphase flow, however, the conventional advection-dispersion model (ADE) failed to capture this phenomenon, therefore, the mobile immobile model (MIM) is employed to model the mass transport and heat transfer instead of the conventional ADE. For predicting the mineral dissolution in heap leaching, we developed a new semi-empirical model which is an alternative to the traditional shrinking core model (SCM), but is more flexible in ability to fit with various dissolution kinetics profiles. The key assumption of this semi-empirical model is validated, and it is calibrated with experiments for chalcopyrite leaching. The software Fluidity, which is an unstructured mesh based finite element/control finite volume modelling, is further developed to implement the reactive mass transport and heat transfer simulation for heap leaching. The numerical schemes for multiphase flow models are control volume finite element method (CVFEM) for spacial discretization and the implicit pressure explicit saturation algorithm (IMPES) for temporal discretization. The mass transport and heat transfer equations are solved implicitly by using the control volume method.\ Before the implementation of various heap leaching simulations, the MIM is validated by experiments and the liquid-solid phase heat transfer models are verified by method of manufactured solution (MMS). Then the reactive transport model for chalcopyrite leaching, which includes the semi-empirical model for predictions of mineral dissolution, is validated by three separate experiments. Various heap leaching simulations are implemented to analyse the leaching performance and efficiency. Four groups of 1D simulations are implemented to evaluate the effects of the bacterial activity, the form of the mass transport model, solution temperature, Fe^(3+) concentrations and solution pH on the leaching system. The large scale 2D simulations for leaching with a heap of trapezoid shape were implemented to evaluate the effects of oblique walls on the leaching performance. There different wall slopes, which are 30°, 45° and 60°, are investigated in the 2D simulations. The main contribution of this project is that a new semi-empirical model and the mobile immobile model are developed and integrated into a chalcopyrite leaching simulator, the simulation results of those models approach to the real physical world better than the conventional models. In conclusion, an improved numerical scheme is provided in this project to investigate and optimise the process of chalcopyrite leaching for industrial purpose.
24
Carter, E. Thomas Jr. "Risk assessment formulation for nitrate leaching". Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/40347.
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25
Dominguez, Kimberly. "Leaching of Silver Nanoparticles from Textiles". Ohio University Art and Sciences Honors Theses / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ouashonors155690445799457.
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26
Abrahamsson, Filip. "Leaching of Pyrrhotite from Nickel Concentrate". Thesis, Luleå tekniska universitet, Industriell miljö- och processteknik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-64934.
Testo completoAbstract (sommario):
Non-oxidative acid leaching of pyrrhotite from Kevitsa’s Ni-concentrate and methods to recover by-products, have been investigated. Selective dissolution of pyrrhotite (Fe1-xS, 0<x<0.25) can enrich the content of the valuable metals, such as Ni and Co, in the final concentrate and will reduce the amount of Fe and S sent to the smelters. The pyrometallurgical smelting of leached concentrate will thus give less formation of smelter by-products in form of slag and SO2. The leaching was studied through an experimental design plan with parameter settings of 38.8% to 57.8% H2SO4 and temperatures from 60 to 100°C. The best results were obtained in experiments carried out at the lower experimental range. Leaching at 60°C with an initial acid concentration of 38.8% H2SO4 was found sufficient to selectively dissolve most of the pyrrhotite; leaving an enriched solid residue. A QEMSCAN analysis of the solid residue confirmed that most of the pyrrhotite had been dissolved and showed that pentlandite was still the main Ni-mineral. Chemical assays showed that more than 95% of the Ni, Co, and Cu remained in the final residue. The utilized leaching process generates by-products, in the form of large quantities of Fe2+ in solution and gaseous H2S. To recover Fe2+, crystallization of iron(ii) sulfate (FeSO4∙nH2O) from leach solution through cooling have been studied. The crystallized crystals were further dehydrated into the monohydrate (FeSO4∙H2O) through a strong sulfuric acid treatment (80%H2SO4). XRD analysis confirmed that FeSO4∙H2O was the main phase in the final crystals, and a chemical analysis showed a Fe content of about 30%, 1.5% Mg, 0.4% Ca, and 0.2% Ni. The possibility to leach the concentrate by circulating the acidic solution from the crystallization stage has been tested. The recirculation of the solution showed no negative effects, as the recoveries of elements and chemical assays of the final solid residue were found to be similar to the obtained assay when the concentrate was leached in a fresh solution.Icke-oxidativ syralakning av magnetkis från Kevitsas Ni-koncentrat har studerats samt metoder för tillvaratagande av biprodukter. Genom en selektiv upplösning av magnetkis (Fe1-xS, 0<x<0.25) kan värdefulla metaller som Ni och Co anrikas i det slutliga koncentratet. Samtidigt som mängden Fe och S som skickas till smältverken minskar, vilket också innebär att mindre biprodukter i form av slagg och SO2 erhålls vid den pyrometallurgiska smältningen av Ni-koncentratet. En experimentell design plan genomfördes för att studera lakningen där syrakoncentrationen varierades från 38.8% till 57.8%H2SO4 och temperatur från 60 till 100°C. Bäst resultat erhölls vid de lägre parameterinställningarna. Lakning vid 60°C med en initial syrakoncentration på 38.8%H2SO4 visade sig vara tillräcklig för att selektivt lösa upp merparten av all magnetkis och lämna kvar en anrikad produkt. Via QUEMSCAN bekräftades att merparten av all magnetkis hade löst upp sig och att huvudsakligt Ni-mineral fortfarande var pentlandit. Kemiska analyser visade att mer än 95% av Ni, Co och Cu stannade kvar i fasta godset. Den tillämpade lakningsmetoden genererar biprodukter i form av stora mängder Fe2+ i lösning och H2S i gasform. För att tillvarata Fe2+ har kristallisering av laklösning som järn(ii) sulfat (FeSO4∙nH2O) studerats genom kylning. De kristalliserade kristallerna avvattnades till monohydrat, FeSO∙1H2O, genom avvattning i stark svavelsyra (80%H2SO4). XRD bekräftade FeSO∙1H2O som huvudfas i slutliga kristallerna och kemisk analys visade på ca 30%Fe med huvudsakliga orenheter i form av 1.5% Mg, 0.4%Ca och 0.2% Ni. Möjligheten till att laka i återcirkulerad lösning efter kristallisering har undersökts. Lakning i återcirkulerad lösning visade inga negativa effekter då liknande halter och utbyten erhölls till det fasta godset.
27
Carter, E. Thomas. "Risk assessment formulation for nitrate leaching /". This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-11182008-063039/.
Testo completo
28
Lazaro-Baez, Maria Isabel. "Electrochemistry of the leaching of chalcopyrite". Thesis, Lazaro-Baez, Maria Isabel (2001) Electrochemistry of the leaching of chalcopyrite. PhD thesis, Murdoch University, 2001. https://researchrepository.murdoch.edu.au/id/eprint/147/.
Testo completoAbstract (sommario):
The potential region in which chalcopyrite dissolves during the oxidative leaching of the mineral in ferric sulphate solutions has been established. These results have been modelled using an extended mixed-potential description of the system. The initial stages of the dissolution process have been studied using a chalcopyrite disk and a platinum ring electrode held at appropriate potentials for the detection of ferrous and cupric ions. These experiments have shown that the initial stages of oxidation of the mineral involve the formation of soluble sulphur species in addition to elemental sulphur. The ring-disk experiments are generally consistent with thiosulphate as this species. The effect of potential and various ratios of ferric to ferrous ions on the rate has been investigated by both electrochemical and chemical analysis techniques. The role of non-oxidative dissolution in the leaching of chalcopyrite has been explored and it has been shown that the initial rate of non-oxidative dissolution is significant and could exceed the oxidative rate at long leach times.
29
Lazaro-Baez, Maria Isabel. "Electrochemistry of the leaching of chalcopyrite". Lazaro-Baez, Maria Isabel (2001) Electrochemistry of the leaching of chalcopyrite. PhD thesis, Murdoch University, 2001. http://researchrepository.murdoch.edu.au/147/.
Testo completoAbstract (sommario):
The potential region in which chalcopyrite dissolves during the oxidative leaching of the mineral in ferric sulphate solutions has been established. These results have been modelled using an extended mixed-potential description of the system. The initial stages of the dissolution process have been studied using a chalcopyrite disk and a platinum ring electrode held at appropriate potentials for the detection of ferrous and cupric ions. These experiments have shown that the initial stages of oxidation of the mineral involve the formation of soluble sulphur species in addition to elemental sulphur. The ring-disk experiments are generally consistent with thiosulphate as this species. The effect of potential and various ratios of ferric to ferrous ions on the rate has been investigated by both electrochemical and chemical analysis techniques. The role of non-oxidative dissolution in the leaching of chalcopyrite has been explored and it has been shown that the initial rate of non-oxidative dissolution is significant and could exceed the oxidative rate at long leach times.
30
Sitando, Onias. "Gold Leaching in Thiosulfate-Oxygen Solutions". Thesis, Sitando, Onias (2017) Gold Leaching in Thiosulfate-Oxygen Solutions. PhD thesis, Murdoch University, 2017. https://researchrepository.murdoch.edu.au/id/eprint/38239/.
Testo completo
31
Muslim, Abrar. "Thiosulfate leaching process for gold extraction". Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/896.
Testo completoAbstract (sommario):
Increasing environmental concerns over the use of cyanide for gold recovery has intensified the need to deeply understand gold thiosulfate leaching system. Therefore, experimental and modelling work for the kinetics and equilibrium adsorption of thiosulfate, polythionates, gold and copper onto strong based anion exchange resin have been conducted in this study, and the results are concisely discussed in the thesis. Experimental procedures, reaction mechanisms and novel dynamic models for the adsorption phenomena were also proposed.
32
McGinnity, Justin. "Sulfur dioxide leaching of zinc sulfide". Thesis, Curtin University, 2001. http://hdl.handle.net/20.500.11937/1033.
Testo completoAbstract (sommario):
Studies were conducted into the mechanism and kinetics of the dissolution of synthetic zinc sulfide and zinc concentrate in aqueous solutions containing sulfur dioxide.Experiments at ambient temperature established that the dissolution of ZnS in aqueous solutions of sulfur dioxide proceeds via acidic non-oxidative dissolution and not by direct reaction of the sulfide with S02(aq). The non-oxidative dissolution reaction generates H2S(aq) or HS-(aq) species which are thought to rapidly react with sulfurous acid species, S02(aq) or HS03-(aq), to possibly produce initially sulfane monosulfonates as intermediates, followed by sulfane disulfonates and elemental sulfur. The formation of sulfane monosulfonates is postulated based upon inhibition observed in ZnS / S02 leaches which is not attributable to either H2S(aq) or occlusion elemental sulfur.At elevated temperatures (100oC - 200oC) the rate of ZnS dissolution in sulfurous acid is affected by the thermal decomposition of sulfurous acid, which produces sulfuric acid, which leaches the mineral non-oxidatively. Increasing the temperature increases the rate of thermal decomposition of sulfurous acid and consequently, the rate of sulfuric acid formation, increasing the rate of ZnS dissolution.The kinetics of the dissolution of ZnS in solutions of sulfuric acid and sulfur dioxide were investigated at temperatures up to 200oC. At 100oC and 150oC, the dissolution of ZnS in H2SO4 was found to obey the relationd[Zn2+]/dt = kfAs[H+] krAs[H2S(aq)]1/2[Zn2+]1/2and equilibria and rate constants for the ZnS / H2S04 reaction were obtained over the range, 100oC to 200oC. The activation energies of the forward and reverse reactions were found to be 56 +/- 11 kJ mol-1 and 45 +/- 15 kJ mol-1, respectively. The equilibrium constants were 4.99x10-4, 1.26x10-3 and 2.83x10-3 at 100oC, 150oC and 200oC, respectively.In the presence of added S02, at low ZnS pulp density (0.5 g L-1), the rate of ZnS dissolution in sulfuric acid increased due to the removal of H2S(aq) by reaction with S02(aq) or HS03-(aq). However the increase in rate was much less than that expected for the complete removal of H2S(aq). As with leaches of ZnS in sulfurous acid at ambient temperature, the inhibition was not attributable to the presence of residual H2S(aq) or to occlusion of unreacted ZnS by elemental sulfur, but is thought to be due to aqueous species that are like "H2S", in that they may react with Zn2+ to reprecipitate W.To this end, sulfane monosulfonates have again been postulated. The rate of ZnS dissolution, under conditions of low pulp density, was independent Of S02 concentration, suggesting that under these conditions the rate of the H2S / S02 reaction is also independent of the S02 concentration.At higher pulp densities (200 g L-1), similar to those expected in an industrial application, synthetic zinc sulfide leached rapidly in H2S04 / S02 solutions to approximately 60% zinc extraction, but was then inhibited by the large amounts of sulfur that formed. These caused agglomerates of zinc sulfide and elemental sulfur to form, even at temperatures below the melting point of sulfur, reducing the surface area of zinc sulfide available for reaction.Leaches of zinc concentrate at low pulp densities in H2S04 / S02 solutions and at temperatures above sulfur's meting point, were inhibited by the formation of molten sulfur. In contrast to synthetic zinc sulfide, zinc concentrate is readily wet by molten sulfur. Three surfactants orthophenylenediamine, quebracho and sodium ligninsulfonate were found to be reasonably effective in preventing molten sulfur from occluding the mineral surface. At high pulp densities, the H2S04 / S02 leach solution was unable to effect, the extraction of zinc from a zinc concentrate beyond approximately 10%.Integral S02 / H2S04 leaching of zinc concentrate was found not to be a commercial prospect. However, sidestream processing of zinc concentrate in an acid leach stage followed by reaction of generated H2S with S02 from the roasting stage to produce elemental sulfur may be viable.
33
McGinnity, Justin. "Sulfur dioxide leaching of zinc sulfide". Curtin University of Technology, Department of Applied Chemistry, 2001. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=12896.
Testo completoAbstract (sommario):
Studies were conducted into the mechanism and kinetics of the dissolution of synthetic zinc sulfide and zinc concentrate in aqueous solutions containing sulfur dioxide.Experiments at ambient temperature established that the dissolution of ZnS in aqueous solutions of sulfur dioxide proceeds via acidic non-oxidative dissolution and not by direct reaction of the sulfide with S02(aq). The non-oxidative dissolution reaction generates H2S(aq) or HS-(aq) species which are thought to rapidly react with sulfurous acid species, S02(aq) or HS03-(aq), to possibly produce initially sulfane monosulfonates as intermediates, followed by sulfane disulfonates and elemental sulfur. The formation of sulfane monosulfonates is postulated based upon inhibition observed in ZnS / S02 leaches which is not attributable to either H2S(aq) or occlusion elemental sulfur.At elevated temperatures (100oC - 200oC) the rate of ZnS dissolution in sulfurous acid is affected by the thermal decomposition of sulfurous acid, which produces sulfuric acid, which leaches the mineral non-oxidatively. Increasing the temperature increases the rate of thermal decomposition of sulfurous acid and consequently, the rate of sulfuric acid formation, increasing the rate of ZnS dissolution.The kinetics of the dissolution of ZnS in solutions of sulfuric acid and sulfur dioxide were investigated at temperatures up to 200oC. At 100oC and 150oC, the dissolution of ZnS in H2SO4 was found to obey the relationd[Zn2+]/dt = kfAs[H+] krAs[H2S(aq)]1/2[Zn2+]1/2and equilibria and rate constants for the ZnS / H2S04 reaction were obtained over the range, 100oC to 200oC. The activation energies of the forward and reverse reactions were found to be 56 +/- 11 kJ mol-1 and 45 +/- 15 kJ mol-1, respectively. The equilibrium constants were 4.99x10-4, 1.26x10-3 and 2.83x10-3 at 100oC, 150oC and 200oC, respectively.In the presence of added S02, ++at low ZnS pulp density (0.5 g L-1), the rate of ZnS dissolution in sulfuric acid increased due to the removal of H2S(aq) by reaction with S02(aq) or HS03-(aq). However the increase in rate was much less than that expected for the complete removal of H2S(aq). As with leaches of ZnS in sulfurous acid at ambient temperature, the inhibition was not attributable to the presence of residual H2S(aq) or to occlusion of unreacted ZnS by elemental sulfur, but is thought to be due to aqueous species that are like "H2S", in that they may react with Zn2+ to reprecipitate W.To this end, sulfane monosulfonates have again been postulated. The rate of ZnS dissolution, under conditions of low pulp density, was independent Of S02 concentration, suggesting that under these conditions the rate of the H2S / S02 reaction is also independent of the S02 concentration.At higher pulp densities (200 g L-1), similar to those expected in an industrial application, synthetic zinc sulfide leached rapidly in H2S04 / S02 solutions to approximately 60% zinc extraction, but was then inhibited by the large amounts of sulfur that formed. These caused agglomerates of zinc sulfide and elemental sulfur to form, even at temperatures below the melting point of sulfur, reducing the surface area of zinc sulfide available for reaction.Leaches of zinc concentrate at low pulp densities in H2S04 / S02 solutions and at temperatures above sulfur's meting point, were inhibited by the formation of molten sulfur. In contrast to synthetic zinc sulfide, zinc concentrate is readily wet by molten sulfur. Three surfactants orthophenylenediamine, quebracho and sodium ligninsulfonate were found to be reasonably effective in preventing molten sulfur from occluding the mineral surface. At high pulp densities, the H2S04 / S02 leach solution was unable to effect, the extraction of zinc from a zinc concentrate beyond approximately ++
10%.Integral S02 / H2S04 leaching of zinc concentrate was found not to be a commercial prospect. However, sidestream processing of zinc concentrate in an acid leach stage followed by reaction of generated H2S with S02 from the roasting stage to produce elemental sulfur may be viable.
34
Lee, Aik Heng. "Prediction of pollutant leaching from landfill". Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/2182.
Testo completoAbstract (sommario):
Landfill is continued to be the most common approach to solid waste disposal. On contrary, landfill practice is still common with increase in water pollution due to leaching of pollutants.Leachate generation from landfill can be defined into two phases, firstly soluble salt produced due to aerobic decomposition or acetogenic phase and secondly methane and carbon dioxide due to anaerobic decomposition or methanogenic phase.Characterization of landfill leachate is used in design to achieve low hydraulic conductivity or decrease permeability as leachate percolating through the waste strata and most important is used to predict level of pollutant in leachate which depend on factors such as temperature, precipitation and waste age. It is therefore crucial for landfill design to take into consideration of factors affecting leachate quality.The purpose of this research is to develop a correlation relationship of factors affecting leachate quality to predict pollutants from landfill which are determined by temperature, precipitation and waste age. The objective of this research is to determine, based the relationship developed and calibration of data obtained from literature review, the optimization of design that reduce pollutants in leachate generated from landfill taking into consideration of basic factors of temperature, precipitation and waste age of landfill.Results of the study revealed that there is a good correlation of pollutants leaching from landfill to the factors of temperature, precipitation and waste age. Higher pollutant concentration is found in average age landfill than the mature age landfill site mainly due to transition from acetogenic phase to methanogenic phase of pollutant decomposition. It is also anticipated that as carbonaceous organic matter decrease in leachate, nitrogeneous organic matter removal is activated in the mature landfill.Using Multiple Regression Analysis Method, mathematic model known as Pollutant Prediction Model is developed to correlate relationship of pollutants to factor affecting leachate quality in the landfill site in terms of temperature, precipitation and waste age.
35
Kaya, Serif. "High Pressure Acid Leaching Of Turkish Laterites". Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12612896/index.pdf.
Testo completoAbstract (sommario):
ABSTRACT
HIGH PRESSURE ACID LEACHING OF TURKISH LATERITES
Kaya, Serif
M.Sc., Department of Metallurgical and Materials Engineering
Supervisor: Prof. Dr. Yavuz A. Topkaya
January 2011, 91 pages
The aim of this thesis study was to investigate and find the most cost effective way of extracting nickel and cobalt into the pregnant leach solution (PLS) from Gördes lateritic nickel and cobalt ore by means of sulphuric acid leaching under high temperature and high pressure conditions.The high pressure acid leach (HPAL) experiments were conducted with nontronitic and limonitic types of Gö
rdes lateritic nickel ore, respectively. Leaching experiments of nontronite ore have shown that almost all of the nickel and cobalt contained in the nontronitic ore were easily extracted into the (PLS). Therefore, the rest of the experiments were concentrated on difficult to leach limonitic sample when compared with the nontronitic one, and higher nickel and cobalt extractions were aimed to be obtained. By taking economic and technical considerations into account, the basic (HPAL) process parameters for the limonitic sample were optimized as
leaching at 255 °
C with a particle size of 100% -850 &mu
with 0.30 sulphuric acid to ore weight ratio in 1 hour of leaching duration. The experiments were conducted with 30% solids ratio and it was found that 87.3% of nickel and 88.8% of cobalt present in the limonitic ore could be extracted into the pregnant leach solution. Nevertheless, these results were found to be below the desired values. Therefore, the possible reasons of this behavior were investigated and the presence of hematite mineral in the limonitic ore was found to be the most probable one. Therefore, in order to dissolve the nickel and cobalt present in the hematite mineral, the additions of HCl, ferrous ions, cuprous ions and sulphur were tried, respectively and they were found to be beneficial in order to increase the degree of nickel and cobalt extractions.
36
George, Anthe. "The leaching properties of co-combustion residues". Thesis, Imperial College London, 2005. http://hdl.handle.net/10044/1/12027.
Testo completo
37
Blancarte-Zurita, Martha Alicia. "Controlled redox potential microbiological leaching of chalcopyrite". Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28627.
Testo completoAbstract (sommario):
Leaching of chalcopyrite by Thiobacillus ferrooxidans under standard microbiological leaching conditions resulted in simultaneous solubilization of copper, iron and sulfur. The sulfide portion was oxidized preferentially over iron in solution suggesting a direct attack mechanism by the bacteria on the mineral particles.
Copper extractions were low, 29-44%, with maximum specific copper extraction rates of the order of 0.001-0.006 h⁻¹ and cell yields per unit of copper released 4-43mg TOC/mg Cu.
Leaching under redox-controlled conditions required a minimum pulp density, ca. 200 g/1, to result in elemental sulfur production. Some unknown factor, resulting from biological leaching activity under standard conditions and transferred with the liquid phase of the inoculum, was needed for the leach to occur under redox-controlled conditions. Copper extractions of 44-100% were achieved. Maximum specific copper extraction rates were of the order of 0.002-0.007 h⁻¹ with cell yield per unit of copper released of the order of 0.12-3.32mg TOC/g Cu for batch cultures. Ferrous iron in solution appeared to be the energy source for cell growth under redox-controlled conditions. The cells' sulfide oxidizing capacity seemed to be inhibited at the metabolic regulation level and not at the enzyme synthesis level. Cells growing under the standard conditions underwent a lag phase, upon transfer to the redox-controlled medium. During this lag phase low metal solubilization rates and low S⁰ production occurred, but when cell growth started, the leaching rates increased and the mineral dissolved rapidly. Electron diffraction X-ray analyses were carried out to investigate the role of silver in the controlled-redox leaching. No silver was observed to be on the surface of the chalcopyrite particles before or after the initial activation stage of the controlled-redox process. Silver deposits were observed after many hours of leaching.
A mathematical model to describe the kinetics of microbial leaching, using a shrinking particle concept as its basis, was developed. When tested against data from the literature for leaching of Zinc from ZnS concentrate it was able to predict particle size as a function of leach time. It also gave reasonable predictions of particle size as a function of leach time for standard leaching of chalcopyrite but failed to predict accurate values for particle size as a function of leach time for the controlled-redox process.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
38
Rademan, Johan Andries Muller. "The simulation of a transient leaching circuit". Thesis, Link to the online version, 1995. http://hdl.handle.net/10019/3146.
Testo completo
39
Stenemo, Fredrik. "Vulnerability assessments of pesticide leaching to groundwater /". Uppsala : Dept. of Soil Sciences, Swedish University of Agricultural Sciences, 2007. http://epsilon.slu.se/200757.pdf.
Testo completo
40
Torstensson, Gunnar. "Nitrogen availability for crop uptake and leaching /". Uppsala : Swedish Univ. of Agricultural Sciences (Sveriges lantbruksuniv.), 1998. http://epsilon.slu.se/avh/1998/91-576-5507-3.gif.
Testo completo
41
Onal, Mehmet Ali Recai. "Pressure Leaching Of Caldag Lateritic Nickel Ore". Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615480/index.pdf.
Testo completoAbstract (sommario):
The purpose of this study was to investigate the process optimization of combined high pressure acid leaching (HPAL) and mixed hydroxide precipitation (MHP) route for the extraction of nickel and cobalt from Çaldag lateritic nickel ore. In order to extract nickel and cobalt values into pregnant leach solution (PLS), several process parameters of HPAL including acid load, temperature, leaching duration and particle size were investigated in comparative manner at constant solid concentration and agitation speed. After HPAL trials, it has been found that more than one combination of parameters offered higher than 90% extraction efficiencies for both nickel and cobalt. Among them, 0.325 kg/kg acid load, 250°
C, 1 hour duration and 100% -1 mm particle size was selected as the optimum conditions with 94.1% Ni and 94.0% Co extractions. A stock of PLS was prepared under the stated conditions that was treated by downstream operations in order to obtain MHP. Initially by two-stage iron removal of downstream operations major impurities iron, chromium and aluminum were nearly completely removed with acceptable nickel and cobalt losses from PLS. Then, the nickel and cobalt were precipitated by two-stage mixed hydroxide precipitation. In the first step of MHP, the optimum conditions were chosen as pH=7.10, 60°
C and 1 hour duration. The intermediate product obtained at these conditions contained 44.3% Ni, 3.01% Co with 3.06% Mn contamination. In summary, it was found that Ç
aldag nickel laterite ore was readily leachable under HPAL conditions and PLS obtained was easily treatable in order to produce saleable MHP.
42
Parada, Torres Fernando Andrés. "The alkaline sodium sulphide leaching of enargite". Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/34016.
Testo completoAbstract (sommario):
Leaching of enargite samples containing approximately 12 % As, 0.5 % Sb and 38 % Cu was studied in alkaline sodium sulphide solutions. Samples were leached in the presence of sodium hydroxide and sodium sulphide, which is expected to hydrolyse and form sodium hydrosulphide. Kinetic parameters studied included temperature, particle size, reagent concentration and stoichiometry in high pulp density tests. Leaching behaviour of arsenic and antimony was very similar; it was enhanced as temperature and reagent dosage was increased and/or particle size decreased. Copper, iron, zinc, and silver were not extracted during the leaching procedure. Through chemical analysis, X-Ray Diffraction and Scanning Electron Microscopy leach solutions and residues were characterised. Arsenic and antimony were efficiently removed, leaving copper-sulphur compounds such as digenite, bornite and sodium copper sulphide (NaCu₅S₃). Some of the leaching results differ from those found in the literature, especially in regards to the nature of the solid residue and the leaching reaction given.
Removal of arsenic from solution was analysed by acidification and crystallization. Acidification removed arsenic and antimony from solution to produce a mixture of oxides and sulphides; however, sulphide was removed from solution most likely as hydrogen sulphide, which would need to be scrubbed in a sodium hydroxide solution. Finally acid consumptions over arsenic plus antimony ratios were too large for a practical application. Crystallization on the other hand is a simpler alternative. The main requirement is to have high concentrations of arsenic and antimony in solution. In this case part of the arsenic and antimony would be recirculated to the leaching stage.
Other aspects included behaviour of chalcopyrite and pyrite in alkaline solutions and the possibility of producing sulphide ions in situ. Unfortunately no considerable amounts of aqueous sulphide were produced. Also, the behaviour of arsenic and antimony (III) in sodium sulphide alkaline solutions was analysed using arsenic and antimony trioxide. These results are in an early phase of study and could be a relevant topic for further research. In both cases a black precipitate formed containing elemental antimony and oxides. However, no crystallization of thio-compounds seemed to have occurred.
43
Zaayman, Yolande. "Leaching kinetics of synthetic heazlewoodite / Y. Zaayman". Thesis, North-West University, 2004. http://hdl.handle.net/10394/646.
Testo completoAbstract (sommario):
The sources of base metals are mainly in the form of oxides or sulphides, of
which the sulphides are predominantly present in South Africa. These metals
are intergrown platinum group and base metals in the form of alloys and
sulphides. In order to produce high grade saleable metals, it is necessary to
effectively separate the base metals from the precious metals.
By means of a hydrometallurgical process, that is leaching, metals can
selectively be extracted from ores. The mechanism of leaching can be
described by oxidation-reduction and acid-base reactions.
During this study, the leaching of a synthetically prepared heazlewoodite
(Ni3S2) nugget was investigated. The parameters that were studied during the
thermal leaching investigation are:
-different acids;
-different temperatures;
-nitrogen and oxygen;
-copper(lI) and iron(llI) ions.
The influence of these parameters is discussed. It was found that the leaching
rate appears to be dependant on the orientation of the crystals. The leaching
process is partly an oxidation process, which is enhanced by the addition of
strong oxidants. This was seen by the high leaching rates yielded by nitric
acid. Oxygen and iron(lll) also accelerated the dissolution process. Leaching
rates were typically in the order of 0.87 ± 0.02 mg.m-2.s-1 in 0.5 mol.dm-3 H2S04 under an oxygen atmosphere. This rate increased to 12.4 ± 0.20
mg.m-2.s-1 and 15.8 ± 0.13 mg.m-2.s-1 in the presence of Fe(lll) and Cu(ll) ions
under an oxygen atmosphere, respectively.
Two activation energies were calculated from the thermal data. These values
were found to be 28.2 kJ.mol-1 for the initial leaching rate, and 45.75 kJ.mol-1
for the final leaching rate. These values are indicative of a surface chemical
rate determining step.
The two electrochemical methods used to investigate the oxidation-reduction
reaction were cyclic voltammetry and chronopotentiometry.
It was found that the dissolution rate determining processes occurred between
0.25 and 0.55 V (v. SHE). Results showed that irreversible oxidation-reduction
processes control the electrochemistry of heazlewoodite. Since the oxidation-reduction
processes are not the only reactions occurring, the presence of
acid-base reactions complicated the description of the dissolution process. A
qualitative description of the voltammograms, as well as an empirical model
describing the leaching process, is given. In this model the formation of an
inert layer is described, which forms by the oxidation of the nickel sulphide
surface. The dissolution of the layer in acid was slower than the dissolution of
the Ni3S2 which resulted in a decreased leaching rate.Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2005.
44
MacArthur, Andrew. "Electrically accelerated leaching of simulated cementitious wasteforms". Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/19959/.
Testo completoAbstract (sommario):
UK disposal plans for intermediate-level nuclear waste (ILW) foresee its encapsulation in blends of Blast Furnace Slag and Portland cement (BFS:PC), held in steel drums and stored in a Geological Disposal Facility. Following groundwater ingress, wasteform degradation through leaching is possible and radionuclides could escape. Due to the long lifetime of hazardous waste, real-time experiments are infeasible, although it is necessary to gain detailed information about leaching performance of the wasteforms for key radionuclides and their transmutation products. This study aims at better understanding the durability of the wasteform by investigating the interactions of caesium and barium with the cement matrix (3:1 BFS:PC) through an accelerated degradation method: Electrically accelerated leaching. 137Cs, a problematic radionuclide in ILW due to its abundance and mobility, decays into 137Ba over time. This study revealed that when intermixed above ~2.8 wt.%, CsNO3 will precipitate without interacting with the 3:1 BFS:PC matrix. When barium is incorporated as Ba(NO3)2 and Ba(OH)2∙8H2O, barite (BaSO4) forms even at 1 wt.%-equivalent of CsNO3, and ettringite formation decreases. The study also revealed that Ca leaching was accelerated by 19.3±1.9 times when 3:1 BFS:PC is electrically leached at a current density of 25 Am-2 for two weeks. This ‘Leaching Acceleration Factor’ was different for every element studied. Leaching of cations into the anode tank, and vice versa for anions, is actually suppressed compared with static leaching. Electric migration of Ba into pre-cured 3:1 BFS:PC containing Cs resulted in formation of barite in the near-surface region of the cement. This suggests that formation of barite likely takes place following the nuclear decay of 137Cs, which is a desirable result as barite is highly insoluble, becoming strongly immobilised in the cementitious wasteform.
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Lok, Jonathan Y. "Acid Leaching of SHS Produced MgO/TiB2". Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/35366.
Testo completoAbstract (sommario):
The stoichiometric Self-propagating High-temperature Synthesis (SHS) thermite reaction involving magnesium oxide (MgO), titanium dioxide (TiO2), and boron oxide (B2O3) forms titanium diboride (TiB2) and MgO as final products. Selective acid leaching is used to remove the MgO leaving high purity TiB2 powder. The SHS method to produce TiB2 is attractive because of the relatively low temperature required to initiate the reaction, fast reaction time, and product purity. This study investigates the acid leaching of SHS produced MgO/TiB2 and a stoichiometric mixture of commercial MgO and TiB2 powders. Leaching was conducted at 90° C, 60° C, and 30° C at pH levels of 4.0, 2.5, and 1.0 by introduction of concentrated aliquots of HNO3. This method maintains a minimum pH target throughout the leaching process, thereby sustaining a dynamic concentration to remove the oxide. The optimal leaching conditions were determined to be at 90° C at a minimum pH target of 2.5 for the SHS produced product. At these conditions, conversion percentages of 83%-84% of MgO were measured with only trace amounts of TiB2 measured in the solution (less than 100 ppm). Conversion percentages for each leaching condition and dissolution mass of solid MgO and TiB2 at each pH are also reported. Results from powder XRD confirm the removal of MgO and minimal dissolution of TiB2, and indicate the formation of unidentified compounds. Inductively coupled plasma mass spectrometry (ICP) was used to analyze the ionic composition and extent of leaching. Scanning electron microscopy (SEM) was used to observe the particle morphology of the leached powders.Master of Science
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Hirato, Tetsuji. "Studies on the Oxidative Leaching of Chalcopyrite". Kyoto University, 1986. http://hdl.handle.net/2433/74697.
Testo completo
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Watson, Jack. "Leaching for Reclamation (AZ Water Series #23)". College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 1999. http://hdl.handle.net/10150/144697.
Testo completoAbstract (sommario):
2 pp.When salts build up in soil, they have to be removed to allow for plant growth. The amount of water required to accomplish this task depends upon the method of water application, the initial salinity of the soil, the final soil salinity desired, and the quality of the irrigation water. This publication provides the soil and water analysis for leaching salts from soil.
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Lim, Hazel. "Leaching of Rare Earths from Eudialyte Minerals". Thesis, Curtin University, 2019. http://hdl.handle.net/20.500.11937/75841.
Testo completoAbstract (sommario):
The (a) sulfuric and (b) citric acid leaching of rare earths from two differently textured eudialyte minerals were investigated through leaching tests conducted using Taguchi and fractional factorial design of experiments. Results of the leaching studies showed that the use of novel method of citric acid yielded comparable leaching recoveries of 70-80 % to conventional sulfuric acid method on direct leaching of large-grained eudialyte. Fine-grained eudialyte required rigorous conditions for rare earths leaching.
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Vu, Quoc Hung. "Modelling pollutants leaching from recycled construction materials". Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/130795/1/Quoc%20Hung_Vu_Thesis.pdf.
Testo completoAbstract (sommario):
This research developed new models to replicate metal leaching characteristics from recycled concrete aggregate (RCA) and reclaimed asphalt pavement (RAP). Model development was supported by a comprehensive experimental and analytical program with multiple influential factors. New models were developed so that they are readily applicable in commercial models to replicate pollutant leaching and solute transport in soil environments. Outcomes of this study will enhance the sustainable use of waste products such as RCA and RAP in the construction industry and relieve the stresses on natural quarry products.
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Vann, Kevin N. "Leaching behavior of personal computer central processing units (CPUs) using standardized and modified toxicity characteristic leaching procedure (TCLP) tests". [Gainesville, Fla.] : University of Florida, 2003. http://purl.fcla.edu/fcla/etd/UFE0001149.
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