O elemento químico neodímio (Nd) atualmente está em evidência pois é parte fundamental em aplicações produzidas por empresas ligadas a tecnologias limpas e de ponta. Porém, é classificado como crítico pelo departamento de energia dos EUA em função do monopólio chinês atuante em sua exploração e comercialização. Devido à crescente demanda frente à restrita disponibilidade, a recuperação deste metal está em ascensão. Uma das aplicações do neodímio é o ímã permanente de neodímio-ferro-boro, utilizado em hard disk drives (HDs) de computadores. Desta forma, este estudo visou caracterizar os ímãs provenientes de HDs de computadores e estabelecer uma rota de recuperação do neodímio por meio de processos mecânicos e hidrometalúrgicos. Por meio da pesagem dos HDs e seus ímãs obteve-se massa média de 3,04 g e 7,91 g para laptop e desktop, respectivamente, representando menos de 3% da massa total do HD. A desmagnetização foi atingida por meio de aquecimento até a temperatura de Curie, em torno de 312 °C, e a cominuição realizada em moinho de facas, onde foram obtidas três granulometrias classificadas em frações A, B e C. Qualitativamente as amostras, foram analisados por meio de difração de raios-X (DRX), onde a fase tetragonal Nd2Fe14B foi o constituinte dominante, e por meio de análise em microscópio eletrônico de varredura (MEV). Semi-quantitativamente os ímãs, seus revestimentos e o precipitado final foram avaliados por meio de espectrometria de fluorescência de raios-X (FRX). A composição média de 21,5% de neodímio e 65,1% de ferro em massa, além de outros elementos químicos, obtida por meio de espectrometria de emissão óptica com plasma (ICP-OES), mostrou teor de neodímio superior aos minérios explorados, tornando este resíduo interessante em relação à recuperação deste metal. O procedimento hidrometalúrgico adotado envolveu a lixiviação das amostras em ácido sulfúrico 2M e a variação de três parâmetros: razão sólido/líquido, temperatura e tempo, em dois níveis. Posteriormente foi realizada a precipitação seletiva por meio de NaOH, formando o duplo sal NaNd(SO4)2.nH2O. Os resultados mostraram que a lixiviação de neodímio atingiu eficiência média acima de 94%, porém todos os experimentos apresentaram material não lixiviado, majoritariamente composto por níquel e cobre. / The chemical element neodymium (Nd) currently is in evidence as it is a fundamental part in applications manufactured by clean and advanced technology companies. However, it is classified as critical by the United States Department of Energy due to Chinese monopoly in its exploration and commercialization. Due to increasing demand in contrast with scarce supply, the recovery of neodymium is growing. One of the applications of this metal is the neodymium-iron-boron permanent magnet, used in hard disk drives (HDDs) of computers. Therefore, this study aimed magnets characterizing from HDDs of computers and then establishing a recovery route for neodymium by mechanical and hydrometallurgical processes. By weighing the HDDs and their magnets it was obtained the average weight of 3.04 g and 7.91 g for laptop and desktop, respectively, representing less than 3% of the HDDs total mass. Demagnetizing was achieved by heating up to Curie temperature of around 312 °C, and the comminution in knives mill resulted in three granulometries classified into fractions A, B and C. Qualitatively, magnets were analyzed by X-ray diffraction (XRD), where the tetragonal phase Nd2Fe14B was the dominant constituent of the sample, and through analysis in a scanning electron microscope (SEM). Semi-quantitatively, the magnets, its covers, and the final precipitate were evaluated by X-ray fluorescence spectrometry (XRF). The average composition of neodymium and iron showed 21.5% and 65.1% by weight, respectively, among other chemical elements. This results were obtained by optical emission spectrometry (ICP-OES), representing a higher neodymium content compared to the ores content, which makes this waste interesting from a neodymium recovery point of view. The procedure adopted involved hydrometallurgical leaching of the samples in 2M sulfuric acid varying three parameters: liquid/solid ratio, temperature and time, each one on two levels. Subsequently, the selective precipitation by NaOH was performed to form the double salt NaNd(SO4)2.nH2O. The results showed that neodymium leaching efficiency reached above 94%, but the experiments showed as well some material left, mainly composed of nickel and copper.

Biolixiviação é um processo econômico para a recuperação de metais que exige baixo custo de investimento e operação. Além disso, é geralmente mais ambientalmente amigável do que muitos processos físico-químicos de extração de metal. O presente trabalho visou a extração de cobre a partir de rejeito da etapa Scavenger (SCV) de circuito de flotação de calcopirita. Foram realizados ensaios de biolixiviação utilizando o rejeito SCV, que contém em torno de 0,73% de cobre, e um consórcio de microrganismos denominado ABL, selecionado a partir de amostras coletadas na Mina do Sossego. Um tratamento ácido do rejeito foi realizado prévio à biolixiviação para redução de carbonatos. Os ensaios em frascos agitados foram realizados variando-se parâmetros como agitação, densidade de polpa, tamanho de partícula e pH. Os resultados mostraram extração de cobre de 70% para a biolixiviação de rejeito Finos Tratado (100% das partículas com tamanho inferior a 0,045 mm) nas seguintes condições: densidade de polpa de 40% (m/v), agitação de 130 rpm e temperatura 35°C. Ensaios em biorreator tipo batelada com rejeito SCV Tratado (82% das partículas com tamanho inferior a 0,045 mm) alcançaram extração de 59% de cobre, resultado parecido ao observado para a biolixiviação de rejeito SCV Tratado em frascos agitados, 55%. Os resultados de extração de cobre encontrados nesse trabalho estão entre os maiores reportados na literatura de biolixiviação de cobre de rejeitos. / Bioleaching is an economical process for metal recovery that requires low investment and operational costs. Furthermore, it is in general more eco-friendly than many other physicochemical metal extraction processes. The present work aimed at the extraction of copper from scavenger tailing (SCV) of chalcopyrite flotation circuit. Bioleaching tests were carried out using the SCV tailing, which contains around 0.73% of copper, and a microbial consortium called ABL, selected from samples collected at Sossego Mine. An acid treatment of tailings was carried out, prior to bioleaching, to reduce carbonates, which consume acid during the bioleaching. Shake flasks tests were performed by varying parameters such as agitation, pulp density, particle size and pH. The results showed 70% copper extraction for the bioleaching of Treated Fine Particles (100% of the particles being smaller than 0.045 mm) under the following conditions: pulp density of 40% (w/v), agitation of 130 rpm and temperature of 35°C. Batch reactor tests with Treated SCV (82% of particles smaller than 0.045 mm) reached a 59% copper extraction, a result similar to that reached through the bioleaching of Treated SCV in shake flasks, 55%. The copper extraction results found in this work are among the highest ones reported on bioleaching of copper from tailings.

A recuperação de metais presentes em equipamentos eletroeletrônicos tem atraído interesse em virtude de novas e diferentes tecnologias que visam a reutilização desses elementos químicos em novos processos produtivos. A recuperação de prata de placas de circuito impresso (PCI) na forma de nanopartículas é uma alternativa para reutilização deste metal nobre. Este trabalho teve como objetivos: recuperar a prata presente em placas de circuito impresso através de uma rota hidrometalúrgica; separar a prata dos demais metais e utilizar a prata recuperada para sintetizar nanopartículas de prata. Para desenvolvimento do trabalho, foram utilizados dois modelos de PCIs com diferentes composições: placa mãe e placa de memória de computadores obsoletos. As placas foram caracterizadas por digestão em água régia, análise granulométrica, análise em lupa binocular, microscopia eletrônica de varredura (MEV) e perda ao fogo. Foi definida uma rota hidrometalúrgica para recuperação da prata após um estudo de três rotas possíveis. A rota hidrometalúrgica definida para recuperação da prata, para os dois modelos de PCIs, envolveu uma primeira lixiviação em meio ácido sulfúrico a 95ºC, por 18 horas e uma segunda lixiviação em ácido sulfúrico em meio oxidante (adição de peróxido de hidrogênio - H2O2) a 95ºC por 6 horas. Esta rota descarta a técnica de separação magnética e separação eletrostática, pois o metal em estudo é encontrado em pequenas concentrações nos resíduos eletroeletrônicos. O licor lixiviado foi caracterizado por espectrometria de emissão óptica com acoplamento de plasma induzido (ICP-OES). Após o processo de lixiviação, a prata foi isolada dos demais metais na forma de AgCl, através de processo de precipitação seletiva utilizando NaCl. A síntese de nanopartículas de prata foi feita utilizando o citrato de sódio como agente estabilizante. Os resultados obtidos neste trabalho permitem concluir que foi possível recuperar 100% da prata presente nas placas de circuito impresso proveniente de computadores obsoletos, por meio da rota hidrometalurgica utilizada. Após a lixiviação, a prata foi isolada. Com a prata isolada, foi possível a síntese de nanopartículas de prata com diâmetro médio de 60 a 80nm. / The recovery of metals present in waste electric and electronic equipment (WEEE) has attracted interest due to the new and different technologies that aim to reuse these chemical elements in new production processes. Recovering silver from printed circuit boards (PCI) into nanoparticles form is an alternative to reuse this noble metal. This work aims to: recover the silver present in printed circuit boards through a hydrometallurgical route; to separate silver from the other metals and to use the recovered silver to synthesize silver nanoparticles. For the development of this work two models of PCIs with different compositions were used: motherboard and random-access memory (RAM) devices from obsolete personal computers. The PCIs were characterized by aqua regia digestion, particle size analysis, stereo microscope analysis, scanning electron microscopy (SEM) and loss on ignition. A hydrometallurgical route for silver recovery was defined after a study of three possible routes. The hydrometallurgical route defined to recover silver from the two models of PCIs involved a first step of leaching in sulfuric acid solution at 95ºC for 18 hours and a second leaching step in sulfuric acid in an oxidizing solution (with addition of hydrogen peroxide - H2O2) at 95° C for 6 hours. This route discards the technique of magnetic and eletrostatic separation because the metal under study is found in a small concentration in the electric and electronic waste. The leached liquor was characterized by inductively coupled plasma optical emission spectrometry (ICP-OES). After the leaching process, the silver was isolated from the other metals in the form of AgCl, through a selective precipitation process using NaCl. The synthesis of silver nanoparticles was accomplished using sodium citrate as stabilizing agent. The obtained results in this work allows to conclude that it is possible to recover 100% of the silver present in printed circuit boards from obsolete computers, through the hydrometallurgical route. After leaching, silver was isolated. It was possible to synthesize nanoparticles with an average diameter of 60 to 80 nm.

Com a expansão do emprego de módulos fotovoltaicos para geração energética, surge o desafio do descarte adequado desse resíduo de equipamento eletroeletrônico. Através da elaboração de um processo multietapas, esse desafio torna-se possível de ser abordado. O presente estudo possui o objetivo de recuperar os materiais presentes nos módulos fotovoltaicos de silício cristalino e de silício amorfo. Diversas técnicas de caracterização física e química foram empregadas para determinar-se composição dos módulos fotovoltaicos e consequentemente o fluxo de processos necessários para recuperação dos materiais identificados. Foi identificado que o módulo de silício cristalino possuía no semicondutor alguns metais como prata (na concentração de 0,063% em massa do módulo) e silício, e na fase polimérica polidimetilsiloxano como encapsulante e PET como backsheet. A separação e recuperação dos polímeros foi realizada através do uso da teoria de dissolução de solventes de Hildebrand, abordando aspectos termodinâmicos e cinéticos. A separação ocorreu em 24h a 860rpm mergulhando-se os módulos em isopropanol, podendo ocorrer separação em até 6h a 860rpm utilizando-se tetrahidrofurano. A lixiviação da prata a partir do semicondutor foi possível com ácido sulfúrico 4mol.L-1, 95°C, sob adição de 6mL de peróxido de hidrogênio a cada 15min, alcançando-se 100% de lixiviação em 2h. Alterando-se a temperatura para 30°C a lixiviação foi completa apenas em 6h de experimento Precipitou-se a prata em solução na forma de cloreto de prata com adição de cloreto de sódio. O módulo de silício amorfo continha EVA na fração polimérica e silício, germânio, prata, estanho e índio (concentração 0,34g/m2 do módulo) na fração metálica, observados tanto por micrografias quanto por análise química quantitativa. A calcinação a 400°C permitiu a remoção do EVA e liberação dos contatos de prata. A lixiviação de índio foi de 100% para uma solução 1mol.L-1 de ácido fosfórico a 75°C, sob 800rpm de agitação e relação sólido-líquido 1g.10mL-1 em 1h. / As the photovoltaic module market grows, an increasingly challenging scenario arises for solar modules end of life management. Such a scenario can be tackled through a process comprising multiple steps. This study has the objective to recover materials present in photovoltaic modules of crystalline silicon and amorphous silicon. Several characterization techniques (physical and chemical) were employed to determine the composition of the modules and thus the process flow needed to recover the identified materials. Along the process, it was noticed that the crystalline silicon module had in its semiconductor metals such as silver (in concentration of at least 0,063% in weight of module) and silicon. Also polydimethylsiloxane was identified as encapsulant and polyethylene therephtalate as backsheet. A separation and recovery of these materials was possible using the theory of solvent dissolution of Hildebrand, comprising thermodynamics and kinetics. The separation occurred in 24h at 860rpm, rising the modules in isopropyl alcohol and potentially reaching 6h at 860rpm when rising them in tetrahydrofuran. The silver leaching from the semiconductor phase was possible in sulphuric acid 4 mol.L-1, 95°C, under addition of 6mL of hydrogen peroxide every 15min, reaching 100% silver leached in 2h. Shifting the temperature to 30°C, the leaching would occur completely only after 6h of experiment. The silver was precipitated as a chloride from the solution by addition of sodium chloride. The amorphous silicon module showed that EVA was present in the polymeric phase and silicon, germanium, silver, tin and indium (the last one at concentration of 0,34g/m2 in area of the module) in the metallic phase, observed on the micrographies and chemical analyses. Calcination was performed at 400°C, removing the EVA and freeing the silver contacts. Indium was 100% leached with a 1mol.L-1 phosphoric acid solution at 75°C, under 800rpm and solid-liquid ratio of 1g.10mL-1 in 1h.

O uso de equipamentos eletroeletrônicos (EEE) tem se tornado tão inerente aos hábitos cotidianos que a demanda por novas tecnologias aumentou, impulsionando o desenvolvimento tecnológico. Assim, houve um aumento em sua rotatividade pela redução do tempo de vida útil, com a chamada obsolescência programada. Esta combinação resulta no aumento da geração de resíduos de equipamentos eletroeletrônicos, os chamados REEE, devido ao descarte após seu ciclo de vida. Os REEE apresentam composição heterogênea em termos de materiais, e podem representar um problema ambiental se forem descartados na natureza, entrando em contato com o solo e corpos hídricos. As placas de circuito impresso (PCIs) estão presentes na maioria dos REEE e apresentam uma ampla gama de metais em sua composição, o que justifica a motivação por aliar interesses ambiental e econômico com sua reciclagem. A prata está presente nas soldas das PCIs lead free e pode ser recuperada por meio da combinação de processamento físico e hidrometalúrgico. Após a purificação, o metal pode ser utilizado como precursor na síntese de nanopartículas de prata, que apresentam potencial para aplicação em diversos setores da indústria, justificando seu valor agregado. Neste trabalho, foi estudada e composição de placas de memória de computadores obsoletos por meio de um processamento físico de cominuição e quarteamento, seguido da caracterização física e química por meio de análise granulométrica, análise em estereoscópio, digestão em água régia e ácido nítrico, ensaio de perda ao fogo e análise em MEV/EDS e ICP-OES. Da fração metálica, 0,045% corresponde à prata, cuja recuperação foi estudada. Para isto, foi realizada uma lixiviação ácida em meio oxidante com H2SO4 2M como agente lixiviante e em 95°C em duas relações sólido-líquido (1:10 e 1:20) e tempos (8 e 12h), de forma que foi possível alcançar 97,3% de extração da prata com relação sólido-líquido de 1:10 em 12h. Paralelamente, o estudo da síntese de nanopartículas de prata pelo método de Turkevich utilizando dois precursores, AgNO3 e AgCl, foi conduzido, variando as proporções molares entre o precursor e o redutor em 1:0,25, 1:1, 1:1,3673, 1:2, 1:3, 1:4 e 1:5, para avaliar as características das nanopartículas e sua estabilidade ao longo do tempo. Na síntese com AgNO3 como precursor sugere-se que as melhores condições combinadas foram referentes à proporção de 1:2. Na síntese com AgCl como precursor, embora nas melhores condições estudadas (proporção molar de 1:5) o resultado em termos de estabilidade, dispersividade e diâmetro médio tenham sido melhores se comparados aos ensaios utilizando AgNO3 como precursor, houve a precipitação de prata micrométrica que era indesejada. / The use of electrical and electronic equipments (EEE) has become so inherent in daily habits that the demand for new technologies increased, boosting technological development. Thus, there was an arising on EEE\'s turnover because of the reduction of the useful time, with the so-called planned obsolescence. This combination results on the increase of the generation of waste electrical and electronic equipments (WEEE) due to discard after the life cycle. WEEEs have heterogeneous composition and may represent an environmental issue if discarded on environment, coming into contact with soil and water bodies. Printed Circuit Boards (PCBs) are present in most WEEE and present a lot of metals in their composition, which justifies the motivation on combine environmental and economic interests with recycling. Silver is present on the weld of lead free PCBs and can be recovered through the combination of physical and hydrometallurgical processing. After the recovery, the metal can be used as precursor on the synthesis of silver nanoparticles, which present potential of application in many industry fields. In this work, the composition of memory boards from obsolete computers was studied through physical processing of comminution and quartering, followed by physical and chemical characterization through granulometric analysis, stereoscope analysis, aqua regia and nitric acid digestion, fire loss test and SEM/EDS and ICP-OES analysis. Of the metallic fraction, 0.045% corresponds to silver, whose recovery was studied. For the recovery, it was performed an acid leaching in oxidant media with H2SO4 2M as leaching agent in 95°C and using two solid-liquid ratios (1:10 and 1:20) and times (8 and 12h), and it was possible to reach 97.3% of silver extraction in 12h for solid-liquid ratio of 1:20. In parallel, it was performed the study of the synthesis of silver nanoparticles by Turkevich method using two precursors, AgNO3 e AgCl, with the variation of molar ratios of the precursor and the reductant in 1:0,25, 1:1, 1:1,3673, 1:2, 1:3, 1:4 e 1:5, aiming the evaluation of nanoparticles characteristics and stability through the time. In the synthesis with AgNO3 as precursor, the combined results suggest the proportion of 1:2 as the best synthesis condition. In the synthesis with AgCl as precursor, even in the best studied conditions (molar ratio 1:5) the results in terms of stability, dispersity and medium diameter was best then obtained using AgNO3 as precursor in same conditions, there was undesirable micrometric silver precipitation.

Spent nuclear fuel (SNF) resultant from the generation of nuclear power is a chemically and radiologically diverse system which is advantageous to chemically process prior to geologic disposal. Hydrometallurgy is the primary technology for chemical processing for light water reactor spent fuels, where spent fuel is dissolved in an acid for liquid based separations. The primary means for recovery of desired metals from the SNF solution is liquid-liquid extraction which is based on distribution (partitioning) of the metal ions between two immiscible phases based on thermodynamic favorability. One of the means of increasing this favorability is by designing extractant molecules to be either "harder" or "softer" bases, which will more preferentially extract harder or softer metal ions respectively. This technique is used in designing extractant molecules for targeted extraction as actinides are slightly softer than lanthanides, and precious metals produced in significant quantities from the fission process are especially soft metals. The work performed in this thesis involved the synthesis of a novel soft electron donor organic extractant molecule for testing of targeted soft metal extraction. The molecule synthesized was bis-dibutanethiolthiophosphinato-methane, or S6, a bidentate neutral extractant molecule with significant thiolysis for a softer electron environment. The synthesis technique was refined and the molecule composition and structure was confirmed by ¹H NMR, ³¹P NMR, and elemental analysis. Two metal groups, f-elements (actinides and lanthanides) and soft transition metals were tested for their extractability from nitric acid solutions into an S6 solution in n-dodecane. Aqueous solutions of nitric acid and n-dodecane as an organic diluent are typical liquid-liquid extraction conditions in spent nuclear fuel reprocessing. As extraction experiments were performed with radiotracers, for the soft metal extraction experiment, a mixture of the selected metals was neutron-activated in the OSU TRIGA reactor, as was europium to create a lanthanide radiotracer. Actinides and lanthanides were not seen to effectively extract into the organic or form a precipitate at all, making their partitioning with this extractant seemingly ineffective. Through gamma spectroscopy of an irradiated metal solution post-extraction, it is seen that only silver and palladium preferentially complex in the mixed metal samples into an insoluble organic ligand, dropping out of solution. This effect was more pronounced at higher acid concentrations, but silver was seen to slightly extract to the organic phase at all acid concentrations as well. This testing has shown that the S6 extractant can be used to recover silver and palladium from a mixed metal aqueous solution, such as one resultant from advanced spent nuclear fuel reprocessing operations. This result shows promise for future development of sulfur based organophosphate ligands for targeted extraction of precious metals from solutions. / Graduation date: 2013

Chemical modeling has become an important subject of research in applied thermodynamics for designing, developing, optimizing and controlling of different industrial processes. In this work, a new database for successful modeling of solid-aqueous phase equilibria in specific hydrometallurgical processes was developed using the Mixed Solvent Electrolyte (MSE(H3O+)) model of the OLI Systems software. The ionic interaction parameters between dominant species in the solution were determined by fitting available binary and ternary experimental data such as mean activity, heat capacity and solubility data; then they were validated in multi-component systems. Developed model predicted the phase behaviour in ammoniacal solutions containing cobalt, nickel, copper, and zinc in the Copper Boil process. New sets of double-salt solubility data were measured and used for accuracy validation of the model. Using HSC 6.1 software linked with MSE model, the copper boil processes was simulated successfully to provide some practical recommendations for the optimum process operation.

Chemical modeling has become an important subject of research in applied thermodynamics for designing, developing, optimizing and controlling of different industrial processes. In this work, a new database for successful modeling of solid-aqueous phase equilibria in specific hydrometallurgical processes was developed using the Mixed Solvent Electrolyte (MSE(H3O+)) model of the OLI Systems software. The ionic interaction parameters between dominant species in the solution were determined by fitting available binary and ternary experimental data such as mean activity, heat capacity and solubility data; then they were validated in multi-component systems. Developed model predicted the phase behaviour in ammoniacal solutions containing cobalt, nickel, copper, and zinc in the Copper Boil process. New sets of double-salt solubility data were measured and used for accuracy validation of the model. Using HSC 6.1 software linked with MSE model, the copper boil processes was simulated successfully to provide some practical recommendations for the optimum process operation.

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 G&ouml / rdes 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 G&ouml / 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 &deg / 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.

Oxidation developed from the surfaces into the cores of the microwaved particles. Metallic particles were also formed during microwave exposure. Lihir gold ore, in which gold was finely disseminated in pyrite and marcasite, was an extremely refractory gold ore. Without pretreatment, only 37-39% of the gold could be extracted with sodium cyanide. However, this was improved after the head ores or floatation concentrates were pretreated by microwave radiation. 74.581.2% of the gold was extracted from the microwave treated head ore. The hydrometallurgical pretreatment of pyrite and marcasite in a microwave field and a conventional heating environment was also investigated.I,n a nitric acid solution, pyrite and marcasite can be rapidly leached. Reaction temperature and the concentration of HNO3 had a significant influence on decomposition rate. Marcasite had a substantially higher i decomposition rate than pyrite. Microwave heating could promote the dissociation of marcasite and pyrite, compared with conventional heating. This was caused by special volumetric heating during microwave exposure that may induce local overheating or improve the interactions between the high dielectric loss minerals and the leaching solution. Kinetic investigations show that the decomposition of both the minerals in a nitric acid medium is controlled by chemical reactions on the surfaces of particles. The decomposition is a second order reaction with respect to nitric acid concentration. Less than 5- 7% of the decomposed sulphur was transformed into elemental sulphur during the leaching of both the minerals