Orientador: Assis Vicente Benedetti / Banca: Denis Ricardo Martins de Godoi / Banca: Daniela Gomes Horta / Resumo: A calcopirita (CuFeS2) é o sulfeto de cobre mais abundante na natureza e pertence ao grupo mais explorado de minerais de cobre, representando cerca de 70% do total de cobre disponível. O objetivo deste trabalho foi estudar as principais etapas de oxidação e redução de calcopirita sólida em solução salina ácida utilizada em biolixiviação usando técnicas eletroquímicas e caracterizar morfológica, química e fisicamente a superfície do eletrodo, a fim de atribuir os diferentes eventos eletroquímicos. Para os estudos eletroquímicos foram utilizadas as técnicas: voltametria linear (LSV) e voltametria cíclica (CV), cronoamperometria (CA), espectroscopia de impedância eletroquímica (EIS) em diferentes intervalos de potencial ou a diferentes valores de potenciais. A caracterização das diferentes espécies formadas em cada condição de potencial ou experimental foi realizada por meio de microscopia eletrônica de varredura (SEM) e microanálise (EDS), difração de raios X (XRD), com o propósito de investigar os fenômenos que ocorrem na superfície da calcopirita sólida e propor possíveis reações envolvidas na lixiviação química. Após os diferentes ensaios eletroquímicos, foi realizada a análise do eletrólito por espectrometria de absorção atômica (AAS) para determinar as concentrações dos íons ferro e cobre em solução. Os voltamogramas cíclicos mostraram mais de 15 picos de corrente diferentes no intervalo de potencial entre +1,5 e -1,5 V/Ag|AgCl|KCl3mol/L. Nas voltametrias cíclicas de baixa... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The chalcopyrite (CuFeS 2 ) is the most abundant copper sulfide in nature and belongs to the exploited group of copper minerals, accounting for about 70% of the total available copper. The aim of this work was to study the main oxidation and reduction steps of solid chalcopyrite in acidic saline solution used in bioleaching using electrochemical techniques, and to characterize morphological, chemical and physically the surface of the electrode in order to assign the different electrochemical events. The following electrochemical tec hniques were used: linear sweep (LSV) and cyclic voltammetry (CV), chronoamperometry (CA), electrochemical impedance spectroscopy (EIS) in different potential intervals or at different potential values. The characterization of the different species formed in each potential or experiment al condition was performed by scanning electron microscopy (SEM) and microanalysis (EDS), X - ray diffraction (XRD), in order to investigate the phenomena occurring on solid chalcopyrite surface and proposing possible reactions involved in chemical leaching. After the different electrochemical tests, the analysis of the electrolyte was performed by atomic absorption spectrometry (AAS) to determine the concentrations of iron and copper ions in solution. The cyclic voltammograms showed more than 15 different cu rrent peaks in the potential range between +1.5 and - 1.5 V/Ag|AgCl|KCl 3mol/L . In cyclic voltammetry at low speed and going to the potential (E) more positive than the open circuit potential (E OCP ), the surface analysis showed a layer rich in copper sulf ide and AAS analysis found copper and iron ions in solution, while scanning in the opposite direction, E < E OCP, the surface analysis indicated the presence of a film rich in elemental sulfur and AAS detected higher concentration of iron and copper ions in so lution. The linear sweep voltammetry to +0.65 V/Ag|AgCl|KCl 3mol/L followed... / Mestre

No description available.

Thesis (PhDApSc(MineralsandMaterials))--University of South Australia, 2001.

Bacterial leaching utilises bacteria, ubiquitous to sulphide mining environments to oxidise sulphide ores. The sulphide mineral chalcopyrite is the most common copper mineral in the world, comprising the bulk of the known copper reserves. Chalcopyrite is resistant to bacterial leaching and despite research over the last 20-30 years, has not yet been economically bioleached. Attempts have been made to use silver to catalyse the bacterial leaching of chalcopyrite since the early seventies. The majority of reported testwork had been performed on finely ground ore and concentrates in agitated batch reactors. This project used silver to catalyse the bioleaching of chalcopyrite in shake flasks, small columns and large columns. The catalytic effect was extensively studied and experimental parameters were varied to maximise copper recovery. Silver was also used to catalyse the ferric leaching of chalcopyrite at elevated temperatures. It was noted that the leaching performance of chalcopyrite in shake flasks compared to columns was markedly different. The specific differences between shake flasks and columns were qualified and separately tested to determine which parameter(s) affected the bioleaching of chalcopyrite. It was found that the ore to solution ratio, aeration, addition of carbon dioxide, solution distribution and small variations in the leaching temperature did not significantly effect the bioleaching of chalcopyrite ore in columns. The method of silver addition to columns did significantly affect the overall copper extraction. The ore in shake flasks was subjected to abrasion between ore particles and with the base of the flask. A test was designed to mimic the shake flask conditions, without the abrasion. The low abrasion test performed similarly to a column, operated with optimum silver addition. This indicated that the inherent equipment difference between shake flask and column operation largely accounted for the difference in leaching performance. Chalcopyrite ore was biologically leached in large columns. The ore crush size and other conditions were typical of those used in the field. The biological leach achieved 65% copper extraction in 160 days. This level of copper extraction is significantly higher than any previously reported results (typically /10% copper extraction) and represents a significant advance in the bacterial leaching of chalcopyrite ore. Due to the inherent high temperature within underground stopes, it was decided to investigate the possibility of separating the leaching and the bacterial oxidation stages. The concept of separate bacterial and ferric leaching has been previously suggested, however the application to a stope, and heat exchange between the process streams was a novel approach. Large column ferric leaches at 70 oC illustrated the technical feasibility of this process. Copper extraction was rapid and high (70% in 100 days of leaching), even when a reduced level of silver catalysis was used. After leaching in large columns, samples of ore were taken for analysis by optical mineralogy. The analysis gave valuable insights into the nature of reaction passivation on chalcopyrite ore. In particular, it was discovered that the precipitation of goethite was a major limiting factor in the bioleaching and ferric leaching of chalcopyrite in columns. In addition, reduced sulphide species were detected on the surface of residual chalcopyrite, giving an indication of the sequential nature of the chalcopyrite reaction chemistry. The bacterial population was characterised using DNA techniques developed during the project. Qualitative speciation was carried out and compared between the columns, down the columns and over time in a column. Comparison of these populations enabled greater mechanistic understanding of the role of bacteria in the leaching of chalcopyrite. This work was the most comprehensive attempt to date made to delineate the complex microbiological/mineral actions using analysis of population dynamics from a mixed inoculum. It was found that the iron oxidiser Thiobacillus ferrooxidans dominated within the columns and leach solutions. The sulphur oxidiser Sulfobacillus thermosulfidooxidans was also prevalent in the columns, particularly during the period of rapid chalcopyrite oxidation. The high temperature, ferric leaching of chalcopyrite was unexpectedly poor in the first round of large columns. The reason for the low extraction was attributed to an increase in pH down the column, resulting in excessive goethite precipitation. The solution flowrate (velocity) was increased by ten times in subsequent columns. There were no operational problems (e.g. break-up of ore agglomerates). The increase in flowrate resulted in a high yield of copper. The kinetics of extraction were faster than a corresponding bacterial leach, confirming the potential advantage of a high temperature leach. The small column studies highlighted that it was important to get an even distribution of silver down the stope to enable maximum catalytic effect. If the ore were agglomerated, silver would be added with acid at that point. However, it may not always be possible to agglomerate the ore. For example, the process may be used in-situ on a fractured ore body, or on an ore that has a low fines content, and hence does not require agglomeration. Various complexing agents were tested for their ability to distribute silver at the start of the leach and to recover silver at the end of the leach. For instance when silver was complexed with thiourea and then trickled through the ore, an even distribution of silver was achieved. After leaching was completed, a thiourea wash recovered a significant amount of the silver. These two techniques minimised the amount of silver required and thus significantly added to the economic viability of the process. The success of the technical work has led to an evaluation of the process in the field. A flowsheet was developed for the high temperature, in-stope ferric leach of chalcopyrite. An economic analysis was performed that illustrated the process would be viable in certain situations. An engineering study considered issues such as acid consumption, aeration, silver distribution, silver recovery and a heat balance of the stope.

Th.--Sci. phys.--Nancy--I.N.P.L., 1985.

Orientador: Denise Bevilaqua / Banca: Sandra Regina Pombeiro Sponchiado / Banca: Daniela Gomes Horta / Resumo: O desenvolvimento tecnológico dos setores industriais associados à mineração e metalurgia vem crescendo nas últimas décadas devido à busca incessante por melhorias na qualidade de vida. Se por um lado a demanda por metais é crescente, por outro, a indústria de mineração est á diante da problemática em relação ao esgotamento das reservas. Isso impõe a necessidade de se extrair metais a partir de minérios de baixos teores e também de rejeitos industriais. Para tanto são necessários processos que exijam baixos custos de investim ento e de operação para que a extração se torne viável economicamente, e a biolixiviação é a tecnologia que aparece como a principal alternativa diante dos processos convencionais. O cobre tem sido um dos metais mais importantes por mais de cinco mil anos, devido a suas propriedades e formação de ligas metálicas. O cobre é um dos metais de maior interesse econômico. Cerca de 70% deste metal é encontrado na natureza na forma de calcopirita (CuFeS 2 ). É o mineral mais abundante entre todos os tipos de minérios de sulfeto de cobre. A biolixiviação de cobre a partir de calcopirita é considerada mais econômica e ambientalmente sustentável que o processo convencional pirometalúrgico, especialmente quando os minérios de sulfeto de cobre estão presentes em baixo teor . No entanto, a taxa de oxidação lenta bacteriana continua a ser um grande problema para ser resolvido na biolixiviação. Sendo assim, estratégias para melhorar a atividade bacteriana na superfície do sulfeto mineral têm sido amplamente exploradas por muito s autores. Recentemente a adição de substâncias de origem biológica como os aminoácidos também tem sido um fator testado em ensaios com o objetivo de melhorar o desempenho do processo, como a L - cisteína, um aminoácido importante sulfuroso que despertou gr ande interesse devido a sua capacidade de acelerar o processo... / Abstract: Technological development of mining and metallurgical industries has increased in recent decades due to constant search for improving life quality. Mining industries are now facing an issue related to the depletion of reserves since the demand for metals is growing progressively year after year. Therefore, he need of extracting metals from low grade ores and industrial wastes become an important key to this sector. For this purpose, processes that require low investment and low operating costs for metal extraction are preferentially used for being economically feasible compared to conventional processes. Bioleaching is one of the main alternative technologies for extracting metals, such as cop per one of the most important metals for over five thousand years, due to its properties and formation of metal alloys. Copper is one of the largest economic interest metals. About 70% of this metal is found in nature as chalcopyrite (CuFeS 2 ). This is the most abundant mineral among all types of copper sulfide ores. Copper bioleaching from chalcopyrite is considered more economically and environmentally sustainable than conventional pyrometallurgical processes. The main microorganisms involved in this proce ss are the well - known Acidithiobacillus ferrooxidans, mesophilic bacteria capable of using ferrous ions and reduced sulfur compounds as energy source through oxidative reactions Leptospirillum ferrooxidans also mesophilic and able to oxidize ferrous ions a s energy source. The addition of carbohydrates, proteins and other substances of biological origin has also been a factor tested in assays aiming to improve the performance of the process. In this context, this study aimed to evaluate the ability to solubi lize copper from chalcopyrite mediated by both At. ferrooxidans and L. ferrooxidans separately and combined, as a consortium. Besides, to evaluate the efficiency of the process adding cysteine in... / Mestre

M.Sc. / As environmental and energy resource concerns have increased, greater emphasis has been placed on development of renewable energy resources such as photovoltaic electric generators. CuInSe 2/ZnO heterojunction solar cells are currently one of the most promising technologies to produce economically viable, clean electrical energy. The reaction of metallic alloys containing copper and indium to a selenium-containing atmosphere is by far the most promising industrial process. In this study ; copper-indium metallic precursors were prepared by electron-beam evaporation. The selenization process was conducted in vacuum in elemental Se vapour and in the presence of a H 2Se/Ar gas mixture at atmospheric pressure. Attention was given to the optimization of the structural features of the metallic alloys as well as the selenization parameters. Structural analysis revealed that the number of multilayers in , the precursor stack significantly influence the morphological features of the absorber films after selenization. The reaction temperature and reaction periods during the selenization process critically influenced the reaction kinetics of metallic phases. In the case of selenization in elemental Se vapour, temperatures as high as 550°C were required to convert the metallic alloys into fully reacted semiconductor thin films. Selenization in the presence of H2Se gas was more reactive and temperatures around 450°C resulted in the complete formation of CuInSe2. In the majority of cases, traces of CuSe were detected in the bulk of the material by XRD studies. The presence of the Cu-rich binary phases rendered solar cell devices useless. After removal of these detrimental segregated phases by KCN etching, glass/Mo/CuInSe2/CdS/ZnO solar cell devices reached conversion efficiencies around 8%.

Ph.D. / The reaction of direct current (DC) magnetron sputtered metallic CuIn and CuInGa alloys to a reactive H2Se/Ar/H2S gaseous atmosphere is an attractive industrial production process to produce Cu-based chalcopyrite absorber films for applications in high efficiency photovoltaic modules. This deposition process is generally referred to as a two-step deposition technology. However, the obvious technological advantages of this deposition technology are overshadowed by growth-related anomalies, such as the separation or at least partial separation of the ternary phases (i.e. CuInSe2, CuGaSe2 and CuInS2) during the high temperature chalcogenization. This in turn prevents the effective band-gap widening of the semiconductor alloys in order to achieve open-circuit voltages in excess of 600mV, which is a critical prerequisite for the optimal performance of thin film solar modules. Against this background, a detailed study was undertaken in order to understand the formation kinetics of quaternary CuIn(Se,S)2 and pentenary Cu(In,Ga)(Se,S)2 alloys deposited with a reproducible two-step growth technology. The main objective of this study was to optimize a complex set of experimental parameters in order to deposit homogenous alloys in which the band-gap value of the resulting semiconductor film could be modified in order to maximize the operating parameters of photovoltaic devices. This was achieved by the homogenous incorporation of S and/or Ga into the chalcopyrite lattice, resulting in shrinkage of the lattice parameters and hence increase in band-gap value Eg. However, the substitution of In with Ga and Se with S proved to be a complex process. It was, for example, observed that separation or at least partial separation of the ternary phases already occurs during the chemical reaction between the hydrogen selenides (H2Se) gas and the metallic precursors. Detailed studies indicated that this phenomenon was strongly related to the selenization parameters (e.g. reactive gas concentration, and reaction temperature and time) as well as the Cu/(In + Ga) atomic ratio. In optimized processes, the metallic precursor films were partially selenized in order to produce at least one partially reacted Cu-III-VI2 ternary alloy and group Cu-VI and III-VI binary phases. The partially selenized alloys were subsequently sulphurized under optimal thermal conditions in a H2S:Ar gas mixture to produce homogeneous single-phase quaternary and pentenary chalcopyrite alloys. X-ray diffraction (XRD) studies revealed that the lattice parameters of the chalcopyrite lattice decreased linearly with the incorporation of S and/or Ga, according to the predictions of Vegard’s law. Gracing incidence x-ray diffraction (GIXRD) studies on the compound semiconductors revealed that the lattice parameters remained virtually constant through the entire depth of the layer. Optical studies revealed a shift in the band-gap value of the absorber films as function of the S concentration. The band-gap of the absorber films could be varied between 0.99 and 1.35eV by controlling the S/Se anion ratio during the diffusion process, while maintaining the Ga/III atomic ratio constant at 0.25. Solar cells were completed by chemical bath deposition (CBD) of CdS and radio frequency (RF) sputtered intrinsic and highly conductive ZnO films onto the absorber films. The cells were evaluated under standard A.M. 1.5 conditions. Devices manufactured from CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 based alloys demonstrated average open-circuit voltages (Voc) and short-circuit current densities (Jsc) values of 470 and 650 mV and 20 and 33 mA.cm-2, respectively. A plot of the open-circuit voltage as function of the band-gap revealed an experimental relationship of: Voc = (Eg/q – 0.6) mV for Eg < 1.3 eV. The fill factor (FF) values varied between 35 and 56% and device efficiencies () between 4 and 13%, depending on the S/Se anion ratio and Ga incorporation. The findings from the studies clearly indicated that a better understanding of the CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 formation process led to absorber material with improved material properties. It was also demonstrated that it is possible to produce a homogenous CuIn(Se,S)2 and Cu(In,Ga)(Se,S)2 absorber films with the scalable two-step deposition process.

M.Sc. / Thin film solar cell devices based on chalcopyrite absorber layers have reached a high performance level over the last few years, especially on laboratory scale. Despite this progress, there is still an urgent need to develop an industrial easily scalable deposition technology for depositing chalcopyrite thin films on a large scale. In this study, homogeneous single-phase quaternary Cu(In1-xGax)Se2 thin films were prepared with a reproducible two-step growth technique. The growth process is based on the controlled selenization of sputtered metallic CuIn0.75Ga0.25 alloys in a H2Se/Ar gas mixture at atmospheric pressure. Attention was mainly focused on the optimization of the reaction parameters such as the temperature profiles, gas concentrations and reaction periods. In an optimal reaction process, the reaction velocities of the binary selenide phases were carefully controlled to prevent the formation of stable group I-III-VI2 ternary alloys during the initial selenization step. The composite alloys were subsequently annealed in an inert atmosphere, followed by a second selenization step to promote the homogeneous alloying of gallium with partially formed CuInSe2. Glancing incident angle x-ray diffraction (GIXRD) at incident angles between 0.2º and 10º revealed virtually no shift in d-spacing with sample depth, which confirmed the monophasic nature of the quaternary alloys. Optical measurements revealed an increase in the band gap value of the chalcopyrite alloy due to the homogeneous incorporation of gallium into the CuInSe2 structure. Solar cell devices were fabricated by depositing cadmium sulphide (CdS) buffer layers and zinc oxide (ZnO) window layers onto the CuIn0.75Ga0.25Se2 absorber films. These devices were measure under standard A.M. 1.5 conditions and favorable conversion efficiencies were demonstrated. / Prof. V. Alberts

M.Sc. / As environmental and energy resource concerns have increased, greater stress has been placed on development of renewable energy resources such as photovoltaic electric generators. CuInSe2/ZnO heterojunction solar cells are currently one of the most promising technologies. CuInSe2 and its related alloys such as Cu(In,Ga)Se2 have been deposited by a number of techniques, including methods which have been demonstrated to be scalable to mass production volumes. In this study, attention was focused on (i) developing a relatively simple deposition technology for the production of chalcopyrite absorber films, (ii) detailed characterization of the semiconductor thin films in terms of the experimental parameters and (iii) production of completed CuInSe2/CdS/ZnO solar cell devices. A new two-stage growth process was developed which involved a low temperature precursor formation step and a subsequent high temperature selenization step. Selenium containing Cu-In-Ga and Cu-In-Ga-Se precursors were deposited by a thermal process in which the constituent elements were evaporated from a single graphite crucible onto heated substrates in presence of a selenium overpressure. These precursors were subsequently reacted in vacuum to elemental selenium vapour or to H2Se/Ar at atmospheric pressure in a separate diffusion reactor. In order to investigate the growth kinetics of the respective processes, the precursors were reacted to the Se in the temperature range between 300„aC and 600„aC. The structural features (morphology, presence of crystalline phases, bulk and in-depth compositional uniformity) of the respective films were compared and correlated against the growth parameters. From this systematic study, optimum growth parameters were determined for the production of completed solar cell devices. / Prof. V. Alberts