Consórcios termofílicos na biossolubilização de concentrado calcopirítico: efeito da adição de íons ferrosos e íons cloreto
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Data
2023-08-17
Autores
Crocco, Laíze Guimarães
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Universidade Estadual Paulista (Unesp)
Resumo
Aproximadamente 85% do cobre mundial é produzido via pirometalurgia, e um interesse cada vez maior tem sido constatado no estudo de processos alternativos, como hidrometalúrgicos ou biohidrometalúrgicos, pois estes apresentam menores impactos ambientais, maior viabilidade econômica e possibilitam a extração de cobre de minérios de baixo teor que não podem ser processados por pirometalurgia. A calcopirita corresponde a 70% das reservas globais de cobre e, por isso, a biolixiviação desse minério tem sido amplamente estudada. Entretanto, sua lenta cinética de dissolução impacta negativamente a extração de cobre, e muitas pesquisas tem sido feitas para tornar o processo aplicável em grandes escalas. Neste cenário, o presente trabalho propõe estudar a dissolução de concentrado calcopirítico na presença de íons cloreto, íons ferrosos e consórcio de microrganismos termofílicos, visando solubilizar o cobre de maneira eficiente e economicamente viável. Para isto, foi avaliada inicialmente a tolerância do consórcio termofílico frente a crescentes concentrações de íons cloreto (0, 50, 100, 250 e 500 mmol L-1 ). Foi conduzido um ensaio de composto central que permitiu construir uma superfície de resposta que correlacionasse a solubilização de concentrado calcopirítico em função da densidade de polpa, concentração de íons ferrosos e íons cloreto. Os resultados mostraram que o consórcio termofílico tolerou as concentrações de íons cloreto empregadas, pois possibilitou o aumento na cinética de extração de cobre do concentrado calcopirítico em todas as condições, principalmente em 500 mmol L-1 de Cl- , na qual obteve-se 100% de extração do metal em 21 dias comparado com 84% em meio abiótico. A melhora na cinética de dissolução do concentrado calcopirítico pode ser atribuída a baixa velocidade de oxidação dos íons Fe2+ por estes microrganismos, contribuindo para manutenção do potencial dos pares iônicos em solução dentro da faixa ótima para a lixiviação da calcopirita. No ensaio de superfície de resposta, os resultados mostraram que a dissolução do concentrado calcopirítico foi influenciada principalmente pela concentração de íons cloreto presente, sendo possível obter maiores extrações de cobre em maiores concentrações destes íons devido a formação de complexos de cloreto de cobre que estabilizam os íons Cu(I) em solução, permitindo que o par redox Cu(II)/Cu(I) contribua para a dissolução da calcopirita, aumentando a extração de cobre contido no concentrado. Os microrganismos aumentaram discretamente a cinética de dissolução do cobre nas condições estudadas por meio do ensaio de superfície de resposta. Ao final dos experimentos, nos resíduos foram detectados enxofre elementar e jarosita, mostrando que estas espécies não causaram passivação do concentrado calcopirítico. Portanto, foi possivel determinar uma condição eficiente e economicamente viável para a recuperação do cobre, sendo ela 2,00% calcopirita, 340 mmol L-1 de Fe2+ e 400 mmol L-1 de Cl- , na qual obteve-se aproximadamente 100% de extração do metal em 28 dias, com consumo de ácido sulfúrico próximo a zero, reduzindo os impactos operacionais e econômicos relacionados ao emprego deste reagente na produção de cobre. Além disso, esta condição sinaliza possibilidade de utilização de água do mar como alternativa à água doce nos processos de extração de cobre em minérios de baixo teor.
Approximately 85% of the world's copper is produced via pyrometallurgy, and an increasing interest has been found in the study of alternative processes, such as hydrometallurgical or biohydrometallurgical, as these have lower environmental impacts, greater economic viability and enable the extraction of copper from copper ores. low grade that cannot be processed by pyrometallurgy. Chalcopyrite corresponds to 70% of global copper reserves and, therefore, the bioleaching of this ore has been widely studied. However, its slow dissolution kinetics negatively impacts copper extraction, and much research has been done to make the process applicable on large scales. In this scenario, the present work proposes to study the dissolution of chalcopyrite concentrate in the presence of chloride ions, ferrous ions and a consortium of thermophilic microorganisms, aiming to solubilize copper in an efficient and economically viable way. For this, the tolerance of the thermophilic consortium to increasing concentrations of chloride ions (0, 50, 100, 250 e 500 mmol L-1 ) was initially evaluated. A core compound assay was conducted which allowed the construction of a response surface that correlated the solubilization of chalcopyrite concentrate as a function of pulp density, concentration of ferrous ions and chloride ions. The results showed that the thermophilic consortium tolerated the concentrations of chloride ions employed, as it enabled an increase in the kinetics of copper extraction from the chalcopyrite concentrate under all conditions, mainly at 500 mmol L -1 of Cl- , in which 100% metal extraction in 21 days compared to 84% in abiotic medium. The improvement in the dissolution kinetics of the chalcopyrite concentrate can be attributed to the low rate of oxidation of Fe2+ ions by these microorganisms, contributing to the maintenance of the potential of ion pairs in solution within the optimum range for chalcopyrite leaching. In the response surface test, the results showed that the dissolution of the chalcopyrite concentrate was mainly influenced by the concentration of chloride ions present, making it possible to obtain greater copper extractions in higher concentrations of these ions due to the formation of copper chloride complexes that stabilize the Cu(I) ions in solution, allowing the Cu(II)/Cu(I) redox couple to contribute to the dissolution of chalcopyrite, increasing the extraction of copper contained in the concentrate. The microorganisms slightly increased the kinetics of copper dissolution under the conditions studied by means of the response surface assay. At the end of the experiments, elemental sulfur and jarosite were detected in the residues, showing that these species did not cause passivation of the chalcopyrite concentrate. Therefore, it was possible to determine an efficient and economically viable condition for the recovery of copper, being 2,00% chalcopyrite, 340 mmol L -1 of Fe2+ and 400 mmol L -1 of Cl- , in which it was obtained approximately 100% metal extraction was achieved in 28 days, with sulfuric acid consumption close to zero, reducing the operational and economic impacts related to the use of this reagent in copper production. In addition, this condition indicates the possibility of using sea water as an alternative to fresh water in copper extraction processes in low-grade ores.
Approximately 85% of the world's copper is produced via pyrometallurgy, and an increasing interest has been found in the study of alternative processes, such as hydrometallurgical or biohydrometallurgical, as these have lower environmental impacts, greater economic viability and enable the extraction of copper from copper ores. low grade that cannot be processed by pyrometallurgy. Chalcopyrite corresponds to 70% of global copper reserves and, therefore, the bioleaching of this ore has been widely studied. However, its slow dissolution kinetics negatively impacts copper extraction, and much research has been done to make the process applicable on large scales. In this scenario, the present work proposes to study the dissolution of chalcopyrite concentrate in the presence of chloride ions, ferrous ions and a consortium of thermophilic microorganisms, aiming to solubilize copper in an efficient and economically viable way. For this, the tolerance of the thermophilic consortium to increasing concentrations of chloride ions (0, 50, 100, 250 e 500 mmol L-1 ) was initially evaluated. A core compound assay was conducted which allowed the construction of a response surface that correlated the solubilization of chalcopyrite concentrate as a function of pulp density, concentration of ferrous ions and chloride ions. The results showed that the thermophilic consortium tolerated the concentrations of chloride ions employed, as it enabled an increase in the kinetics of copper extraction from the chalcopyrite concentrate under all conditions, mainly at 500 mmol L -1 of Cl- , in which 100% metal extraction in 21 days compared to 84% in abiotic medium. The improvement in the dissolution kinetics of the chalcopyrite concentrate can be attributed to the low rate of oxidation of Fe2+ ions by these microorganisms, contributing to the maintenance of the potential of ion pairs in solution within the optimum range for chalcopyrite leaching. In the response surface test, the results showed that the dissolution of the chalcopyrite concentrate was mainly influenced by the concentration of chloride ions present, making it possible to obtain greater copper extractions in higher concentrations of these ions due to the formation of copper chloride complexes that stabilize the Cu(I) ions in solution, allowing the Cu(II)/Cu(I) redox couple to contribute to the dissolution of chalcopyrite, increasing the extraction of copper contained in the concentrate. The microorganisms slightly increased the kinetics of copper dissolution under the conditions studied by means of the response surface assay. At the end of the experiments, elemental sulfur and jarosite were detected in the residues, showing that these species did not cause passivation of the chalcopyrite concentrate. Therefore, it was possible to determine an efficient and economically viable condition for the recovery of copper, being 2,00% chalcopyrite, 340 mmol L -1 of Fe2+ and 400 mmol L -1 of Cl- , in which it was obtained approximately 100% metal extraction was achieved in 28 days, with sulfuric acid consumption close to zero, reducing the operational and economic impacts related to the use of this reagent in copper production. In addition, this condition indicates the possibility of using sea water as an alternative to fresh water in copper extraction processes in low-grade ores.
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Palavras-chave
Hidrometalurgia, Lixiviação bacteriana, Calcopirita, Minérios, Cobre