Estudo eletroquímico de minério concentrado de calcopirita em ensaios de lixiviação
Carregando...
Data
2022-05-18
Autores
Peres, Riberto Nunes [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Universidade Estadual Paulista (Unesp)
Resumo
A calcopirita é a principal fonte de cobre disponível no mundo, representando aproximadamente 70% do todo, porém é extremamente resistente ao ataque químico e bacteriano. A lenta dissolução da calcopirita em diferentes condições experimentais tem sido atribuída à formação de uma camada passiva, ao caráter semicondutor intrínseco do mineral, ou à modificação da superfície pela liberação preferencial de íons ferrosos nos estágios iniciais de dissolução, resultando em depleção de metais dentro de alguns nanômetros de espessura. Esse assunto ainda é controverso e requer mais estudos para entender os diferentes processos de oxidação/redução da calcopirita e os fatores limitantes da dissolução. Este trabalho teve como objetivo avaliar os processos de oxidação e redução de eletrodos maciços e preparados a partir de pó de concentrado de calcopirita por diferentes técnicas eletroquímicas convencionais em solução salina ácida (pH = 1,8), com suporte de análise morfológica, microestrutural e da composição química da superfície antes e após os diversos processos eletroquímicos, e da quantificação em solução dos íons produzidos durante os processos eletroquímicos. Os resultados eletroquímicos permitiram conhecer vários processos dependentes do potencial, associados à formação de espécies químicas na superfície do mineral, sendo as mais prováveis S2-, S22-, SOx2-, So, fosfato férrico, covelita e calcocita, bem como a liberação de íons cobre e ferro em solução e H2S gasoso. A adição de íons cobre e/ou ferro em solução modificou a resposta eletroquímica da calcopirita, alterando os potenciais dos picos de oxidação e redução, diminuindo a impedância do sistema eletrodo/solução e facilitando a dissolução do mineral. A análise dos resultados não sustenta a formação de uma camada passiva na superfície da calcopirita como responsável pela baixa taxa de dissolução e sugere que a lenta dissolução da calcopirita está associada com o caráter semicondutor do tipo-n do mineral. Os resultados também apontam para uma possível contribuição da difusão de íons dentro de camadas com depleção de metais.
Chalcopyrite is the main source of copper in the world, amounting to nearly 70% of the copper reserves, nonetheless, chalcopyrite is highly recalcitrant to chemical and biological processing. The slow chalcopyrite dissolution under different experimental conditions has been basically attributed to the passive layer formation, less to the intrinsic semiconductor character of the mineral, or in few works to the surface modification by the preferential release of ferrous ions in the initial dissolution stages, resulting in metals depletion within a few nanometers thick. This issue is still controversial and requires further studies to understand the different oxidation/reduction processes of chalcopyrite and the limiting factors of dissolution. The aim of this work was to evaluate the oxidation and reduction processes of massive electrodes and prepared from powdered chalcopyrite concentrate by different conventional electrochemical techniques in acid saline solution (pH=1.8), supported by the morphological, microstructural, and chemical composition analyses of the surface before and after the different electrochemical processes, besides the quantification in solution of the ions produced during the electrochemical processes. The electrochemical results allowed to know several potential-dependent processes associated with the chemical species formation on the mineral surface, the most likely being S2-, S22-, SOx2-, So, ferric phosphate, covellite and chalcocite, as well as the ions released in solution and H2S gas. The addition of copper and/or iron ions in solution modified the electrochemical chalcopyrite response, altering the potentials of oxidation and reduction peaks, reducing the impedance of the electrode/solution system and facilitating the dissolution of the mineral. The analysis of the results does not support the formation of a passive layer on the chalcopyrite surface as responsible for the low dissolution rate and suggests that the slow dissolution of chalcopyrite is associated with the n-type semiconductor character of the mineral. The results also point to a possible contribution of ion diffusion within metal-depleted layers.
Chalcopyrite is the main source of copper in the world, amounting to nearly 70% of the copper reserves, nonetheless, chalcopyrite is highly recalcitrant to chemical and biological processing. The slow chalcopyrite dissolution under different experimental conditions has been basically attributed to the passive layer formation, less to the intrinsic semiconductor character of the mineral, or in few works to the surface modification by the preferential release of ferrous ions in the initial dissolution stages, resulting in metals depletion within a few nanometers thick. This issue is still controversial and requires further studies to understand the different oxidation/reduction processes of chalcopyrite and the limiting factors of dissolution. The aim of this work was to evaluate the oxidation and reduction processes of massive electrodes and prepared from powdered chalcopyrite concentrate by different conventional electrochemical techniques in acid saline solution (pH=1.8), supported by the morphological, microstructural, and chemical composition analyses of the surface before and after the different electrochemical processes, besides the quantification in solution of the ions produced during the electrochemical processes. The electrochemical results allowed to know several potential-dependent processes associated with the chemical species formation on the mineral surface, the most likely being S2-, S22-, SOx2-, So, ferric phosphate, covellite and chalcocite, as well as the ions released in solution and H2S gas. The addition of copper and/or iron ions in solution modified the electrochemical chalcopyrite response, altering the potentials of oxidation and reduction peaks, reducing the impedance of the electrode/solution system and facilitating the dissolution of the mineral. The analysis of the results does not support the formation of a passive layer on the chalcopyrite surface as responsible for the low dissolution rate and suggests that the slow dissolution of chalcopyrite is associated with the n-type semiconductor character of the mineral. The results also point to a possible contribution of ion diffusion within metal-depleted layers.
Descrição
Palavras-chave
Calcopirita, Eletroquímica, Microscopia eletrônica, Enxofre, Minérios de cobre