Carbon-Assisted Bioleaching of Chalcopyrite and Three Chalcopyrite/Enargite-Bearing Complex Concentrates

Abstract

Overcoming the slow-leaching kinetics of refractory primary copper sulfides is crucial to secure future copper sources. Here, the effect of carbon was investigated as a catalyst for a bioleaching reaction. First, the mechanism of carbon-assisted bioleaching was elucidated using the model chalcopyrite mineral, under specified low-redox potentials, by considering the concept of Enormal. The carbon catalyst effectively controlled the Eh level in bioleaching liquors, which would otherwise exceed its optimal range (0 ≤ Enormal ≤ 1) due to active regeneration of Fe3+ by microbes. Additionally, Enormal of ~0.3 was shown to maximize the carbon-assisted bioleaching of the model chalcopyrite mineral. Secondly, carbon-assisted bioleaching was tested for three types of chalcopyrite/enargite-bearing complex concentrates. A trend was found that the optimal Eh level for a maximum Cu solubilization increases in response to the decreasing chalcopyrite/enargite ratio in the concentrate: When chalcopyrite dominates over enargite, the optimal Eh was found to satisfy 0 ≤ Enormal ≤ 1. As enargite becomes more abundant than chalcopyrite, the optimal Eh for the greatest Cu dissolution was shifted to higher values. Overall, modifying the Eh level by adjusting AC doses to maximize Cu solubilization from the concentrate of complex mineralogy was shown to be useful.

Bioleaching of tennantite concentrate: influence of microbial community and solution redox potential

“…Where Eh naturally increases in the system due to the presence of “strong” Fe-oxidisers, the carbon catalyst can effectively suppress and control the Eh level in the bioleach liquors because the carbon catalyst surface acts as an electron mediator to couple the reduction of Fe 3+ ( Uchida et al, 2000 ) and the oxidation of reduced inorganic sulfur compounds (RISCs). The Eh level was thus controlled by counterbalancing microbial Fe 2+ oxidation ( Oyama et al, 2020 , 2021 ;). The effect of activated carbon has also been reported in the bioleaching of low-grade primary Cu sulfide ores ( Zhang and Gu, 2007 ).…”

“…This is due to the passivation of the enargite surface by Fe(III)-bearing minerals formed during the dissolution of pyrite. Our previous studies have shown that as a compromise to mitigate this competition effect, suppressing the Eh value to around <700 mV is preferable to maintain a more stable and prolonged Cu dissolution from enargite while minimising the passivation effect of Fe(III)-bearing minerals, allowing better control of the leaching process and Cu recovery ( Oyama et al, 2018 , 2020 , 2021 ; Okibe et al, 2022 ). Accordingly, the need for Eh control is different for chalcopyrite and enargite.…”

“…Accordingly, the need for Eh control is different for chalcopyrite and enargite. In the case of bioleaching enargite/chalcopyrite-bearing complex concentrates, the optimum Eh for maximum Cu dissolution increased with higher enargite/chalcopyrite ratios in the concentrate ( Oyama et al, 2021 ).…”

“…A similar ferric arsenate precipitation mechanism was also likely to occur in the actual enargite bioleaching situation. This is because the loss of Eh control (leading to higher Eh) resulted in sudden pyrite dissolution, providing SO 4 2− ions that compete with AsO 4 3− and triggering the re-solubilisation of ferric arsenate precipitates ( Oyama et al, 2021 ).…”