Bioleaching of Enargite/Pyrite-rich “Dirty” Concentrate and Arsenic Immobilization

Abstract

Bioleaching of arsenic (As)-rich, so-called “dirty” concentrates can produce additional Cu value from the flotation waste while simultaneously releasing toxic As. This study bioleached three such concentrates of varying pyrite/enargite ratios ([Py]/[Ena] = 0.7, 1.3 and 2.4) at a pulp density of 20%. The dissolution behavior of Cu and As in relation to the solution redox potential (Eh) was studied with and without activated carbon (AC) as a potential Eh-controlling catalyst. At this high pulp density, Eh was naturally suppressed, without a need for AC dosing, to <700 mV (a rapid pyrite dissolution is prevented in this Eh range). The effect of AC dosing on Eh varied depending on the type of concentrate; Eh was further reduced only in the case of the most enargite-rich concentrate, DC-I. Among the three concentrates, the highest Cu dissolution (35%) was seen in DC-I (without AC dosing), which simultaneously achieved the lowest As solubilization. Arsenic was immobilized as amorphous precipitates, likely in a mixture of ferric arsenate, cupric arsenate, basic ferric sulfate and sulfur. Arsenic immobilization became increasingly ineffective as the pyrite content increased in the concentrate. Based on these results, setting a lower [Py]/[Ena] ratio prior to the dirty concentrate bioleaching could be a useful approach to promote Cu dissolution and As immobilization simultaneously.

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

“…caldus KU and Sb. sibiricus N1 was shown to be effective for the bioleaching of As-containing minerals, thus included in this study ( Tanaka et al, 2015 ; Okibe et al, 2022 ).…”

“…The XRD results identified the peaks of tennantite, pyrite and sphalerite in the original tennantite concentrate, of which the tennantite peaks decreased significantly as the bioleaching progressed in both the AC-free and AC-0.01% systems (Figures 6A,B, respectively). Relative to tennantite, pyrite peaks tended to persist throughout the bioleaching reaction, probably due to the low Eh conditions created during the bioreactor tests, which facilitated tennantite leaching while preventing the pyrite dissolution (Oyama et al, 2018(Oyama et al, , 2020Okibe et al, 2022). Secondary electron (SE) image and EDS analysis (Aztec Ins.…”

“…During the flotation process, As-rich concentrates can be produced as a waste if the ore being processed contains significant amounts of As-bearing minerals, while the other, cleaner Cu-rich concentrates are sent to the smelting circuit. To recover the residual Cu value from such flotation wastes, bioleaching, can be considered as one of the most promising technologies from an environmental and economic point of view ( Stanković et al, 2015 ; Okibe et al, 2022 ). The conditions favoured by the hydrometallurgical reaction of Cu sulfides have been extensively studied, with more emphasis on chalcopyrite than on enargite.…”

“…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.…”

“…Bioleaching at elevated temperatures (typically in the range of 60–70°C) has several advantages, including more efficient oxidation and dissolution of enargite and precipitation of dissolved As as crystalline scorodite ( Takatsugi et al, 2011 ; Okibe et al, 2014 , 2017 , 2020 ; Tanaka and Okibe, 2018 ). However, bioleaching at less energy-intensive, moderately thermophilic temperatures (e.g., 45°C) can also promote Cu dissolution and As immobilisation by controlling the Eh level during bioleaching reactions ( Oyama et al, 2020 ; Okibe et al, 2022 ).…”