Cyclic biomachining of copper: Maximum metal removal rate with minimum depleted solution.

[Display omitted] • A consecutive process alternating bioleaching and oxidant regeneration was proposed. • The SMRR peaked during the 1st hour and decreased significantly after 3 h. • The copper limit for reusing the biologically active solution was 10.7 g L−1. • A. ferrooxidans oxidation action become relevant for Fe3+/Fe2+ ratios lower than 0.3. • The alternate process contributed to the sustainable reduction of waste generation. Bacterially assisted leaching has been proposed for many innovative applications, such as urban mining or micromachining, but many technical challenges including substrate toxicity and downstream processing of the leach liquor must be solved before its industrial implementation. This study was conducted with the final goal of improving the average specific metal removal rate (SMRR) and reducing the amount of depleted solution generated in the leaching process of copper workpieces, with special attention paid to the detection of microbial activity inhibition. The copper leaching rate is almost entirely dependent upon the Fe3+ concentration with Fe3+/Fe2+ ratios higher than 0.3, after which A. ferrooxidans oxidation action becomes relevant. In both biotic and abiotic experiments, the SMRR peaked after the first hour of treatment, and it decreased sharply after three hours. A consecutive process alternating bioleaching and oxidant regeneration stages was proposed to improve performance, which considerably reduced both the time needed to dissolve a certain amount of metal and waste generation. The decrease in copper removal (25 %) and the increase in the time required for oxidant regeneration after five leaching cycles (longer than 90 h) were attributed to bacterial inhibition in the presence of 10.7 g Cu2+ L−1, which was established as the limiting metal concentration for reusing the biologically active solution. [ABSTRACT FROM AUTHOR]