Bioleaching of an organic-rich polymetallic concentrate using stirred-tank technology

The bioleaching of a concentrate produced from a black shale ore in an industrial operation in Poland was assessed. Following preliminary batch culture tests, processing in continuous conditions was tested to determine the main specifications for the application of the stirred-tank technology to this organic-rich polymetallic concentrate.The experimental work was carried out in a laboratory-scale unit consisting of three stirred tanks (50 L or 20 L) using an acidophilic and moderate thermophilic (42 °C) bacterial population. Different configurations of the unit and key operating parameters were tested (nutrient medium composition, solids concentration, agitation and aeration rates). The analysis of both bacterial community structure and mineralogical characteristics of the concentrate and the bioleach residues were implemented in order to better understand the chemical and biochemical reactions occurring in the system. Using the data produced during the continuous operation, downstream processing assessment for both copper and silver recovery was also carried out.The best copper recovery obtained in the continuous operation was 92% and hot brine leaching of the bioleaching residue (PLINT Process) permitted the recovery of 92% of the silver. Copper and silver recoveries seemed to be limited by incomplete chalcopyrite dissolution. A preliminary techno-economical evaluation of the concentrate bioleach processing, including bioleaching and copper and silver recoveries, demonstrated the potential economical feasibility. Silver recovery plays an important role in the process's finances. This study presents promising results that encourage further investigation of bioleach processing.