Implementation of biological and chemical techniques to recover metals from copper-rich leach solutions

Abstract

Pregnant leach solutions (PLS) resulting from (bio)leaching of copper ores are characterized by low pH, high concentrations of Fe (III), Cu, Zn and often significant amounts of Ni and Co. In order to make the metals available for further processing they require selective recovery form the acidic, multi-metal solution. Commonly, copper and other base metals are recovered by solvent-extraction/electro-winning (SX/EW) technologies from acidic, metal-rich solutions. This study describes the application of chemical and microbiological process steps for the selective recovery of base metals from the PLS. A multi-stage metal recovery system, involving initial Cu-SX/EW to recover copper, followed by iron hydroxy sulfate precipitation to recover the high amounts of these two metals before introducing the more sensitive biological step, is proposed. The biological route is based on a sulfidogenic bioreactor housing acidophilic bacteria producing hydrogen sulfide directly from the acidic, sulfate-rich PLS. The bioreactor promotes and controls the selective precipitation of CuS and ZnS in two connected vessels and the recovery of Ni and Co as metal sulfides within the bioreactor. The sulfidogenic system has additionally the advantage of lowering the sulfate concentration of the PLS and contribution to an increase in pH. A parallel alternative chemical metal recovery pathway allows the selective recovery of remaining Cu and other metals (e.g. Zn, Co, Ni) via ion exchange (IX). Both the biological and chemical routes lead to a modified PLS which can be reintroduced into the bioleaching operation. Silver and lead are recovered from solid (bio)leach residues by hot brine leaching. The system has been designed to selectively recover all relevant metals from the PLS following a zero waste concept, and its modular arrangement allows an independent operation of the units and the integration of further modules, depending on the nature of the leach solutions.