Continuous bioreactor leaching of nickel sulfide concentrates with moderately thermophilic bacteria and archaea

Abstract

A commercial process for bioreactor leaching of a nickel concentrate by-product of talc mining has been described previously. It was developed and operated (2016–2018) at about 45–46 °C. Further features of bioleaching that concentrate have now been investigated in laboratory-scale reactors with continuous feeds of up to 10% (w/v) solids and an emphasis on temperatures at and a few degrees above that of the commercial process. The sulfur-oxidizing At. caldus was more abundant than the sulfide mineral-oxidizing S. thermosulfidooxidans and Atm. siderophilum at 48 °C but was essentially lost with a 3 °C temperature rise, simultaneously with a rise in pH and in iron precipitation from solution, without adversely affecting nickel leaching. The relative abundance among bacteria was similar between two reactors operated in series but there was more than a fourfold increase in the relative abundance of the ferrous-iron oxidizing, heterotrophic archaeon Ac. cupricumulans in the secondary reactor, most likely in response to an increase in the acidity as the sulfide concentrate oxidation proceeded.