Use of lignosulfonate for elemental sulfur biooxidation and copper leaching

Abstract

The surface-active properties of lignosulfonate, a solid by-product from the sulfite papermaking industry, were investigated in several aspects of a proposed Barrick copper heap leaching process where sulfur is added to the heap to be oxidized in-situ to produce acid. In this copper heap leaching process, lignosulfonate could affect sulfur milling, sulfur biooxidation, acid consumption, copper recovery, and solvent extraction of the copper pregnant leach solution. In milling, lignosulfonate was shown to reduce the measured Bond work index of sulfur in a batch mill, but not in a continuous mill. In biooxidation, lignosulfonate increased the growth rate of sulfur-oxidizing microorganisms, but the faster rate was not sustained during the whole biooxidation period. Lignosulfonate accelerated the kinetics of sulfur biooxidation in certain leach environments. In copper leaching, lignosulfonate did not have negative effects on copper recovery, acid consumption, or leach kinetics, but neither did it improve the kinetics of copper recovery. In solvent extraction, the separation of the organic and aqueous phases was rapid and clean if lignosulfonate was previously in contact with the copper ore or the sulfur particles. Based on these various outcomes, lignosulfonate did not have a negative impact on the copper heap leaching process tested, but does not constitute an essential additive to the process.