The influence of lime and sodium hydroxide conditioning on sulfide sulfur behaviour in pyrite flotation

Abstract

The influence of two alkaline pH modifiers, namely sodium hydroxide and calcium hydroxide was investigated to evaluate and compare their effectiveness in pyrite rougher flotation of a refractory gold ore with a high sulfide sulfur grade (13% S2-), using potassium amyl xanthate as the collector and Nascol 422 as the frother. The focussing question for this study was to determine if there was a promising premise for substituting lime with sodium hydroxide as a pH regulator in the rougher flotation of Lihir and possibly other ores, where there is excess sulfur to be treated in the downstream oxidation processes relative to the amount of gold present in the rougher concentrate. If this replacement is possible, then the sulfide sulfur levels of the rougher concentrates could be optimised for a direct autoclave feed. The potential of sodium hydroxide to modify the flotation response of gold-rich pyrite versus low-gold pyrite could be established. The sulfide sulfur results from the flotation tests show that, for identical rougher flotation conditions, the use of sodium hydroxide compared to lime conditioning increased the gold to sulfur ratio (Au:S) of the rougher concentrates and enhanced the gold recovery rates.