LAUSR

ABSTRACT A pressure oxidation (POX)-hot cure (HC)-lime boil (LB) process is used in industry to recover silver from refractory gold sulphide ores containing minerals such as pyrite and arsenopyrite. Pressure oxidation is used to oxidise minerals and liberate occluded gold particles. As such, iron goes into solution and under acidic and high-temperature conditions often precipitates as basic iron sulphate (BFS). BFS consumes excess lime during neutralisation before cyanidation. Therefore, a hot cure stage is required to re-dissolve BFS back into solution. BFS re-dissolution consumes acid and produces ferric sulphate. In the presence of silver, these conditions favour the slow formation of silver jarosite. Silver jarosite is refractory to cyanidation and must be broken down before cyanidation. This is done in the lime boil to produce a cyanide-soluble silver hydroxide. A study was conducted to investigate parameters that affect the precipitates that form in each stage of the POX-HC-LB process.