EFFECTIVENESS OF LEAD AS AN ALTERNATIVE TO COPPER ACTIVATION IN GOLD BEARING IRON SULFIDE FLOTATION

摘要

Refractory gold ores generally comprise of gold bearing iron sulfide minerals, such as pyrite and arsenopyrite, where the gold cannot simply be extracted by cyanide leaching. Pre-treatment stages, such as flotation, are therefore an integral part of refractory gold ore processing. Iron sulfide flotation using thiol collectors require surface activation to enhance collector adsorption and improve recovery. Copper sulfate is a commonly used activator and concentrations generally build up within the circuit to levels that far exceed the required amount, particularly where process water is recycled. These excess copper ions form Cu-CN complexes in downstream leaching processes thereby increasing the consumption of cyanide appreciably and reducing gold loadings on activated carbon. To overcome these problems, lead nitrate has been used in some North American operations but its use has not been widespread due to limited understanding of the mechanisms involved and the conditions required. This study investigates and compares the flotation performance of both CuSO_4 and Pb(NO_3)_2 as activators for the iron sulfide minerals, arsenopyrite and pyrite, in acidic and alkaline media. Studies show that the activation of iron sulfide minerals is affected mainly by interacting variables such as, pH, collector type and its concentration. In this work, the interactive effects of these variables on lead and copper activation have been investigated using techniques such as; solution and mixed potential measurements, cyclic voltammetry experiments, zeta potential measurements and batch flotation trials. Factorial experimental designs were used for all experiments in order to analyse the significance of the main variables and their interactions. It has been shown that Pb(NO_3)_2 can effectively replace CuSO_4 as an activator of both pyrite and arsenopyrite in slightly acidic conditions and that its effectiveness on arsenopyrite under these conditions is more pronounced than for pyrite. The optimal dosages of the reagents have also been established.