The effect of flotation collectors on the electrochemical dissolution of gold during cyanidation

Abstract

Gold-bearing ores, especially the sulphidic ones, are often treated by flotation prior to cyanidation. Following flotation process, the flotation concentrate or tailings are redirected to the cyanidation circuit for gold extraction that may contain appreciable amounts of collector used in flotation, and also remained sulfide minerals, i.e., predominantly pyrite. This current research examines the effect of collector on gold leaching by conditioning gold prior to cyanidation and direct addition in cyanidation in a packed bed leach reactor. Effects of pyrite, and solid-liquid separation on gold leaching and its electrochemical behaviour in presence of collector were also investigated. It was found that conditioning of gold with Aerophine 3418A in absence of pyrite has a detrimental effect especially on leach kinetics of gold since it adsorbs onto gold and decreases its further dissolution. In presence of pyrite, a significant improvement was obtained in gold leaching due to the positive galvanic interactions. These findings suggest that although collector adsorption adversely affects gold leaching, i.e., partial passivation, yet galvanic interactions could continue to enhance its extraction. Following conditioning, solid-liquid separation prior to cyanidation is shown to moderately increasing gold leaching by up to 10%. When Aerophine 3418A was added directly during cyanidation, gold leaching showed a slight increase in absence of pyrite. Conversely, in presence of pyrite, a significant increase in gold leaching was observed. Moreover, if collector was added after the first one hour of cyanidation, gold leaching kinetics was enhanced. Cyclic voltammetry tests within open circuit potential findings support the cyanide leaching results. SEM-EDS analysis of leach residues has demonstrated that there is less amount of gold in the residue both when pyrite is present and collector is added directly. XPS analyses have confirmed the presence of metallic gold in leach residues. These results have revealed the effect of Aerophine 3418A on gold leaching is different when it is directly added than that of conditioning and the positive galvanic effect of pyrite occurs even in the presence of collector.