Developing a selective flotation process for antimony and arsenic sulfides in complex gold ore processing

Composite gold-antimony ores contain fine-dispersed submicroscopic gold which is concentrated together with iron sulfides, such as pyrite, arsenopyrite, pyrrhotite. Such ores are considered refractory ores and characterised with low recovery of gold in cyanidation. Commercial concentrations of antimony in such ores make such deposits much more valuable. The product of gold-antimony ore processing is a bulk gold-antimony concentrate. Antimony concentrate is produced by separating the bulk gold sulfide concentrate as flotation froth. Bulk-selective flotation is used for processing of arsenic-antimony ores. In this process, all sulfides are extracted in the concentrate. For selection, depressants are used to surpress pyrite and arsenopyrite flotation. A low contrast between the flotation properties of stibnite versus arsenopyrite in the presence of conventional collectors and modifiers creates a need for new efficient regimes of selective flotation. This paper describes, and provides experimental evidence for, a flotation technique for separating antimony and arsenic sulfides when processing complex gold ores, which is based on the use of new selective reagents – modified diethyldithiocarbamate and tannin modifier. It was established that the application of tannin modifier in combination with diethyldithiocarbamate increases the flotation contrast between antimony and arsenic minerals. The mechanism of arsenopyrite depression implies a generation of the adsorption layer of Fe (II) and Fe (III) tannates, which account for 40% of the mineral surface area and produce a hydrophilic effect during flotation. Tannin does not react with antimony or adsorb on the stibnite surface. Consequently, it does not impede the flotation of stibnite with diethyldithiocarbamate thus ensuring its efficient separation from stibnite and chalcopyrite during the selection of bulk gold sulfide concentrate. Potential applicability of the developed technique was proved on a sample of gold-antimony ore from the Olimpiada deposit containing Au 2.5 g/t. In ore flotation conditions, the concentration of Sb in the concentrate sees a double rise while its recovery rises from 66 to 81%. At the same time, the concentration of arsenic drops from 1.38 to 0.77% while its recovery decreases from 95.6 to 90.8%. The concentration of gold in the concentrate increases from 15 to 22 g/t with the recovery being 88–90%.