Alternatives to xanthate collectors for the desulphurization of ores and tailings: Pyrite surface chemistry

Abstract

Xanthate is the most commonly used sulphide collector in the mining industry, however, its toxicological, ecological, and health and safety risks make alternative options increasingly attractive. In this study, two alternative collectors, one a mixture of dithiophosphate and mercaptobenzothiazole (DTP-MBT) and the other a mixture of dithiocarbamate and mercaptobenzothiazole (DTC-MBT), were tested for non-selective sulphide flotation. The adsorption of these collectors on pure pyrite surfaces was quantitatively and qualitatively characterized after conditioning at natural pH values (4–4.5) and alkaline pH values (10.5 using soda ash and lime). The adsorption of each collector was characterized through UV–vis spectrophotometry and direct surface observations using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The maximum amount of the three collectors adsorbed on pyrite surfaces was at least twice as great when conditioning was performed at natural pH values than at pH 10.5. Additionally, xanthate showed a greater affinity for pyrite surfaces than the DTP-MBT or DTC-MBT collectors. Surface characterizations showed that conditioning with collector resulted in the solubilization and modification of the oxidized species on pyrite surfaces. The nature of these superficial species and the collection mechanisms varied according to collector type, conditioning pH, and type of pH modifier used. At natural pH values, the vibrations detected in the spectra from the alternative collectors were mainly the CNH or NCS groups belonging to the 2-mercaptobenzothiazole compounds adsorbed on the pyrite surface, which could correspond to an iron mercaptobenzothiazole complex. At alkaline pH values, the main species characterizing the adsorption of these collectors on pyrite were difficult to identify because of their lower affinity for the pyrite surface. The only adsorption signature appearing on the pyrite surfaces at high concentrations was a CNH group of the MBT component; this also indicated the presence of a Fe-MBT complex on the pyrite surface.This study attempted to apply the above findings to the desulphurization of an ore from Goldex mine (Val-d'Or, Quebec). These tests were carried out with the three collectors at pH 6 (using sulphuric acid) and at pH 9.5 (using NaOH or CaO) in order to compare sulphur recoveries and sulphide cleaning in the final tailings. The desulphurization efficiencies of DTP-MBT at pH 9.5 were about 74.0% and 73.1% using NaOH and CaO, respectively. This was similar to the efficiency of xanthate (˜75%), but the alternative collectors showed slower flotation kinetics. In contrast, the performance of DTC-MBT was lower than for xanthate i.e., 69.9% with NaOH and 66.6% with CaO. For the three collectors, sulphide flotation at pH 6 was less efficient than at pH 9.5 (efficiency did not exceed 67% regardless of collector). According to the calculated acid-generation and neutralization potentials, none of the final desulphurized tailings should be considered as acid-generating.