THE FLOTATION OF PYRITE USING MIXTURES OF DITHIOCARBAMATES AND OTHER THIOL COLLECTORS

This paper presents results which show that when mixtures of dithiocarbamates are used to float pyrite each component has a synergistic effect on the performance of the others. In particular cyclo-hexyl dithiocarbamate which produced the lowest recovery when used as a pure collector had a significantly advantageous effect on recovery and grade when mixed in small quantities with another dithiocarbamate. Different molar ratios of cyclo-hexyl (oC6) and di-n-propyl (di-n-C3) dithiocarbamates (DTC) in the mixtures were tested. In all cases 90:10 and 10:90 mixtures produced higher recoveries and grades than did 50:50 mixtures or the pure components. Recoveries increased from 74.0% for pure oC6 DTC and 83.5% for pure di-n-C3 DTC to 89.5% for the 90:10 mixture. Grades increased from 14.5% for pure oC6 DTC and 18.5% for pure di-n-C3 DTC to 20.5% for the 50:50 mixture. The effect of mixtures was less marked at higher dosages indicating that for the same performance lower dosages of mixtures were required compared to those required by the pure components. The mixtures resulted in faster rates of flotation as well as a greater recovery of coarse particles. Increased recoveries and grades were obtained in the first minute due to an enhancenment in the rate of flotation. When mixtures were used the p50 of the concentrate increased showing that coarser material was collected. This effect was greater in the first concentrate than the final concentrate. Mixtures of dithiocarbamates and other thiol collectors, viz. xanthate, sodium mercaptobenzothiazole and dithiophosphate further enhanced recoveries and grades to a maximum recovery of 96.0% and grade of 21.0% for a mixture of 90% potassium n-butyl xanthate (PNBX) and 10% oC6 DTC. The method (premixing or separate) and sequence of collector addition had little effect on recoveries or grades. The effect of copper sulphate addition varied. In the case of cyclo-hexyl dithiocarbamate, the addition of copper sulphate dramatically reduced recoveries and grades but when other collectors were present this did not occur. Generally the addition of copper sulphate slightly enhanced recoveries and grades and greatly enhanced water recoveries probably due to a froth stabilization effect.