The effect of thiol collector mixtures on the flotation of pyrite and galena

Thiol collector mixtures are commonly used in the flotation of base metal sulphides and platinum-bearing ores. There are synergistic benefits claimed for these collector mixtures, with mixtures lowering total dosage requirements, improving coarse particle recovery and the rate of flotation. Some of the secondary collectors are known to act as frothers. Therefore, a previous study aimed to decouple froth and pulp effects and considered only the bubble-particle attachments in the pulp. This was achieved through microflotation experiments, where various ratios of the ethyl and isobutyl chain lengths of xanthates, dithiocarbamates and dithiophosphates were used as collectors. Results from these experiments showed a marked increase in galena recovery using mixtures of xanthate with either dithiophosphate or dithiocarbamate. In the current study, the froth phase was introduced in the form of batch flotation studies to determine whether benefits noted during microflotation experiments would be carried through to a more realistic froth flotation scenario. The pure minerals used were galena or pyrite and these were tested separately. The findings show that a higher galena recovery (92.2%) was obtained when using a 10:90 mixture of ethyl xanthate (SEX) with diethyl dithiophosphate (SEDTP) compared to 89.0% with the best single collector. Galena and pyrite minerals showed marked differences in their respective frothing effects and in their preferences for collector type. The best collectors for galena were the worst for pyrite (SEDTP and ethyl dithiocarbamate (SEDTC)). The best overall collector for pyrite was a 75:25 SIBX:SEDTP mixture (93.4% recovery compared to 89.8% for SIBX alone). In general, it was found that the batch flotation cell and microflotation cell gave quite different results. This was attributed to the different internal energies of the cells and to differences in particle hydrophobicities, with particles of optimum hydrophobicity stabilising the froth. Actual recoveries of the mixtures were compared to an expected recovery based on the calculated weighted recoveries of the single collectors. This showed that most collector mixtures achieved greater recoveries than would be expected based on their additive performance alone. This synergistic behaviour was most notable for mixtures of strong and weak collectors. Antagonistic behaviour was noted for mixtures of two strong collectors. (C) 2013 Elsevier Ltd. All rights reserved.