2-mercaptobenzothiazole and derivatives in the flotation of galena, chalcocite and sphalerite: A study of flotation, adsorption and microcalorimetry

The results of flotation, using 2-mercaptobenzothiazole (MBT) and its derivatives, 6-methyl-MBT (MMBT), 6-methyloxy-MBT (MOMBT), 6-propyloxy-MBT (PrOMBT), and 6-pentyloxy-MBT (POMBT) on pure mineral samples showed some important advantages in the flotation of galena at neutral pH and low collector dosages. It has been found that MBT shows a high affinity towards surfaces containing lead and copper but no selectivity. The introduction of a pentyloxy ring substituent led to a change in the adsorption kinetics, as shown by microcalorimetry, and an improvement of the affinity towards galena. The basic mechanism of adsorption of MBT on galena and chalcocite has been studied by thermochemical measurements, showing that the adsorption mechanisms of MBT on both minerals are comparable in the initial step, involving the chemisorption of the collector. At concentrations above monolayer a second surface reaction of MBT on galena has been observed and attributed to an oxidative dimerisation. Comparative experiments on adsorption properties of mercapto-benzo-oxazole (MBO) show the important role of the endocyclic element composition on the sorption process. The endocyclic O-atom in MBO prevents chemisorption on galena whereas strong coordinative bonds will be formed on Cu containing surfaces.