As part of other work related to the studies of kinetic factors that influence the flotation of specific sulphide minerals, specially designed kinetic flotation experiments at Cominco included work done on -65 + 100 mesh and -100 + 150 mesh, high purity galena. The flotation collector used was sodium isopropyl xanthate containing radioactive sulphur-35. Radiation monitoring of the galena fractions from stage flotation tests indicated that the adsorbed radioactive xanthate was uniformly distributed among the floated fractions and the non-floated, or residual portion of the galena.
Experiments on the flotation kinetics of sulphide minerals included detailed investigations of -65 + 100 and -100 + 150 Tyler mesh, high purity galena. In each of these detailed investigations, a stage flotation technique (1) was used to float and collect several galena fractions.
For each test, the results are represented by two curves – one showing the amount of xanthate with the floated fractions, and the other showing the xanthate with the tailing. For example, the curves corresponding to test 2 show results when the concentration of xanthate was 1.55 ppm and the pH was adjusted to 11.5 with limewater. The broken curve shows amount of adsorbed xanthate possessed by the concentrates sequentially collected during that kinetic flotation test. The horizontal curve corresponds, to the adsorbed xanthate possessed by the tailing recovered from the same test.
Comparison of the radiation data among the floated fractions and the tailing suggested that the radioactive xanthate was distributed “uniformly” among all the flotation products from a given test. The expression, “distributed uniformly”, does not refer to the regularity of surface coverage by the collector.
Inherent mineralogical properties of galena, as well as changes in its surface properties were suspected as being most likely responsible for the non-floated galena apparently having adsorbed as much xanthate collector as any of the galena recovered in the froth.
Visible differences of mineral surfaces were not observed microscopically. Trace amounts of various minerals, hosted by galena, were observed but only verified the previous semi-quantitative and detailed spectrographs analyses.
Structural differences between the floated and non-floated mineral particles were not detected by x-ray diffraction. To discern structural distortions within the lattice, line-broadening techniques would be required. Such x-ray equipment, utilizing this technique, was unavailable at the time. Furthermore, proper interpretation of line-broadening observations associated with lattice distortions, is an involved and lengthy study.
Galena is one of many naturally occurring minerals with semiconductor-properties. Several investigators have attempted to associate the flotation response of these semiconductor-type minerals to certain electrical transport properties and surface property measurements. Thermoelectric potentials have been used to distinguish between n-type and p-type sulphide mineral semi-conductors. One such thermoelectric measurement involves detecting the Seebeck voltage or coefficient. The Seebeck effect, which measures a thermally induced e.m.f., can be considered simply as the thermoelectric detection of non-stoichiometric composition, i.e. an excess of either sulphur or lead atoms within the lattice, or else the presence .of minor amounts of foreign atoms occurring substitutionally or interstitially within the PbS lattice.