INVESTIGATIONS INTO THE SURFACE CHEMISTRY OF SOME SULFIDE MINERALS USING A NATURAL POLYSACCHARIDE

摘要

Detailed adsorption, electrokinetic and flotation studies have been carried out to investigate the interaction of a natural polysaccharide, guar gum, with sulfide minerals namely galena, sphalerite, chalcopyrite and pyrite. The adsorption densities of guar gum onto the above minerals show a characteristic adsorption maximum at pH = 11.5, 10, 9.5 and 7.5 for galena, pyrite, chalcopyrite and sphalerite respectively. All the adsorption isotherms exhibit Langmuirian behavior and in some cases a high affinity trend is observed. The amount of guar gum adsorbed onto these minerals may be arranged as follows in decreasing order of magnitude: PbS ZnS > FeS_2> CuFeS_2. Electrokinetic experiments indicate that the isoelectric point (iep) of pyrite is at pH = 6.8 whereas for the other sulfide minerals studied, it is found to be located below pH = 3. The addition of different concentrations of guar gum correspondingly reduces the negative electrophoretic mobilities in proportion to the polymer concentration, without any shift in the iep value, resembling the influence of an indifferent electrolyte. The results of the dissolution and co-precipitation tests performed to examine whether the lattice ions interact with the guar gum in the bulk solution, indicate release of metal ions from the minerals and confirm guar gum-metal ion interaction in the bulk solution. An interesting observation is that the pH of maximum precipitation of the respective metal ion coincides with the pH of the adsorption maximum of the corresponding minerals. This metal-ion guar gum interaction has been reinforced by the results of the solution conductivity tests. Microflotation tests on the individual minerals in the presence of guar gum reveal that the depressant ability of the polymer is in line with the adsorption data. The magnitude of depression at pH =11 using guar gum may be arranged in the following sequence: PbS > FeS_2> CuFeS_2> ZnS. Typical differential flotation tests on a synthetic mixture of galena and sphalerite reveal that galena can be effectively depressed by guar gum. Based on the interfacial and bulk solution studies carried out, possible mechanisms of interaction between guar gum and the sulfide minerals are discussed.