GB1010082A - Purification of zinc sulphide - Google Patents

Abstract

Ionic impurities are removed from zinc sulphide by contacting an aqueous suspension thereof with an anion-exchange resin in the hydroxyl form, preferably one having quaternary ammonium functional groups, and a cation-exchange resin in the hydrogen form, preferably one having sulphonic acid functional groups, in the form of membranes in an electro-dialysis cell. The cation-exchange membrane, e.g. Permaplex C20, separates a cathode compartment containing dilute acid, e.g. 0.2N H2SO4 from a middle compartment containing the suspension to be treated, while the anionexchange resin, e.g. Permaplex A20, separates an anode compartment containing dilute alkali, e.g. 0.2N NaOH, from the middle compartment. By applying a potential difference of 250 volts D.C. across two platinum foil electrodes immersed in the outer compartments, the conductivity of a stirred suspension of 3 gms. zinc sulphide in 300 c.c. water may be reduced to 1.6x10-6 ohm-1 cm.-1 in seven hours, and purified zinc sulphide recovered therefrom.ALSO:Ionic impurities are removed from zinc sulphide by contacting an aqueous suspension thereof with an anion exchange resin in the hydroxyl form, preferably one having quater-nary ammonium functional groups, and a cation-exchange resin in the hydrogen form, preferably one having sulphonic acid functional groups. The resins may be in the form of granules, and contact may be by stirring followed by filtration of the zinc sulphide suspension from the resin, or in a column packed with a uniform mixture of the two types of resin, or the two types may occupy upper and lower zones of the column. The zinc sulphide is preferably subjected to a preliminary purification by water washing. Purified zinc sulphide may be separated by, e.g. centrifuging from a solution whose conductivity has been reduced to, e.g. 3 x 10-6ohm-1cm.-1 Alternatively the resins may be in the form of membranes in an electrodialyses cell (see Division C7).