In mine water, a small amount of cadmium ion is sometimes contained together with appreciable amounts of ferrous and zinc ion.
The removal of cadmium ion from mine water has been studied by using xanthates as the selective precipitant.
The solubility product of cadmium xanthate reduces with increasing the chain length of an alkyl group. It is found that the amount of methyl, ethyl, butyl and amyl xanthate necessary for precipitating 90% of cadmiumion is about 120, 10, 1.5 and 1 equivalent to cadmium ion involved in the solution, in the case of cadmiumion concentration of solution is 1mg/l.
The formation of the precipitate of cadmium xanthate depends very much on the condition of agitation of the solution in a Denver-type flotator used as reaction cell and the precipitate is effectively formed by vigorous agitation. Owing to the strong hydrophobic property of cadmium xanthate, it is possible to remove the precipitate of cadmium xanthate from the solution by the flotation technique. The romoval of cadmium as cadmium xanthate from the solution is prevented to some extent by the coexistence of zinc and ferrous ions.
When ferric ion is contained in mine water, it is necessary to remove the ferric ion before xanthation by leading it into ferric hydroxide with the addition of calcium carbonate, because xanthate ion is oxidized by ferricion.
It is possible to reduce cadmium ion concentration below 0.1mg/l from an artificial mine water containing 1mg/l of cadmium, 100mg/l of zinc and 500mg/l of ferrous ion, by the addition of 2-3 equivalent of butyl and amyl xanthate, or 5-6 equivalent of propyl xanthate to cadmium ion involved.
This result is proved by the actual mine water, too.
