GB958355A - Improvements in or relating to the recovery of gold and silver from aqueous cyanide liquors and to anion exchange resins therefor - Google Patents

Abstract

Gold and/or silver values are recovered from a gold and/or silver bearing aqueous cyanide liquor by treatment with one or more anion-exchange mixed base resins containing base groups of the type -CH2NRR0, where R and R0 are each an alkyl group which may be the same or different having at least 3 carbon atoms, such alkyl groups being branched or unbranched, the branch not being in the one or two carbon position of the groups, and from 1 to 35% of quaternary groups of the type -CH2NR1R2R3, where R1, R2 and R3 are alkyl groups which may be the same or different and which contain either two or three carbon atoms, and then eluting the gold and/or silver values from the resin, preferably by means of an aqueous or polar organic solvent solution of an alkali metal or ammonium thiocyanate. The anion-exchange resins may be based upon a cross-linked polystyrene e.g. a polystyrene obtained by using 1% to 5% of divinyl benzene or other cross-linking agent. Such a resin may be converted into an anion-exchange resin by chloromethylation (using chloromethyl ether in the presence of catalyst) followed by amination with one or more secondary amines RR0NH and one or more tertiary amines R1R2R3N. The alkyl groups R, R0 in the secondary amines should be those required in the main anion-exchange group -CH2NRR0, and R1, R2, R3 in the tertiary amines should be those required in -CH2NR1R2R3. Specifications 808,909, 808,910 and 958,356 are referred to.ALSO:An N-methano dialkylamine anion-exchange mixed base resin containing base groups of the type -CH2NRR0 and from 1 to 35% of quater nary groups of the type -CH2NR1R2R3 where R and R0 are each alkyl groups, the same or different, having at least three carbon atoms, said alkyl groups being unbranched or branched, the branch not being in the one or two carbon position of the groups, and R1, R2 and R3 are alkyl groups which may be the same or different and which contain either two or three carbon atoms is used to recover gold and silver values (see Division C1). Preferably R and R0 should have at least four carbon atoms. The resin may be based on a cross-linked polystyrene, such as a modified polystyrene obtained by using 1 to 5% of divinyl-benzene as a cross-linking agent. Such resins are preferably converted into the required anion-exchange resins by first halomethylating e.g. chloromethylating using chloromethyl ether in the presence of stannic chloride, the more volatile reaction products boiling below 53 DEG C. being removed by fractional distillation during the early stages of the chloromethylation, and then aminating with one or more secondary amines RR0NH and one or more tertiary amines R1R2R3N. The amination, which may be performed with or without water, is preferably carried out in the presence of a polystyrene swelling agent such as dioxane or chlorobenzene. In the examples chloromethylated polystyrene beads are treated with di-n-butylamine and either triethylamine or tri-n-propylamine. Specifications 808,909, 808,910 and 958,356 are referred to.