GB492344A - Improved treatment of ammoniacal solutions of metal salts - Google Patents

Abstract

Ammoniacal metal salt solutions, after clarification if necessary, are passed through a cation exchanger of acid character whereby the metals in complex solution are absorbed in the form of ammine while the ammonia passes through unabsorbed. Suitable exchangers are coal activated with acid, resins having an acid character, e.g. as described in Specification 450,308, silica gel and hydrogen zeolites. The ammoniacal filtrate may then be re-used as such, if desired after replenishment with ammonia, e.g. in metallurgical leaching. Alternatively, the ammonia may be retained in a subsequent filter charged with an absorbent of feeble acid character, i.e. silica gel, from which the ammonia may be recovered by thermal treatment, e.g. by means of steam. The exchanger charged with metal values may be regenerated by treatment with a suitable acid, the resulting solution containing salts of the metals and ammonium salt equivalent to the ammonia content of the metal ammine. If desired, the ammonium content of the metal ammine can be wholly or partly removed by heat treatment prior to the acid treatment. A selective removal of heavy metals from a solution may be achieved by the use of hydrogen ion exchangers which exert selective absorption. If in the subsequent stage, it is desired to recover also the ammonia present as ammonium salt, the liquid is passed through a hydrogen ion exchanger of strong acid character, e.g. a sulphonated resin, which may be regenerated by treatment with acid with the formation of the corresponding ammonium salt. If it is desired to recover the total ammonia as free ammonia, the filtrate is passed through a hydroxyl ion exchanger, e.g. an amine resin as described in Specification 450,309, the ammonia now present in the free form being finally bound by an absorbent having having a feeble acid character. According to examples: (1) an ammoniacal copper solution is passed first through silica gel in which copper tetramine is absorbed and subsequently recovered by treating the gel with hydrochloric acid and then through further silica gel in which the ammonia is absorbed and recovered by treatment with steam; (2) an ammoniacal solution containing copper, zinc, cobalt and traces of silver obtained by leaching burnt copper pyrites with aqueous ammonia containing ammonium chloride is passed through a condensate of phenol sulphonic acid with formaldehyde, the filtrate after replenishment with ammonia being returned to the leaching step and the absorbent being regenerated as described in example (1); (3) silica gel is shown to be more favourable to the absorption of zinc, and anthracite sulphonated with oleum more favourable to the absorption of copper, when brought into contact with an ammoniacal solution containing both these metals; (4) an ammoniacal solution containing copper and zinc is passed through a battery of filters consisting of a phenol-formaldehyde condensation product containing-o -sulphonic acid groups, the copper being absorbed prior to the zinc.