Method for recovering gold by solvent extraction
Patents Granted (Contd.) (SI) International Classification: C01G 7/00 (2006.01) C22B 11/06 (2006,01) C22B 3/26 (2006.01) (54) ntie Method for recovering gold by solvent extraction (57) Abstract The invention relates to a method for recovering gold by solvent extraction from an acidic chloride-containing aqueous solution or from slurry containing gold- bearing solids using a diester-based reagent that is poorly soluble in water as organic extraction solution. In accordance with the method, gold is extracted extremely effectively, but other precious metals and many other metals quite sparingly. Gold is stripped from the extraction phase with pure water, from which the gold can be reduced either chemically or eiectrochemically (56) Documents Cited : FORM 25 (12)PATENT (19) ΑΡ (11) Patent No : ΑΡ 3223 (73) Applicant(s) OUTOTEC OYJ, Riihitontuntie 7, FIN-02200 Espoo, Finland (21) Application No: AP/P/2012/006625 (22) Filing Date : 07.06.2011 (24) (45) Date of Grant &03/04/2015 Publication : (30) Priority Data (72) Inventors (33) Country (31) Number (32) Date HAAPALAINEN Mika, Finland FI 20100243 09.06.2010 PAATERO Erkki, Finland (84) Designated States: (74) Representative MW ΖΜ ΝΑ ΚΕ UG ZW ADAMS AND ADAMS MOZAMBIQUE, Mozambique The invention relates to a method for recovering gold by solvent extraction from an acidic chloride-containing aqueous solution or from slurry containing gold-bearing solids using a diester-based reagent that is poorly soluble in water as organic extraction solution. In accordance with the method, gold is extracted extremely effectively, but other precious metals and many other metals quite sparingly. Gold is stripped from the extraction phase with pure water, from which the gold can be reduced either chemically or electrochemically. A method for extracting gold selectively from its acidic chloride-based aqueous solution or solid-containing slurry by solvent extraction to produce pure gold, characterised in that a diester of 2,2,4-trialkyl-1,3-pentanediol is used as the organic extraction reagent in solvent extraction; the gold-bearing organic solution that is formed is scrubbed with an acidic aqueous solution, after which gold is stripped into water, from where it is reduced to form pure gold. A method according to claim 1, characterised in that a mixture of a diester of 2,2,4-trialkyl-1,3-pentanediol and a branched long-chain alcohol is used as the extraction reagent. A method according to claim 1 or 2, characterised in that the diester of 2,2,4-trialkyl-1,3-pentanediol is 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate or a derivative of it. A method according to claim 2, characterised in that the long-chain alcohol is 2-ethylhexanol. A method according to claim 3, characterised in that there is a hydrogen atom or some other alkyl group or aryl group in place of one or more methyl groups in the side chain of the molecular structure of 2,2,4-trimethyl-1,3-pentanediol di-isobutyrate. A method according to claim 1 or 2, characterised in that extraction takes place simultaneously with the leaching of the gold-bearing solid contained in the slurry. A method according to claim 6, characterised in that the gold-bearing solid is at least one of the following group: gold ore, concentrate, anode slime, ash, scrap, or ion exchanger, activated carbon or adsorbent used in gold recovery. A method according to claim 1, characterised in that after the solvent extraction stage the gold-bearing organic extraction solution is routed to a scrubbing stage in order to scrub out of the extraction solution the impurity metals extracted into it, where an aqueous solution of hydrochloric acid with a concentration of 1.5 - 8 mol/L, preferably 2 - 6 mol/L, is used as the scrubbing solution. A method according to claim 8, characterised in that the scrubbing stage contains at least two scrubbing steps, where the hydrochloric acid concentration of its aqueous solution is greater than 2 mol/L in the first scrubbing step and the hydrochloric acid concentration of the second scrubbing step is the same or lower than that in the first scrubbing step. A method according to claim 8, characterised in that in the scrubbing step the selenium, antimony and tellurium extracted into the organic extraction solution is scrubbed out of it, and the scrubbing solution is routed to a selenium extraction stage, in which a diester is used as the organic extraction solution. A method according to claim 1, characterised in that the stripping stage of the organic extraction solution exiting the scrubbing stage is performed as a crosscurrent extraction. A method according to claim 1, characterised in that the stripping stage of the organic extraction solution exiting the scrubbing stage is performed as a countercurrent extraction. A method according to claims 1 and 11, characterised in that the gold stripping stage of the organic extraction solution is performed after the scrubbing stage in at least two steps using pure water in both stages. A method according to claim 11 or 13, characterised in that the gold-bearing aqueous solutions exiting the stripping steps are combined and pure gold is recovered from the aqueous solution of stripping in a reduction stage. A method according to claim 1, characterised in that gold is reduced from the aqueous solution of stripping by means of oxalic acid or its salt. A method according to claim 1, characterised in that gold is reduced from the aqueous solution of stripping by means of sodium borohydride. A method according to claim 1, characterised in that gold is reduced from the aqueous solution of stripping by electrolysis. A method according to claim 1, characterised in that the acidic chloride-bearing aqueous solution containing gold or the solid-bearing slurry is an aqueous solution of hydrochloric acid.