United States Patent to 3,997,337 Pittie et al. 45 Dec. 14, 1976 (54) SEPARATION AND/OR PURIFICATION OF 56 References Cited PRECIOUS METALS UNITED STATES PATENTS (75) Inventors: Willem H. Pittie, Rooderpoort, 3,413, l l 4 1 1/1968 Illis et al. ........................... 75/83 X Transvaal; Gerhardus Overbeek, Florida, Transvaal, both of South Africa Primary Examiner-M. J. Andrews 73 Assignee: Swarsab Mining, Exploration & Attorney, Agent, or Firm-Cushman, Darby & Development Company Cushman (Proprietary) Limited, Johannesburg, South Africa 57 ABSTRACT 22 Filed: Aug. 29, 1975 A process for the treatment of a concentrate of by-met (21) Appl. No.: 609,155 als comprises heating the concentrate at between 1100 C and 1500°C, preferably at about 1300C, in a gase (30) Foreign Application Priority Data ous stream which comprises oxygen. The heating step is Apr. 3, 1975 South Africa ..................... 75.12093 effected for a period of time sufficient to ensure quanti tative removal of one or more of lead, arsenic, silver, 52 U.S. C. ................................... 75/121; 75/108; bismuth and/or tellurium and the oxidation of ruthe 423/22; 423/44; 423/88; 423/97; 4231508; nium, rhodium and iridium to their oxides. 423/593 (51) Int. Cl.'......................................... C22B 11/00 58) Field of Search ...................... 75/121, 83, 108; 423/22, 44, 88,97, 508, 593 9 Claims, 1 Drawing Figure EtOH By-Metal Concentrate Recycle Wapours Air Precipitate Filtrate Residue KO HCl 5 Ho Filtrate Precipitate Residue To Waste Filtrate HCl + HO 4. NO -45 trate Recycle Rese Os Rh + r. Eto Filtrate Precipitate HClo 7 Ru U.S. Patent Dec. 14, 1976 3,997,337 EtOH By-Metal Concentrate Recycle Vapours Air Precipitate NaOh O 42 Filtrate Residue O KOH HC. Filtrate Precipitate Residue To Waste Filtrate HC - H2O2 Filtrate Recycle Residue Os Rh - Ir EtOH Recycle Filtrate 6 Precipitate HClo 7 R 3,997,337 1. 2 fusion. The iridium has to be separated from large SEPARATION AND/OR PURIFICATION OF quantities of lead and other impurities present in the PRECIOUS METALS concentrate which have been rendered soluble by the sodium peroxide (NaO2) fusion, BACKGROUND OF THE INVENTION 5 The above process is often carried out on what appli This invention relates to the separation and purifica cant considers to be unecessarily large quantities of tion of precious metals which consist, in the context of concentrates thereby using correspondingly large this specification, of the platinum group metals and quantities of costly reagents. Also, the impurities, in gold. More particularly the invention is concerned with particular tellurium are sometimes difficult to remove. the separation and/or purification of what are com 10 monly termed secondary platinum group metals or SUMMARY OF THE INVENTION by-metals, which consist of rhodium, ruthenium, irid It is the object of this invention to provide a process ium and osmium. for the treatment of a by-metal concentrate which will In all processes within applicants's knowledge a pre assist in the removal of troublesome impurities such as cious metal concentrate is initially split into two 15 Te, As, Bi, Ag, and Pb which will remove osmium, and groups, one of which consists basically of platinum, which will reduce the bulk of the by-metals being re palladium and gold, and the other of which comprises fined with a consequent saving of reagents and cost of the by-metals. In one known process the by-metals are equipment. alloyed with lead to separate a substantial amount of In accordance with this invention, there is provided a base metals therefrom initially. (“Base metals' in the 20 process for the treatment of a concentrate of by-metals context of this specification include all metals apart comprising the heating of the concentrate at between from precious metals and silver). Lead is then dissolved about 1 100° C and 1500 C in a gaseous stream which using dilute nitric acid and platinum, palladium and comprises oxygen, the heating being effected for a gold are dissolved by means of aqua regia. period of time sufficient to ensure quantitative removal The resultant reside constitutes a feed to a by-metal 25 of one or more of lead, arsenic, silver, bismuth and/or separations and purification stage of the whole process. tellurium and the oxidation of ruthenium, rhodium and As an example of the type of concentrate which may be iridium to their oxides. obtained from the above process steps, the following is Further features of the invention provide for the given by way of illustration with the relative propor gaseous stream to be air, for the gaseous stream to be tions of the metals being given in weight percentages: 30 scrubbed after leaving the heating region, for the scrub bing liquid to be treated for the recovery of osmium, ELEMENT PERCENT and for the heating to be effected at about 1300° C. Platinum (Pt) 1 - 5 The invention also provides a method of treating the Palladium (Pd) 1 - 3 35 ignited by-metal concentate for the separation of ruthe Gold (Au) 0, 1 - 0,5 Rhodium (Rh) 5 - 15 nium from the other platinum group metals therein, Ruthenium (Ru) 30.50 comprising fusing the ignited concentrate with potas ridium (r) 4 - 10 Osmium (Os) 0 - 5 sium hydroxide and leaching the melt with water to Silver (Ag) 2 - 5 dissolve ruthenium complexes formed in the fusion Copper (C) () - 4. 40 process. Nickel (Ni) () - 4 Iron (Fe) 0 - 1 Further features of this aspect of the invention pro lead (Pb) 20 - 50 vide for the residue obtained after the water leach to be Telhurium (Te) 0 - 1 Bismuth (Bi) 0 - 0,5 treated for the dissolution of the platinum group metals Arsenic (As) 0 - 0,5 by the action of hydrochloric acid, and hydrogen pe 45 roxide with the reactants being placed in a suitable bomb and heated to a moderate temperature, for exam Such a by-metal concentrate may be fused with potas ple, about 150° C. sium bisulphate (KHSO) which renders the rhodium water soluble by converting it to the sulphate, Rh DETAILED DESCRIPTION OF THE INVENTION (SO4)3. 50 In its preferred form the invention is implemented After water treatment to remove rhodium, the resi basically as follows, the process steps being clearly due is separated from the dissolved rhodium and sub shown in the accompanying flow sheet: jected to a sodium peroxide (NaO) fusion which con A by-metal concentrate is heated at 1 in a stream of verts the ruthenium and osmium to water soluble so air at about 1300 C for 20 hours. dium salts of the oxo-anions of the two metals (e.g. 55 it has been found that under these conditions osmium RuO and OsO, respectively) and iridium to an acid is removed quantitatively from the concentrate to soluble hydrous oxide probably IrOnHO. The ruthe gether with lead, arsenic, silver bismuth and tellurium, nium and osmium are then separated from the iridium while less than 10% of the ruthenium and only traces of by treating the sodium peroxide melt with water fol the other PGMs are volatilized. The vapours are scrub lowed by filtration while the iridium is dissolved by 60 bed at 2 with a 10% NaOH solution which precipitates treating the resultant residue with hydrochloric acid. all the metals as hydrous oxides (which settle to the The metals thus separated from one another are then bottom of the receiving vessel) except the ruthenium treated for further purification. The ruthenium and and osmium oxides which are converted to soluble osmium are normally purified by a collective chlorine sodium salts according to the following reactions: distillation, followed by a nitric acid distillation for 65 osmium. The rhodium is treated for the removal of Ruo, + 2NaOH -> Na(RuO) + 'AO + HO OsO. impurities such as palladium, tellurium and other base + 2 NaOH -> Na(OsO(OH)) metals which are also rendered soluble by the KHSO 3,997,337 3 4 The ruthenium is precipitated at 2 from the alkali fusion. This technique has been found to give superior solution by the addition of ethanol which reduces the results. Also the cost and corrosiveness of KOH are far oxo-anion RuO' to an insoluble hydrous oxide which less than that of NaO. is probably RuOnHO. This precipitate is filtered off e. Due to the KOH-fusion the iridium- and rhodium together with the sludge in the receiver which contains 5 oxides present in the residue are found to be almost the other metals which have been volatized and is recy quantitatively soluble in HCl + H2O, at 150° C in the cled to the lead alloying stage of the metal process or to subsequent bomb dissolution. some other convenient point of lead alloying is not utilized. EXAMPLE OF THE INVENTION The osmium which remains in solution is then precip 10 STEP 1 itated at 3 at room temperature as a hydrous oxide, 100g of a by-metal concentrate (an analysis of which probably OsOnH2O by acidifying the solution with is given in table I) was roasted in a stream of air at HCl to a pH = 4,0 1300° C for 20 hours. Na(OsO(OH),)- AS Na(OsO)-HGOso, nHo soluble soluble The osmium thus obtained may be purified by redis 20 TABLE I solution at 4 in HNOa and subsequent distillation. ANALYSS OF BY-METAL CONCENTRATE It is considered that the above mentioned tempera (In % by weight) ture of 1300° C is important since if the temperature is Element % (By weight) Weight grams too high, too much ruthenium is lost and if it is too low Os 38 38 the reaction rate is too slow.