Patented May 15, 1951 2,552,709 UNITED STATES PATENT OFFICE 2,552,709 PRocess FoR THE PURIFICATION OF RHODUM Francis Sidney Ceraents and Alan Richardson Raper, London, England, assignors to The In ternational Nickel Company Incorporated, New York, N. Y., a corporation of Delaware. No Drawing. Application July 5, 1950, Serial No. 172,202. In Great Britain July 8, 1949 6 Claims. (C. 23-50) 2 This invention-relates to the purification of rhodium to the high degree of purity required rhodium. by modern industry. - . Most of the world's production of rhodium It was, therefore, decided that experiments comes from platinum metal concentrates. No at should be carried out to determine Whether the tempt. is made to separate the rhodium in the existing processes could be modified, or an im early-stages of refining and the first aim usually proved process discovered, which would efficiently is to remove gold, platinum, and palladium by remove lead, bismuth, tellurium and other im aqua regia treatment. After this preliminary purities from potassium hexachlororhodate or treatment the rhodium is obtained in association other coin plex Salt of rhodium. Modifications to with iridium, ruthenium, small amounts of the 10 existing processes proved satisfactory to a degree other metals of the platinum group, base metals but it was considered that such modifications from-cementation residues such as copper, bi Were really additional operations to an already smuth, lead, tellurium, and siliceous material. lengthy proceSS. The most promising results . Whatever method is employed in the further Were obtained when an entirely new process of treatment of this material the rhodium is ulti treating potassium hexachlororhodate was carried mately obtained in aqueous solution containing out. It was also found that this process could be appreciable amounts of the base metals men applied to other complex rhodium salts and the tioned above and some of the precious metals. corresponding free-acids. 5. It is fairly common practice at some stage in It is an object of this invention to provide an refining to convert the rhodium to the soluble 20 in proved process for the purification of rhodium Sodium-hexanitritorhodate Na3 IRh(NO2) 6 and using a cation exchange resin. to-precipitate the rhodium from solution as the It is a further object of this invention to pro insoluble potassium or ammonium salts. These vide a process for the purification of rhodium latter. salts are - then decomposed with hydro whereby the content of base metal impurities chloric acid to form the soluble potassium or am which normally occur in rhodium refining opera monium hexachlororhodates, e. g. K3 IRhCls. tions, such as copper, bismuth, silver, lead, tel Part of the base metal content, particularly lead, lurium, tin, chroniuim, aluminium, manganese bismuth and tellurium, is carried along with the and iron is considerably reduced. rhodium, and Special steps have to be taken to It is a still further and more particular object produce high purity: rhodium. In one method of the invention to provide a process for the sodium sulphide is added to the solution of sodi- . purification of rhodium whereby about 95% or um hexanitritorhodate to precipitate base metals more of the impurities are removed in a single together with a part of the rhodium as sulphide. cycle of operations. After this treatment the rhodium is precipitated In accordance with the process of the present as the ammonium salt. and this salt decomposed with hydrochloric acid. This cycle of operations 35 invention for the purification of rhodium an may have to be repeated five or six times to re aqueous Solution of a water-soluble complex rho move all traces of lead and other impurities. Al dium compound in which the rhodium is present ternatively base metals may be removed from the in the anion in which the concentration of the solution of sodium hexanitritorhodate by hydro Said compound is up to o molar is treated with lytic precipitation at controlled pH with or with 40 a cation exchange resin containing a sulphonic out the addition of a suitable carrier, but the op acid group to remove impurities from the solu eration may have to be repeated several times tion. and is difficult to apply if much copper is present. The Water-soluble complex rhodium compound Many other methods for removing base metals may be a complex rhodium. Salt or a correspond from rhodium have been used from time to time. 45 ing free acid. Some commercial refiners have separated the The cation exchange resins containing sul rhodium as metal in an impure state and have phonic acid groups may have a sulphonic acid relied on the chlorination of rhodium at elevated group in a nucleus or in a nethane Sulphonic temperatures to remove part of the base metals 50 group. Particularly preferred cation exchange by volatilisation and have then leached the in resins which contain Sulphonic acid groups are soluble rhodium chloride with water, hydro Zeo-Karb 215 and DOWeX 50. chloric acid or aqua regia. - - - - - DOWex 50 contains nuclear Sulphonic acid. Most of the procedures described above are too groups and its preparation is described in United complex for the routine commercial refining of 55 States specification No. 2,366,007. 2,552,709 3 4. Zeo-Karb 215 is a resin in which the active When the resin had replaced cations by Hions groups are largely sulphonic acid groups. to its fullest extent it WaS regenerated. This WaS It will, however, be understood that the present effected by passing 2 NHCl through the exhaust invention is not limited to the use of these tWO ed resin which replaced the K, Pb and Bi and resins but other cation exchange resins contain- 5 other cations by H ions with the result that the ing sulphonic acid groups may be used. resin reverted to itS Original Condition. Regen Thus, polyfunctional cation eXchange resins eration appeared to take place Without deteriora may be used provided that they contain Sulphonic tion of the resin. The resin was regenerated acid groups although the carboxyl and hydroxyl more than 1000 times Without apparent change. groups take little part in the exchange at the 10 The Solution resulting from the paSSage of po pH values prevailing in the process of the preS- tassiuin hexachlororhodate through the cation ent invention. Examples of these resins are the exchange resin may be concentrated, ammonium following: (a) Dowex 30. This is a Sulphonated chloride added thereto and the annonium Salt phenol-formaldehyde resin containing Sulphonic thus produced may be ignited in air and reduced acid and hydroxyl groups. It is prepared by the 15 to rhodium metal which may then be subjected condensation of o- and p-phenol Sulphonic acids to hydrogen fluoride treatment for the removal With formaldehyde. (b) Wolfatiit KS. This is of Silica. While the use of annonium chloride a resin containing Sulphonic acid, carboxyl and is convenient and has the advantage Of easy re hydroxyl groups. It may be made by the Con- moval and the benefit of a slight additional puri densation of benzaldehyde disulphonic acid with 20 fication, other SaltS Such as alkali metal Salts resorcinol and formaldehyde (see British Intelli- or alkaline earth metal Salts may be used, if de gence Objectives Sub-Committee Report No. 621). Sired. (c) Sulphited phenol-formaldehyde resins which By the process of the present invention from contain methylenic Sulphonic acid and hydroxyl potaSSium hexachlororhodate crystals contain groups. These are made by heating phenol and 25 ing 0.29% Pb, 0.015% Bi and >0.10% Te ex formaldehyde with a mixture of Sodium Sulphite preSSed as a percentage of the rhodium content, and sodium metabisulphite (see United Kingdom rhodium of Very good purity was obtained. While Specification No. 498,251). (d) Sulphonated lig- the degree Of purity depended on the conditions nite types of resin typified by Zeo-Karb H, con- enployed the condition considered to be most taining Sulphonic acid and carboxyl groups. 30 Suitable for process refining gave metal contain Preferably the concentration of the complex ing 0.004% Pb, 0.0001% Bi, and 0.002%. Te. In rhodium compound is between to and 1/100 molar. addition, Sn, Cr and Al were completely eliminat The initial pH of the solution under treatment ed, Min and Fe were almost completely eliminat should be between 1 and 5. ed., While the amounts of Ag and Cui present were The process of the present invention may be 35 considerably less than the amounts present in combined with other processes of purification the original material. and therefore it may be used to remove the Whole The following examples illustrate how the proc or only a part of the impurities. eSS of the invention may be carried into effect While the invention conveniently employs po- and the advantages thereof: tassium hexachlororhodate as the starting ma- 40 l. Six Solutions of impure potassium hexa terial other corresponding Water-Soluble Salts chlororhodate, Varying in concentration from 10 may be used such aS Sodium hexachlororhodate, g./l. Rh (0.097 M) to 20 g/l. Rh (0.194 M) were ammonium hexachlororhodate and the corre- paSSed through Zeo-Karb 215 cation exchange sponding free acid H3 (RhClel. The process of resin in the hydrogen form. The treated solu the invention also includes the treatment of com- 45 tions were examined for impurities by spectro plex SaltS Such as the potassium and ammonium graphic methods. aquapentachlororhodates, e. g. K2 (RhCl5H2O). The resultS obtained are shown in the follow The corresponding bromine compounds may be ing Table, in which the amounts of base metal used such as potassium, Sodium and ammonium are expressed as a percentage of the precious hexabronorhodates. Furthermore, the nitrite 50 metal content of the treated solution:

Concen No. rtie, E. (i. Pesent PerSent PerSent

Original.------>0. 4. >0. 0.9 45 10 0.097 0.001 0.0036 0.06 54 2 0.17 0.032 O.OO33 0.20 63 4. 0.36 0.04 0.008 0.020 72 6 0. 55 0.30 0.020 0.030 S. 8 O. 75 0.20 0.080 0.035 90 2) 0.94 0.290 >0.100 0,040 analogues may be employed in the case of the so 2. A concentrated solution of impure rhodium diurn Salt and the free acid, i. e. compounds of Chloride containing more than 0.1% of lead, the formulae Na3 Rh (NO2) 6 and H3Rh (NO2) 61. 65 more than 0.005% of bismuth and more than According to a preferred embodiment of the in 0.02% of tellurium (all expressed as a percentage wention an aqueous Solution of potaSSium hexa Of the rhodium content). and obtained by dis chlororhodate in a concentration not exceeding Solving an impure rhodium hydroxide in the molar is passed through a bed of cation ex minimum of hydrochloric acid, was diluted so Change resin. During the paSSage of the Solution 70 that the rhodium content was reduced from 57 cations are replaced by hydrogen ions, whereas g./l. to 10 g./l. The hydrolytic precipitate of anions paSSed through unchanged. In this way impUIrities Was filtered off and the filtrate was potassium, lead and bismuth ions were removed paSSed through Zeo-Karb 215 resin in the hydro While the RhCls anions passed through unal gen form. The treated solution was concen tered. 75 trated by evaporation and the rhodium was

2,552,709 6 crystallised out as ammonium hexachlororhodate process of the present invention and those of th by the addition of ammonium chloride. When earlier processes of purification, it was found ignited the salt gave rhodium metal containing: that the process of the present invention purifies Per cent the rhodium to a much higher degree in consid Pb ------0.0003 5. erably fewer operations. It is true that the proc Bi ------0.0001 ess of the present invention involves the use of nore dilute Solutions than those usually emi Te ------0.001 ployed in the normal processes of purification 3. A sample of ammonium hexachlororhodate and consequently gives greater volumes of Solu containing >.1% lead (expressed as a percent it) tion for evaporation. However, evaporation of age of the rhodium content) and a very low the treated solution takes place quickly and content of bismuth and tellurium, was dissolved Without difficulty. in water to give a solution containing 10 g./l. of What we claim is: rhodium. The Solution was passed through Zeo 1. A process for the piirification of iodiur. Karb 215 resin in the hydrogen form. The which comprises treating an aqueous Solution of treated solution was concentrated by evapora a water-solubie comple:K rinodiulia coinpound in tion and the rhodium was crystallised out as which the rhodiuin is present in the anion in ammonium hexachlororhodate by the addition which the concentration of the Said compound is of ammonium chloride. On ignition this salt up to A0 molar with a cation eXchaige resin gave rhodium metal containing: containing a sulphonic acid group to remove irin Per cent purities from the Solution. Pb ------<0.0003 2. A process for the purification of rhodium Bi ------0.0001. which comprises treating an aqueous Solution of Te ------<0.001 a water-soluble complex rhodium Salt in which 4. 38.931 kgs. of impure potassium hexachoro the rhodium is present in the anion in Which the rhodate Was dissolved in hot water to give a solu concentration of the said salt is up to 40 molar tion containing 10 gms. per litre of rhodium, and with a cation exchange resin containing a Sul was passed, in a series of charges, through 35 phonic acid group to remove impurities from the lbs. of Zeo-Karb 215 resin in a column 5 ft. long solution. and 6 ins, diameter. The pure Solution of 30 3. A process for the purification of rhodium rhodium chloride emerging from the column which comprises treating an aqueous Solution of was concentrated and converted to ammonium a Water-soluble complex rhodium acid in which hexachlororhodate by the addition of pure am the concentration of the said acid is up to Ao nonium chloride. On ignition the ammonium molar with a cation exchange resin containing a hexachlororhodate yielded rhodium metal. The sulphonic acid group to remove inpurities from impurities in the impure potassium hexachloro the Solution. rhodate were 0.015% of lead, 0.005% of bis 4. A process for the purification of rhodium muth and 0.060% of tellurium, all expressed as which comprises treating an aqueous Solution of a percentage of the rhodium content of the salt. potassium hexachlororhodate in a concentration The final yield of pure rhodium was 8.836 kgs. 40 of up to Ao molar with a cation exchange resin containing 0.0002% of lead, less than 0.0001% of containing a sulphonic acid group to remove in bismuth and 0.002% of tellurium. purities from the solution. 5. A solution of impure Sodium hexanitrito 5. A process for the purification of rhodium rhodate containing 10 g./l. of rhodium, was which comprises treating an aqueous Solution of passed through a column of Dowex 50 cation a Water-soluble complex rhodium compound in exchange resin in the hydrogen form. The which the rhodium is present in the anion in effluent from the column was examined Spectro which the concentration of the said coinpound is graphically for impurities. As the starting up to Ao molar and having a pH between i and 5, material was heavily contaminated with copper, With a cation exchange resin containing a sul nickel and magnesium, it was difficult to obtain phonic acid group to remove impurities from the exact figures for the initial concentration of Solution. impurities. 6. A process for the purification of rhodium The degree of purification brought about by which comprises passing an approximately Ao the process is shown in the following Table, in molar aqueous Solution of potassium hexachloro which the amounts of base metal are expressed rhodate having a pH between 1 and 5 through a as a percentage of the rhodium content of the column of a cation exchange resin containing solution. a Sulphonic acid group to remove impurities from the Solution. Per ceilt in son. Per cent in Soln. FRANCIS SIDNEY CLEMENTS, Impurity before treatinent after treatment 60 AIAN RICHARDSON RAPER Pb------approx. 0.003---- 0.001. REFERENCES CITED Bi------>0.10------0.008. Te------>0.10------0.10. The following references are of record in the Fe. -->0.10--- 0.05. K0.001. file of this patent: Very faint. Do. 65 Mellor: “Comprehensive Treatise on Inorganic Fairly strong. and Theoretical Chemistry,' vol. 15, 1936, pages 549, 550, pub. by Longmans, Green and Co., New Comparing the separate Operations of the York.