United States Patent (19) (11) 4,374,008 Natansohn et al. 45) Feb. 15, 1983 (54) PROCESS FOR SEPARATING TUNGSTEN 56) References Cited FROM CONAGEMETALS U.S. PATENT DOCUMENTS 4,278,643 7/1981 Natansohn et al. ................... 423/54 (75) Inventors: Samuel Natansohn, Sharon; Gary Czupryna, Salem, both of Mass. 4,287,159 9/1981 Natansohn et al. ................... 423/54 FOREIGN PATENT DOCUMENTS (73) Assignee: GTE Laboratories incorporated, 2025211 12/1971 Fed. Rep. of Germany ...... 204/109 Waltham, Mass. Primary Examiner-R. L. Andrews Attorney, Agent, or Firm-Jerry F. Janssen Appl. No.: 269,192 (21) 57 ABSTRACT 22) Filed: Jun. 1, 1981 A process for cleanly separating coinage metals from alloys of coinage metals and tungsten comprises electro 51 Int. Cl. ........................... C25C1/08; C25C 1/22 winning the coinage metal from an electrolyte solution (52 U.S. C. .................................... 204/109; 204/112; which is contacted with an ion exchange resin to selec 75/101 BE tively remove the tungsten. (58 Field of Search ................... 75/101 BE; 204/109, 204/112 11 Claims, 1 Drawing Figure U.S. Patent Feb. 15, 1983 4,374,008 4,374,008. 2 are placed in contact with an anode plate 35 which rests PROCESS FOR SEPARATING TUNGSTEN FROM in the anode chamber basket 30. COINAGE METALS A cathode plate 50 rests on the bottom of the electro winning cell 10 and the entire assembly is filled with BACKGROUND OF THE INVENTION 5 electrolyte solution 25. In the embodiment of the pres This invention relates to processes for separating ent invention wherein silver is separated from silver metals. More particularly, it is concerned with a process tungsten alloy mixtures, the electrolyte solution 25 is for separating tungsten from the coinage metals, nota preferably saturated aqueous silver nitrate. Anode 35 bly silver, during electrowinning. and cathode 50 are electrically connected to a direct In the manufacture of electrical switchgear equip 10 current source 60. ment, relays, motor controllers and the like, composites As the process of electrowinning the coinage metal or alloys oftungsten with the coinage metals, especially proceeds, crystals of the coinage metal 45 separate from silver, are used as electrical contact points. Cost consid solution and are deposited at cathode plate 50. During erations dictate that both tungsten and silver be recov this process there is a tendency for small amounts of ered from any scrap generated by the manufacturing 15 tungsten to codeposit with the coinage metal crystals at process. the cathode plate. In the particular case of the separa It has been the practice in the art to recover silver or tion of silver from silver-tungsten alloys, the concentra other coinage metal from tungsten-containing alloy tion of tungsten in the silver crystals deposited at the scrap by conventional electrowinning techniques. A cathode can often reach levels of 2000 ppm and above. major drawback, however, is the contamination of the 20 The presence of this undesirable tungsten contaminant coinage metal collected at the cathode of the electro in the coinage metal deposited at the cathode in prior winning cell with unwanted tungsten inclusion. art processes required multiple electrowinning steps to SUMMARY OF THE INVENTION obtain a coinage metal of sufficient purity for subse 25 quent use. It has been found, however, in accordance with the In the process in accordance with this invention, present invention that silver or other coinage metal can contamination of coinage metal deposited at the cath be cleanly separated from tungsten-containing alloys in ode is minimized by removing the electrolyte solution an electrowinning process which includes continuous 25 from electrowinning cell 10 by means of pump 80 or or batch extraction of tungsten from the electrolyte by 30 other transfer means, and passing the electrolyte solu solid-liquid extraction. In accordance with the present tion through an anion exchange resin to selectively invention, a process for separately recovering tungsten remove tungsten. Employing the method of this inven and a coinage metal from alloys or mixtures thereof tion, the coinage metal deposited at the cathode follow comprises electrowinning the coinage metal from an ing the selective removal of tungsten contains less than electrolyte solution contained in an electrowinning cell 35 50 ppm contaminating tungsten. having an anode, comprising said alloy or mixture of As depicted in the drawing FIGURE, the anion ex tungsten and a coinage metal, and a cathode. The elec change resin is contained in columns 160 and 170 shown trolyte solution is maintained substantially free of dis with appropriate 3-way valving to permit parallel oper solved tungsten during the electrowinning process by ation of the two columns. Valves 100,120, 130, 180, 190, contacting the electrolyte solution with an anion ex 40 and 200 are shown in the drawing FIGURE positioned change resin to selectively remove tungsten from the so as to permit the off-line regeneration of column 170 electrolyte solution and to deposit the coinage metal at while column 160 is employed in purifying the electro the cathode of the electrowinning cell in a form substan lyte solution. Although the process is shown in the tially free of tungsten contamination. drawing FIGURE employing a two column system, the The coinage metal is recovered from the cathode 45 invention also contemplates use of a single column oper chamber of the electrowinning cell and the tungsten is ated in a batch mode or a multiple column system oper subsequently recovered from the anion exchange resin ated in a parallel mode, depending on the particular by elution and from the anode chamber of the electro requirements of an application. winning cell. The process of this invention affords a Removal of tungsten from the electrolyte solution 25 method of cleanly separating tungsten from alloys with 50 may be by the batch mode in which the electrolyte is the coinage metals, notably silver. removed from the cell and contacted with the resin when the tungsten concentration in the solution be BRIEF DESCRIPTION OF THE DRAWING comes unacceptably high, or by the continuous mode in The sole drawing FIGURE is a schematic represen which the electrolyte solution 25 is continually circu tation of one embodiment of an apparatus employing 55 lated through the resin column(s) and the cell during the process of the present invention. the electrowinning of the coinage metal. It has been For a better understanding of the present invention, found that the coinage metal deposited at the cathode together with other and further objects, advantages, tends to become contaminated with unacceptable levels and capabilities thereof, reference is made to the follow of tungsten even in situations where the tungsten con ing disclosure and appended claims in connection with centration in the electrolyte solution is quite low. For this reason, the continuous mode of the process of this the above-described drawing. - - - - invention is preferred. OETAILED DESCRIPTION The preferred anion exchange resin employed in the Referring to the drawing FIGURE, tungsten-con process of the present invention is of the gel-type, taining coinage metal alloy or other mixture of tungsten 65 weakly basic, polyamine functional resin. A commer and a coinage metal 40 is placed in a permeable basket cially available resin of the preferred type is Amberlite 30 which forms the anode chamber of an electrowin IRA 68 (8) resin, manufactured by Rohmad Haas Com ning cell 10. The pieces of tungsten-containing alloy 40 pany, Philadelphia, PA. 4,374,008 3 4. Resins of this type have been found to stand up well was placed in a 50 ml burette to form a column of about to the conditions imposed by the process of the present 26 ml volume. The resin column was then washed with invention and to possess high selectivity for removal of 25 bed volumes of water at a flow rate of about 5 ml tungsten in the presence of large concentrations of coin min-1cm-2. age metals such as silver. A solution containing 49.3 g/1 of silver ion, 10 g/1 In applications where the process is employed to copper ion and 590 ppm tungsten was next passed recover tungsten and silver from electrical contact through the column at a flow rate of 5 ml min-1cm-2. scrap alloy, it is preferred that the resin be converted The solution was passed through the column and the from the normal free base hydroxyl form or the chlo 10 effluent analyzed for tungsten and silver content. The ride form to either the nitrate or sulfate form to prevent data are presented in Table 1 where it can be seen that chemical precipitation of silver on the resin. This is through 254 bed volumes of solution passed through the accomplished by repeated washings of the resin with column (through fraction 11), the weighted average successive portions of 3 M nitric acid or 1.5 M sulfuric extraction efficiency for tungsten exceeded 98% while acid until the washings indicate the absence of chloride 15 that of silver was less than about 0.1%, demonstrating ion. the high degree of specificity of this resin for extraction In either the batch or continuous mode of operation, of tungsten in the presence of large concentrations of contacting the electrolyte solution with the anion ex silver. change resin is continued until the resin becomes loaded In fractions 12 through 14, the tungsten extraction with tungsten and the efficiency of tungsten extraction 20 efficiency of the column dropped rapidly to about drops to a point where tungsten is being returned to the 49.3% indicating the loading of the column with tung electrowinning cell. At this point, the electrolyte solu sten.