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United States Patent (19) 11) 4,132,569 Depablo Et Al

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United States Patent (19) 11) 4,132,569 Depablo Et Al United States Patent (19) 11) 4,132,569 DePablo et al. (45) Jan. 2, 1979 (54) RUTHENIUM RECOVERY PROCESS 3,997,337 12/1976 Pittie et al. ........................ 423/22 X (75) Inventors: Raul S. DePablo, Painesville; David 4,002,470 l/1977 Isa et al. ............................ 423/22 X E. Harrington, Mentor; William R. OTHER PUBLICATIONS Bramstedt, Chardon, all of Ohio Biswas et al., Indian J. Chen, "A Note on the Alkali (73) Assignee: Diamond Shamrock Corporation, Nitrate Fusion for Quant. Est. of Ru'', vol. 6, Jan. 1968, Cleveland, Ohio pp. 51-52. 21) Appl. No.: 845,437 Durkin, Metallurgia, "How to Descale Titanium', May 1954, p. 256. 22) Filed: Oct. 25, 1977 (51) Int. Cl’................................................ B08B 3/08 Primary Examiner-Marc L. Caroff (52) U.S. C. .......................................... 134/3; 134/10; Attorney, Agent, or Firm-John C. Tiernan 134/13; 252/415; 423/22; 423/491 57 ABSTRACT (58) Field of Search ................. 134/3, 10, 13; 423/22, 423/491; 75/83, 121; 252/415 Ruthenium is stripped from a catalyst or electrode sub strate by immersion in a fluoboric acid solution, con (56) References Cited verted to ruthenium oxide, and the ruthenium oxide is U.S. PATENT DOCUMENTS then converted to the alpha ruthenium trichloride for 3,573,100 3/1971 Beer ......................................... 134/3 use in the preparation of fresh catalyst and/or elec 3,706,600 12/1972 Pumphrey et al... 4 & or 134/3 trodes. 3,761,312 9/1973 Entwisle et al. ..... ... 134/3 X 3,761,313 9/1973 Entwisle et al. ..... 84 134/3 8 Claims, No Drawings 4,132,569 1. 2 nium coating is flaked from the substrate and allowed to RUTHENIUM RECOVERY PROCESS precipitate to the bottom of the stripping container; (b) BACKGROUND OF THE INVENTION the insoluble precipitate is oxidized to ruthenium tetroX ide in an alkali metal hypochlorite solution; and (c) the The present invention relates to a process for the 5 ruthenium tetroxide is distilled, the vaporous ruthenium separation and recovery of ruthenium from substrates of tetroxide then being passed to a collection means con catalysts and/or electrodes and, more particularly, to a taining concentrated hydrochloric acid, in which the process for the recovery of ruthenium in a form in ruthenium tetroxide is condensed and converted to which it can be directly recycled for the preparation of ruthenium trichloride. fresh catalyst and/or electrodes. 10 There precipitate can be directly oxidized or con Various salts of ruthenium have long been known to verted to the tetroxide, or it can first be converted to the have utility in a wide variety of catalytic applications. alkali metal ruthenate, then oxidized. In the direct oxi Most commonly, a suitable salt of ruthenium, either dation procedure, the precipitate, the ruthenium con alone or with salts of one or more additional metals, was taining insoluble residue from the stripping solution, is deposited on a catalyst support such as alumina, titania, 15 suspended in an excess of alkali metal hydroxide solu zinconia, silica, or silica alumina. tion and gaseous chlorine is bubbled through the sus More recently, ruthenium has found significant com pension until the solution becomes acidic to phenolph mercial application as a coating for electrodes, particu thalein. In this procedure, the alkali metal hydroxide larly so-called dimensionally stable anodes. In such acts as a suspending agent and the bubbling of chlorine applications, the ruthenium may be deposited by elec 20 gas through the suspension promotes in situ formation troplating or by other deposition means, either as the of alkali metal hypochlorite, which oxidizes the ruthe metal or in the form of a suitable salt, on an electrode nium to ruthenium tetroxide. substrate such as, for example, titanium, tantalum, or the Alternatively, the oxidation can be preceded by a like. Such electrodes and the method of their prepara fusion step, in which the ruthenium containing insoluble tion are described, for example, in U.S. Pat. No. 25 residue from the stripping solution is mixed with an 3,096,272, U.S. Pat. No. 3,236,756, U.S. Pat. No. alkali metal nitrate, and this mixture is added in small 3,265,526, and U.S. Pat. No. 3,711,385 to mention but a portions to molten alkali metal hydroxide where the few. ruthenium is converted to the corresponding alkali The wide variety of advantages obtained by the use metal ruthenate. Any alumina, titanium, silica, etc., will of such electrodes almost immediately established them 30 be converted into the corresponding alkali metal alumi as commercially significant. Since their first introduc nate, titanate, silicate, etc. When all the mixture has tion, these electrodes have not only found almost uni been dissolved in the molten alkalimetal hydroxide, it is versal acceptance in their original commercial applica cooled and dissolved in water to form the alkali metal tions, but are continually being modified for an ever hydroxide suspension, through which gaseous chlorine widening variety of additional commercial applications. 35 is bubbled to form the hypochlorite, proceeding as de This, in turn, made it more and more economically scribed above. For convenience, this alternative proce desirable to recover the ruthenium from used or defec dure, adding the fusion step, will be referred to hereinaf. tive anodes. ter as the "fusion process,' as distinguished from the Historically, the treatment and recovery of precious "direct oxidation process.” metals and their salts, at least at the commercial level, 40 The fusion process for oxidation of the ruthenium can has been largely a matter of proprietary information be employed to recover ruthenium from any catalyst or rigidly maintained as confidential of which a little, if electrode, generally without regard to the conditions to any, has been published in the patent or technical litera which the catalyst and/or electrode was previously ture. U.S. Pat. No. 3,761,313 (issued Sept. 25, 1973) subjected. The direct oxidation process, on the other discloses and claims a method of stripping the coating 45 hand, can generally be employed effectively only where from such electrodes by immersing the electrode in an the catalyst or electrode was not subjected to substan aqueous solution of hydrofluoric acid and at least one tial periods at temperatures in excess of about 500 C. other strong mineral acid (other than nitric acid). In Under such conditions, it appears significant amounts of spite of this, the accepted commercial procedure for ruthenium dioxide may have been formed and that the removal of the noble metal coating from such elec 50 sodium hypochlorite oxidation, by itself, will not fur trodes continues to be a mechanical abrasive procedure ther oxidize all the ruthenium dioxide to ruthenium (such as, for example, the so-called wheel-abrator pro tetroxide as readily, or as in as satisfactory a yield, as cess), even though this contaminates the precious metal when the added fusion step is employed. residue with large quantities of iron filings, sand, and hydrochloric acid. In fact, in commercial application, 55 PREFERRED EMBODIMENT such a mechanical abrasive procedure provides residues The preferred process of the present invention in containing only about one to ten percent (on a dry basis) cludes the additional fusion step, the stripping solution precious metal. comprises a mixture of hydrogen peroxide and fluobo ric acid (HBF4), and the precipitate is mixed with ap SUMMARY OF THE INVENTION proximately a stoichiometric equivalent of potassium The novel process of the present invention provides nitrate, and this mixture is then dissolved in a large for recovery of ruthenium not only in high yield but in stoichiometric excess of molten potassium hydroxide. a form which, for most applications, can be directly The precipitate from the stripping step may optionally employed in preparation of fresh catalyst and/or elec be washed in hydrofluoric acid to remove any titanium trodes. In the process of the present invention, the ru 65 or tantalum and/or hydrochloric acid to remove any thenium is: (a) stripped from the catalyst and/or elec tin, antimony or copper. trode by immersing the catalyst or electrode in a hydro The use of fluoboric acid (which acts more slowly fluoric acid based stripping solution, in which the ruthe than hydrofluoric acid) permits much closer control of 4,132,569 3 4. the stripping step, thereby reducing the unnecessary show if any ruthenium VIII was present). This solution loss of substrate and/or inefficient employment of the may be used directly (for instance, to prepare coating acid. Further adjustment of the stripping step can be solution), or may be evaporated to dryness to obtain achieved by addition of a suitable peroxide, preferably RuCl3 x H2O. Table II presents results obtained using hydrogen peroxide. In general, the molar ratio of perox- 5 this process. ide to fluoboric acid should be from about 0.01:1 to about 2:1 and, preferably, from about 0.05:1 to about Table II Ruthenium Recovered from Spent Catalyst 0.5:1. Via Hypochlorite Process The following examples will serve by way of illustra Catalyst Composition, % R. tion and not by way of limitation to describe the process 10 Taken, g % Ru on AlO3 Recovered of the present invention. 6.483 09 79 8,585 0.94 92 EXAMPLE I 7.455 0.94 90 7.37 102 85 Two dimensionally stable anodes were stripped in 5.864 02 85 17.257 1.01 9. fluoboric acid (HBF)-based solutions. The solid solu- 15 3.349 4.4 87 tion flaked from the titanium substrate and accumulated 7.250 0.93 90 on the bottom of the stripping container. The solutions 7.200 0.93 91 were filtered, residuals collected, and dried.
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