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. The HBF4 Average = 87.7% containing solutions were evaporated to dryness. The residuals and evaporated filtrates were analyzed by 20 X-ray fluorescence spectrometry (XRF) and x-ray dif EXAMPLE II - FUSION PROCESS fraction (XRD). As in Example II, if not already in the powdered The first was stripped in a solution containing 48% condition, the sample was ground and freed from or HBF4 (fluoboric acid) only. The residual from this strip ganic matter by heating in air at 350-400° C. The pow ping procedure is Sample A, and the evaporated fil- 25 dered sample was then mixed with approximately the trate 1B. The second anode was stripped in a solution stoichiometric amount of potassium nitrate required to containing 40 ml of 48% HBF4 and 10 ml of 30% hydro oxidize the ruthenium (and any other oxidizable compo gen peroxide (H2O2). The residual from this stripping nent) to their respective highest valences. A nickel procedure is Sample 2A, and the evaporated filtrate is crucible was charged with about 4-5 times the theoreti D. 30 cal amount of potassium hydroxide required to trans XRD analysis indicated that the residuals (1A and form all the ruthenium into potassium ruthenate (plus 2A) were composed of RuO2 as the major constituent. the theoretical amount necessary to convert any alu Filtrates (1B and 2B) contained TiOF2. The results of mina, titanium, silica, etc., to the corresponding alumi the analysis are described in Table I. nate, titanate, silicate, etc.). The caustic was then melted Table I 35 and heated to a temperature of about 550° C. The mix XRF Qualitative Analysis" of ture was then added in small portions to the molten Filtrates and Residuals potassium hydroxide with stirring, maintaining the tem Sample perature of approximately 550 C. After all the mixture Element 1A 2A 1B 2B had been added to the molten caustic, the crucible was Sn L M S S 40 maintained at a temperature of about 500-550° C. for Sb M S O Ta L M S S approximately 1 hour (or until all the mixture had been T M L L L dissolved). The crucible was then cooled to a tempera Ru L L WWD DO Rh M O ture of less than about 100 C. and cautiously sub Cu L L merged in warm (50-80 C.) water to dissolve all the r S 45 contents of the crucible. The temperature was reduced L = large; to below about 10 C., and the solution was adjusted to M = moderate; S = small a volume of approximately 200 ml per theoretical gram (Quantity estimated by relative peak heights). of ruthenium. This was, generally, most expeditiously achieved by simply adding crushed ice directly to the The residuals were subsequently washed first in hy- 50 solution. The solution was then transferred to a glass drofluoric acid and then in hydrochloric acid. This distillation pot provided with stirring and having inlets further upgraded the samples and removed substantially for air and chlorine. Vapors from this pot were passed all the non-ruthenium components. through a condenser to three containers of concen trated hydrochloric acid arranged in series, the last two EXAMPLE II - DIRECTOXIDATION PROCESS 55 being placed in an ice bath. By maintaining the cooling If not in a powdered condition, the sample (such as water in the condenser at a temperature of about produced in Example I) was ground and freed from 26-27 C., it is possible to prevent solidification of the organic matter by heating in air at 350-400 C. It was ruthenium tetroxide, until it reached the concentrated then suspended in an excess of sodium hydroxide solu hydrochloric acid. Chlorine was bubbled through the tion and chlorine was bubbled through the suspension 60 solution (about 4-5 bubbles per second) while stirring until the solution became acidic to phenolphthalein. Air and simultaneously sweeping the gas phase with air. was then passed, after which the solution was brought When the solution was acidic to phenolphthalein, the to a boil, and maintained there for a period of about 10 chlorine was shut off, but the passage of air was contin to 15 minutes. The vapors were passed to a condenser ued to prevent any back absorption. The solution was whose delivery tube fed to a container of cool concen- 65 then heated to the boiling point (approximately trated hydrochloric acid. The ruthenium -HCl solu 101-102 C.) and maintained at that temperature for tion was allowed to stand until all the ruthenium tetroX about 15-20 minutes, while continuing the passage of ide had reacted with the HCl (an aliquot was tested to air. When distillation was completed, the distillation pot 4,132,569 5 6 was disconnected from the first condenser and the ru tainer. The modification noted above might be the key thenium solution was allowed to stand for about 15 to very good recoveries, particularly, working with hours. Alternatively, the solution can be boiled under much more highly concentrated solutions of ruthenium. an efficient condenser, which will greatly accelerate It also might help the recoveries in the direct oxidation transformation of the ruthenium tetroxide and ruthe process, nium tetrachloride into ruthenium trichloride and re In view of the foregoing, it will be clear to those move any free chlorine. skilled in the art that many changes and substitutions Again, as in Example II, the acidic solution of ruthe can be made in the steps and operating conditions of the nium trichloride may be used directly for preparation of novel process of the present invention without prod catalysts or anodes and/or coatings, or may be concen 10 ding from the scope of the invention herein disclosed. It trated in a steam bath and taken for dryness in an oven is, therefore, our intention to be limited only by the at 105-110' C. to product a solid residue of Ruci X appended claims. H2O. Tables IV and V below present recoveries ob What is claimed is: tained by the fusion process. 1. A process for recovery of ruthenium from a coat Table IV Ruthenium Recovered from Different Samples Via Fusion Procedure Sample Taken Sample Type Sample Composition (g or ml) Recovered Spent Catalyst 4.4%, Ru, 95.6%. AlO3 6.025 85 Spent Catalyst FF p 6.186 90 Spent Catalyst F 6.257 87 Spent Catalyst F p 4.130 89 Spent Catalyst A. 3.075 91 Spent Catalyst 2.6% Ru, 97.4% TiO 1,006 91 Spent Catalyst 4.1%, Ru, 95.9% A6, 4.50 94 Spent Catalyst f f 4.68 9 Spent Catalyst 5.9% Ru, 94.1%. Al2O3 39.16 Spent Catalyst f FF 400 91 Spent Catalyst 400 98.5 Spent Catalyst A. p 40.0 97.0 Spent Catalyst A. 40.0 97.0 Spent Catalyst t 100.0 94.5 Spent Catalyst f 99. 88.4 Average Recovery = 92.4%

Table V Ruthenium Recovered from Different Samples Via Fusion Procedure Sample 35 Taken % ing on a catalytic or electrode substrate, comprising: Sample Type Sample Composition (g or ml) Recovered (a) stripping the ruthenium-containing coating from Mixed Ru. Oxides 70% Ru 51.29 g 96 Mixed Ru Oxides F. 56.02 96.5 the substrate by immersion in a fluoboric acid strip Mixed Ru Oxides f 100,09 96.6 ping solution containing an amount of fluoboric Mixed Ru. Oxides P 37.19 96.5 Average = 96.4% acid effective to strip the coating from the sub Beer's Solution 42 gpl Ru, 43 gpl Ti 500 m 95.5 strate, wherein said ruthenium coating is flaked Beer's Solution 42 gp1 Ru, 43 gpl Ti 1000 95 Beer's Solution 37.8 gp1 Ru 600 98.3 from the substrate and permitted to precipitate to Beer's Solution 600 92.2 the bottom of said solution; Beer's Solution PA 600 90.5 Average = 94.3% (b) separating and collecting said precipitate; Metallic Ru 100% Ru 20 g 92.5 45 (c) subjecting said precipitate to oxidation in an alkali Metallic Ru FF 20 94.7 metal hypochlorite solution containing an amount Metallic Ru f 20 95.7 Metallic Ru F 20 98.9 of hypchlorite effective to oxidize said ruthenium, Metallic Ru P 20 99.0 whereby said ruthenium is oxidized to ruthenium Metallic Ru t 20 97.8 Metallic Ru 20 94.6 tetroxide; and Metallic Ru 40 96.7 50 (d) distilling said ruthenium tetroxide and feeding the Metalic Ru F 40 95.6 distilled ruthenium tetroxide into a concentrated Average = 96.2% hydrochloric acid solution containing an amount of hydrochloric acid effective to convert said distilled A modification of Example III may improve the total ruthenium tetroxide to ruthenium trichloride. amount of ruthenium recovered. After the chlorination 55 2. The process according to claim 1 wherein said is discontinued (when the pot solution is about 0.05 N in stripping solution is a mixture of a peroxide compound hydroxide) and the solution is allowed to stand at room and fluoboric acid. temperature for 15-20 hours, the chlorination is reinitia 3. The process according to claim 1 wherein prior to ted, as in the original procedure. In this way, it is possi said oxidation of said precipitate, said precipitate is ble to recover 99% from 57 grams of Ru in a volume of 60 mixed with approximately a stoichiometric equivalent 8 liters. It is very probable that in such an alternative of an alkali metal nitrate, and said mixture is added to at procedure, the standing period of 15-20 hours could be least a 100% stoichiometric excess of molten alkali shortened without decreasing the yield, and six to eight metal hydroxide, dissolving said mixture in said alkali hours would probably be sufficient. metal hydroxide, whereby said ruthenium is converted It seems that the oxidation of ruthenium VI to ruthe 65 to the corresponding alkali metal ruthenate. nium VIII is rather a slow reaction. For this reason, it 4. The process according to claim 3 wherein said should be allowed sufficient time to proceed to comple stripping solution is a mixture of a peroxide compound tion, either in the distillation pot or in a separate con and fluoboric acid. 4,132,569 7 8 The process according to claim 2 wherein after collecting said precipitate, said precipitate is washed collecting said precipitate, said precipitate is washed with hydrofluoric acid. with hydrofluoric acid. 6. The process according to claim 2 wherein after s. The process according to claim 4 wherein after collecting said precipitate, said precipitate is washed 5 collecting said precipitate, said precipitate is washed with hydrochloric acid. with hydrochloric acid. 7. The process according to claim 4 wherein after e

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