3,536,479 United States Patent Office attented Oct. 27, 1970 2 a hydrogen pressure of at least about 15 pounds per 3,536,479 square inch gauge (p.S.i.g.). METHOD FOR THE PRODUCTION OF HIGH PURTY (OSMUM The concentrated osmium-containing solution can ad Alexander Ellis, Clarkson, Ontario, and Alan Manson, vantageously be prepared from a dilute osmium-contain Oakville, Ontario, Canada, assignors to The Interna 5 ing solution as described hereinafter. However, most gen tional Nicke Company, Inc., New York, N.Y., a cor erally the concentrated solution will be prepared by poration of Delaware scrubbing gases containing osmium tetroxide with a Solu No Drawing. Filled Dec. 13, 1967, Ser. No. 690,083 tion containing, by weight, about 5% to 40% sodium hy Claims priority, application Canada, Feb. 21, 1967, droxide to produce a sodium perosmate solution which 983,421 10 contains about 5 grams per liter (gp.l.) to about 100 nt. C. C22b 7/00, 11/04 g.p.l. of osmium, e.g., about 60 g.p.l. of osmium. Gen U.S. C. 75-108 29 Claims erally at this stage only minor amounts of ruthenium, i.e., less than about 0.5 g.p.l. of ruthenium, accompany the osmium and can be precipitated with only minor ABSTRACT OF THE DISCLOSURE 5 amounts of osmium occluded therein from the concen Metallic osmium is recovered from a slurry of an trated osmium-containing solution by adding a Water osmium-containing material to which sufficient hydro soluble, mild organic reducing agent such as methyl al chloric acid has been added to assure a final pH value cohol and ethyl alcohol. The mild organic reducing agent in the slurry of about 1 to 9 by heating the slurry to a also reduces the sodium perosmate in solution to the temperature of at least about 150 F. under a hydrogen 20 sodium osmate state which is highly advantageous since pressure of at least about 15 p.S.i.g. sodium perosmate solutions display substantial vapor pressures even at room temperature whereas sodium os mate solutions at room temperature display only negli The present invention relates to the recovery of gible vapor pressures. In order to precipitate ruthenium osmium, and more particularly to recovery and purifi 25 and to reduce sodium perosmate to sodium osmate, the cation of osmium by hydrometallurgical techniques. mild organic reducing agent is added to the concentrated It was long suspected that the nickel-containing com osmium-containing solution at least in amounts effective plex sulfide ore deposits of the Sudbury district of On to reduce sodium perosmate to sodium osmate and to tario, Canada, contained osmium but the presence of precipitate ruthenium, e.g., about 1% to about 10% by osmium in recoverable amounts was only confirmed re 30 volume of the alkaline solution and advantageously about cently when it was determined that most of the osmium 4% to about 6%. Advantageously, the volatilized osmium was lost during treatment of the slimes resulting from tetroxide is collected in an alkaline scrubbing solution the electrorefining of nickel. U.S. patent application Ser. containing the water soluble, mild organic reducing agent No. 506,899 filed on Nov. 8, 1965, now Pat. No. to increase the scrubbing efficiency and to precipitate 3,413,114, discloses that osmium-bearing materials such ruthenium. as secondary nickel anode slimes can be treated to con Metallic osmium sponge is precipitated from solution centrate the precious metal content without undue losses by adding sufficient hydrochloric acid to the solution to of osmium being encountered by treating the anode slimes provide after precipitation a final pH value of about 1 with sulfuric acid at temperatures below about 500 F. to 9. The hydrochloric acid addition is required to neu to sulfate the base metals such as copper and nickel 40 tralize excess alkali and the control of the final pH is and removing the sulfated base metals by leaching. The important since at pH values below about 1 precipitation residue containing osmium is then treated to oxidize and is incomplete and the osmium sponge is likely to be con volatilize osmium as osmium tetroxide which is collected taminated as a result of corrosion of the apparatus and in an alkaline solution such as sodium hydroxide to form at pH values above about 9 precipitation is also incom a dilute osmium-containing solution. The dilute osmium 45 plete. Advantageously, the hydrochloric acid addition is containing solution is then treated to form a more con controlled so that after precipitation the final pH value centrated solution of sodium osmate from which osmium is between about 4 and 7. Substantial precipitation of is then recovered. Treatement of the dilute alkaline solu osmium occurs upon addition of the hyrochloric acid to tion to ultimately recover osmium required a number of the concentrated solution resulting in a slurry. Although carefully controlled operations and often involved inter 50 the hydrochloric acid can be added directly to the con mediate products which presented materials-handling centrated sodium osmate solution, such direct additions problems. are not always accurate and there is a distinct possibility It has now been discovered that purified metallic os of osmium losses due to volatilization of osmium tetrox mium sponge can be recovered from concentrated osmi ide. Therefore, it is highly advantageous to treat the um-containing solutions in an economic manner and that 55 concentrated sodium osmate solution to produce an os dilute solutions of osmium can be treated to form con mium-containing material to which accurate hydrochloric centrated osmium-containing solutions from which metal acid additions can be made without encountering losses lic osmium sponge of high purity can be precipitated. of osmium through volatilization. Such an osmium-con It is an object of the present invention to precipitate taining material can be produced by the intermediate step metallic osmium sponge from concentrated osmium 60 of adding an excess of a potassium hydroxide solution, containing solutions. advantageously as a saturated solution of potassium hy It is a further object of the present invention to produce droxide, to the concentrated sodium osmate solution to concentrated and purified osmium-containing solutions precipitate violet crystals of potassium osmate, from which metallic osmium sponge can be precipitated. Broadly stated, the present invention contemplates a KOsO4.2H2O process for precipitating osmium from an aqueous solu After separation, washing with alcohol and water and tion by forming a concentrated osmium-containing slurry then with pure alcohol and drying, the violet crystals of which contains sufficient hydrochloric acid to give a final potassium osmate can be slurried with cold water and pH value between about 1 and 9 after precipitation and 70 easily determined stoichiometric amounts of hydrochloric then precipitating metallic osmium sponge by heating the acid are added to provide a slurry which can readily be slurry to a temperature of at least about 150 F. under treated with hydrogen at elevated temperatures and pres 3,536,479 3 4. sures to precipitate metallic osmium sponge. Regardless When the evolution of gases such as sulfur dioxide sub of whether hydrochloric acid additions are made directly sides or ceases, an oxidizing reagent such as Sodium chlo to the concentrated Sodium osmate solution or to a slurry rate, sodium bromate or nitric acid in amounts equivalent of precipitated potassium osmate crystals, metallic os to sodium chlorate additions from about 1% to about mium sponge is precipitated from the resulting osmium 10%, by weight of the pulp, is added to the pulp. Heat containing solution by heating the solution to a temper ing is then continued to volatilize osmium tetroxide which ature of at least about 150 F., e.g., about 200 F. to is collected in a solution of about 5% to about 40% 350 F. and at a hydrogen partial pressure of at least Sodium hydroxide, by weight, to form a purified con about 15 p.s.i.g., e.g., advantageously about 300 p.s.i.g. centrated sodium perosmate solution. to 700 p.s.i.g. O In carrying the invention into practice, it is preferred Metallic osmium sponge precipitated from solution by to gradually heat an osmium-containing material which hydrogen reduction contains substantial quantities of ad can also contain Sulfur, Selenium and ruthenium to a sorbed hydrogen and trace amounts of other impurities temperature of from about 1200' F. to about 2000 F. and can be purified by washing the osmium sponge with at a rate of about 50 F. to 100 F. per hour in a free an aqueous solution of hydrochloric acid at a temperature oxygen-containing atmosphere to volatilize osmium as below about 100 F., e.g. at room temperature. Impur osmium tetroxide. Gradual heating is necessary to avoid ities such as iron, nickel and chromium react with the fusion of the osmium-containing material before osmium aqueous solution of hydrochloric acid to form soluble is volatilized therefrom. The osmium tetroxide along with chlorides which are removed from the osmium sponge sulfur, Selenium and dust is collected in an aqueous so while adsorbed hydrogen is concomitantly released. The dium hydroxide solution to form a dilute osmium-con aqueous solution of hydrochloric acid advantageously has taining solution. The aqueous sodium hydroxide solution a normality of about 0.5 to 5. advantageously contains between about 5% and 40% Another advantageous embodiment of the present in Sodium hydroxide by weight. An osmium-containing pre vention is to heat osmium sponge purified in accordance cipitate is recovered from the Solution without separation with the present invention to a temperature of at least of the solids from the collecting solution since the solids about 1500 F. in a reducing atmosphere containing hy contain osmium by bubbling therethrough sulfur dioxide drogen. Reducing atmospheres containing up to about while maintaining the solution at a temperature of from 100% hydrogen can be employed. However, reducing about 70 F. to about 120 F. The osmium-containing atmospheres containing hydrogen in amounts as low as precipitate is separated from the solution and is then about 3%, by volume, or lower and the balance essen 30 slurried with water to form a slurry with about 2% to tially nitrogen are advantageously employed. Such heat about 20%, by weight, Solids. Sulfuric acid in amounts ing renders the normally pyrophoric osmium sponge non of about 10% to about 40%, by weight, of the water, pyrophoric. is added to the slurry. The slurry of the osmium-con Dilute osmium-containing solutions can be formed by taining precipitate and sulfuric acid is then heated to the collecting osmium tetroxide, which is volatilized from 35 boiling point while bubbling air therethrough to volatilize an osmium-containing material by heating to elevated Sulfur as Sulfur dioxide. After evolution of sulfur dioxide temperatures in a free oxygen-containing gas such as air, from the slurry ceases, an oxidizing reagent such as so either in an aqueous solution containing a mild reducing dium chlorate, sodium bromate and nitric acid is added agent Such as an aqueous solution Saturated with Sulfur to the slurry and heating is continued to volatilize osmium dioxide or selenium dioxide either in a solution of about 40 tetroxide from the slurry. Volatilized osmium tetroxide 5% to about 40% sodium hydroxide by weight. An osmi is collected in an aqueous solution containing about 5% lum containing precipitate is then precipitated from the di to about 40%, by weight, sodium hydroxide to form a lute osmium-containing solution by passing therethrough concentrated aqueous solution of sodium perosmate. At a reducing gas such as sulfur dioxide and/or hydrogen this stage of the process little or no ruthenium, if original sulfide at a temperature of about 70 F. to about 180° F. ly present in the osmium-containing material, accompa After separation from the solution the osmium-contain nies the osmium. However, if the concentrated sodium ing precipitate is slurried with water at about 2% to about perosmate Solution does contain ruthenium, the concen 20% solids, by weight, and is then treated with an oxi trated sodium perosmate solution is treated with a water dizing agent at elevated temperatures to form osmium soluble mild organic reducing agent such as ethyl alcohol tetroxide which is collected in a solution of about 5% 50 and methyl alcohol to precipitate ruthenium with small to about 40%, by weight, sodium hydroxide to form a amounts of osmium occluded therein and to reduce so concentrated, purified solution of sodium perosmate. All dium perosmate to sodium osmate. Any precipitated ru oSmium-containing materials can be treated in the afore thenium is then separated from the sodium osmate solu described manner to produce a concentrated solution of tion. Hydrochloric acid is then added to the concentrated sodium perosmate. However, when the original osmium 55 Sodium Osmate solution in amounts effective to neutralize containing material contains substantial quantities of sul excess alkali and the resulting solution is then treated with fur and selenium it is advantageous in terms of cost of hydrogen at pressures of from about 300 p.s.i.g. to about reagents and continuity of operation to precipitate an 700 p.S.i.g. and at elevated temperatures of from about osmium-containing precipitate by passing sulfur dioxide 200 F. to about 350 F. to precipitate osmium sponge. at a temperature of about 70 F. to about 120 F. 60 A more dense form of osmium sponge can be obtained through the dilute osmium-containing solution. Sufficient by precipitating osmium at temperatures in excess of about sulfur dioxide is passed through the dilute sodium peros 250 F. Densification of the osmium sponge can also be mate solution to end up with a solution having a pH obtained by recycling at least a portion of previously pre value of about 6 to 8, e.g., about 7. Advantageously, cipitated osmium sponge. Advantageously, the concen most of the excess alkali can be neutralized by the addi 65 trated Sodium osmate solution can be treated with potas tion of Sulfuric acid to a pH of between 8 and 10 and sium hydroxide to precipitate hydrated crystalline potas completing neutralization by the addition of sulfur diox sium osmate which is readily filterable. The hydrated ide gas to precipitate an osmium-containing material. potassium osmate is separated from the aqueous phase The osmium-containing precipitate is separated from the and is then washed with alcohol and water and then solution and is then pulped at about 2% to 20% solids, pure alcohol to obtain a relatively stable salt of known by weight, with an aqueous solution containing from about composition. After Washing and drying at room tempera 10% to about 40% sulfuric acid, by weight of the water. ture, the hydrated potassium osmate is slurried with water The resulting pulp is then heated to the boiling point to form a slurry containing about 2% to about 20% while passing air therethrough to volatilize sulfur dioxide Solids, by weight. Hydrochloric acid is then added to the and any carbon-containing gases such as carbon dioxide. 5 slurry at least in amounts equivalent to the potassium 3,536,479 5 6 in the potassium osmate salt. Osmium sponge is then pre sodium perosmate solutions showed the osmium distribu cipitated from solution by hydrogen as described here tion to be as follows: inbefore for precipitating osmium sponge from a con centrated sodium osmate solution to which hydrochloric Osmium, Distribution. acid has been added. grams percent Osmium spong precipitated from either of the before 5 Head Sample------38 00 Sodium perosmate solution.-- 37.5 98.7 described processes is then treated with an aqueous hydro Distillation solids.------. 0.1 0.3 chloric acid solution having a normality of about 0.5 to listillation solutions------0, 4 1.0 5 at temperature below about 100 F., e.g., about 60° F. to about 80° F., to purify the osmium by removing there O The brown sodium perosmate solutions from five such from hydrogen and traces of iron, nickel and chromium. distillations, containing 6.0 troy ounces of osmium were The purified osmium sponge is washed with water and combined and treated with 5 ml. of ethyl alcohol to pre dried in a hydrogen atmosphere at a temperature of about cipitate any ruthenium present and to convert the per 200 F. to about 220 F. If it is preferred to render the osmate to the osmate. The ruthenium precipitate which osmium sponge non-pyrophoric, the dried sponge is heated included a small amount of occluded osmium was re to a temperature of at least about 1500 F. in a reducing moved by filtration and reserved for further treatment. atmosphere containing hydrogen. The filtrate was transferred to a plastic beaker and about For the purpose of giving those skilled in the art a an equal volume of saturated potassium hydroxide solu better understanding of the invention and/or a better ap tion was added to precipitate violet crystals of potassium preciation of the advantages of the invention, the follow 20 OSmate. ing illustrative examples are given: The salt was allowed to settle, the supernatant liquor EXAMPLE I decanted and replaced with a mixture of equal parts eth anol and water followed by stirring and settling. The A precious metals concentrate weighing 133 kilograms supernatant liquor was again removed and the washing (kg.) and containing 10.93 troy ounces of osmium was 25 repeated three more times. Finally, the salt was trans heated in a furnace under oxidizing conditions for 24 ferred to a Number 50 whatman filter paper, washed again hours at gradually increasing temperatures up to 1700 F. with the alcohol-water mixture and finally with pure The furnace off-gases were passed through a 10% solu alcohol. The salt was allowed to dry at room temperature tion of sodium hydroxide to recover the osmium as so overnight. The weight of dry salt, analyzing 51.6% dium osmate contaminated with sulfur, selenium, dust, etc. 30 osmium, obtained was 350 g. or 96.3% of the osmium The alkaline osmium solution was treated with sulfur di originally present in the sodium perosmate solution. The oxide gas to pH 7.0 and at room temperature to precipi decants and washings which contained 3.7% of the tate a crude osmium concentrate. The solids were recov osmium were treated separately for recovery of this ered by filtration and contained 10.7 troy ounces of element. osmium. The filtrate was found to be virtually osmium Approximately 100 g. of the dry potassium osmate was free. The calcined solids were sampled and analyzed for stirred into 950 ml. of distiled water and 44 ml. of 12 N osmium content. The results of the test are summarized hydrochloric acid was added. The mixture was charged as follows: into a titanium metal pressure apparatus. Hydrogen gas was passed through the apparatus at room temperature 40 to displace any air and then heat was applied until a temperature of 240° F. was reached. Hydrogen was then Weight OSmium bubbled into the slurry to a presure of 500 p.s. i.g. and ------Dist., agitation was applied for one hour. After cooling, the Kg. Percent Percent Tr., Oz. percent apparatus was flushed with nitrogen to displace the hydro Head sample--- 100 9.25 10.93 00 gen and the contents were emptied into a beaker. The Calcined residue 80.0 0.005 0.175 ... 6 Osmium concentrate 6.44 3.8 10.70 98.0 Supernatant solution having a pH value of 6 was decanted Barren solution------0.05 0.4 and replaced with 1 N hydrochloric acid. When all the adsorbed hydrogen was released, the solids were allowed to settle and the solution was decanted. The solids were 50 washed with about ten displacements of distilled water until virtually chloride free, and then filtered. The moist Crude osmium concentrate was treated in lots of one osmium sponge was packed into a clean porcelain boat kilogram each for recovery of osmium according to the and dried overnight in a tube furnace at about 200 F. following method: while a hydrogen-containing gas was continually pased The wet solids were blended to a smooth pulp in three 5 5 through the tube. The next day the temperature of the liters of water using a high speed mixer to break down any furnace was gradually raised to 1700 F. and maintained lumps. The slurry was transferred to a twelve liter, three there for one hour. The tube was removed from the neck distillation flask with another two liters of water. furnace, its contents cooled to room temperature, and the Three liters of 12 N sulphuric acid solution were then hydrogen was displaced with a stream of nitrogen. The added and the flask fitted with an air inlet tube, a reagent 60 sintered Solids, weighing 50 g., were ground to a fine addition flask and a condenser. Heat was applied and a powder and analyzed 99.98% pure. current of air was pulled through the slurry for about 30 minutes by means of a vacuum system to remove any free EXAMPLE II sulfur dioxide or carbon dioxide. The condenser outlet As an alternative to the production of making the po was then connected to three absorbers in series, the first 65 tassium osmate salt in accordance with Example I, the containing about 200 ml. of 20% by weight sodium hy ruthenium-free osmate solution of Example I was reduced droxide and the others about 100 ml. each at the same to Sponge osmium directly. The ruthenium-free solution, concentration. About 400 ml. of 20% sodium chlorate containing 60 g. of osmium, was treated with concen solution was added to the boiling slurry over about a 20 trated hydrochloric acid to pH 7.0. The mixture was minute period to oxidize the osmium to the volatile tetroX charged into a titanium metal pressure apparatus and the ide which was caught in the alkaline scrubbers as sodium System was flushed with hydrogen gas. The temperature perosmate. The distillation was continued for about 90 was raised to 250 F. and hydrogen was introduced to minutes to recover the maximum amount of the osmium, a pressure of 350 p.s.i.g. for one hour with agitation. The about 25 ml. of the Sodium chlorate solution being added final pH value of the solution was 8. The apparatus was every 15 minutes. Analysis of the distillation residue and 5 then cooled, flushed with nitrogen and the osmium sponge 3,536,479 7 8 produced was treated as in Example I to give a final prod about 1200 F. to 2000 F. in a free oxygen-containing uct weighing 58 grams and analyzing 99.97% osmium. gas to volatilize osmium tetroxide, collecting the voia Although the present invention has been described in tilized osmium tetroxide in an aqueous solution selected conjunction with preferred embodiments, it is to be under from the group consisting of sodium hydroxide solutions, stood that modifications and variations may be resorted saturated sulfur dioxide solutions and saturated selenium to without departing from the spirit and scope of the dioxide solutions to form a dilute osmium-containing invention, as those skilled in the art will readily under Solution, precipitating an osmium-containing precipitate stand. Such modifications and variations are considered to by passing a reducing gas through the dilute osmium-con be within the purview and scope of the invention and taining solution, forming a slurry of the osmium-contain appended claims. 10 ing precipitate with aqueous sulfuric acid, voltalizing We claim: osmium tetroxide from the slurry by adding to the slurry 1. A process for recovering metallic osmium which an oxidizing reagent and by heating the slurry to the boil comprises forming a basic concentrated osmium-contain ing point, collecting the volatilized osmium tetroxide in ing slurry, adding sufficient hydrochloric acid to give a a Sodium hydroxide solution to form a concentrated so final pH value between about 1 and 9 after precipitation dium perosmate solution, adding a mild organic reducing of metallic osmium, then precipitating metallic osmium agent to the concentrated sodium perosmate solution to by heating the solution to a temperature of at least about reduce Sodium perosmate to sodium osmate, adding hy 150 F. under a hydrogen pressure of at least about 15 drochloric acid in an amount effective to give a final pH p.s. i.g. and recovering said metallic osmium. value between about 1 and 9 after precipitation of metal 2. A process as described in claim wherein metallic lic osmium, precipitating metallic osmium by heating the osmium is precepitated at a temperature from about 200 Solution to a temperature of at least about 150 F. under F. to 350 F. under a hydrogen pressure of about 300 a hydrogen pressure of at least about 15 p.s.i.g. and re p.s.i.g. to 700 p.s.i.g. covering said metallic osmium. 3. A process as described in claim wherein the pre 11. A process for recovering osmium from an osmium cipitated metallic osmium is washed with an aqueous 2 5 containing material which comprises gradually heating solution of hydrochloric acid at a temperature below about the osmium-containing material to a temperature from 100 F. to remove trace impurities and to free the metallic about 1200° F. to 2000 F. in a free oxygen-containing osmium of adsorbed hydrogen. gas to voltatilize osmium tetroxide, collecting the vola 4. A process as described in claim 1 wherein the washed tilized osmium tetroxide in a sodium hydroxide solution metallic osmium is dried and is then heated to a tempera 30 to form a dilute osmium-containing solution, precipitat ture above about 1500 F. in a reducing atmosphere con ing an osmium-containing precipitate by passing a reduc taining hydrogen to render the metallic osmium non ing gas through the dilute osmium-containing solution, pyrophoric. forming a slurry of the osmium-containing precipitate 5. A process as described in claim 1 wherein a denser with water, volatilizing osmium tetroxide from the slurry form of metallic osmium is obtained by precipitating by adding to the slurry an oxidizing reagent and by heat metallic osmium at temperatures in excess of about ing the slurry to the boiling point, collecting the vola 250° F. tilized osmium tetroxide in a sodium hydroxide solution 6. A process as described in claim 1 wherein a more to form a concentrated sodium perosmate solution, adding dense form of metallic osmium is obtained by recycling a mild organic reducing agent to the concentrated Sodium at least a portion of previously precepitated osmium 40 perosmate solution to reduce Sodium perosmate to so Sponge. dium osmate, precipitating hydrated potassium osmate 7. A process for precipitating metallic osmium from a from the concentrated sodium osmate solution by adding concentrated sodium osmate solution which comprises thereto an excess of potassium hydroxide, forming a slurry adding hydrochloric acid to the concentrated sodium of the precipitated potassium osmate in water, adding osmate solution in an amount effective to give a final pH hydrochloric acid to the slurry in an amount effective to value between about 1 and 9 after precipitation, precipi give a final pH value between about 1 and 9 after pre tating metallic osmium by heating the solution to a tem cipitation of metallic osmium, precipitating metallic osmi perature of at least about 150 F. under a hydrogen pres um by heating the solution to a temperature of at least sure of at least about 15 p.s.i.g. and recovering said metal about 150 F. under a hydrogen pressure of at least about lic osmium. 15 p.s.i.g. and recovering said metallic osmium. 8. A process for recovering osmium from a concen 12. A process for recovering osmium from an osmium trated sodium osmate solution by precipitating metallic containing material which can contain sulfur and rutheni osmium from an aqueous solution which comprises adding um which comprises gradually heating the osmium-con sufficient potassium hydroxide to the concentrated sodi taining material to a temperature from about 1200° F. lim osmate Solution to precipitate hydrated potassium 5 5 to 2000 F. in a free oxygen-containing atmosphere to osmate, forming a slurry of the precipitated potassium volatilize osmium tetroxide, collecting the osmium tetroX osmate and water, adding hydrochloric acid to the slurry ide in an aqueous solution of sodium hydroxide to form in an amount effective to give a final pH value between a dilute osmium-containing solution, passing sulfur di about 1 and 9 after precipitation of metallic osmium, pre oxide through the dilute osmium-containing solution to cipitating metallic osmium by heating the slurry to a tem 60 form an osmium-containing precipitate, forming a slurry perature of at least about 150 F. under a hydrogen pres of the osmium-containing precipitate with water and sul Sure of at least about 15 p.S.i.g. and recovering said metal furic acid, heating said slurry while passing air there lic osmium. through to volatilize any sulfur in the osmium-contain 9. A process for recovering osmium from hydrated ing precipitate as Sulfur dioxide, adding an oxidizing re potassium osmate which comprises forming a slurry of agent to the slurry after evolution of sulfur dioxide ceases potassium osmate and water, adding hydrochloric acid to volatilize osmium tetroxide, collecting the osmium to the slurry in an amount effective to give a final pH tetroxide in an aqueous Solution of sodium hydroxide to value between about 1 and 9 after precipitation of metal form a concentrated solution of sodium perosmate, add lic osmium, precipitating metallic osmium by heating the ing a mild organic reducing agent to the concentrated Solution to a temperature of at least about 150° F. under perosmate Solution to precipitate any ruthenium and to a hydrogen pressure of at least about 15 p.s. i.g. and re reduce Sodium perosmate to sodium osmate, adding hy covering said metallic osmium. drochloric acid to the concentrated sodium osmate solu 10. A process for recovering osmium from an osmium tion in an amount effective to give a final pH value be containing material which comprises gradually heating tWeen about 1 and 9 after precipitation of metallic osmi the osmium-containing material to a temperature from um, precipitating metallic osmium by heating the solu 3,536,479 9 10 tion to a temperature of at least about 150 F. under a ide, forming a slurry of the precipitated potassium osmate hydrogen pressure of at least about 15 p.s.i.g. and re in water, adding hydrochloric acid to the slurry in an covering said metallic osmium. amount effective to give a final pH value between about 1. 13. A process as described in claim 12 wherein metallic and 9 after precipitation of metallic osmium, precipitating osmium is precipitated at a temperature from about 200 metallic osmium by heating the solution to a tempera F. to 350 F. under a hydrogen pressure of about 300 5 ture from about 200 F. to 350 F. under a hydrogen p.s.i.g. to 700 p.s.i.g. pressure of about 300 p.s.i.g. to 700 p.s.i.g. and recovering 14. A process as described in claim 12 wherein the said metallic osmium. volatilized osmium tetroxide is collected in a sodium 22. A process as described in claim 21 wherein the hydroxide solution to which the mild organic reducing O OSmium-containing material is heated to a temperature of agent has been added to form a concentrated Sodium about 1200 F. to about 2000. F. at a rate effective to osmate solution. avoid fusion of the osmium-containing material. 15. A process as described in claim 12 wherein the 23. A process as described in claim 21 wherein the osmium-containing material is heated to a temperature osmium-containing material is heated to a temperature from about 1200. F. to about 2000. F. at a rate effective from about 1200' F. to 2000 F. at a rate of about 50 to avoid fusion of the osmium-containing material. F. per hour to 100 F. per hour. 16. A process as described in claim 12 wherein the 24. A process as described in claim 21 wherein sulfur osmium-containing material is heated to a temperature dioxide is passed through the dilute osmium-containing from about 1200 F. to 2000 F. at a rate of about 50 Solution until the pH value of the solution is about 6 to 8. F. per hour to 100 F. per hour. 20 25. A process as described in claim 21 wherein sulfuric 17. A process as described in claim 12 wherein the acid is added to the dilute osmium-containing solution in precipitated metallic osmium is washed with an aqueous amounts effective to give a pH value between about 8 Solution of hydrochloric acid at a temperature below and 10 before passing sulfur dioxide through the dilute about 100 F. to remove trace impurities and to free the osmium-containing solution. metallic osmium of adsorbed hydrogen. 26. A process as described in claim 21 wherein the 18. A process as described in claim 17 wherein the precipitated metallic osmium is washed with an aqueous washed metallic osmium is dried and is then heated to a Solution of hydrochloric acid and an oxidizing agent at a temperature of at least about 1500 F. in a reducing temperature below about 100 F. to remove trace impuri atmosphere containing hydrogen to render the metallic ties and to free the metallic osmium of adsorbed hydrogen. osmium non-pyrophoric. 30 27. A process as described in claim 21 wherein the 19. A process as described in claim 12 wherein a more Washed metallic osmium is dried and is then heated to a dense form of metallic osmium is obtained by precipitat temperature of at least about 1500 F. in a reducing at ing metallic osmium at temperatures in excess of about mosphere containing hydrogen to render the metallic 250 F. osmium non-pyrophoric. 20. A process as described in claim 12 wherein a more 28. A process as described in claim 21 wherein a more dense form of metallic osmium is obtained by recycling dense form of metallic osmium is obtained by precipitat previously precipitated osmium sponge. ing metallic osmium at temperatures in excess of about 21. A process for recovering osmium from an osmium 250° F. containing material which can contain sulfur and rutheni 29. A process as described in claim 21 wherein a more um which comprises heating the osmium-containing ma 40 dense form of metallic osmium is obtained by recycling terial to a temperature of about 1200° F. to about 2000 previously precipitated osmium sponge. F. in a free oxygen-containing atmosphere to volatilize oSmium tetroxide, collecting the osmium tetroxide in an References Cited aqueous solution of sodium hydroxide to form a dilute UNITED STATES PATENTS oSmium-containing solution, passing sulfur dioxide 45 through the dilute osmium-containing solution to form 2,044,366 6/1936 Pierson ------75-108 an osmium-containing precipitate, forming a slurry of the 2,371,119 3/1945 Nachod ------75-108 OSmium-containing precipitate with water and sulfuric 3,150,960 9/1964 Hunter ------75-108 X acid, heating said slurry while passing air therethrough 3,238,038 3/1966 Hunter ------75-108 X to volatilize any sulfur in the osmium-containing precipi 50 3,390,981 7/1968 Hoffman ------75-108 tate as Sulfur dioxide, adding an oxidizing reagent to the 3,413,114 11/1968 Illis et al. ------75-83 X slurry after evolution of sulfur dioxide ceases to volatilize OTHER REFERENCES osmium tetroxide, collecting the osmium tetroxide in an aqueous solution of sodium hydroxide to form a concen Thorpe's Dictionary of Applied Chemistry; vol. IX; trated Solution of sodium perosmate, adding a mild or 55 4th ed., Longmans, Green and Co., London, 1949, pp. ganic reducing agent to the concentrated perosmate solu 133, 134. tion to precipitate any ruthenium and to reduce sodium HENRY W. TARRING II, Primary Examiner perosmate to Sodium osmate, precipitating hydrated potassium osmate from the concentrated sodium osmate U.S. Cl. X.R. Solution by adding thereto an excess of potassium hydrox. 60 75-83,99, 114, 116, 121