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ATTORNEY. Patented Oct. 7, 1941 2,258,441

UNITED STATES PATENT OFFICE 2,258,441 MANUFACTURE OF ANTIMONY OXDES Abe R. Bozarth, Cleveland, Ohio, assignor to The Harshaw Chemical Company, Elyria, Ohio, a corporation of Ohio Application December 27, 1939, Serial No. 311,143 9 Claims. (Cl. 23-144) This invention relates to the production of This step results in the production of Sb2O3 con antimony compounds of high purity and more taining mainly selenium, SO3 and lead as im particularly to the conversion of an impure purities. If, as a starting material, I use anti grade of Sb2O3, that is, one which contains im- . mony values which do not contain any non purities such as sulfur, selenium and lead, and Volatilizable impurities, this first step may be is not in proper physical state for pigment use, Omitted. The kiln temperature may vary from to a purified grade in finely divided state and 650° C. to 1000 C., but is preferably kept between white enough for pigment and ceramic purposes. 700 C. and 800° C., most desirably approxi It has been common practice to produce pig mately 800° C. ment grade antimony oxide (Sb2O3) by oxidiz O Second step.-I then: heat the impure. Sb2O3 ing pure antimony metal. This method, al in an oxidizing atmosphere at a temperature be though productive of an excellent product, is low the melting point of Sb2O3, ... that is, below expensive and, therefore, a simple, effective and 650° C., preferably in the range 500° C. to 600° relatively inexpensive process of producing this C., and most desirably at approximately 550° C. grade antimony oxide is needed. 15 Under these conditions, the Sb2O3 is oxidized, I have now discovered that antimony con Without melting, to Sb2O4 which remains in the pounds of high purity can be produced from im form of a fluffy powder. The temperature should pure antimony values very cheaply and very Sim not be allowed to go above the melting point of ply by effecting the separation of the antimony Sb2O3 until oxidation to Sb2O4 is complete. values from the volatilizable and the non-vola 20 After oxidation is complete, the temperature tilizable impurities in separate operations, the may be raised to any desired point short of the volatilizable impurities being removed by Vola decomposition temperature of Sb2O4, which is tilization while the antimony is in the form of about 1000 C., Inasmuch as Sb2O4 has an ap the tetroxide and the non-volatilizable impuri preciable vapor pressure and local overheating ties being removed by volatilizing the antimony 25 is possible, it is not desirable to approach too in the form of the trioxide. The latter of these closely to its decomposition temperature even operations is, of course, old, per se. Antimony after oxidation is complete. I prefer to oxidize tetroxide, in finely divided form, that is, in pull between 500 C. and 600° C. and then raise the verulent or granular form, can be heated Well temperature to a point not exceeding 900° C. above the melting point of antimony trioxide preferably between 700° C. and 800° C. The and remain infinely divided form. For this oxidation may occupy from 1 to 2 hours, and I reason, impurities which cannot be volatilized may then heat at the higher temperature for out of antimony trioxide can easily be removed from 1 to 3 hours, preferably from 2 to 3 hours, from antimony tetroxide as gases or vapors. So in order to reduce as far as possible the quanti far as I am aware, no one prior to my invention 3 5 ties of impurities. has appreciated the advantages to be derived I am not certain as to the state in which the from these properties of antimony tetroxide as Sulfur, Selenium, lead, etc. are present in the set forth and claimed herein. Indeed, I am not Sb2O3 nor in what manner they are eliminated, aware that the properties themselves have been but I believe that they are present in Sb2O3 in fully understood heretofore. Some state of solid solution or chemical combi Accordingly, my invention contemplates the nation and that under the conditions above de novel process as broadly Stated foregoing and as Scribed, they are volatilized and eliminated as stated in the various claims appended hereto. In the drawing, the figure is a flow diagram gaseous oxides in the case of sulfur and selenium, Of the preferred embodiment of the invention. and as a basic sulfate in the case of lead. First step-In the preferred practice of the While I prefer to carry out this second step invention, I first heat the starting material, in the manner indicated above, it is obvious that which may be an impure antimony oxide or the advantages of the invention may be realized sulfide, such as an ore or previously processed in Some degree by operating at a single tempera impure material containing non-volatilizable 0. ture instead of at two-temperatures. Thus, by impurities. This material is heated in an oxidiz the treatment below the melting point of Sb2O, ing atmosphere, preferably not departing more the impurities are removed to a considerable ex than necessary from neutral, under temperature tent and extended heating at such temperature conditions such as to volatilize the antimony would remove more. On the other hand, heat trioxide, and the vapors are then condensed. 5 5 ing above the melting point of Sb2O3 would re 2. 2,258,441 move impurities to a large extent but would re trioxide, the steps of heating antimony tetroxide, sult in loss of antimony. containing one or more impurities of the class Third step.-The substantially pure Sb2O4 is consisting of sulfur, selenium and lead, under then mixed with carbon or other suitable reduc oxidizing conditions to volatilize Such impurity ing agent under conditions to reduce the Sb2O4 5 or impurities, removing the volatilized impuri to Sb2O3. This result is best obtained by mixing ties from the antimony tetroxide and then re just the proper amount of substantially pure, ducing the so purified tetroxide to the trioxide. finely divided carbon such as lamp black, ground 3. In a process for producing a pure antimony Wood charcoal or the like and heating at a ten trioxide, the steps of heating pulverulent anti perature sufficient to volatilize the Sb2O3 as it 10 mony tetroxide, containing one or more impuri is formed. The retort in which this operation ties of the class consisting of Sulfur, Selenium is carried out is placed under Suction so as to and lead, under oxidizing conditions to volatilize Withdraw. Sb2O3 as formed and this product is such impurity or impurities and then reducing cooled so as to precipitate a very finely divided the so purified tetroxide to the trioxide. material. 5 4. In a process for producing a pure antimony Alternatively, I may conduct the first step trioxide, the steps of heating antimony tetroxide, under Sufficiently highly oxidizing conditions to containing one or more impurities of the class form the tetroxide from, for example, the Sull consisting of sulfur, selenium and lead, under fide ore, prolonging the heating to remove the oxidizing conditions and above the melting point volatilizable impurities such as sulfur, selenium 20 of Sb2O3 to volatilize such impurity or impuri and lead, thereby producing a product contain ties and then reducing the so purified tetroxide ing only non-volatilizable impurities, and then to the trioxide. reduce the tetroxide to the trioxide under condi 5. In a process for producing a pure antimony tions to fume off the latter as formed, leaving the trioxide, the steps of heating pulverulent anti non-volatilizable impurities behind. 25 mony tetroxide, containing one or more impuri Obviously, if the third step is omitted, the ties of the class consisting of Sulfur, selenium process is well adapted to the production of and lead, under oxidizing conditions and above highly pure antimony tetroxide. the melting point of Sb2O3 to volatilize such im Eacample purity or impurities and then reducing the SO 30 purified tetroxide to the trioxide. Stibaite was heated in a rotary retort at a 6. A process of purifying antimony trioxide, temperature held between 800° C. and 1000° C. containing one or more impurities of the class and in an oxidizing atmosphere until the anti consisting of Sulfur, Selenium and lead, Compris mony content had been fumed off in the form ing the steps of converting the same to the tetroX of Sb2O3. This Sb2O3 and other gases produced 35 ide by heating under oxidizing conditions below therewith Were passed into a cooler and bag the melting point of the trioxide, then elevating filter Where the Sb2O3 and Some impurities were the temperature to a point above the melting collected. Uncondensed impurities, mainly SO2, point of the trioxide but below the decomposi were removed. The Sb2O3, now free of non tion temperature of the tetroxide maintaining volatilizable inpurities was roasted at a tem- 40 Such elevated temperature while removing the perature maintained between 500° C. and 600° C. volatilized impurities until the desired purity is in an oxidizing atmosphere for a period of 2 attained and then reducing the substantially pure hours until the Sb2O3 was converted to Sb2O4. tetroxide to the trioxide. The temperature was then raised to and main 7. A method of producing substantially pure tained between 750° C. and 850° C. for a period 45 antimony tetroxide comprising oxidizing anti of 3 hours. The substantially pure Sb2O4 was mony trioxide to the tetroxide by heating under then mixed with wood charcoal in theoretical oxidizing conditions below the melting point of quantity required to reduce the Sb2O4 to Sb2O3 the trioxide until the oxidation is substantially and heated to a temperature of 800° C. to 1000° C. complete, thereby forming a pulverulent, finely whereby the Sb2O4 was reduced to Sb2O3 and 50 divided tetroXide and then heating the resulting funned Off as formed. The Sb2O3 was condensed tetroxide under Oxidizing conditions at a tem and recovered as a pure white finely divided perature above the melting point of the trioxide product containing less than 0.1% sulfur, less and below the decomposition temperature of the than 0.01% selenium, and less than 0.1% lead. tetroxide whereby to remove impurities by vola Having thus described my invention, what I 55 tilization. claim is: 8. In purification of antimony values, that im E. A method of producing pure antimony com provement which comprises removing volatiliz pounds comprising removing volatilizable and able impurities by heating antimony tetroxide non-volatilizable impurities from antimony containing Such impurities under oxidizing con values by separate operations, volatilizable im- 60 ditions at a temperature above 650° C. and below purities including one or more elements of the 1000° C. class consisting of Sulfur, selenium and lead, be 9. In purification of antimony values, that ing removed by volatilization while the antimony improvement which comprises the steps of con is in the form of the tetroxide, and non-volt Werting finely divided antimony trioxide con atilizable impurities being removed by volatiliz- 65 taining Wolatilizable impurities into finely ing the antimony in the form of the trioxide, divided antimony tetroxide by heating in an oxi whereby. Such impurities are left behind, the dizing atmosphere below 650° C. and then remov volatilized antimony trioxide being condensed ing volatilizable impurities by heating in an oxi at a place Spaced from such non-volatilizable dizing atmosphere at a temperature above 650° impurities. 70 C. and below 1000° C. 2. In a process for producing a pure antimony ABE R. BOZARTH.