UNITED STATES PATENT OFFICE METHOD of MAKING CERYSTALLINE ALU 'MINASAME and a PRODUCT CONTAINING the Raymond R

Reissued Nov. 2, 1937 Re.20,547 UNITED STATES PATENT OFFICE METHOD OF MAKING CERYSTALLINE ALU 'MINASAME AND A PRODUCT CONTAINING THE Raymond R. Ridgway, Niagara Falls, N. Y., as signor to Norton Company, Worcester, Mass, a corporation of Massachusetts No Drawing. Original No. 2,003,867, dated June 4, 1935, Serial No. 690,589, September 22, 1933. Application for reissue January 8, 1936, Serial No. 58,235 31 Claims. (CI, 23-142) This invention relates to the electrochemical remove impurities, but such products must there manufacture of crystalline alumina of required after be re-fused in order that the purifled crys chemical and given physical properties for use in talline alumina may have the desired physical as various industrial arts. -- well as chemical characteristics. These alterna 5. In the electrometallurgical production of crys tive methods, which involve over-purification and talline alumina from alumina-containing Ores, reduction of some of the alumina in the original such as bauxite, the elimination of the impuri furnacing of bauxite, have not produced in prac ties of the ore by reduction with carbon has had tice the desired results, since the oxidizing agents serious limitations, from the standpoint of pu have remained as contaminations in the final 10 rity and stability of the resultant alumina crys product, or else the reactions have been incon- 0 tals. Commercial bauxite contains as high as plete. Moreover, those processes which involve 4% of titania, and 2% of zirconia, as well as sil an intermediate purification and a subsequent ica and alkaline metal oxides. It has been cus second fusion of the material are expensive anti tomary to purify the alumina oxide incomplete involve great technical difficulties. There has l6 ly and to leave contaminating metal oxide in been no practical method for converting an im- lis purities in the fused bath to serve as a buffer, pure alumina, such as bauxite, to a high purity which protects the alumina from reduction. In crystalline alumina of the required physical accordance with the prior methods, such as de structure by means of a single furnacing process. scribed in the patent to Saunders No. 1,269,224, In accordance with the U. S. patent to Ridg 20 bauxite may be greatly enriched in its alumina way and Glaze No. 1,719,131, a high purity alu- 20 content by fushion with carbon and iron in a mina may be obtained by the use of a limited w Higgins type of electric furnace, as shown in the quantity of iron sulfide which is so proportioned United States Patent No. 775,654, and the puri with respect to the carbon reducing agent as to fication may be carried on easily up to about produce a small quantity of hydrolyzable alumi 25 96A,% alumina. As an example of a calcined num sulfide in the melt. This causes a complete 25 bauxite ore before and after reduction by fluison removal of the titania, and zirconia during the with carbon, the following analyses are to be reduction process, but requires the presence of noted: the unstable aluminum carbide in solid solution in the alumina. In order to remove this alumi 30 Original Reduced num carbide, as well as the droplets of ferro- 30 Oe or alloy, the fused material has to be cooled rapidly to produce minute crystals of the order of 0.1 mm. w Percent Perce and then be broken up by hydrolysis to a very Alumina---------------------------------- 80.0 98.5 Titania----------- 3.0 1.5 fline subdivision so as to expose the impurities. 35 Zirconia. 0.6 0.2 Consequently, the resultant disintegrated crys- 35 Silica-------------- 5.5 0.5 Iron Oxide--------- 10.0 0. tals have been too fine in size to be of direct Alkaline metal oxides--- C.9 1 Commercial use, and it has been necessary to re melt the alumina, after the impurities have been Up to this degree of purity, aluminum carbide or separated therefron, and to recrystallize the 40 other reduction compounds of alumina are not product in a slower cooling operation to obtain 40 formed to any material extent. On the other Crystals of commercial sizes. hand, various impurities present are combined in The final ingot of crystalline alumina, as pro a slag or glass phase, which surrounds and ce duced by such prior processes, is a massive solid ments together the crystals of alpha alumina, body which requires expensive crushing and 45 and some of this glass appears as an inclusion screening operations to obtain grains of the de- 45 in the alumina crystals. sired sizes. The requirements of the various An alternative procedure, as employed to re abrasive and refractory industries call for grain duce the last trace of titania, is to over-purify sizes ranging ordinarily from 8 meshes to the the alumina by various methods and then to oxi linear inch to the very fine flours, but the max 50 dize the aluminum carbide, or other reduced imum requirements are within the range of grit 0. aluminum compounds thus produced, by treat sizes 30 to 60, with the largest demand for grit ing the original furnace melt with various Solid size 40. The standard operation of breaking the and gaseous reagents. Also, such an over-puri ingot into large lumps, sorting out the various fied and reduced mass has been treated after impurities, and then crushing these lumps in a 55 solidification by available means which serve to rock crusher to the required sizes, and finally SS 2 20,547 screening the material to obtain the different For example, I may fuse bauxite, or other suit grades, has involved not only a large expense able crude alumina, in the presence of a reduc but also a loss of a considerable amount of very ing agent, such as carbon, which is proportioned fine material which has to be thrown away or to reduce the metal oxide impurities, and with else returned to the furnace to be remelted and metallic iron, which forms a desired ferro-alloy recrystallized. with metals of the oxide impurities, these re An object of this invention is, therefore, to agents being proportioned to reduce the refrac overcome such problems and to provide a single, tory oxides, as above explained, and produce direct furnacing treatment for bauxite or other alumina of a maximum purity of 96%%. In or O impure aluminous ores, which results in the pro der to purify the alumina further and cause O duction of Coarse sized crystals of alumina of a it to crystallize as desired, I also include in the high degree of purity and chemical stability, melt a small amount of an alkaline metal sul which have the physical or structural character fide capable of forming a glassy matrix which istics useful in the various industries. carries and thus removes from the fused alu A further object is to produce crystalline alu nina, the unreduced compounds of zirconium, t 15 nina, grains of usable commercial sizes in which tanium, Silicon and other metal impurities which each grain is a discrete particle Consisting of a do not form a ferro-alloy. The ingot is easily single large crystal or aggregates of large crys disintegrable because of the presence of the alka tals, which are substantially free from unstable, line metal sulfide, but if desired the matrix glass reduced inclusions and are not contaminated may comprise the Water hydrolyzable aluminum 20 with other metal oxides. sulfide to hasten the decomposition. The alka A further object is to provide a method of di line metal sulfide may be formed from its corre rectly melting and purifying bauxite which does sponding. Oxide and the aluminum sulfide from not require intermediate chemical purification the alumina in the bath by the addition of fer 25 processes or multiple furnacing operations and rous sulfide and carbon in suitable proportions. which will produce alumina Substantially free The required quantity of sulfide or sulfides, as from titanium and zirconium compounds, as well herein defined, or reagents capable of developing as the alkali metal and alkaline earth metal im the same, which are capable of forming said purities, which are normally present in the crude matrix, may be added to the furnace charge 30 ores. Other objects will be apparent in the either before fusion or at any time up to that 30 following disclosure. at which the purification has reached the state In accordance with my discovery, I have found indicated in the Second column of the above ta that the impurities in bauxite or other aluminar ble. After the fusion of the furnace charge, it bearing materials, such as diaspore, calcined alu is slowly cooled in a large mass by allowing 35 nite, etc., may be readily removed by a single, the ingot to stand at room temperature and dis 35 direct furnacing operation and that the product sipate its heat after the furnace shell has been may be readily disintegrated into crystal parti removed therefrom and without the aid of a cles of a high purity, above 96%% by Weight of cooling medium, except the water which was . alumina, the major portion of which are larger employed to cool the iron shell of the Higgins than 100 grit size and which may be made large furnace during the fusion stage, thus forming 40 enough to meet the average or maximum re large crystals. quirements of the industry. The purification The presence of an alkaline metal sulfide in is achieved by introducing into the original baux proper amount serves: (1) to prevent the for ite or the furnace melt a reagent comprising the mation of aluminum carbide in the crystalline sulfide of an alkali metal or alkaline earth metal, alumina; (2) to cause the impure metal oxides herein termed an “alkaline metal sulfide', Such which normally dissolve in the

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