US2805140A - Briquette of synthetic chromium ore - Google Patents

Description

United States Patent BRIQUETTE OF SYNTHETIC CHROMIUM ORE Joseph C. Schumacher, Los Angeles, Calif., assignor to American Potash & Chemical Corporation, a corporation of Delaware No Drawing. Application March 9, 1951, Serial No. 214,850

1 Claim. (Cl. 75-3) This invention relates to a synthetic weatherproof chromium ore having a high chromium oxide content, and to methods for making the same.

One object of the invention is to provide a synthetic weatherproof chromium ore of high chromium oxide. Another object is to provide a synthetic weatherproof chromium ore of high chromium content and relatively low iron content from low grade natural chromite ore. Another object is to provide synthetic chromium ore for use in metallurgical operations and in the stock-piling of chromate ore for subsequent use in metallurgical operations. Still another object is to provide a process for making synthetic weatherproof chromium ore of any desired chromium content.

For use in metallurgical operations, and for use in stock-piling for subsequent use in metallurgical processes, it is required that the chromium to iron content of the ore be in the ratio of 2.8 to 1, to 3.0 to 1. Domestic chromium ores are available in which the chromium content is acceptable, but in which the ratio of chromium to iron is about 2.5 to 1, or lower.

I have discovered that a synthetic ore for use in blending to raise the chromium to iron ratio of a natural chromite ore to an acceptable value may be produced by chemically processing unacceptable grades of chromium oxide to produce a product having a chromium oxide up to 98 percent, which may then be formed into weatherproof briquets or pellets by mixing with a binder such as powdered calcium silicate glass and heating the formed mixture to the required temperature for binding the chromium oxide.

My preferred process consists of first calcining low grade chromite with sodium carbonate in a rotary kiln at 900 to 1,200 degrees centigrade in an oxidizing atmosphere, thus producing soluble sodium chromate. The proportion of sodium carbonate depends upon the nature and chromium oxide content of the ore. One and onehalf pounds of sodium carbonate for each pound of chromium oxide in the ore being treated is a generally satisfactory amount. The soluble sodium chromate is then leached from the insoluble residue with water and the solution is neutralized or made slightly acid with mineral acid, for example, sulphuric acid. Sufficient acid is added so that the silica and alumina which may have also been extracted as sodium salts from the calcined material are precipitated. The insoluble precipitate is then separated from the soluble chromate solution and, if desired, the alumina and silica may be recovered in useful condition by suitable further processing.

The aqueous sodium chromate solution is then treated with sulphur dioxide gas preferably by means of a turbomixer, which treatment reduces the chromium from the hexavalent to the tetra-, trior di-valent states, depending upon the completeness of the chemical reduction by the Patented Sept. 3, 1957 sulphur dioxide gas. In my preferred method, I reduce to a mixture of tetra-valent and tri-valent chromium compounds. The following reactions are believed to take place:

The chromium is precipitated as chromium hydroxide Cr(OH)4 or Cr(OH)3 by neutralizing the reduced solution with a caustic alkali. The precipitated chromium hydroxides are then treated in washing thickeners to re move the soluble sodium compounds, after which the insoluble chromium hydroxide compounds are filtered out, preferably on a continuous rotary vacuum filter, and the filter cake is dried. I

The mother liquor and the wash water from the above operation may be causticized with lime to recover the sodium as sodium hydroxide, or they may be discarded. The weak sodium hydroxide solution may be used in whole or in part for neutralizing the chromium solution after the reduction with sulphur dioxide.

Other chemical processes for producing substantially pure chromium hydroxides or oxides relatively free from iron compounds may be used.

The dried filter cake containing chromium hydroxides is then mixed with a binder such as powdered glass, or with lime and silica powders in the proper proportion to form glass. The amount of binder depends upon the degree of binding as well as upon the fineness of both binder and chromium oxide, from 2 to 10 percent by weight being generally satisfactory. The mixture is then formed into pellets or briquets in pelletizing or briquetting machines and these are calcined or heated to the bonding temperature, for example, by passing them in cars through a tunnel kiln where the temperature is held at 900 to 1,000 degrees centigrade. This heating operation produces dense, hard, water insoluble pieces which have excellent weathering resisting qualities. The synthetic chromium ore may be mixed as required with the natural ore for stock-piling, or it may be used for immediate metallurgical operations, either alone or mixed with natural chromium ores.

The chemically prepared chromium hydroxides or oxides without briquetting may be mixed as required with natural ore for immediate reduction to ferrochrome, in which form the chromium may be stock-piled for subsequent use.

I claim:

A weatherproot briquette having high chromium oxide and low iron oxide content consisting essentially of a vitrified mixture of chemically prepared impure chromium oxides relatively free from iron oxide with a vitrifiable silicate type bonding agent, the chromium oxide content being above percent of weight.

References Cited in the file of this patent UNITED STATES PATENTS 1,104,124 Mathesius July 21, 1914 1,121,226 Buddeus Dec. 15, 1914 1,422,703 Head July 11, 1922 r 1,586,590 Wild June 1, 1926 2,131,006 Dean Sept. 20, 1938 2,197,146 Erasmus et a1. Apr. 16, 1940 2,243,785 Udy May 27, 1941 2,416,550 Udy Feb. 25, 1947 2,416,551 Udy Feb. 25, 1947 2,480,184 Erasmus Aug. 30, 1949