Amax Incorporated

Andrew B Case

Ranko P Crnojevich

Edward I Wiewiorowski

Felix D Rando

John D Sweeney

The present invention is directed to a method for treating a sludge containing substantial amounts of chromium, aluminum, calcium, iron, and phosphorous. The method comprises forming a slurry of the sludge; reacting the slurry with an acid to dissolve substantially all the aluminum and chromium and provide a solids residue comprising mostly calcium sulfate; separating the chromium/aluminum-containing solution from the solids residue; raising the pH of the chromium/aluminum solution to precipitate chromium as chromium hydroxide; and separating the chromium hydroxide from the remaining aluminum-containing solution. The chromium hydroxide is then enriched with an alkali or earth alkali compound and calcined in an oxidizing atmosphere to convert the chromium to a chromate. The calcine is leached in an aqueous medium at a controlled pH to yield a high concentration, high purity chromate solution suitable for producing metallic chromium or a variety of chromium chemicals.

Recovery of chromium in high purity state from waste materials of

A method is provided for treating sludge containing substantial amounts of chromium, aluminum and iron and residuals of other elements. The method comprises forming a slurry of the sludge in water at a temperature ranging from ambient to 150.degree. F. with the specific gravity of the slurry ranging from about 1.05 to 1.25, and adding a mineral acid to the slurry to provide a pH ranging from about 0.1-3 to dissolve selectively the aluminum and the chromium and leave a solids residue containing gangue material comprising an oxidized iron compound, calcium sulfate, calcium fluoride, calcium silicate among other solids. The pH of the solution is controlled at range of about 2 to 3.5 to precipitate undesirable elements, including iron, without substantially adversely affecting the dissolved chromium and aluminum. The chromium/aluminum-containing solution is separated from the solids therein to provide a substantially purified solution of chromium/-aluminum, and the pH of the solution raised to a range of about 12 to 13.8 to precipitate chromium as chromium hydroxide and provide a pregnant aluminate solution. The chromium hydroxide-containing solution is then subjected to solid/liquid separation to extract chromium hydroxide therefrom and providea pregnant aluminate solution which is thereafter treated to recover alumina therefrom.

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Harvey, LA, United States of America

Andrew B Case