METHOD OF PRODUCING METALLURGICAL ALUMINA BY AN ACID-ALKALINE METHOD Russian patent published in 2019 - IPC C01F7/20 C01F7/30 C01F7/46 C22B3/10 C22B21/00 C25C3/06 

FIELD: metallurgy.

SUBSTANCE: invention can be used in processing low-grade high-silicon alumina-containing material. To produce metallurgical alumina, kaolin clays are leached in autoclave with hydrochloric acid for 60–180 minutes at temperature of 130–190 °C. Pulp after leaching is filtered at temperature of 55–75 °C. Gaseous hydrogen chloride is passed through the clarified aluminum chloride solution to crystallize aluminum chloride hexahydrate. Obtained crystals are subjected to calcination at 700–900 °C to obtain rough alumina. Rough alumina is fed for two-stage leaching. First leaching step is carried out at atmospheric pressure, temperature of 90–115 °C for 60–140 minutes. Second leaching stage is performed in autoclave at pressure 5–15 bar, temperature of 130–180 °C and duration of 60–140 minutes. Aluminate solution after leaching is separated from undissolved residue and directed for decomposition for precipitation of aluminum hydroxide, which is subjected to calcination at temperature of 1,000–1,200 °C.

EFFECT: invention increases purity of metallurgical alumina and lowers power consumption when producing said alumina.

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