Southwire Company, LLC

National Steel Corporation

Earth Sciences Limited

Larry D Jennings

Helge O Forberg

Wayne W Hazen

David L Thompson

Julian V Copenhaver

Douglas Stevens

An improvement in the process for the recovery of aluminum from alunite in which the alunite in particulate form is dehydrated, sulfur and alkali metal compounds removed from the dehydrated ore leaving a particulate residue containing aluminum values, the residue digested with at least one alkali metal hydroxide to convert the aluminum values to soluble aluminates, silicon removed from the soluble aluminate solution, and aluminum values precipitated from the aluminate solution, the improvement comprising: multiple stage digestion of the particulate residue accomplished by dividing the particulate residue into two fractions, digesting one fraction first and using the first stage liquor from the first digestion step to digest the remaining fraction. The fraction digested first may be the one having the smaller particle size, or the one having the larger particle size. The objective is to contact the caustic digestion liquor at its lowest aluminum content (lowest A/C ratio) with that fraction of the residue having the highest extractable aluminum content. The result is the production of a liquor for final recovery of aluminum values which has a higher aluminum to caustic ratio than that produced by prior digestion procedures. The improvement provides a higher recovery of aluminum from the alunite ore.

Process for recovering aluminum from alunite

This invention relates to a method for recovering aluminum hydroxide from alunite ore by roasting the ore to remove water of hydration, roasting it again in a reducing atmosphere to remove sulfate, roasting a third time in an oxidizing atmosphere to convert any sulfides formed in the second roast, leaching with a weak base, leaching with water to remove potassium and sulfate, extracting the aluminum content with a mixture of sodium hydroxide and potassium hydroxide, removing contaminant silica from the leach solution, and precipitating aluminum hydroxide by cooling and seeding the solution.

Redox treatment of alunite ore

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Arvada, CO, United States of America

Larry D Jennings