Science: Backyard Aluminum

“This is the greatest contribution to aluminum metallurgy since the Hall process of 1886—if it is cheap as the inventor says.” So commented the Aluminum Co. of America on a new process for extracting alumina from common clay announced last week by Chemical Engineer Arthur W. Hixson of Columbia University.

Heretofore the only commercial source of alumina—the oxide from which the pure metal is produced—has been bauxite, about half of which is now imported from British and Dutch Guiana, since there are only some 13,000,000 tons of known high-grade bauxite deposits in the U.S.—about a three-year supply at the present rate of consumption.

Hixson believes his process will not only free the U.S. from dependence on imported ores but will provide alumina cheaper than present methods of extracting it from high-grade bauxite ores. The process takes advantage of the fact that part of the aluminum silicate of which clay is largely composed is aluminum oxide. Boiling hydrochloric acid, Hixson found, combines with the oxide to form aluminum chloride dissolved in water (though it does not affect the silica). Impurities such as iron chloride (formed at the same time) are then removed with an ether. The remaining aluminum’ chloride solution is then heated, aluminum is precipitated as hydrated oxide, and baking changes it to alumina ready to be electrolyzed by the Hall-Héroult process to produce the metal. The hydrochloric acid is recovered to be used again.

This is at least as simple as the present method of making alumina from bauxite ore, which is by no means pure when mined. Its gross impurities, such as sand, are removed by crushing, washing, sifting. It is then dissolved in hot caustic soda or “lye,” which does not dissolve the subtler impurities. When the hot lye cools in towering tanks, pure aluminum hydroxide separates from it and is ready to be baked and electrolyzed.

Hixson thinks his process can produce alumina from rich clays and low-grade bauxite for about $31 per ton. Present cost of alumina made from rich bauxite ores is estimated at between $30 to $40 per ton.

Alcoa engineers reported that they knew nothing of his discovery except what they had read in the newspapers. Professor Hixson said he had turned his process over to the Government and expected a pilot plant would shortly be erected to substantiate his cost estimates in actual production. It will probably be located near the cheap-power source of the Tennessee Valley. Raw material can be mined in almost anybody’s back yard since aluminum, the commonest of all metals, is one of the three principal components of the earth’s crust.

Several other processes for recovering alumina from clay have also been announced. TVA has been experimenting with one for the past five years (TIME, Sept. 23, 1940). If they work, bauxite can be crossed off the list of raw materials for which nations scheme, dicker, bicker, fight.