Abstract: A process is described for the formation of high purity alumina from Bayer Process alumina trihydrate (gibbsite). The solid hydrated alumina is reacted with concentrated HCl to cause partial or complete conversion to aluminum chloride hexahydrate (ACH). The ACH or mixture of ACH and unreacted hydrated alumina is recovered as a solid and calcined in a single or multistage calcination to high purity alumina. Soda contents in the product anhydrous alumina can be reduced by 98% or greater. Contents of other impurities, such as silica, iron, magnesium, etc., are also markedly reduced. Different degrees of impurity reduction can be obtained by controlling the degree of conversion of the hydrated alumina to ACH and by recycling and treating the acid after solid/liquid separation. The purified products find use in the specialty ceramics field, as catalyst supports, as adsorbents, in electronic components, in prosthetic devices or other applications in which alumina of controlled degrees of purity offers an advantage.

Abstract: In an electrolytic reduction cell in which molten metal is produced by electrolysis of a molten electrolyte, less dense than the molten metal product, the molten product metal collects at the bottom of the cell. A filter is provided at this location and is constructed from a material which is resistant to attack by both the molten metal and molten electrolyte, and which is wetted by the molten metal, but not by the electrolyte. By correcting sizing of the passage or passages in the filter molten metal product can be drawn out of the cell without simultaneous withdrawal of molten electrolyte. In the case of a cell for the production of aluminium the filter is preferably constructed from titanium diboride.

Abstract: An improved method of producing anhydrous aluminum chloride via aluminum chloride hexahydrate is provided. In a preferred embodiment the method is incorporated into a process for producing aluminum from aluminous ores, and particularly from domestic ore sources comprising (1) acid leaching an aluminous ore to produce aluminum chloride hexahydrate (ACH); (2) calcining the ACH to a specific temperature of above about 450.degree. C. to produce highly reactive aluminous particles containing high residual chloride and low residual hydrogen levels; (3) reductively chlorinating the calcined ACH at a low temperature to produce anhydrous aluminum chloride suitable for electrolytic reduction; and (4) electrolytically reducing the anhydrous aluminum chloride in a fused salt to produce aluminum metal and chlorine which is recycled to step (3).

Abstract: A method for recovery of fluoride values from spent potlining and fluoride containing insulating materials associated with the potlining is disclosed. Spent potlining and the insulating materials are reduced to a fine particle size and incinerated. The ash residue is leached with a dilute caustic and the leachate is treated with a calcium compound to precipitate calcium fluoride. The calcium fluoride is dried to a moisture content of less than 0.1 percent and is treated with about 93 to 99 percent concentration of sulfuric acid to produce hydrogen fluoride gas and a metal sulfate. The hydrogen fluoride gas is fed into an alumina dry scrubber to produce alumina with absorbed fluorides to be used as feed material to reduction cells used in the manufacture of aluminum by electrolytic reduction. The metal sulfate residue is treated with lime and constitutes an environmentally safe product which can be disposed of as landfill material.

Abstract: In an electrolytic reduction cell for the production of molten metal, particularly aluminium, by electrolysis of a less dense salt monolayer of ceramic shapes is located on the floor of the cell. Such shapes are formed of a ceramic material, wettable by molten aluminium, but not wettable by the cell electrolyte. The spacing between adjacent shapes and/or the apertures in individual shapes is selected such that interfaced surface forces prevent entry of electrolyte between the shapes. The shapes may be tiles, honeycombs, cylinders, tubes, balls etc. The product metal may be collected in a sump for periodic withdrawal from the cell or withdrawn continuously or at short intervals through a selective filter that permits passage of molten metal, but not of molten cell electrolyte, at low withdrawal rates.

Abstract: For the clearance of anode effects in operation of electrolytic cells for aluminium production, movement in the metal pool is induced to effect short-circuiting of the cell and disturbance of any gas film on the face of the anode(s) by raising the anode(s) and then lowering them to datum position and/or tilting the anode in relation to datum position. Upward movement is terminated either after a predetermined distance or when a predetermined cell voltage is attained. Fresh alumina is introduced into the cell by breaking alumina crust by anode movement or by independent supply.