Apparatus for the fabrication of pure alumina from Al.sub.2 O.sub.3 and silica containing raw materials by leaching with hydrochloric acid

Apparatus for the production of pure alumina from silicate containing raw materials comprising means for feeding said raw material into an acid resistant leaching tower from the top portion thereof;

• means for feeding a leaching liquor containing hydrochloric acid into the bottom portion of said leaching tower, so as to continuously flow said leaching liquor upward countercurrently through said raw material flowing downward in order to leach out the alumina as a solution enriched in aluminum chloride, leaving a raw material solid residue;
• means for withdrawing said solution enriched in aluminum chloride from the top portion of said tower;
• means for withdrawing said raw material solid residue from the bottom portion of said tower;
• means for providing a flowing carrier liquid for conveying said solid residue away from said leaching zone and into a separator means and separator means for removing said solid residue from said carrier liquid;
• means to convey said solution enriched in aluminum chloride at about 120.degree. C. from said leaching tower into and through a balancing container means and into a backwashable sand filter;
• means for conveying said solution enriched in aluminum chloride from said backwashable sand filter into the cold crystallizer section of a crystallizer-thermal-decomposer combination, comprising a rotating, inclined tube made of acid and heat resistant material and containing a mother liquor, causing said aluminum chloride to precipitate in said crystallizer as AlCl.sub.3 . 6 H.sub.2 O crystals;
• screw conveyor flights within said tube for transporting said precipitated crystals through an intermediate washing means into a hot thermal decomposer to convert said AlCl.sub.3 . 6 H.sub.2 O crystals into al(OH).sub.3 and into vapors of HCl and water;
• means for conveying said vapors countercurrent to said crystals from said thermal decomposer through said intermediate washing means and into said crystallizer;
• means to recover said Al(OH).sub.3 ;
• means providing a fluid-tight feeding shaft inside the upper end portion of said leaching tower;
• and means for adding amounts of new raw material into said feeding shaft to a sufficient height to absorb rising HCl vapors and to prevent escape of said vapors into the atmosphere.