Process for obtaining pure alumina by the hydrochloric attack of aluminous ores and extraction of the impurities by means of a sulphuric treatment

A process for obtaining pure alumina from calcined or uncalcined ore containing impurities of metals selected from the group consisting of iron, titanium, sodium, potassium, magnesium, and calcium comprising:

• (a) attacking the ore with hot hydrochloric acid to provide a residue and a liquor containing dissolved aluminum chloride and impurities,
• (b) separating the attacking liquor from the residue,
• (c) washing the separated residue with aqueous medium to extract water solubles,
• (d) recycling the wash liquor from step (c) to constitute a part of the liquor used to attack the ore in step (a),
• (e) concentrating the liquor separated from the residue in step (b) until at most 75% of the alumina is precipitated as aluminum chloride hexahydrate,
• (f) separating the precipitated aluminum chloride hexahydrate from the remaining liquor containing in solution dissolved aluminum chloride and impurities;
• (g) introducing gaseous HCl into the liquor separated from the precipitated aluminum chloride hexahydrate in step (f) to precipitate residual aluminum chloride hexahydrate from the solution,
• (h) separating the aluminum chloride hexahydrate precipitate in step (g) from the hydrochloric liquor which still contains dissolved impurities,
• (i) recycling the aluminum chloride hexahydrate separated in step (h) to the liquor separated from the residue in step (b),
• (j) mixing the hydrochloric acid liquor from step (h) with sulphuric acid liquor and HCl,
• (k) heating the mixture of step (j) to concentrate the mixture and release HCl,
• (l) absorbing the HCl released from the mixture in step (k)
• (m) washing the aluminum chloride hexahydrate separated from the liquor in step (f) with the HCl liquor from the absorption step (l)
• (n) separating the wash liquor from the aluminum chloride hexahydrate washed in step (m),
• (o) recycling the wash liquor from step (n) to make up a part of the hydrochloric acid liquor for attacking the ore in step (a) and
• (p) thermally decomposing the separated aluminum chloride hexahydrate from step (n) to produce pure alumina.