Recovery of alumina from siliceous minerals

Claim 1

A process for the production of alumina from siliceous materials containing substantial quantities of combined aluminium and calcium, comprising the steps of: (i) grinding the mineral to a fine particle size; (ii) treating the ground mineral with a hot acid liquor containing chloride, fluoride and calcium ions to extract alumina values from said mineral; (iii) separating the acid extract from the spent mineral residues; (iv) sparging the separated extract to precipitate aluminium chloride; (v) separating the precipitated aluminium chloride from the spent acid extract; (vi) recycling one fraction of the spent extract to the mineral extraction stage (ii); (vii) evaporating another fraction of the spent extract to dryness and heating the solid residue with active silica in the presence of water vapour to regenerate hydrogen chloride gas; (viii) recycling the regenerated hydrogen chloride gas directly to the extraction stage (ii) and/or sparging stage (iv) or absorbing said gas in water for recycling.