Recovery of aluminum from alunite ore using acid leach to purify the residue for bayer leach

A process for recovering aluminum hydroxide from alunite ore which comprises:

• a. grinding the ore to particulate form;
• b. oxidation roasting the particulate ore to remove water and sulfur and convert the aluminum values to alumina;
• c. grinding the calcined ore;
• d. leaching the roasted and ground ore with water to remove compounds of sulfur and alkali metal including potassium sulfate resulting in a residue containing aluminum values and silicates, and a solution containing soluble sulfates including K.sub.2 SO.sub.4 ;
• e. separating the residue and solution of step (d);
• f. leaching said residue of step (d) with a 10 to 35 percent solution of sulfuric acid to convert the aluminum values therein to soluble aluminum sulfate, and leaving a residue containing SiO.sub.2, said leaching process to be carried out at a temperature between about 120 and 180.degree. C.
• g. separating the residue of step (f) from the solution of step (f);
• h. crystallizing aluminum sulfate from the solution of step (f);
• i. calcining the aluminum sulfate of step (h) to drive off sulfur dioxide and convert the aluminum sulfate to aluminum oxide;
• j. digesting the calcined alumina of step (i) with caustic to convert the aluminum values therein to soluble aluminates;
• k. filtering the liquid of step (j) to remove insoluble impurities;
• l. precipitating aluminum hydroxide from the filtered liquid of step (k).