Process for recovering aluminum from alunite

A process for recovering aluminum hydroxide from aluminum-bearing ore containing substantial amounts of potassium and sulfate comprising the following steps:

• (a) roasting the ore to remove water and leaching the roasted ore with an alkaline solvent or water to remove compounds of sulfur and alkali metals including potassium sulfate resulting in a residue containing aluminum values and a solution containing potassium sulfate;
• (b) separating the residue and solution of step (a);
• (c) recovering potassium sulfate from the solution of (b) by crystallization while bleeding off a portion of potassium sulfate from the mother liquor;
• (d) contacting the potassium sulfate bleed stream with a cation exchange agent loaded with sodium ions to exchange potassium ions for sodium ions on the agent followed by contacting the potassium loaded agent with sodium hydroxide to exchange sodium ions for potassium ions on the agent to form potassium hydroxide and recycling said potassium hydroxide to the leaching of step (a);
• (e) digesting the residue from step (b) with at least one alkali metal hydroxide at a concentration and at a temperature sufficient to dissolve substantially all of the aluminum values from said solid portion as aluminates;
• (f) separating the liquid and solid portions of the slurry resulting from step (e);
• (g) removing silica from the liquid portion resulting from step (f) by precipitation as a desilication product which is essentially sodium aluminum silicate;
• (h) separating the liquid and solid portions resulting from step (g), and
• (i) precipitating and recovering aluminum hydroxide from the aluminates in the liquid portion resulting from step (h).

A process for recovering aluminum hydroxide from aluminum-bearing ore containing substantial amounts of potassium and sulfate comprising the following steps:

• (a) roasting the ore to remove water and leaching the roasted ore with potassium hydroxide to remove compounds of sulfur and alkali metals including potassium sulfate, resulting in a residue containing aluminum values and a solution containing potassium sulfate;
• (b) separating the residue and solution of step (a);
• (c) recovering potassium sulfate from the solution of step (b) by crystallization, while removing a bleed stream of potassium sulfate from the mother liquor;
• (d) digesting the residue from step (b) with sodium hydroxide at a concentration and at a temperature sufficient to dissolve substantially all of the aluminum values from said solid portion as aluminates;
• (e) separating the liquid and solid portions of the slurry resulting from step (d);
• (f) removing silica from the liquid portion resulting from step (e) by precipitation as a desilication product which is essentially sodium aluminum silicate;
• (g) separating the liquid and solid portions resulting from step (f);
• (h) precipitating and recovering aluminum hydroxide from the aluminates in the liquid portion resulting from step (g);
• (i) cycling the liquid portion of step (h) to the digestion step (d), while removing a bleed stream therefrom containing sodium hydroxide;
• and
• (j) contacting the potassium sulfate bleed stream of step (c) with the separated desilication product of step (g), as a cation exchange agent, to exchange potassium ions for sodium ions on the agent, followed by contacting the potassium loaded agent with the sodium hydroxide bleed stream of step (i) to exchange sodium ions for potassium ions on the agent to form potassium hydroxide, and cycling said potassium hydroxide to the leaching of step (a).