Production of monobasic potassium phosphate by electrodialysis

A continuous process for producing aluminum and monobasic potassium phosphate from alunite ore and apatite ore which comprises:

• (a) reacting apatite ore with sulfuric acid to produce phosphoric acid;
• (b) roasting and leaching the alunite ore to remove water and compounds of sulfur and alkali metals resulting in a residue containing aluminum values and a solution containing potassium sulfate;
• (c) digesting the residue from step (b) with at least one alkali metal hydroxide to convert substantially all of said aluminum values to soluble aluminate;
• (d) removing silica from the aluminate formed in step (c);
• (e) recovering aluminum values from the aluminate remaining from step (d);
• and
• (f) converting phosphoric acid from step (a) and potassium sulfate from step (b) to monobasic potassium phosphate by electrodialysis.

A process for producing aluminum and monobasic potassium phosphate from alunite and apatite rock which comprises:

• (a) reacting apatite rock with sulfuric acid to produce phosphoric acid;
• (b) roasting and leaching the alunite ore to remove water and compounds of sulfur and alkali metals resulting in a residue containing aluminum values and a solution containing potassium sulfate;
• (c) digesting the residue from step (b) with at least one alkali metal hydroxide to dissolve substantially all of the aluminum values from said solid residue;
• (d) separating the liquid and solid portions of the slurry resulting from step (c);
• (e) removing silica from the liquid portion resulting from step (d) leaving a desilication product which is essentially sodium aluminum silicate;
• (f) separating the liquid and solid portions resulting from step (e);
• (g) precipitating aluminum hydroxide from the liquid portion resulting from step (e);
• (h) recovering aluminum values from the aluminum hydroxide precipitate of step (g);
• and
• (i) converting the phosphoric acid from step (a) and the potassium sulfate from step (b) by electrodialysis into monobasic potassium phosphate.

The process for producing monobasic potassium phosphate from phosphoric acid and potassium sulfate by electrodialysis in a single frame electrodialysis cell, said unit comprising:

• in successive positions, an anion compartment, an intermediate compartment, a cation compartment;
• an anion permselective membrane between the anion and intermediate compartments, a cation permselective membrane between the intermediate and cation compartments;
• the arrangement forming anion and cation compartments and an intermediate compartment, which process comprises:
• adding water to the anion compartment, potassium sulfate to the intermediate compartment, phosphoric acid to the cation compartment, and applying a direct current electrical potential across the electrodes to produce sulfuric acid in the anion compartment, dilute potassium sulfate in the central compartment and monobasic Potassium Phosphate in the cathode compartment.

The process for producing monobasic potassium phosphate from phosphoric acid and potassium sulfate by electrodialysis in a single frame electrodialysis cell, said unit comprising:

• in successive positions, an anion compartment, a first intermediate compartment, a second intermediate compartment, and a cation compartment;
• an anion permselective membrane between the anion and first intermediate compartments, a cation permselective membrane between the intermediate compartments and an anion permselective membrane between the second intermediate and the cation compartments;
• the arrangement forming anion and cation compartments and two intermediate compartments;
• which process comprises:
• adding water to the anion compartment, potassium sulfate to the first intermediate compartment, water to the second intermediate compartment and phosphoric acid to the cation compartment, and applying a direct current electrical potential across the electrodes to produce sulfuric acid in the anion compartment, dilute potassium sulfate in the first intermediate compartment, monobasic potassium phosphate in the second intermediate compartment, and dilute phosphoric acid in the cation compartment.