Ion-exchange process

A process for ion-exchanging an exchangeable-ion containing solid material, comprising:

• (1) mixing an exchangeable-ion containing solid material and water to produce a first slurry;
• (2) subjecting the first slurry to a solid-liquid separation to produce a second liquid and a second solid;
• (3) contacting the second liquid with an ionic compound and oxalic acid to produce an aqueous ion-containing solution and controlling the aqueous ion-containing solution to a pH of 4-6.5, and then subjecting the pH-controlled solution to a solid-liquid separation to produce a treatment liquid, and subjecting the resulting treatment liquid to bipolar membrane electrodialysis to produce an acid liquid;
• (4) ion-exchanging at least a part of the second solid with the resulting acid liquid in an ion-exchange vessel to produce a slurry containing the ion-exchanged solid material, then subjecting the resulting slurry containing the ion-exchanged solid material to a solid-liquid separation to produce a first liquid and a first solid, and treating the first solid to produce a finished product or sending the first solid back to the ion-exchange vessel for further treatment;
• and
• (5) adjusting the first liquid with a basic substance to a pH of 4-6.5, then subjecting the pH-adjusted first liquid to a solid-liquid separation to produce second treatment liquid, and subjecting the second treatment liquid to bipolar membrane electrodialysis to produce a second acid liquid.