PURPOSE: To obtain gluconic acids useful as cleaning agents, coagulating agents, etc., from gluconic acid salts which are easily obtained by concentrating and cooling the waste water of the regeneration of an anion-exchange resin, discharged from the process of the preparation of sorbitol.

CONSTITUTION: Sorbitol prepared from glucose is purified with an ion-exchange resin. In waste water produced in the regeneration treatment of this resin, 10W50%, based on solid content, of sodium gluconate is contained. The waste water is collected, concentrated and cooled to give sodium gluconate easily, from which free gluconic acid can be obtained by using a cation-exchange resin. The gluconic acid is further converted into glucono-δ-lactone, calcium gluconate, etc.

EFFECT: Advantageous also from the respect of the treatment of waste water in the preparation of sorbitol.

USE: Acidifying condiments, pH-lowering agents, calcium sypplying agents, and additives for cement.