Method for producing deionized water

摘要

A method for producing deionized water by an electro-regenerating deionization method, which comprises employing a deionized water producing apparatus comprising an electrodialyzer (1), wherein cation exchange membranes (K) and anion exchange membranes (A) are arranged alternately between an anode compartment (2) provided with an anode and a cathode compartment (3) provided with a cathode so as to form demineralizing compartments (R1,...,Rn) partitioned by the anion exchange membranes on the anode side and partitioned by the cation exchange membranes on the cathode side and concentrating compartments (S1,...,Sn) partitioned by the cation exchange membranes on the anode side and partitioned by the anion exchange membranes on the cathode side, and ion exchangers being accommodated in the demineralizing compartments, supplying water to be treated (6) in the demineralizing compartments and supplying a concentrated water (8) which is an electrolyte solution to the concentrating compartments under applying a voltage to transfer and remove impurity ion contained in the water to be treated, wherein the concentrated water (9) at the outlet of the concentrating compartments has a S value of 7 or more as defined by the following formula (1) and a pH of 2.5 or more: S value=( gamma -420000xA) / (Bx(1-(A/0.004))<3>) ;Formula (1) wherein gamma is electro-conductivity( mu S/cm), A is hydrogen ion concentration (mol/ l ), and B is magnesium ion concentration (ppb).