Methods, and various apparatus therefor, are disclosed for the electrolytic treatment of an acidic solution. Generally the method comprises: (a) providing an electrolytic cell, the cell comprising: (i) an anode chamber and an anode therein; (ii) a cathode chamber and a cathode therein; and (iii) a diaphragm. Usually the diaphragm is of a non-isotropic fibrous mat comprising 5-70 weight percent organic halocarbon polymer fiber in adherent combination with about 30-95 weight percent of finely divided inorganic particulate impacted into said fiber during fiber formation, the diaphragm having a weight per unit of surface area of about 3-12 kilograms per square meter. The method can continue by (b) introducing the acidic solution into the cell; (c) impressing a current on the anode and the cathode causing the migration of ions through the diaphragm; and (d) recovering a product of the electrolytic treatment from the anode chamber, or the cathode chamber, or from both chambers. In one method, the acidic solution is a cell bath circulated to the anode chamber, while rinse solution downstream of the cell bath is circulated to the cathode chamber. The method, and apparatus therefor, are particularly applicable to the recovery of hexavalent chromium from a dilute chromium electroplating rinse solution.
This is a divisional of application Ser. No. 08/401,381, filed Mar. 9, 1995, (now U.S. Pat. No. 5,474,661) which is a continuation of U.S. patent application Ser. No. 08/067,918, filed May 27, 1993 (now U.S. Pat. No. 5,405,507), which in turn is a continuation-in-part of U.S. patent application Ser. No. 07/799,653, filed Nov. 29, 1991 (now U.S. Pat. No. 5,246,559).
