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Pollution Prevention and Control Technologies for Plating Operations
Section 4 - Chemical Solution Maintenance
4.4 ION EXCHANGE
4.4.4 Technology/Equipment Description
This subsection contains a description of commercially available ion exchange equipment that is manufactured and/or sold by vendor survey respondents. This is intended to provide the reader with information and data on a cross section of available equipment. Mention of trade names or commercial products is not intended to constitute endorsement for use.
Eco-Tec Inc. manufactures a Decationzation Unit (DCU) that consists of a patented Recoflo™ ion exchange bed (see description in Section 3.4.1.3), filter, piping, valves and control panel. The DCU is an integrated ion exchange system as defined in Section 3.4.1.2. Depending on the model selected, the unit treats 50 to 200 gal (200 to 750 l) of chromic acid plating bath per run. The process is initiated by transferring the solution to be treated into a feed tank. The DCU is then activated and the process proceeds automatically. The unit automatically dilutes the acid to between 100 and 150 g/l (13 to 20 oz/gal) to reduce oxidation of the resin before the contaminated chromic acid passes through the bed. The DCU continuously operates a three step cycle where contaminated chromic acid is fed through the unit and the bed is rinsed and regenerated (sulfuric acid) in a counterflow direction. The treated solution is transferred to another holding tank and is returned to the bath. The surface evaporation of the bath makes up for the small quantity of water added during the process. According to Eco-Tec, the process removes 80 to 90% of the bath contaminants and generates about 3 gal/hr of residual (regenerant). The expected resin life is 6 to 12 months (ref. 385). Eco-Tec also markets a batch treatment system for treatment of the regenerant from this process.
Kinetico Engineered Systems, Inc. (Kinetico) manufactures a modular ion exchange system (see definition in Section 3.4.1.3) for hexavalent and trivalent chromium bath maintenance. The modular design is referred to as "point of use" by Kinetico. The ion exchange service unit consists of a bath purification ion exchange station and an ion exchange tank. The station consists of a bath recirculation pump, cartridge filter unit, timer mechanism and controls mounted on a skid assembly. The ion exchange tank is a separate unit that connects to the service station. The service units are located at the point of use (near the plating tank) for bath treatment and the tanks are transported to a central regeneration station after use. The central regeneration station is similar in appearance to the ion exchange station, but performs the function of regeneration. The central regeneration station can be rigged to treat both hexavalent and trivalent baths. After regeneration, the tanks are returned to the point of use. Specifications for a range of Kinetico models are shown in Exhibit 4-9.