The APU is in use world-wide for the purification and recovery of stainless steel pickle liquors. The Eco-Tec APU is designed to ensure minimal floor space requirements. Acid Sorption and Water Wash steps Increased metal removal capacities are achieved by increasing the diameter of the resin bed. The basic operation of the unit is shown in Figure 3 as depicted for an aluminum anodizing application. During the sorption step, acid is pumped upward through the resin column.
Free acid is sorbed by the resin, while the metal salt solution passes through.
During the desorption step, water passes down through the resin column to extract the free acid product from the resin. The equipment alternates automatically from sorption to desorption every few minutes. The net result is a virtually continuous process for acid purification and metal salt removal. Typical operating conditions are shown in Table 2 for an APU operating on an aluminum anodizing feed solution. Eco-Tec Inc. is a private company that has been designing and manufacturing chemical recovery systems for the metal finishing industry since 1970.