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Pollution Prevention and Control Technologies for Plating Operations


Section 4 - Chemical Solution Maintenance

4.5 ACID SORPTION

4.5.4 Technology/Equipment Description

This subsection contains a description of commercially available acid sorption equipment that is manufactured and sold by a respondent to the Vendors Survey. This is intended to provide the reader with information and data on available equipment. Mention of trade names or commercial products is not intended to constitute endorsement for use. The information contained in this section describes the Eco-Tec APU™, which was the only commercial acid sorption process identified during the Vendors Survey.

A standard APU™ consists of a cartridge filter, a vessel containing a resin bed, plastic piping, valving and a control system, all mounted on an epoxy coated steel frame. There are four standard APU™ sizes. Small APUª models use hydro-pneumatic tanks to meter the flow of acid and water through the resin bed and larger units use a microprocessor-controlled flow sensor. The smallest unit has the dimensions 42 in. (107 cm) x 63 in. (160 cm) x 80 in. (204 cm) (high) and the largest unit has the dimensions 80 in. (204 cm) x 142 in. (361 cm) x 80 in. (204 cm) (high). Options include additional pre-filters, pumps, and high-temperature-resistant construction (ref. Eco-Tec file).

The operational steps of an APU™ were previously shown in Exhibit 4-13. There are two basic steps of the cycle, the upstroke and the downstroke. During the upstroke, metal-contaminated acid is pumped into the bottom of the APUª resin bed. Acid is adsorbed by the resin bed, and the deacidfied metal salt solution, referred to as the "by-product," is collected from the top of the bed. During the downstroke, water is pumped into the top of the bed, desorbing the purified acid from the resin so that a purified acid product is collected from the bottom of the bed. The entire upstroke/downstroke cycle takes only about five minutes to complete. The equipment is fully automated to allow the cycles to repeat continuously (ref. 364). Eco-Tec has published "typical results for various applications." These are shown in Exhibit 4-15.

In addition to the standard APU™ components, some acid sorption installations may require cooling and additional filtration equipment. Cooling is needed when oxidizers such as nitric acid or hydrogen peroxide are present. These types of applications require cooling to approximately 90F (32C). Sulfuric and hydrochloric acid can be processed at temperatures up to 158¡F (70¡C). Eco-Tec indicated that city water is typically used for cooling and, to reduce water consumption, it can be reused for regeneration of the acid bed. Filtration is needed for most applications to minimize the pressure drop across the resin bed. The manufacturer recommends using a multimedia filter followed by a polishing cartridge filter for most applications.


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