Pollution Prevention and Control Technologies for Plating
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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