Pollution Prevention and Control Technologies for Plating
Section 4 - Chemical Solution Maintenance
4.8 DIFFUSION DIALYSIS
4.8.6 Performance Experience and Operational and Maintenance
As indicated previously, none of the respondents to the Users
Survey indicated that they have employed this technology and therefore
no firsthand performance experience is available. Various literature
sources have reported on the efficiency of the diffusion dialysis
process (ref. 192, 252, 336). These articles and conference papers,
written by equipment manufacturers and suppliers, indicate that
80 to 95 percent of the initial acid can be recovered with 60
to 95 percent of the contaminant metal removed (i.e., a residual
metal content of 5 to 40 percent of original concentration remains
in the recovered acid).
Vendors of the technology suggest that the extremely low pressure
feed of diffusion dialysis puts minimal stress on the stack components
and therefore, increases the longevity of the units. However,
as with any membrane technology, there is concern over membrane
fouling and deterioration. Membrane fouling is most frequently
caused by the presence of solids in the acid feed solution. It
is reported (ref. 252, 336) that prefiltering will effectively
eliminate the potential fouling problem. With prefiltering, membrane
cleaning is required approximately two times per year (ref. 252).
Organic substances (e.g., oil and grease) can also cause membrane
fouling. This problem can be overcome using a pretreatment of
the raw acid solution with activated carbon.
Membrane life is reported to be three to seven years (ref. 252,
336). Membrane life will be shortened when the technology is used
with hydrogen peroxide, chromic acid, and nitric acid with concentrations
over 20 percent, as well as temperatures over 45C and organic
substances such as oil and grease, solvents or cleaners (ref.
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