Pollution Prevention and Control Technologies for Plating
Section 4 - Chemical Solution Maintenance
4.4 ION EXCHANGE
4.4.7 Operational and Maintenance Experience
The following summarizes the respondent's O&M experiences
and provides operating labor information.
- Six shops provided operating labor data. For these shops,
the average number of annual operating hours per ion exchange
system were 220 hrs/yr. The labor category most frequently used
for O&M was a trained technician or a wastewater treatment
plant operator. The following is a breakdown of the responses
for skill requirements:
Environmental Engineer: 0
Process/Chemical Engineer: 0
Plumber/Pipe Fitter: 0
Senior-Level Plater: 2
Junior Level Plater: 0
Wastewater Treatment Operator:4
Trained Technician: 6
Common Labor: 0
- In general, the commercial equipment used for chromium bath
maintenance requires little maintenance and has a relatively long
equipment life. Most shops indicated that the downtime for this
technology was low and none identified any major O&M problems
except for PS 273.
- Long equipment life was evidenced by the fact that only one
shop (PS 273) in the survey indicated that they used this process
and subsequently discarded it due to deterioration (note that
one shop purchased their equipment in 1983 and later sold it and
that PS 244 eliminated the need for this equipment). The oldest
system identified in the survey that is still operating was purchased
in 1975 (PS 131). Shops estimated the life of this equipment to
be between 5 and 20 years and the average estimate was 11.5 years.
- The percentage of down time for this technology was low. Nearly
one-half of the respondents indicated that downtime was 1% or
- Several shops pointed out that there are two key technical
restrictions for this technology: chromic acid concentration and
temperature (PS 049, PS 150, PS 165, PS 273). Two shops indicated
that the solution temperature must be 90oF or less before ion
exchange treatment is performed (PS 165). Two shops pointed out
that the chromic acid concentration must be below 142.5 g/l (19.0
oz/gal) CrO3 for treatment (PS 165). One respondent indicated
that their operating conditions (160°F and 16 oz/gal CrO3)
may have contributed to resin damage (PS 273).
- One shop indicated that elements and filters must be changed
two times per year (PS 165).
- The shop operating an ion exchange unit for trivalent chromium
bath maintenance reported that they experience mechanical breakdowns
about four times per year. They also indicated that the downtime
of their unit was less than one percent.
- PS 131, the respondent that has used this process the longest
(since 1975), indicated that the process dilutes the hard chrome
bath and raises the sulfate level, causing them to adjust the
solution chemistry following treatment.
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