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Pollution Prevention and Control Technologies for Plating Operations
Section 2 - General Waste Reduction Practices
2.8 OTHER RINSING INFORMATION
This subsection contains information on methods applied for rinse water use reduction that are not discussed in detail elsewhere in the report.
One shop indicated that they use in-tank filtration in large rinse tanks (PS 228) and another shop indicated that they use external filtration for some rinses (PS 275). The filtration technology, which is more frequently applied to process baths than to rinse tanks, removes particulate matter from solutions. The source of particulates for these two shops was not indicated on their survey forms. However, it is known that suspended solids in rinses can be caused by precipitation (e.g., mixing of alkaline cleaner drag-out and metal-bearing drag-out) or airborne material.
Although it is not widely applied to rinsing, the use of ultrasonics can improve its effectiveness. Ultrasonics loosen soil particles that are not completely removed during the cleaning step. Although one would expect the use of ultrasonics to be limited to small rinse tanks and critical operations due to its high capital costs, one shop reported that it uses ultrasonics in a large rinse tank (12' x 30" x 40" deep) following electropolish (PS 022). Another respondent suggests that ultrasonics be used in rinse tanks whenever feasible (PS 068).
Most existing process lines suffer from a lack of rinsing. When use of additional counterflow rinse tanks is suggested, the most common complaint is that there is no space, thus rinsing suffers and flow rates remain high. To gain additional tankage, some shops partition large rinse tanks into two or more smaller sections (ref. 9).