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* References 66 and 67.

b Arsenic present as arsenite (AsO'j) or arsenate (AsOt"}). e Chromium (VI) present as chromate (CrO^"!) or dichromate (CrjQ/*). " Not detected.

┬░ Uranium present as uranyl carbonates (U03(C0j);": and U02(COj)3"4].

Chelating ion exchange resins have shown promise in the printed circuit board industry for recovery of copper. When operated at a pH of 4 to 5, these resins have been sufficiently selective in removing this metal from complexina agents, allowing the complexing agents to pass through to the effluent. The resin is then regenerated with sulfuric acid, producing a mixture of sulfuric acid and copper sulfate. The copper is recovered by electrowinning onto flat stainless steel plates. The effluent from the eIectrowinning cell should contain 1 to 2 grams of copper per liter and therefore needs to be returned for treatment. Activated carbon adsorption is used to remove organics that could foul the ion exchange resin.

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lon exchange is a coiimon conmercia! nethod for removal/reuse of metals from wastewaters generated in the metal - finishing, electroplating, fertilizer manufacture, printed circuit hoard, and pigment manufacturing industries. The ion exchange process is also being used to recover chromates from cooling water blowdown," General Dynamics is currently using an ion exchange system coupled with electrowinning equipment to recover copper from rinse water and process bath solutions generated from the ┬╗anufacture of printed circuit boards. Full-scale commercial ion-exchange electrolytic recovery systems (Memtek Corp,J have been used to remove tin ind lead from contaminated wastewaters.' Pilot-scale studies have been conducted on bleach-fix process baths for the recovery of silver in the photographic industry.* Currently, 1 to 2 percent of the photographic industry is using ion exchange to recover silver. Because of EPA regulations, the majority of the photographic industry is expected to be using this technology within the ntxt 5 years.** Ion exchange has been used by the electroplating industry for wastewaters since 1910, and with the advent of new synthetic selective ion resins, ion exchange systems are improving. The resins, however, are highly specialized organic chemicals and are often expensive.

Table 46 shows the potential applicability of the ion exchange process for metal-bearing RCRA wastes. Although the ion exchange process is used primarily for wastewaters, sludge leachates can also be treated; however, no commercial use of ion exchange on sludge leachates for metals removal/reuse has been reported.

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