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Pollution Prevention and Control Technologies for Plating Operations


Section 3 - Chemical Recovery

3.4 ION EXCHANGE

3.4.2 Development and Commercialization

Ion exchange is a versatile separation process with potential for broad application in the metal finishing industry. The ion exchange process has been commercially available for many years, but early use was primarily for water deionization or softening. Widespread interest in the process for metal finishing pollution prevention and control is a more recent application that has grown rapidly over the past 10 to 20 years.

Although the ion exchange process was first recognized in 1850, and defined as a reversible process in 1858, the first practical application of the process did not occur until 1905 when the inorganic sodium aluminosilicate cation exchanger was synthesized and used to soften water. In the early 1930's a cation material was developed from sulfonated coals, which extended the operable pH range of the process. In 1935, condensate polymers were first used as structural substrates for various functional groups, thereby creating both anion and cation exchange materials. The early anion product was not the strong base anion exchanger available today. Instead, it acted as an acid adsorbent capable of removing only free acids from the process stream. The cation and anion forms were used in series for the first time and deionization was accomplished; however it was limited in application. Strong base anion exchange materials were developed in the 1940's that extended the use of the process. In 1945 synthetic organic polymers were developed using styrene and divinylbenzene as the monomers. These were later prepared in bead form (earlier, only granular products were available). This gave rise to the modern "gel" type ion exchange materials. Improvements during the 1950's focused on reducing the fouling of resins by organic substances (ref. 383). One of the earliest applications of ion exchange to metal finishing mentioned in the literature was a hard chromium bath maintenance system operated by the Rock Island Arsenal in 1952 (ref. 368). The use of ion exchange as a pollution control and chemical recovery tool progressed steadily as pollution control regulations became more widespread and more stringent. As with many technologies, ion exchange use for pollution control in the metal finishing industry increased very rapidly in the late 1970's and early 1980's with the implementation of the Federal effluent guidelines. The most recent developments have focused on expanding the range of applications (e.g., cyanide plating and electroless plating baths) with new resins, equipment and techniques.


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