Ion Exchange and Chelating Resins

Anion exchange and chelating resins are commercially used in chlor-alkali plants in Japan and Sweden (Gardiner 1971; Aktiebolaget Billingsfors-Langed; Ajinomoto Co., Inc.; Terraneers, Ltd.). Untreated influent is first adjusted for pH and oxidation reduction potential and is filtered. Anion resins remove the mercury down to an effluent concentration of 100-200 ppb. Chelating resins further reduce mercury concentration to 2 ppb. Anion resins and some chelating resins can be regenerated with sodium sulfite, sodium hydrosulfite, or hydrochloric acid. Mercury can be recovered from backwash stripping solutions by electrolysis or with sodium amalgam, or the mercury-rich solu

FIG. 8.3.5 Treatment for mercury removal with ion exchange resin beds followed by a chelating resin bed. Mercury is stripped from the ion exchange resin by stripping liquid and then is reduced by sodium amalgam and recovered. A chelating resin is a heterocyclic compound that will combine with a metallic ion to form a chelate, i.e., a compound with the metallic ion attached by co-valent bonds to two or more nonmetallic atoms in the same compound.

FIG. 8.3.5 Treatment for mercury removal with ion exchange resin beds followed by a chelating resin bed. Mercury is stripped from the ion exchange resin by stripping liquid and then is reduced by sodium amalgam and recovered. A chelating resin is a heterocyclic compound that will combine with a metallic ion to form a chelate, i.e., a compound with the metallic ion attached by co-valent bonds to two or more nonmetallic atoms in the same compound.

tion can be used as is. Mercury is recovered from some chelating resins and filter solids by distillation.

The untreated influent wastewater is adjusted to a pH between 6 and 8, and chemicals are added to destroy oxidizing substances (Figure 8.3.5). Then the effluent is filtered. The use of an activated carbon filter removes some mercury and destroys oxidants that might exist because of faulty pretreatment. Precipitates may accumulate in the resin beds; consequently, occasional backwashing with water and air is required.

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