Activated carbon is used as filter-aid and also in granular beds. Removal performances from 100-200 ppb (influent) to 10-20 ppb (effluent) are reported. For the filtration of 50% caustic soda from mercury cells, a precoat type filter with activated carbon precoat, such as Nuchar 722, is used. At the start of a cycle, mercury concentration is 10 ppb in the filter effluent, but increases to the Codex (National Academy of Sciences 1971) limit of 500 ppb when the filter is backwashed. Mercury is recovered from the activated carbon by distillation.
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