Reduction

Reduction of mercury to the metallic state followed by filtration may be suitable for small volumes of concentrated effluent, and can be accomplished by electrolysis, reduction with a less noble metal, or a reducing agent. Mercury can be recovered in a relatively pure state at the cathode of a special electrolytic cell. When metallic reducing agents such as copper, iron, zinc (New Jersey Zinc Co. 1971), aluminum, and sodium amalgam are used, the mercury is recovered as an amalgam or as droplets coalescing on the surface of the metal. Mercury is recovered in the pure state by distillation. Mercury ions are replaced by the reducing metal ions according to equations 8.3(24) and 8.3(25).

In the latter case, mercury is recovered in the amalgam form.

Reducing agents such as hydrazine, hydroxylamine, hy-pophosphorous, formaldehyde, and sodium borohydride (Anon. Chem Eng. News 48 1970) are suggested. The mercury is recovered by coalescence and/or filtration. Mercury concentrations remaining in the filter effluent (filtrate) are reported in the 100 ppb range after treatment through a 5-micron filter.

SOLIDS H«s

FIG. 8.3.4 Sulfide treatment for mercury removal—a continuous process.

SOLIDS H«s

FIG. 8.3.4 Sulfide treatment for mercury removal—a continuous process.

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