Process for removing mercury from brine sludges

A process for recovering and concentrating the mercury content of mercury cathode brine electrolysis cell sludge containing minor concentrations of mercury by sequentially:

• (1) acidifying said sludge to a pH below 2.5, (2) leaching said sludge with aqueous hypochlorite solvent at a pH above 5, (3) separating said solvent from the leached sludge, and (4) isolating the major part of the mercury content of said separated solvent.

In an improved process for making elemental chlorine and sodium-mercury amalgam by the electrolysis of brine in a mercury cathode electrolysis cell wherein depleted brine from said cell is treated with alkali-metal carbonate or alkali-metal hydroxide to precipitate impurities as clarifier sludge, said sludge containing minor concentrations of mercury, separating said sludge from said brine for disposal outside the cell, and adding to the electrolysis cell metallic mercury in amount at least equal to the mercury retained by said separated clarifier sludge;

• the improvement which comprises:
• recovering the mercury content of said sludge by sequentially:
• (1) acidifying said sludge with hydrochloric acid to a pH below 2.5, (2) leaching said sludge with aqueous hypochlorite solvent at a pH above 5, (3) separating said solvent from the leached sludge, (4) isolating the major part of the mercury content of said separated solvent, (5) converting the insolubilized mercury to metallic mercury or chloride of mercury, and (6) returning said metallic mercury to a cathode of a mercury cathode brine electrolysis cell.

In an improved process for making elemental chlorine and sodium-mercury amalgam by the electrolysis of brine in a mercury cathode electrolysis cell wherein depleted brine is reconcentrated by contact with solid sodium chloride and returned to said electrolysis cell, said contact with sodium chloride resulting in the accumulation of insoluble impurities as saturator sludge, said sludge containing minor concentrations of mercury, separating said sludge from said brine for disposal outside the cell, and adding to the electrolysis cell metallic mercury in amount at least equal to the mercury retained by said saturator sludge;

• the improvement which comprises:
• recovering the mercury content of said sludge by sequentially:
• (1) acidifying said sludge with hydrochloric acid to a pH below 2.5, (2) leaching said sludge with aqueous hypochlorite solvent at a pH above 5, (3) separating said solvent from the leached sludge, (4) isolating the major part of the mercury content of said separated solvent, (5) converting the insolubilized mercury to metallic mercury or chloride of mercury, and (6) returning said metallic mercury to a cathode of a mercury cathode brine electrolysis cell.