GB1439803A - Recovery of mercury - Google Patents

Abstract

1439803 Electrolytic recovery of mercury using mercury cathode IMPERIAL CHEMICAL INDUSTRIES Ltd 13 May 1974 [5 June 1973] 26731/73 Addition to 1339261 Heading C7B [Also in Division C1] Mercury is removed from chlorine containing waste brine from a mercury cell by adding sulphide or hydrosulphide to the brine in an amount to produce a redox potential of the brine, relative to a saturated KCl-calomel electrode of a value more negative than +0.45 volts so as to precipitate the mercury as mercury sulphide. The mercury sulphide precipitate is removed by passage of the brine downwards through a filter comprising at least two directly superimposed layers of granular filtration material whose average particle size decreases and whose specific gravity increases from layer to layer from the top of the filter downwards. The precipitated mercury sulphide is removed from the filter by treatment with a liquor, such as sodium hypochlorite in brine, which dissolves the mercury sulphide and the mercury rich liquor drained off. Metallic mercury can be obtained from such liquors by recycling the liquor to a mercury cell and reducing electrolytically mercury. It is preferred to remove as much chlorine as possible from the mercury containing brine before precipitation of the mercury sulphide and further to remove insoluble matter, such as graphite, from the waste brine by for e.g. filtration. Examples of suitable materials for making mixed media filters include anthracite, coal, activated carbon, graphite, quartz, flint, silica, magnesia, alumina, garnet and sand.