| Summary: | The present work involves a study of various parameters which affect the removal of mercury(II) from solution, using a dissolved-air flotation technique. Initially, removal of mercury(II) was achieved from aqueous solution using a laboratory-scale apparatus and optimum removal using various coagulating agents was investigated. The mercury(II) concentration was determined by cold vapour atomic absorption spectrometry. The effect of pH, admitted water volume, coagulation time, and nature and quantity of added tensides and polymeric flocculants was studied using experimentally established optimum removal conditions. The optimum percentage removal achieved using iron(III) chloride, aluininium(III) sulphate and copper(II) sulphide in aqueous solution was 75.6, 33.1 and 99.3, respectively. A major source of mercury(II) in effluents is from depleted brine in the chlor-alkali industry and so removal from solutions containing high chloride ion concentrations was investigated. For solutions containing 17Z w/v sodium chloride, the optimum percentage removal of mercury(II) using iron(IILchlor.idetsodium_sylphi4,_ and copper(II) suiphide was 18.7 and 89.0, respectively. The efficiency of the laboratory process was assessed under industrial conditions by using a pilot plant at a chloralkali works. The optimum percentage removal of mercury(II) using iron(III) chloride, aluminium(III) sulphate and copper(II) sulphide from brine effluent was 92.8, 93.0 and 91.4, respectively. A study was undertaken to investigate the surface chemical interactions of flotation by using a microelectrophoresis technique. Model iron(III) and copper(II) sols were prepared by forced hydrolysis and the effect of pH, tensides and polymeric flocculants on electrophoretic mobility was determined.
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