Removal of Cadmium, Lead, Mercury, Tin, Antimony, and Arsenic from Drinking and Seawaters by Colloid Precipitate Flotation

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Abstract
The removal of Cd(II), Pb(II), Hg(II), Sn(II), Sn(IV), Sb(III), Sb(V), As(III), and As(V) from aqueous solutions by colloid precipitate flotation using sodium sulfide as the coagulent and oleic acid (HOL) as the surfactant has been investigated. The complete flotation (about 100%) of these elements was attained at pH values of 5.5–6.5, 3–6.5, ≤1, 1–4, 0.5–3, and ≤2, respectively. The effects of some other factors, such as surfactant and coagulent concentrations, sequence of adding reagents, some selected foreign ions, ionic strength, and temperature, on the floatability of these elements have been studied. It was found that both temperature and ionic strength have no appreciable effect on the flotation efficiency of the metal ions investigated. The method was successfully applied to remove completely these metal ions added to 1 L samples of drinking and seawaters at the optimum conditions for each element. Moreover, the mechanism of flotation is proposed.