Adsorption of Methylmercury(II) Chloride and Mercury(II) Chloride on Thiohumic Acidt

Abstract

When carboxyl group of humic acid is replaced by thiocarboxyl group, thiohumic acid (THA)is formed. THA was prepared from the regenerated humic acid obtained by the oxidation of Miike bituminous coal with nitric acid as shown below:
THA has an excellent adsorptive ability for methylmercury (II) chloride (Fig.1) and this adsorptive ability is scarcely influenced by pH or NaCl present in an aqueous solution of methylmercury (11) chloride. THA which adsorbs methylmercury (II) chloride can be regenerated by the treatment with 4 N HCl (Fig.3). THA has an excellent adsorptive ability also for mercury (II) chloride. By adding 100 mg of THA to 100 ml of an aqueous solution of Hg (II) whose concentration is 1 ppm, the concentration of Hg(II) can be reduced below 1 ppb (Fig.4). The adsorptive ability of THA for mercury (II) chloride is not affected by the addition of HClO₄ (Fig.5) and scarcely affected by the addition of HC1 or NaCI when the concentration of HC1 or NaCl is less than 0.1 mol/1 (Fig.6, 7). About 10000 ppm of Ca²⁺ or Fe³⁺ coexisted in an aqueous solution of Hg(II) does not affect the adsorption of Hg (II) on THA (Fig.8). In comparison of the adsorptive ability of THA with that of humic acid, it was concluded that the coordinate bond between COS^- group and mercury contributes markedly to the adsorption of mercury on THA. THA containing CO^- group, a soft base, was found to have a selective adsorptive ability for mercury.