Adsorption of HgBrn Complexes on Activated Carbon

Takashi SHIRAKASHI*, Kuniaki TANAKA, Toshiyasu TAMURA†† and Sachio YOSIHARA*

Department of Energy and Environmental Science, Graduate School of Engineering,
Utsunomiya University; 7-1-2 Youtou, Utsunomiya-shi 321-8585 Japan
Suginomashin Co. Ltd.; 2410 Motoe, Uodu-shi 937-0805 Japan
†† Department of Applied Chemistry, Facurty of Engineering, Utsunomiya University;
7-1-2 Youtou, Utsunomiya-shi 321-8585 Japan

Adsorption states of mercury on activated carbon in the presence of Br ion were studied with an analysis of average coodination number and a thermal analysis of activated carbon adsorbed mercury. Activated carbons which were made from coal (A. C. B) and coconut shell (A. C. C) were used. Average coodination number of Br ion adsorbed on activated carbon was calculated from Br ion concentration obserbed with Br ion electrode and mercury concentration in final solution. These activated carbons reduced Hg2+ at pH 7 but the reduction of Hg2+ was not clarified at pH 1.4. Main adsorption species of Hg(II) were [HgBr2] and [HgBr3] at pH 7 and pH 1.4 and the amount of adsorbed [HgBr3] was increased with an increase in Br ion concentration. Furthermore, adsorption of Br ion and/or [HgBr4]2− were suggested at higher Br ion concentration at pH 1.4. Adsorption ability of both activated carbons for [HgBr2] and [HgBr3] at pH 7 and for [HgBr3] at pH 1.4 resembled each other. When the activated carbons were oxidized with Fe3+ in acidic solution, Hg2+ was not reduced at pH 7 and adsorbability of [HgBr3] on A. C. C increased but decreased on A. C. B.
From these results, it is clarified that activated carbon reduces Hg2+ at pH 7 even if Br ion is present and adsorption species varies with Br ion concentration.

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