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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