Removal of mercury(II) from aqueous solution on a carbonaceous sorbent prepared from flax shive

Treatment of flax shive with sulfuric acid produced a carbonaceous material which has been used to remove mercury(II) from aqueous solution. The kinetics of sorption follows a first order reaction equation with the rate of sorption being higher for the wet material than for that which had been previously dried. Sorption of mercury depends on the pH of the aqueous solution with maximum uptake occurring in the pH range 6-7. Sorption capacity also increases with the increase of temperature. The presence of other metal ions such as K⁺, Na⁺, Mg²+ and Ca²+ decreases Hg(II) uptake capacity. A high capacity which exceeds the cation exchange capacity was observed, cumulative Hg(II) sorption exceeding 1 gg^-1. This arises from the reduction of mercury(II) to mercury(I) chloride and elemental mercury from chloride media and to elemental mercury from nitrate media. This was confirmed from the identification of deposits on the carbon surface by scanning electron microscopy and X-ray diffraction. The reduction of mercury was accompanied by the oxidation of the carbon which was confirmed by the evolution of carbon dioxide. This observation was also supported by changes in the infra-red spectrum of the carbon after reaction. The sorption mechanism is discussed. (C) 2000 Society of Chemical Industry.