DISTRIBUTION OF MERCURY BETWEEN ELECTROLYTE AND NATURAL BENTONITE

Investigations of mercury adsorption and desorption on natural sodium and calcium bentonite in various buffer systems were carried out. The major component ions released from bentonite into deionized water, the volatilization of dissolved Hg-degrees, and the influence of the pH a nd chloride concentration on adsorption, as well as the formation of v arious inorganic mercury complexes, were investigated. In deionized wa ter, a high amount of cations and anions was released from Na bentonit e. High loss of Hg was found from the buffer solution at pH 6 by escap e into the atmosphere. In the pH range from 3 to 13, dissolved Hg(II) adsorbed well on bentonite as correlated with Hg(OH)2 which are the pr edominant species in weakly acidic to alkaline solutions. With increas ing concentration of chloride ions, the uptake of Hg was reduced becau se of the occurrence of negatively charged chloro-complexes. At pH 5.0 0-5.50 bentonite adsorbs Hg(II) species from the solution with a capac ity of 0.32 mol/kg and follows the Langmuir model. The adsorption kine tics of mercury on bentonite depends on the solution composition and t he form of the bentonite. A low adsorption rate of dissolved Hg(II) on Ca-bentonite was found at pH 8. Remobilization studies with various e lectrolytes are presented. Up to 80% of the adsorbed Hg on bentonite r edissolves in 0.1 M hydrochloric acid.