Adsorption of Cu by Smectite and Kaolinite Clays from Natural Deposits in Bulgaria

I. ATANASSOVA and R. ILIEVA
X-Ray diffraction Lab., “N. Poushkarov” Soil Science Instititute, BG-1080 Sofia, Bulgaria

Abstract

ATANASSOVA, I. and R. ILIEVA, 2003. Adsorption of Cu by smectite and kaolinite clays from natural deposits in Bulgaria. Bulg. J. Agric. Sci., 9: 673–678

Copper adsorption was investigated in kaolinite and smectite clays, which contained 2.3 % and 2.8 % free Fe-oxides impurities. Concentrations of Cu were 3 – 274 g.kg–1 (13 and 112 % CEC) for smectite and 1.8–4 g.kg–1 (37 and 82 % CEC) for kaolinite so that to determine the role of the permanent and variable charge in the sorption. Specific Cu sorption was evaluated on the basis of the discrepancy in the quantities of Cu2+ ions adsorbed / Ca2+ ions desorbed, which relates to the ability of the clays to fix Cu in a non-exchangeable form. The pH-dependant specific Cu sorption shifted to the lower pH (< 4) as Cu additions increased. At pH > 4 Cu was already specifically adsorbed. This fact was also confirmed by X-ray diffraction for smectite. The surface of kaolinite exhibited a higher affinity for Cu (log Kd values of the distribution coefficient) with increasing pH than the smectite surface. This is due to the higher percentage of weakly acidic cation exchange sites (CECwa), where Cu could be adsorbed by a mechanism different from divalent exchange with Ca2+ ions.

Key words: copper adsorption; calcium desorption; kaolinite; smectite