Competitive adsorption behavior of heavy metals on kaolinite.
Polluted and contaminated soils can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a soil system will be affected by the presence of other metals. In this study we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto kaolinite in single- and multi-element systems as a function of pH and concentration, in a background solution of 0.01 M NaNO3. In adsorption edge experiments, the pH was varied from 3.5 to 10.0 with total metal concentration 133.3 microM in the single-element system and 33.3 microM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH50 (the pH at which 50% adsorption occurs) was found to follow the sequence Cu<Zn<Pb<Cd in single-element systems, but Pb<Cu<Zn<Cd in the multi-element system. Adsorption isotherms at pH 6.0 in the multi-element systems showed that there is competition among various metals for adsorption sites on kaolinite. The adsorption and potentiometric titrations data for various kaolinite-metal systems were modeled using an extended constant-capacitance surface complexation model that assumed an ion-exchange process below pH 7.0 and the formation of inner-sphere surface complexes at higher pH. Inner-sphere complexation was more dominant for the Cu(II) and Pb(II) systems.
Srivastava
Prashant
P
Faculty of Agriculture, Food and Natural Resources, University of Sydney, NSW 2006, Australia. psri0762@mail.usyd.edu.au
Singh
Balwant
B
Angove
Michael
M
D000327:Adsorption; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry*; D019216:Metals, Heavy / Q000737:chemistry*; D011522:Protons; D013499:Surface Properties; D014867:Water / Q000737:chemistry
D019216:Metals, Heavy; D011522:Protons; D014867:Water; D007616:Kaolin