Investigation of Single and Bi-solute Retention Isotherms of Copper and Lead in Acidic and Alkaline Soils

ABSTRACT: In order to study the retention characteristics of Cu and Pb under single and bi-solute conditions acidic and alkaline soil samples were equilibrated with the solutions containing different concentrations of Cu and/or Pb between 0.15 to 3 mM for 24 h, the suspensions were centrifuged and the solution was filtered and the filtrate was analyzed for Cu and Pb and the adsorption data were fitted to the Langmuir and the Freundlich isotherms. Both Pb and Cu adsorption data well fitted to the Langmuir isotherm as evidenced by relatively high R2 values and low SE values. The adsorption data for Pb did not show satisfied fits to the Freundlich isotherm. The adsorption data for Cu showed moderately conformity to the Freundlich isotherm. In both acidic and basic soils, the amounts of monolayer adsorption maxima, qm, for Cu decreased under bi-solute condition as compared to the single condition demonstrating the lower sorption capacity for Cu due to the occupation of some adsorption sites by Pb. In a similar trend with Cu, the values of qm for Pb was lower under bi-solute condition as compared to the single condition in both acidic and basic soils studied. Overall, the values of qm was higher for Pb in comparison with Cu in both acidic and basic soils studied. In acidic soil, bonding strength was higher for Pb than Cu demonstrating the lower accessibility of Pb as compared to Cu. Bonding strength for Cu and Pb were higher under single and bi-solute systems, respectively.