Effects of Common Ions on Zn Sorption in Some Calcareous Soils of Western Iran

Zinc (Zn) is essential to plant growth and relatively mobile in soils. This study was conducted to assess the effect of common ions (Ca, K+, Na+, NH4+, Cl-, NO3-, and H2PO4-) on sorption of Zn in surface samples of ten calcareous soils from western Iran using 10 mmol L-1 KCl, KNO3, KH2PO4, Ca(NO3)(2), NaNO3, and NH4NO3 solutions as background electrolytes. The results indicated that both NH4+, K+, and Ca2+ equally decreased Zn sorption as compared to Na+. Zinc sorption was decreased by H2PO4-, as compared to NO3- and Cl-. The Langmuir and Freundlich equations fitted closely to the sorption data of all ions. The Langmuir maximum, bonding energy constant, and Freundlich distribution coefficient for Zn sorption differed among the various ionic background electrolytes. Langmuir sorption parameters showed that the presence of H2PO4-, decreased the maximum Zn adsorbed, but increased the bonding energy. Although K+ and NH4+ equally influenced maximum Zn adsorbed, they differed in their effect on the distribution coefficient of Zn in soils. Values of saturation index calculated using Visual MINTEQ indicated that at the low Zn concentration, Zn solubility was controlled by sorption reactions and at the high Zn concentration, it was mainly controlled by sorption and mineral precipitation reactions, such as precipitation of Zn-3(PO4)(2)center dot 4H(2)O, Zn-5(OH)(6)(CO3)(2), and ZnCO3. For most ionic background electrolytes, soil pH, CaCO3, and cation exchange capacity (CEC) were significantly correlated with sorption parameters.