Effect of Carbonates Removal on Zinc Sorption in the Selected Calcareous Soils of Iran

Zinc is one of the micronutrients for plants and its deficiency is common in calcareous soils. On the other hand, many features of arid and semi-arid soils are affected by the presence of carbonates. To evaluate carbonates influence, Zn sorption was studied in 20 composite soil samples (0-30 cm) collected from the central region of Iran before and after carbonates removal. Carbonates were removed with sodium acetate buffer (pH=4.75). X- ray diffraction (XRD) analysis showed that calcite was the most commonly carbonate found in the studied soils. Original and free carbonate soils described L- curves isotherm and carbonate removal did not change the isotherm type. With increasing the applied Zn concentration, the effect of carbonate removal became more obvious. Upon carbonates removal, specific surface areas of the soils decreased and so did the amount of sorbed Zn (mg Zn/ kg soils). Sorbed Zn in per unit particles surface area (mg Zn/m2 soil) however, significantly increased. Freundlich empirical model () adequately described Zn sorption data in both original and carbonate free samples and the K – Freundlich variation was much higher than the n- coefficient. Single site Langmuir sorption model did not properly describe Zn sorption data, but double site Langmuir equation was well fitted to the data. The results showed that, k1 and k2 coefficients considerably decreased after carbonate removal.