Zinc Sorption in Calcareous Soils of the Kurdistan Region of Iraq : Soil Science

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Zinc Sorption in Calcareous Soils of the Kurdistan Region of Iraq

Mam-Rasul, Ghafoor Ahmed

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Soil Science 184(2):p 60-68, April 2019. | DOI: 10.1097/SS.0000000000000252


Zinc (Zn) sorption was studied in four calcareous soils of the Kurdistan Region of Iraq. The experiment was conducted by equilibrating 5 g of soil in 50 mL of a 0.01 M CaCl2 solution containing different levels of Zn. Suspensions were centrifuged and filtered, and the concentrations of Zn in the filtered solutions were determined. The sorption of Zn was evaluated using four adsorption isotherms (Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich); the data were best fit by a linearized Langmuir model as evidenced by the higher coefficient of determination (R2) values and lowest standard error (SE) values. For the Langmuir and Freundlich isotherms, the separation factor (RL) was 0 < RL < 1, and the adsorption intensity (n) was 1 < n < 10, respectively, indicating a favorable (spontaneous) Zn sorption process in the soil. The Dubinin-Radushkevich isotherm indicated a physisorption process of Zn in the soil (E < 8 kJ mol−1). Thermodynamic parameters ΔGo, ΔHo, and ΔSo were also determined at three different temperatures. The ΔGo values were negative and ranged from −7.45 to −7.80, −9.56 to −10.28, and −11.36 to −12.85 kJ mol−1, at 278, 298, and 318 K, respectively, where negative values of ΔGo indicate the Zn sorption was endothermic. The values of ΔHo were positive and ranged from 17.23 to 29.25 kJ mol−1, and the values of ΔSo were positive and ranged from 89.87 to 132.15 J mol−1 K−1. The positive values of ΔHo and ΔSo indicate that the sorption of Zn in the soil is an endothermic process. The results indicate that the studied soils had a high capacity of Zn sorption, which leads to decline in the availability of Zn.

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