Sorption-Desorption of Zn by a Rhodic Khandiustult in the Northern Guinea Savanna of Nigeria

Zinc adsorption at concentrations between 0-50 mg Zn l-1 was evaluated in surface and subsurface samples of a basaltic soil in the Northern Guinea Savanna, a Rhodic khandiustult. After adsorption, 3 consecutive extractions (desorption) in sequence where performed to the samples by using 25 mL of 0.1 NHCl. The results showed that the Ap and Bt horizons have large capacities to adsorb zinc. While the desorption showed that the sorbed zinc was not rigidly bound. The amount of zinc released in the Ap horizon was slightly more than that released in the Bt horizon, i.e., Zn was more difficult to release in the Bt horizon than in the Ap horizon. The adsorption data did not fit the linear form of either the Langmuir or the Freundlich isotherms. The amount of Zn needed to be added to give a critical level of 1.0 mg kg-1 was estimated to be 20 mg kg-1 of Zn and above in the Ap horizon. Whereas it was estimated to be 40 mg kg-1 and above for the Bt2 horizon. The examined soil could offer an effective way to increase or decrease zinc ions concentration.