Adsorption of nitrate and chloride in some Tanzania soils dominant in allophanic and kaolinitic clays

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University of Dar es Salaam
Nitrate and chloride adsorption in some virgin Tanzanian soil dominant in allophanic (x-ray amorphous) and kaolinitic clays as affected by the electrolyte (equilibrating solution) concentration, pH and anionic composition (complementary ion effect) were investigated. The adsorption of both N03 and C1 (in both leached and unleached samples) in all the solid increased with increasing electrolyte concentration. A transition from negative absorption of both anions at lower concentration to positive adsorption at higher concentration was observed in nearly all the soils. The Freundliah adsorption isotherm model was suitable to N03 adsorption in all and C1 adsorption in some of the soils. Description studies revealed that the amount of C1 desorbed increased with the increasing concentration of N03 in the electrolyte and on the colloidal surfaces. The N03 ion was found to be a better extractant of C1 than the S04 ion which in turn was better than the 0H ion. Adsorption of N03 (except in two soils) and C1 in all the soils increased with increasing pH of the electrolyte solution. This was contrary to the usual observation that anion adsorption increases with decreasing electrolyte pH. Surface preference (anionic competition) study revealed that the soils preferred N03 over C1. The adsorption of N03 increased in the presence of C1 in the mixture and vice versa. Destruction of the soil organic matter prior to equilibration with the electrolyte solutions of different pH values increased the magnitude of N03 adsorption at pH 3.3 and 6.0. However, the adsorption of C1 was decreased by a similar treatment.
Available in print form, East Africana Collection, Dr. Wilbert Chagula Library, Class mark (THS WRE TD365.J67)
Adsorption, Clay (Kaolinite), Clay (allophanates), Tanzania
Parmar, K. H. (1978) Adsorption of nitrate and chloride in some Tanzania soils dominant in allophanic and Kaolinitic clays, Masters dissertation, University of Dar es Salaam. Available at