Effects of salts on phosphorus adsorption in alkalize Tunisian soil

Many previous studies have been conducted in an attempt to determine phosphorus (P) adsorption in soil. Often, these studies cannot be compared, because the reports did not give a satisfactory characterization of the dynamics of soil P in saline conditions. In our experiment, three salts extracts (CaCl2, NaCl and KCl) with the same concentration (0.01 M) were used to determine the amount of P adsorption in Solonetz soil samples of the semi-arid areas of Kondar region (Tunisia). Also, we focused on the influence of contact time on P-Salts adsorption in the alkalize soil. The analytic data were approached from the following kinetics' models: pseudo first order, pseudo second order and Elovich model. Results obtained showed that salts addition increased significantly the amount of P adsorption with the following order of salts extracts (P-CaCl2 > P-NaCl > P-KCl > P). The mechanism of phosphate ions adsorption by soil was studied using IR spectroscopy. Infrared spectral characteristics of the amorphous material indicated that the adsorption is due to exchange phenomena of phosphate ions with surface groups. It was also demonstrated that the addition of CaCl2 salt caused a shift and an increase of OH, Si-O (Si-O-Si, Si-O-Al) and Al-OH absorption bands which favored the adsorption of P ions. Moreover, the second-order model was shown to be the best fit for describing phosphorus adsorption associated with different salts, as seen from the correlation coefficient R2 which ranged from 0.98 to 0.99.