Leaching Kinetics of Sulphates in Acidic Soil

Aims: Present study is concerned about the leaching kinetics of sulphate anions in soil using glass column method.

Study Design: we have focused our attention on the mechanism of solute transport via leaching.

Place of Study: Soil samples were collected from the barren field located in the industrial area near Hapur district

Methodology: The leaching study of sulphate is carried out in the laboratory by using the glass column. During the entire course of study the flow rate of deionised water or salts solution from glass column was maintained at 10±0.2 mL/10 min. Three salts of sulphates Na2SO4, MgSO4 and Al2(SO4)3 were used to study the leaching kinetics of sulphates in soil.

Results: Initial leaching rate profiles are determined for each salt. On increasing [SO42-]i, LRobs values are seen to increase for all sulphate salts. The log-log plots of [SO42-]i and LRobs indicated to be the fractional order in [SO42-]i. The effect of temperature on sulphate leaching was studied in the range 20-50°C. It is clear that total initially leachable content i.e. [SO42-]i increases with the increase in temperature, probably due to the mobilization and leaching of some insoluble sulphate. LRobs values increases with the size of cation. The results can be explained on the basis of covalent character and radii of the hydrated ions. Initial water content or water filled porosity (θ) of the soil column was varied from .33 to .51 cm3 cm-3. LRobs calculated values were found to increase only slightly on increasing initial water content of the soil column. Leached concentration were found time dependent and varied with time as the pore volume of effluent increased with time. The first order kinetics and Elovich model has been found to have excellent correlation for the desorption/Leaching of the sulphate confirmed by SEE and high r2 values. However there is little correlation for the zero order and parabolic profiles.

Conclusion: Present study proves that leaching of sulphate salts can be studied by initial rate method, which can also be applied for monitoring the fate of applied sulphate in agricultural fields and its diffusion into soil solution for plants uptake as well as in calculating the downward transportation of sulphate from polluted site to the underground water.