Kinetics of Phosphate Interaction with Very Fine Chromic Haplustert Soil

The kinetics of phosphate interaction with very fine chromic Haplustert soil could be-described by two simultaneous second order reactions. The initial phosphate interaction was ascribed to heterogeneous nucleation of calcium phosphate mineral on the soil surface. The second reaction was interpreted to be associated with amorphous precipitation of calcium phosphate over the nucleated sites. The initial heterogeneous nucleation of octocalcium phosphate on soil surface involved higher amount of activation energy (8.1 k cal mol⁻¹) and enthalpy of activation than the amorphous precipitation process. Higher entropy of activation for heterogeneous nucleation than amorphous precipitation indicates greater specificity pinhosphate anion for the former than the latter process. Free energy of activation for the interaction of phosphate is similar for the both the processes.