Pore Transport--Controlled Shrinking-Core Systems Involving Diffusion, Migration, and Homogeneous Reactions: Part II. Application of Model for PbSO4-Carbonate System to Experimental Data

The comprehensive shrinking-core model for the reaction of PbSO4 in alkaline carbonate solutions, formulated in Part I of this article, has been applied to available experimental data. Least-squares analysis was carried out to fit the model to data for the concentration dependence of the parabolic rate constant (kp), using a single adjustable parameter that determines the effective diffusion coefficients of the mobile species in the system. Simulations of the effects of electrolyte composition on kp show good agreement between model predictions and experimental observations. Since the model accounts explicitly for the temperature dependencies of the solution density and the equilibrium constants for the various reactions, it has been possible to reanalyze the available temperature data and obtain the activation energy for transport processes alone. Model calculations of the concentration profiles of the various species provide insight into the rate-controlling mechanism, which is otherwise inaccessible from experiments. A mechanism in which the transport of OH ions through the hydrocerrusite product layer is rate-controlling has been found to be most consistent with the experimental observations and modeled behavior under commonly encountered conditions.