Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Civil and Environmental Engineering

Supervisor

Dr. Clare Robinson

Abstract

This work has focused on the kinetic dissolution of the lead (II) carbonate hydrocerussite (Pb3(CO3)2(OH)2) under four pH conditions (7.5, 8, 9, 10), three dissolved inorganic concentrations (DIC; 10, 20, 50 mg C/L), and three initial hydrocerussite concentrations (10, 20, 50 mg/L) in batch experiments. Experiments were performed in at least duplicate to determine total dissolved lead dissolution curves at short time scales (hr.). All equilibrium dissolved lead concentrations were achieved in 40 minutes or less, and matched trends from previous studies; pH 7.5 and pH 10 corresponding to the highest and pH 9 presenting the lowest equilibrium lead concentrations. The formation of cerussite may have interfered with the dissolution reaction at a pH 7.5. The dissolved lead equilibrium concentrations decreased with increasing DIC. All experimental values were within the range of expected equilibrium concentrations predicted by PHREEQC using solubility constants from literature for cerussite and hydrocerussite. The geochemical modelling program PHREEQC was used to speciate total dissolved lead equilibrium concentrations under experimental conditions to determine an approximate solubility product for hydrocerussite of ‑15.98 ± 0.36.

The kinetic dissolution data of total dissolved lead was evaluated by an integral approach. It was found that, in general, the kinetic dissolution rate constant increased with both increasing pH and DIC. The correlations of the kinetic rate constants determined under varying pH, DIC, and initial hydrocerussite conditions was combined into a rate expression which can be used to evaluate the influence of these parameters. This kinetic dissolution expression matched the experimental data very well and can be used to predict total dissolved lead levels.


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