THE REACTION OF ANGLESITE (PBSO4) CRYSTALS WITH SODIUM-CARBONATE SOLUTIONS

The reaction of anglesite (PbSO4) crystals with Na2CO3 solutions was investigated using a rotating disk technique. Near-parabolic kinetics, indicative of rate control by diffusion through the progressively thickening product layer formed on the PbSO4, were observed. Surprising is the fact that the rate decreases with increasing Na2CO3 concentrations to 0.7 M, but increases at higher Na2CO3 concentrations. The rate increases systematically with increasing temperature, and the activation energy is 20 kJ/mol in 0.1 M Na2CO3 solutions and 56 kJ/mol in 0.7 M Na2CO3 media. The rate is independent of the disk rotation speed, and similar rates are obtained whether Na2CO3, K2CO3 or (NH4)2CO3 solutions are used. The rate decreases systematically with increasing concentrations of NaCl or Na2SO4. The complex concentration dependencies are related to changes in the composition and porosity of the reaction products formed on the PbSO4 crystals.