Surface acid–base characteristics of natural manganese mineral particles

In this paper, the acid–base characteristics of natural manganese mineral collected from Guangxi Province, China, are investigated by potentiometric titration and solubility experiments. The constant capacitance surface complexation model is used to interpret experimental data. The calculations are performed with the least-squares FITEQL program 2.0. All the model parameters are determined on the base of the experimental data. This study indicates that the proton reactions in the acidic blank can be successfully described by those of Mn2+ in solution. To explain the surface acid–base behavior of manganese mineral particle, two protonation models are proposedModel I: MnOH2+↔MnOH+H+, Ka1int=3.52&0xFFFD;3.60MnOH↔MnO−+H+, Ka2int=4.04&0xFFFD;4.88Model II: MnOH↔MnO−+H+, Kaint=5.06–5.62Optimization results indicate that these two models can simulate the experimental results very well. The applicability of the constant capacitance model (CCM) in describing the surface reaction of natural manganese mineral is further verified.