Surface complexation modeling of uranyl ion sorption on mesoporous silica

Sorption of uranium on MCM-41 was studied as a function of pH, time, [U(VI)] and [CO32−]. In the absence of carbonate the sorption edge occurs at pH 2 and the percentage sorption increased to 95% when the pH of the solution is 6. Further increase in pH results in complete sorption (99%) of uranium. In the presence of carbonate the percentage sorption decreased from 94 to 75% when the pH was varied from 6 to 11. The acid–base property of MCM-41 was investigated by titration of the sorbent with HNO3/NaOH at constant ionic strength. Three surface complexation models, namely, the constant capacitance model (CCM), diffuse layer model and non-electrostatic chemical equilibrium model (CEM) were employed to simulate the amphoteric behaviour of MCM-41 and uranium sorption on it. Various model parameters used for describing the sorption property of the sorbent were obtained from the non-linear regression of the experimental data. The sensitivity analysis and goodness-of-fit indicated that only CEM and CCM could be used to the description of the experimental data.