Removal of strontium(II) ions by potassium tetratitanate whisker and sodium trititanate whisker from aqueous solution: Equilibrium, kinetics and thermodynamics

Removal of strontium(II) ions from aqueous solutions by potassium tetratitanate whisker (PTW) and sodium trititanate whisker (STW) was studied by the batch sorption system. Both PTW and STW possessed special lamellar structure, high surface area and strong ability for cation exchange which were all benefit for the sorption process. The batch mode sorption experiments with respect to different pH, ionic strength, temperature, initial concentration and contact time were investigated. The sorption capacity of PTW and STW were both increased with increasing pH, temperature and initial concentration of strontium(II) ions. Moreover, the sorption capacity of STW was more sensitive to the ionic strength than that of PTW. The Langmuir model represented a better fit to the experimental data than Freundlich isotherm model, and the monolayer sorption capacity of PTW was higher than that of STW at the same conditions. The kinetic data were well fitted to the pseudo-second-order kinetic model and the ion-exchange model was important only in the fist 30 min. Intraparticle diffusion increased with the increase of temperature and initial concentration. Three distinct steps were involved in the strontium(II) ions sorption onto PTW and STW, and the whole sorption processes were controlled by the film diffusion. The thermodynamic parameters (positive values ΔG°, ΔH° and ΔS°) confirmed the non-spontaneous, endothermic and entropy gained nature within the temperature range evaluated.

Research highlights▶ PTW and STW mainly possessed mesopores, high surface area and big pore volume which were both benefit for the sorption capacity. ▶ The sorption properties such as equilibrium, kinetics and thermodynamics were demonstrated by batch mode sorption experiments. ▶ The ionic strength in the solution significantly affect the adsorption behavior. ▶ The ion-exchange model and the variation in solution pH were investigated. ▶ The intraparticle diffusion plots multi-linearity indicated that three steps were involved in the Sr2+ sorption. ▶ The intraparticle diffusion, pore diffusion, film diffusion in the processes of Sr2+ sorption onto PTW and STW were studied.