Competitive Adsorption Between Fluoride And Coexisting Ions On Modified-pullulan Absorbent

Aluminum chloride had been used with Mg OP for defluorination to investigate their regulation of the p H of the solution after the treatment. By studying the defluoridation in the presence of aluminum chloride, it can be found that aluminum chloride can have complexation with fluoride under the acid environment, resulting in forming stable precipitation or complex. By contrast, the reaction is likely to be destroyed under the alkaline environment. As p H of aqueous solution rised with the increasing contact time, the complexation weakened. When p H exceeded 6, the part of fluoridate that had complexation with aluminium ions returned to aqueous solution, which caused the slight increase of the concentration of fluoride in aqueous solution.The fluoride adsorption on Mg OP in the presence of aluminum chloride follows Langmuir isotherm and is spontaneous and endothermic in nature. The adsorption rate closely follows the pseudo-second-order kinetic model and can be characterized by the intra-particle diffusion model.When Mg OP was used to treat multi-solutes system, the results show that when the initial concentrations of fluoride and phosphate were both 10 mg/L and the absorbent dose was 2 g/L, the removal efficiencies of fluoride and phosphate were more than 90% and p H of aqueous solution had no effect on fluoride adsorption capacity and phosphate adsorption capacity. The equilibrated time of phosphate adsorption in multi-solutes system was earlier and the capacity of Mg OP had negligible change compared to the single-solute system. By contrast, the adsorption rate of fluoride was influenced by phosphate while the adsorption capacity and the equilibrated time had few changes. In addition, some typical forms of phosphate had a minimal influence on the fluoride adsorption capacity of Mg OP. Moreover, in the multi-solutes system, the adsorption of fluoride on Mg OP follows Langmuir isotherm and is spontaneous and endothermic in nature. The adsorption rate closely follows the pseudo-second-order kinetic model and can be characterized by the intra-particle diffusion model. Additionally the maximum fluoride adsorption capacity and phosphate adsorption capacity were 164.79mg/g and 464.9mg/g respectively. Also, the different order of addition had an effect on the fluoride adsorption capacity and phosphate adsorption capacity.To sum up, Mg OP is effect in adsorption and could be applied to remove fluoride and phosphate simultaneously. In addition, aluminum chloride could improve p H of treated aqueous solution after adsorption. Meanwhile, the experimental results show that in the multi-solutes system when the initial concentrations of fluoride and phosphate are low, the fluoride and phosphate adsorption capacities of Mg OP have no change but the adsorption rates have a little change.