Competitive Adsorption of Fluoride and Phosphate on MgAl-Co<sub>3</sub> Layered Double Hydroxides

Abstract

Competitive adsorption experiment of fluoride and phosphate on MgAl-CO3 LDHs has been conducted. A series of batch experiments were performed to study the influence of various experimental parameters such as pH, adsorbent dosage and contact time on the adsorption of fluoride and phosphate on MgAl-CO3 LDHs. Three kinetic models have been evaluated in order to attempt to fit the experimental data, namely the pseudo-first order, the pseudo-second order and the Weber and Morris intraparticle diffusion model. The effects of the initial concentration and the addition order of fluoride and phosphate on their adsorption by MgAl-CO3 LDHs were also investigated. The results show that the optimal pH is 4 to 5, adsorbent dosage is 2 g/L and it takes about 2 hours to attain equilibrium. It was found that the pseudo-second order most closely describes the kinetics. The initial concentration and the addition order of fluoride and phosphate influence the adsorption of fluoride to a certain extent, but they have relatively small influence to the adsorption of phosphate on MgAl-CO3 LDHs.