Effect of preparation methods on phosphate removal of lanthanum-modified bentonite

Excess phosphate in water can cause eutrophication, resulting in the destruction of water ecosystems. Phosphate removal has become one of the most important issues in wastewater treatment, and the adsorption is one of the important methods. Bentonite has been widely used for phosphate -containing wastewater treatment due to its low cost and large reserve. However, the unmodified bentonite usually has a relatively weak phosphate removal ability because of its negatively charge. Here, the lanthanum-modified bentonites were prepared by three methods (impregnation, acidification- impregnation, and ion exchange) in order to improve the phosphate removal capacity. The structures of the lanthanum-modified adsorbents were characterized and the effects of the modification method and adsorption conditions on the phosphate removal were investigated. The results show that the phosphate removal efficiency of the bentonite was increased after the lanthanum modification. In particular, the lanthanum-modified bentonite prepared by impregnating 0.1 mol & BULL;L-1 La3+ solution has the largest pore size and pore volume, which are 7.4 nm and 0.423 cm3 & BULL;g-1, respectively. This lanthanum-modified bentonite also has the highest phosphate adsorption capacity, which is about 24.9 mg & BULL;g-1 at the optimal working conditions (initial phosphate concentration of 50 mg & BULL;L-1, adsorbent dosage of 2 g & BULL;L-1, temperature of 30 & DEG;C, and pH of 6). The corresponding removal rate is as high as 99.5% in 30 min, while that of the raw bentonite is only about 26.8% in 60 min. The results show that the lanthanum-modified bentonite prepared by impregnation method could be a promising adsorbent for efficient phosphate removal.