Phosphorus fixation in lake sediments using LaCl3-modified clays

Fourteen types of clay, including soils and sediments from Lake Taihu, were modified by LaCl3, and their abilities of phosphorus (P) sorption (the total P up-taken) and fixation (the unleachable P retained in modified clays) were investigated. Results showed that P sorption rates of LaCl3-modified clays were all higher than 90%, while the fixation rates were raised from 3-14% to 52-95%. Kaolinite was selected to study the pH effect on P sorption and desorption of La3+ from the modified clays. In the pH range of 4-8, P sorption on LaCl3-modified kaolinite could reach over 80%, with a maximum of 97% at pH 5. The desorption rate of La3+ decreased with the increase of pH, which was lower than <0.006% at pH > 6.12. This study may provide a solution for internal P pollution from lake sediments.