Effect of La-Modified Zeolite on Phosphate Sorption of Taihu Lake Sediments

Through batch sorption tests, effect of La-modified zeolite (LMZ) on phosphate sorption of Taihu Lake sediments was investigated. Langmuir and Freundlich equations were found to be quite useful to describe sorption equilibrium of phosphate (1-15 mg•L^-1 in concentration) on Taihu Lake sediments in the lake. According to the Langmuir isotherm model, the maximum phosphate sorption capacity of the original Taihu Lake sediment was 791 mg•kg^-1, and that of the Taihu Lake sediments amended with 10, 25 and 50 g•kg^-1 LMZ was 937, 1 037 and 1 505 mg•kg^-1, respectively. The pseudo-second-order model could be used to describe phosphate sorption kinetics of the Taihu Lake sediments in the lake. The phosphate sorption capacity of the Taihu Lake sediments decreased with increasing solution pH. The sorption of phosphate on the Taihu Lake sediments was a spontaneous endothermic process. The phosphate adsorption/desorption equilibrium concentration of the Taihu Lake sediments amended with 10-50 g•kg^-1 LMZ was 0.129 - 0.241 mg•L^-1, which wase much lower than that of the original Taihu Lake sediments (0.386 mg•L^-1).The phosphate adsorption/desorption equilibrium concentration of the LMZ-amended Taihu Lake sediments decreased with increasing LMZ dosage. Sequential extractions of phosphorus from phosphate-sorbed original Taihu Lake sediments and LMZ-amended Taihu Lake sediments indicate that most of the phosphate adsorbed by LMZ in the sediments existed in the forms of NaOH-P and HCl-P, which are quite stable and unlikely to get released under anaerobic conditions.