Adsorption Performance Of Cerium Hydroxide For Phosphate

Cerium hydroxide was characterized by thermogravimety (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and other methods. The TG analysis revealed that the weight loss of cerium hydroxide was ended at600℃, and the rate of weight loss is17.9%. It can be confirmed that the molecular formula of cerium hydroxide is Ce(OH)4, contrasted with the theoretical weight loss rate, which is17.3%. The SEM images showed that the surface of cerium hydroxide is rough and macroporous. For cerium hydroxide, there was a Ce-O characteristic adsorption peak at the wavenumber of523.14cm-1.Cerium hydroxide has been used for phosphate adsorption from aqueous solutions as adsorbent, and the effects of dosage of cerium hydroxide, pH of the aqueous solutions, initial concentration of phosphate, temperature of experiment and adsorption time were investigated. Through the orthogonal experiment design of L25(55), the optimum experimental conditions were determined that the pH of phosphate solution is3, the initial concentration of phosphate is200mg·L-1, the dosage of lanthanum oxide is0.1g and the temperature of experiment is25℃. On this basis, the effect of co-existing anions, such as Cl-, SO42-, NO3-and CO32-, was studied, and the results indicated that the effect of co-existing anions is insignificant.The kinetic analysis showed that the process of phosphate adsorption on cerium hydroxide could be well described by the pseudo-second-order model. Meanwhile, the adsorption process was fitted better by the Langmuir adsorption isotherm model, and it explained that the process is monomolecular layer adsorption. The thermodynamics studies showed that Gibbs free energy is less than zero (△G0<0) and adsorption enthalpy is greater than zero (△H0<0), which indicated the phosphate adsorption onto cerium hydroxide is a spontaneous and endothermic process.The desorption experiments was performed in NaOH solution (6mol·L-1) and ammonia liquor, and the results showed that the desorption effect of NaOH solution was better than ammonia liquor, and the maximum desorption rate is70.1%.In order to research the mechanism of phosphate adsorption, cerium hydroxide was calcined at100℃,200℃,300℃,400℃,500℃and600℃, and adsorption experiments were performed with the calcined products. Through the fit linear of experiment data, the relation between calcination temperature and adsorption capacity was obtained:q=116.12402-0.20796T. The chemical composition of calcined products was calculated respectively according to the pattern of Ce02-0.5x(OH)x based on TG analysis. The results indicated that the calcined products at different temperature are in the state between Ce(OH)4and CeO2, moreover, the relation between calcination temperature and the number of hydroxyl group was x=5.88614-0.00693T, meanwhile, the relation between the number of hydroxyl group and the adsoption capacity was acquired, as the eqation q=2.35049+29.4831x, which were obtained with linear fitting. The results indicated that the number of hydroxyl group and the adsorptive capacity of cerium hydroxide decreased with the calcination temperature increasing, furthermore, hydroxyl group plays an important role in the process of phosphate adsorption by cerium hydroxide.