Lanthanum hydroxide showed best application potential in La-based materials based on its stable phosphate adsorption properties in complex water environments

Abstract

Three lanthanum morphology materials encompassing all lanthanum composites were synthesized by the direct precipitation method, and their phosphate adsorption order was determined as La2(CO3)3 > La(OH)3 > La2O3. Further comparison of the adsorption performance between La2(CO3)3 and La(OH)3 revealed that the former exhibited a twofold higher rate of adsorption compared to the latter. The presence of SO42−, HCO3−, Mg2+, and HA in the water led to a decrease in the phosphate adsorption of La2(CO3)3 and La(OH)3, while Ca2+ enhances the adsorption of phosphoric acid by both materials. Compared to La2(CO3)3, La(OH)3 exhibited stronger resistance against coexisting ions. The pH was the limiting factor for phosphate adsorption in both cases, and their adsorption capacity decreased significantly as the pH increased. The phosphate adsorption mechanism of La2(CO3)3 was ligand exchange to form inner-sphere complexes, while the phosphate adsorption mechanism of La(OH)3 involved ligand exchange, inner-sphere complexation, and electrostatic attraction. The stability of La(OH)3 exhibited superior performance compared to that of La2(CO3)3 over 5 adsorption-desorption cycles. Although La2(CO3)3 had a higher initial phosphate adsorption capacity than La(OH)3, its phosphate adsorption capacity decreased by 40% after five adsorption-desorption cycles, while that of La(OH)3 decreased by 2.3%. Additionally, the amount of La(OH)3 adsorbed after five cycles was 25.6% higher than that of La2(CO3)3. Therefore, La(OH)3 performs better regeneration adsorption than La2(CO3)3. Furthermore, a smaller dosage of La(OH)3 was required compared to La2(CO3)3 in a test aimed at lowering the actual phosphate concentration in water to 0.5 mg/L. In summary, La(OH)3 is a more suitable substrate for cyclic adsorption for phosphorus removal than La2(CO3)3 and has better potential for practical application. In conclusion, La(OH)3 proves to be a more suitable substrate for cyclic adsorption in phosphorus removal compared to La2(CO3)3 and exhibits superior potential for practical application.