Removal of phosphate and ammonium from aqueous solution by lanthanum modified zeolite

Abstract:

In this study, lanthanum modified zeolite (LaMZ) was used as an adsorbent to remove phosphate and ammonium from aqueous solution. The effects of various parameters such as adsorbent dosage, solution pH, reaction time, initial adsorbate concentration, temperature, ion strength and coexisting ions on the removal of phosphate and ammonium by LaMZ were investigated using batch experiments. Results showed that LaMZ was effective for the removal of phosphate and ammonium from aqueous solution. The kinetic studies showed that the adsorption of phosphate and ammonium onto LaMZ could be described by a pseudo second order kinetic model. The equilibrium adsorption data of phosphate on LaMZ fitted well with the Langmuir isotherm model, and the equilibrium adsorption data of ammonium on LaMZ fitted well with the Langmuir, Freundlich and Dubinin Radushkevich isotherm models. The thermodynamic studies revealed that the adsorption of phosphate and ammonium on LaMZ was spontaneous and endothermic process. The phosphate adsorption capacity for LaMZ decreased gradually with increasing pH from 3 to 10, but decreased greatly with increasing solution pH from 10 to 12. The ammonium adsorption capacity for LaMZ was relatively high at pH 3-8, but decreased with increasing solution pH from 8 to 12. The presence of coexisting anions such as Cl^-, HCO₃^- and SO₄^2- had negligible influence on phosphate removal by LaMZ. Coexisting Mg²⁺ had negligible influence on ammonium removal by LaMZ, but coexisting cations such as K⁺, Na⁺ and Ca²⁺ had negative influence on ammonium removal by LaMZ. The main mechanisms for phosphate removal by LaMZ include electrostatic interaction, ligands exchange and Lewis acid base interaction depending on solution pH. The main mechanism for ammonium removal by LaMZ is cation exchange.