Synthesis of Lanthanum Modified Titanium Pillared Montmorillonite and Its Application for Removal of Phosphate from Wastewater

In this research, the sodium bentonite clay collected from Ling'an Clay Mines, Zhejiang Province, China, was utilized as a precursor to produce titanium pillared clay by doping with lanthanum, mixed lanthanum/titanium pillared clay (La/Ti-PILC) for the removal of phosphate from wastewater. The Ti-PILC and La/Ti-PILC were characterized with the help of powder X-ray diffraction (XRD). The phosphate adsorption on the PILCs tends to increase with a decrease of pH, maximum adsorption occurred at around pH < 5.0 for Ti-PILC and pH < 6.0 for La/Ti-PILC. The adsorption capacities of the La/Ti-PILC were greater than of the Ti-PILC. The equilibrium adsorption of P on the PILCs could be well described using the Langmuir isotherm, and the kinetics of P adsorption could be well described by both the pseudo-second-order and Elovich models. An increase in La contents in the Mt-complexes could enhance the initial kinetic rate of P adsorption, as suggested by the Elovich models. It was inferred that a great number of La-related active sorption sites have been located on the outer surfaces of the La/Ti-PILC, as indicated by extremely high alpha value in the Elovich model. The adsorption process was spontaneous and exothermic in nature. La/Ti-PILC was successfully tested as an adsorbent for simulating phosphorus wastewater and regenerated for reuse by removing the adsorbed phosphate with NaOH. The present study confirmed that La/Ti-PILC would be one of candidates for phosphate adsorbent.