Effect of modification and regulation on physicochemical properties of clinoptilolite, as well as nitrogen and phosphates removal performance

Natural clinoptilolite was modified by NaCl-firing to produce modified clinoptilolite. Afterwards, the modified clinoptilolite was regulated by LaCl3 to produce composite clinoptilolite. Modified clinoptilolite and composite clinoptilolite were used to adsorb ammonia-nitrogen and phosphates from wastewater. The modified clinoptilolite and composite clinoptilolite had high sorption efficiency and removal performance. The ammonia-nitrogen and phosphate removal rate of the modified clinoptilolite reached 96.46 % and the phosphate removal rate of the composite clinoptilolite reached 86.26 %. Furthermore, the structure was characterized by SEM, EDS, XRD, IR, and N2-porosimetry analyses. Results showed that the surface of modified clinoptilolite became loose and some pores appeared, which increased the specific surface area. In addition, total pore volume, micropore area and average pore width increased after modification by NaCl firing and LaCl3 regulation, where in the micropore area exhibited the highest increase. The modification process did not change the overall skeletal structure and structural holes for both the modified clinoptilolite and the composite clinoptilolite. The main components were Si, Al, and O. The Na ion content of the modified clinoptilolite increased from 0.77 % to 2.45 % and the La ion content of composite clinoptilolite increased from 0 % to 2.52 %. The modification and regulation mechanisms were based on the Na+ replace Ca2+ and Mg2+ of clinoptilolite. Hydrous lanthanum oxide could be loaded only to the surface of clinoptilolites. In addition, the ion-exchange capacity of both the modified clinoptilolite and the composite clinoptilolite improved compared with natural clinoptilolite.