Comparison of the efficiency of modified clinoptilolite with HDTMA and HDP surfactants for the removal of phosphate in aqueous solutions

Clinoptilolite (CP) and its modified forms with two cationic surfactants (HDTMA-Br and HDP-Br) were used to remove phosphate as an important anionic environmental contaminant using batch and continuous methods. The modification was analyzed by FT-IR and DTG characterization techniques. The effects of some interfering anions on the removal extent of phosphate were investigated and more interference was observed by arsenate so the removal extent of phosphate decreased to 0.3 mmol/kg. The removal efficiency of phosphate confirmed that HDTMA-modified zeolite (SMZ-HDTMA) was more efficient than HDP-modified zeolite (SMZ-HDP). ΔG values of −6.4, −9.5 and −12.0 kJ/mol for the raw CP, SMZ-HDP and SMZ-HDTMA, respectively, confirm that the removal reaction of phosphate is spontaneous for the raw and modified sorbents. Results of study of pH showed that stronger basic pHs are suitable for removal of phosphate by the raw and modified adsorbents so the removal efficiencies of 8.1, 376 and 675 mmol/kg were, respectively, obtained for CP, SMZ-HDP and SMZ-HDTMA at pH 12.