Modified zeolite as a sorbent for removal of contaminants from wet flue gas desulphurization wastewater.

The aim of the present work was to prepare and investigate the sorption efficiency of unwashed cationic surfactant-modified natural zeolite (Cp) for the simultaneous removal of selected inorganic compounds (NH4+, SO42-, NO3-, Fe, Mn, Zn, and Ni) from wet flue gas desulphurization (WFGD) wastewater. The Cp was modified using hexadecyltrimethylammonium bromide (HDTMA-Br) salt in an amount not exceeding its external cation exchange capacity (1.0 ECEC). The present analysis showed that the modification process was completed by forming an incomplete monolayer by the uptaken HDTMA ions. Fourier transform infrared (FTIR) and textural analysis indicated that the adsorbed HDTMA ions formed a disordered, macroporous structure onto Cp surface. Batch adsorption experiments with different sorbent dosages revealed an increase in the sorption efficiency of NH4+ and NO3- with the increase in the amount of modified Cp. The highest removal efficiency was observed at adsorbent dosage of 150 g/L. The studies also revealed, that the SO42- removal did not change significantly regardless the sorbent dosage. The kinetic tests showed that a substantial amount of inorganic compounds was removed within 2 h, and the sorption kinetics of each compound were best fitted to the pseudo-second order model. The studies of adsorption mechanism revealed that cation exchange, anion exchange with Br- counterion, electrostatic interaction between the surfactant and inorganic ions, as well as precipitation of insoluble salts might be involved simultaneously in the immobilization of NH4+, SO42-, NO3-, Fe, Mn, Zn, and Ni.