Removal of humic acid from water by adsorption onto dodecyltrimethylammonium bromide-modified zeolite in a fixed bed reactor

Modification of natural zeolite (NZ; mordenite) surface by a surfactant, dodecyltrimethylammonium bromide (DTAB), was characterized and employed for the removal of humic acid (HA) from water using a fixed bed column. The optimum loading of surfactant was later utilized in adsorption studies. X-ray diffraction spectrum (XRD), Fourier-transform infrared spectrometry (FTIR), nitrogen adsorption–desorption isotherms and Brunauer–Emmett–Teller specific surface area, field emission scanning electron microscopy, and thermographic analysis and derivative thermographic analysis (TGA–DTA) were used to study the surface properties of the NZ and surfactant-modified zeolite (SMZ-DTAB). The effects of a variety of experimental conditions, such as the flow rate (Q), initial HA concentration (C0), and bed depth (Z), were studied. Optimization studies demonstrated that the SMZ bed with DTAB loading of 150% of ECEC (SMZ-DTAB-150%) exhibited enhanced adsorption performance compared to NZ. An insight of the adsorption mechanism of SMZ-DTAB-150% proved that a monolayer formation is the main viable packing that allows maximum removal of HA. HA adsorption on SMZ-DTAB surfaces is largely a result of the hydrophobic interaction and hydrogen bonding. The adsorption data were utilized on two well-established fixed bed adsorption models, namely Thomas and Adam–Bohart. The results fitted well for Thomas model for the description of whole breakthrough curve with correlation coefficient, R2 ≥ 0.87 and low error function value less than 13.