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 (C-0), 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, R-2 >= 0.87 and low error function value less than 13.