Removal of diethyl phthalate via adsorption on mineral rich waste coal modified with chitosan

Phthalic acid esters or phthalates in wastewater are priority pollutants and demand efficient method for remediation. Here we present a novel utilization of low grade coal, which is otherwise a waste, modified by chitosan as adsorbent for removal of diethyl phthalate (DEP) via adsorption. A low carbon and high silicate content coal was chosen, characterized by CHN analyzer, energy dispersive X-ray analysis and by X-ray diffraction. A composite of mineral rich coal and chitosan is prepared via electrostatic interaction and hydrogen bonding between the hydroxyl groups of chitosan and the silicate group of coal; confirmed by Fourier transformed infrared spectroscopy, thermogravimetry analysis and zeta potential measurements. An optimized 9:1 weight ratio of coal-chitosan composite exhibited a positive zeta potential value in aqueous medium and corresponded to 91.1% DEP adsorption at an optimized condition e.g., pH 5.8, adsorbent dose of 4 mg/mL and contact time of 4 h. The adsorption is thermodynamically favorable and followed pseudo-second order kinetics, and attributable to chemisorption process, is attributed to electrostatic interaction and hydrogen bonding between the DEP and the functional groups in the composite. The adsorption isotherm data was best fitted non-linearly by Sips isotherm model, which is consistent with Freundlich adsorption isotherm for lower concentration of DEP (5 to 100 mg/L), while Langmuir adsorption was favored for adsorption of higher DEP concentrations (100 to 400 mg/L). The qmax was 42.67 mg/g, which is a significant improvement in DEP sorption from aqueous medium among the readily degradable adsorbents reported so far. The practical application of coal-chitosan composite as adsorbent has been demonstrated by its re-usability and ability for sorption of DEP from spiked municipal wastewater, supported by decrease in chemical oxygen demand value of treated wastewater.