Kinetics, thermodynamics and mechanisms of phosphate sorption onto bottle gourd biomass modified by (3-chloro-2-hydroxypropyl) trimethylammonium chloride

The sorption kinetics and thermodynamic parameters of phosphate removal from aqueous solution using quaternary ammonium–modified bottle gourd biomass as a sorbent were studied in a batch reactor. The cationic sorbent, containing trimethylammonium and hydroxypropyl groups, was obtained through the chemical reactions of the lignocellulosic Lagenaria vulgaris shell with (3-chloro-2-hydroxypropyl)trimethylammonium chloride. Experimental data of phosphate sorption from aqueous solutions of different initial concentrations (5–140 mg P L−1) have been analysed by reaction kinetics and diffusion models. The characteristic rate constants calculated by linear and non-linear regression analyses of the experimental results are presented. The phosphate sorption reaches equilibrium in 20–30 min, depending on the initial phosphate concentration. The maximum sorption capacity of quaternary ammonium–modified bottle gourd (QABG) sorbent was 18 mg P g−1 at 20 oC. The sorption system is best described by a non-linear equation of the pseudo first-order model (R2 > 0.996). The Weber–Morris model indicated that the sorption process took place in three steps, whereby the intra-particle diffusion is not the only rate-controlling step. In addition, the effect of temperature (20 oC–50 oC) on sorption kinetics was also investigated. The various thermodynamic parameters suggest that phosphate sorption is favoured and is an exothermic process. The activation energy and the sticking probability confirmed that anion exchange is the dominant mechanism. These results provide valuable information for the potential use of agricultural residues in the treatment of wastewaters.