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

Abstract

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.

Bottle Gourd (Lagenaria vulgaris) Shell as a Natural, Biodegradable, Highly Available, Cheap, Agricultural by-Product, Miscellaneous Biomass, Ion Exchanger, Biosorbent and Fertilizer

“…At higher temperatures, the process of anions desorption from the biosorbent surface is favored. This fact and a slight decrease in the disorder of the system at the biosorbent/solution interface, confirm ion exchange as the most likely sorption mechanism [58][59][60].…”

“…The complex nature of the sorption process, based on both surface sorption and diffusion within the biosorbent particles, was confirmed by the Weber-Morris model. This model indicated the dominant effect of the boundary layer, which has a direct influence in limiting the overall speed of the sorption process [58][59][60]. Phosphate sorption equilibrium is subject to laws of Freundlich and Sips isotherms, which indicates the complex nature of the sorption process (physical sorption and ion exchange).…”

“…The mutual interaction of sorbed anions represents the accompanying mechanism, which leads to the formation of a multimolecular layer of phosphate on the biosorbent surface. On the other hand, the equilibrium of nitrate sorption is subject to the laws of the Sips and Langmir isotherms, which means that nitrate sorption takes place in a monomolecular layer, on an energetically uniform surface of the biosorbent with a finite number of active binding centers, without mutual interaction and trans-migration of ions on the biosorbent surface [58][59][60]. The corresponding model of phosphate and nitrate sorption on the biosorbent surface is shown in Figure 11.…”