Removal of endosulfan from water by municipal waste incineration fly ash-based geopolymers: Adsorption kinetics, isotherms, and thermodynamics

Abstract

Alkali-activated municipal waste incineration fly ash (MWFA)-based geopolymers (GPA, GPB, and GPC) were synthesized under different sodium silicate to sodium hydroxide (SS/SH) ratios. The geopolymers were applied in the removal of endosulfan, a persistent and toxic chemical, from water. The adsorbents were characterized by XRD, SEM-EDX, and FTIR. Variation of SS/SH ratios resulted in morphologically distinguishable geopolymers with different compositions. The adsorption equilibrium data were best described by the Langmuir isotherm. The maximum adsorption capacities increased with an increase in SS/SH ratios in the order 1.87, 15.89, 16.97, and 20.01 mg/g for MWFA, GPA, GPB, and GPC, respectively. The kinetic data were best described by the pseudo-first-order model wherein the adsorption rate (k1) was independent of the SS/SH ratios and the geopolymer composition. The thermodynamic parameters, that is, enthalpy (∆H > 0), Gibbs free energy (∆G < 0), entropy (∆S > 0), and activation energy (Ea > 0), show that the processes were endothermic, spontaneous, physical (Ea and ∆H < 40 kJ/mol), and entropy-driven. Alkalination was beneficial since the geopolymers had a higher adsorption capacity (∼8–10 times) and affinity for endosulfan (∼30 times) than the precursor material (MWFA). The adsorption mechanism entailed electrostatic interactions and hydrogen bonding. The MWFA-based geopolymers are, therefore, potential alternative low-cost adsorbents for the removal of endosulfan from water and a strategy for the valorization of MWFA.

Synergistic co-adsorptive removal of crystal violet and chromium(vi) from water by pozzolan-charcoal based geopolymer composites

“…1 The aluminosilicate sources preferentially used can be natural (volcanic slag, pozzolana, metakaolin, pumice, and laterite), industrial (fly ash, blast furnace slag, and dolochar) 2,3 or ashes derived from incineration of solid wastes. 4 Surface properties such as specific surface area, cation exchange capacity and functional group identities and distribution make geopolymers excellent low-cost emerging adsorbents for the removal of dyes, toxic metals, personal and pharmaceutical care compounds (PPCCs) and surfactants from wastewater. 5 Dyes and heavy metals constitute a prevalent class of water pollutants.…”

“…21 Additionally, geopolymers are known to be better adsorbents than their precursors. 4,13,15,16,23 While the use of coal powders (CPs) as adjuvants in the synthesis of geopolymers is hypothesized to reduce accessibility of CV to the acidic sites, the resultant antagonistic or protagonist effect in the binary elimination of anionic Cr(VI) is also unknown. Furthermore, while adsorption capacities at equilibrium of adsorbents in binary systems have been evaluated, adsorption kinetics/rates in binary systems are seldom evaluated.…”