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Calcium ion incorporated hydrous iron(III) oxide: synthesis, characterization, and property exploitation towards water remediation from arsenite and fluoride

Ghosh, Abir, Paul, Suparna, Bhattacharya, Sayan, Sasikumar, Palani, Biswas, Krishna, Ghosh, Uday Chand
Environmental science and pollution research international 2019 v.26 no.5 pp. 4618-4632
adsorption, arsenic, arsenites, atomic force microscopy, calcium, chelation, entropy, fluorides, ion exchange, iron, iron oxides, models, pH, phosphates, porous media, remediation, surface area
Calcium ion-incorporated hydrous iron(III) oxide (CIHIO) samples have been prepared aiming investigation of efficiency enhancement on arsenic and fluoride adsorption of hydrous iron(III) oxide (HIO). Characterization of the optimized product with various analytical tools confirms that CIHIO is microcrystalline and mesoporous (pore width, 26.97 Å; pore diameter, 27.742 Å with pore volume 0.18 cm³ g⁻¹) material. Increase of the BET surface area (> 60%) of CIHIO (269.61 m² g⁻¹) relative to HIO (165.6 m² g⁻¹) is noticeable. CIHIO particles are estimated to be ~ 50 nm from AFM and TEM analyses. Although the pH optimized for arsenite and fluoride adsorptions are different, the efficiencies of CIHIO towards their adsorption are very good at pH 6.5 (pHzₚc). The adsorption kinetics and equilibrium data of either tested species agree well, respectively, with pseudo-second order model and Langmuir monolayer adsorption phenomenon. Langmuir capacities (mg g⁻¹at 303 K) estimated are 29.07 and 25.57, respectively, for arsenite and fluoride. The spontaneity of adsorption reactions (ΔG⁰ = − 18.02 to − 20.12 kJ mol⁻¹ for arsenite; − 0.2523 to − 3.352 kJ mol⁻¹ for fluoride) are the consequence of entropy parameter. The phosphate ion (1 mM) compared to others influenced adversely the arsenite and/or fluoride adsorption reactions. CIHIO (2.0 g L⁻¹) is capable to abstract arsenite or fluoride above 90% from their solution (0 to 5.0 mg L⁻¹). Mechanism assessment revealed that the adsorption of arsenite occurs via chelation, while of fluoride occurs with ion-exchange.