Enhanced Adsorption of Trivalent Arsenic from Water by Functionalized Diatom Silica Shells

Abstract

The potential of porous diatom silica shells as a naturally abundant low-cost sorbent for the removal of arsenic in aqueous solutions was investigated in a batch study. The objective of this work was to chemically modify the silica shells of a diatom Melosira sp. with bifunctional (thiol and amino) groups to effectively remove arsenic in its toxic As(III) form (arsenite) predominant in the aquatic environment. Sorption experiments with this novel sorbent were conducted under varying conditions of pH, time, dosage, and As(III) concentration. A maximum adsorption capacity of 10.99 mg g-1 was achieved within 26 h for a solution containing 12 mg L-1 As(III) at pH 4 and sorbent dosage of 2 g L-1. The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume. As(III) adsorption was best fitted with the Langmuir-Freundlich model, and the adsorption kinetic data using pore surface diffusion model showed that both the external (film) and internal (intraparticle) diffusion can be rate-determining for As(III) adsorption. Fourier transform infrared spectroscopy (FTIR) indicated that the thiol and amino groups potentially responsible for As(III) adsorption were grafted on the surface of diatom silica shells. X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups. Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

Abstraction of arsenic(III) on activated carbon prepared from Dialium guineense seed shell: kinetics, isotherms and thermodynamic studies

“…The mostly available forms of As in water are the inorganic species arsenate [As(V)] and arsenite [As(III)]. The As(V) species occurs as oxyanions (H 2 AsO 4 − and HAsO 4 2− ) at neutral pH, while the arsenic(III) species is neutral H 3 AsO 3 [1][2][3]. As(III) is more toxic and more difficult to remove by physico-chemical treatment than As(V) [4].…”

Production and Characterization of a Bioflocculant Produced by Bacillus salmalaya 139SI-7 and Its Applications in Wastewater Treatment

“…Bioflocculants such as diatom silica shells and Arthrobacter spp. biomass are applicable in removing heavy metals, including arsenate, from wastewater [ 6 , 7 ]. Bioflocculation is considered an active process caused by living cells due to the production of exopolymeric macromolecules.…”

Review on Biosorption of Arsenic From Contaminated Water

“…In addition, thermodynamically decreased randomness at the solid–solution interface was indicated by the negative value of S (−92.20 ± 1.42 kJ mol −1 K −1 ) and the adsorption process was found to be exothermic in nature due to H values (−35.31 ± 0.44 kJ mol −1 ). Collectively, all of these results suggested that the mechanism mainly responsible for the adsorption is chemisorption . The thermodynamics data of As using copper(II) oxide nanoparticles suggested that the process was feasible, spontaneous and endothermic in nature with H = 120.78 kJ mol −1 which falls in the physicochemical adsorption process range .…”

“…The Sips model can be expressed as shown in Eq. : where q m is the monolayer adsorption capacity of the sorbent (mg g −1 ), K LF (L mg −1 ) 1/b is the Langmuir–Freundlich constant, and b (dimensionless) is the Langmuir–Freundlich heterogeneity constant . For adsorption of As(III) on modified diatom silica shells, this model was found to fit best with the experimental data ( R 2 = 0.94–0.99).…”