Optimization of Arsenic Removal from Aqueous Solutions Using Amidoxime Resin Hosted by Mesoporous Silica

Abstract

The paper reports on the performances of cross-linked amidoxime hosted into mesoporous silica (AMOX) in the removal of As(III) and As(V). The optimum pH for sorption of As(III) and As(V) was pH 8 and pH 5, respectively. The PFO kinetic model and the Sips isotherm fitted the best the experimental data. The thermodynamic parameters were evaluated using the equilibrium constant values given by the Sips isotherm at different temperatures and found that the adsorption process of As(III) and As(V) was spontaneous and endothermic on all AMOX sorbents. The spent AMOX sorbents could be easily regenerated with 0.2 mol/L HCl solution and reused up to five sorption/desorption cycles with an average decrease of the adsorption capacity of 18%. The adverse effect of the co-existing inorganic anions on the adsorption of As(III) and As(V) onto the sorbent with the highest sorption capacity (AMOX3) was arranged in the following order: H₂PO₄ ^- > HCO₃ ^- > NO₃ ^- > SO₄ ^2-.

Figure 1

Characterization of AMOX composite sorbents: (a) FTIR spectra of SiO₂/PAN22 and of the AMOX1 sorbent; (b) BET isotherm of AMOX composites; and (c) SEM image of the AMOX1 sorbent; mag 500× (the inset image shows the interior morphology of AMOX1; mag. 5000×).

Figure 2

Effect of initial solution pH on the sorption of As(III) and As(V) oxyanions onto AMOX1 (a); streaming potential as a function of pH for the composite sorbents (b); sorption kinetics of As(III) (c) and As(V) (d) oxyanions onto AMOX sorbents fitted by PFO, PSO, and Elovich models; and IPD model fitted on the sorption of As(III) (e) and As(V) (f) oxyanions onto AMOX sorbents. Sorption conditions: sorbent dose 0.010 g; C_i = 100 mg/L; V_sol = 10 mL; pH = 8, for As(III), and 5 for As(V); temp. 22 °C.

Figure 3

Sorption isotherms of As(III) (a) and As(V) (b) onto AMOX sorbents and influence of co-existing anions on the adsorption of As(III) (c) and As(V) (d) onto AMOX3 sorbent.

Figure 4

FTIR spectra of the AMOX sorbent before and after loading with As(III) and As(V).

Figure 5

(a, b, c) Experimental sorption isotherms for the adsorption of As(III) and As(V) fitted by Sips isotherm. (d) Plot of ln K^o vs 1/T for the sorption of As(III) and arsenate oxyanions onto AMOX sorbents.

Figure 6

Reusability of AMOX composites in the removal of As(III) (a) and As(V) (b) as a function of sorption/desorption cycle number: sorption conditions: sorbent dose 1 g/L, pH 8, for As(III), and pH 5 for As(V), temperature 22 °C, contact time 8 h; desorption conditions: elution with 0.2 M HCl (8 h), regeneration with 0.1 M NaOH (6 h).