| has received increasing interest in recent years for its magnetic property and higher surface affinity towards arsenic. In this study, synthesized Fe3O4-HBC composite was utilized as a precursor material to obtain calcined and MnO2modified adsorbents. Consequently, these two kinds of adsorbents were employed for the adsorptive removal of low concentration As(III) and As(V) in aqueous media. Laboratorial batch experiments were conducted to investigate the optimal conditions for arsenic removal and to analyze the adsorption mechanism. Characterization techniques including SEM, XRD and FTIR were used to reveal the textural and mineralogical variation in the adsorbent composite.Higher calcination temperature has great impact on arsenic removal efficiency of Fe3O4-HBC composite, especially at1000℃.However, calcination at low temperature (400℃) has little effect on the adsorbent surface morphology. A sharp decline of arsenic removal efficiency was observed of the adsorbent calcined at1000℃under air. In contrast, the removal efficiency of arsenic was significantly enhanced by the adsorbent calcined at1000℃under nitrogen condition, and the maximum adsorption capacity for As(Ⅴ) and As(Ⅲ) were increased from1.581,1566mg/g to3.297,3.131mg/g, respectively. Furthermore, As(V) and As(Ⅲ) adsorption data fitted well to Langmuir isotherm model.MnO2loaded ratio has an influential effect on arsenic removal efficiency using MnO2-Fe3O4-HBC as adsorbent. The loading ratio as n(Fe3O4):n(MnO2)=3:2performed better than that of n(Fe3O4):n(MnO2)=2:1and n(Fe3O4):n(MnO2)=1:1, respectively. Further analysis of the data revealed that Langmuir isotherm has explained better the performance for As(V) adsorption, while for As(Ⅲ) Freundulich isotherm was found more reasonable.Initial pH is an important factor for As(V) and As(Ⅲ) removal efficiency either using calcined/uncalcined or MnO2modified Fe3O4-HBC as an adsorbent. When the pH ranged4-10than the both As(Ⅴ) and As(Ⅲ) adsorptions remained stable (about 100%) for Fe3O4-HBC-1000oC(N2). Increasing or decreasing pH caused to drop the removal rate significantly. However, both As(V) and As(III) removal efficiencies decreased with the increasing of pH for MnO2-Fe3O4-HBC and the good performance (above90%) was noticed in the pH range (pH≤7).An increased and decreased As(V) and As(III) removal efficiencies were observed for both calcined/uncalcined and MnO2modified Fe3O4-HBC along with the contact time. The concentration of As(V) was decreased from100μg/L to less than1μg/L in6h using Fe3O4-HBC-1000℃(N2). Although in such condition the removal rate of As(Ⅲ) was relatively slow and it reached to3μg/L after10h. Moreover, the application of MnO2-Fe3O4-HBC ensured the concentrations of both As(V) and As(Ⅲ) below10μg/L in6h and that meet the drinking water standard limits set by World Health Organization (WHO). Pseudo-first order and pseudo-second order kinetics models were introduced to fit the kinetics of As(Ⅴ) and As(Ⅲ) adsorption on uncalcined/calcined and MnO2modified Fe3O4-HBC composites. The results showed that pseudo-second order had a better description using these two kinds of adsorbent system rather than the pseudo-first order indicating that the adsorption mechanism is more complex.Furthermore, anions including Cl-, NO3-, SO42-, HCO3-, PO43-in some extent inhibited the adsorption of As(V) and As(Ⅲ). Anions like; Cl-, NO3-and SO42-had little effect on the adsorption of As(V) and As(Ⅲ), while PO43-adversely influenced for As(Ⅴ) and As(Ⅲ) adsorptions on both uncalcined/calcined and MnO2modified Fe3O4-HBC composites. The removal efficiencies of As(Ⅴ) and As(Ⅲ) were significantly decreased with the presences of only0.1mmol/L PO43-in aqueous solution system. |
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