A Comparison Study on the Arsenate Adsorption Behavior of Calcium-Bearing Materials

Abstract

The calcium-bearing adsorbents are widely used in the treatment of arsenic-containing wastewater due to their excellent treatment effect and economy. In order to obtain high-efficient adsorbents for arsenate (As(V)) removal, the adsorption behavior of calcium oxide (CaO), calcium fluoride (CaF₂) and calcium carbonate (CaCO₃) on As(V) in aqueous solution at different concentrations were explored. The adsorption mechanism was also explored based on surface characteristics: morphology, specific surface area, as well as their effective calcium content. Not only that, the chemical stability of these materials was further studied. Results exhibited that the As(V) removal capability of these materials is in the following order, CaO > CaF₂ > CaCO₃. When CaO served as an absorbent, As(V) with initial concentration of 0.2 mg/L can be reduced to 0.383 × 10^-3 mg/L in 10 min. Moreover, the capabilities of CaO, CaF₂ and CaCO₃ for removing As(V) are positively correlated with their effective calcium content in aqueous solution, which provide the basis for selecting calcium-bearing materials with excellently comprehensive properties for the field of As(V) removal in aqueous solution. What's more, all three materials exhibit great chemical stability after adsorption of As(V).

Keywords: As(V); adsorption mechanism; adsorption properties; calcium-bearing materials.

Figure 1

(a) Thermogravimetric analysis (TGA) curve of CaCO₃, (b) and (c) X-ray diffraction (XRD) patterns of CaO and CaCO₃ at different two-theta testing angle ranges of 5–80° and 38–45°.

Figure 2

Arsenate (As(V)) adsorption capacities of three calcium-bearing materials at the As(V) initial concentration of 0.2 mg/L and 30 mg/L. (The dosage of calcium-containing materials was 10 g/L, the adsorption time was 24 h, the pH value of aqueous solution was 7, and the reaction temperature was 25 °C.)

Figure 3

As(V) adsorption capacities of three calcium-bearing materials as function of adsorption time at (a) 0.2 mg/L and (b) 30 mg/L. (The dosage of calcium-containing materials was 10 g/L, the pH value of aqueous solution was 7, and the reaction temperature was 25 °C.)

Figure 4

SEM images of (a) CaO, (b) CaF₂ and (c) CaCO₃.

Figure 5

N₂ adsorption and desorption isotherms of three calcium-bearing materials.

Figure 6

The XRD patterns of (a) CaO, (b) CaF₂ and (c) CaCO₃ before and after adsorption of As(V).