Adsorption of arsenite and arsenate onto muscovite and biotite mica

Arsenite and arsenate sorption was studied on two silt-sized phyllosilicates, namely muscovite and biotite, as a function of solution pH (pH 3–8 for muscovite, and 3–11 for biotite) at an initial As concentration of 13 μM. The amount of arsenic adsorbed increases with increasing pH, exhibiting a maximum value, before decreasing at higher pH values. Maxima correspond to 3.22±0.06 mmolkg−1 As(V) at pH 4.6–5.6 and 2.86±0.05 mmolkg−1 As(III) at pH 4.1–6.2 for biotite, and 3.08±0.06 mmolkg−1 As(III) and 3.13±0.05 mmolkg−1 As(V) at pH 4.2–5.5 for muscovite. The constant capacitance surface complexation model was used to explain the adsorption behavior. Biotite provides greater reactivity than muscovite toward arsenic adsorption. Isotherm data obeyed the Freundlich or Langmuir equation for the arsenic concentration range 10−7–10−4 M. Released total Fe, Si, K, Al, and Mg in solution were analyzed. Calculation of saturation indices by PHREEQC indicated that the solution was undersaturated with respect to aluminum arsenate (AlAsO4⋅2H2O), scorodite (FeAsO4⋅2H2O), and claudetite/arsenolite (As4O6).

Graphical abstractArsenite and arsenate sorption onto muscovite and biotite increase with increasing pH, exhibiting a maximum value, before decreasing at higher pH values. Maxima corres pond to 3.22±0.06 mmolkg−1 As(V) at pH 4.6–5.6 and 2.86±0.05 mmolkg−1 As(III) at pH 4.1–6.2 for biotite, and 3.08±0.06 mmolkg−1 As(III) and 3.13±0.05 mmolkg−1 As(V) at pH 4.2–5.5 for muscovite. Biotite provides greater reactivity than muscovite toward arsenic adsorption.Figure optionsDownload full-size imageDownload as PowerPoint slide