Arsenic binding mechanisms on natural red earth: A potential substrate for pollution control

摘要

Natural red earth (hereafter NRE) was used as a novel adsorbent to examine its retention behaviour in different inorganic arsenic species (As (Ⅲ) and As (Ⅴ)) that are abundant in natural water. Adsorption isotherms were constructed at pH ～ 5.5 for As(Ⅲ) and As(Ⅴ) in 0.01 M NaNO_3 at 298K for 5 g/L NRE system. The initial arsenic [As(Ⅲ) or As(Ⅴ)] concentrations varied between ～ 10~(-5) and ～ 10~(-4) M. The experimental data were quantified using single site or stepwise Langmuir models. Sorption maximum, was observed at ～ 0.173 mM of As(Ⅴ). To reach the maximum surface coverage of red earth at pH ～ 5.5 As(Ⅲ) requires ～ 0.308 mM of initial loading. When compared to As (Ⅲ), As(Ⅴ) shows strong affinity for NRE surface sites. This study suggests the potential of NRE as a starting material in decontaminating water polluted with As species.