Stabilization of soil arsenic by natural limonite after mechanical activation and the associated mechanisms

Arsenic (As) is an environmentally hazardous contaminant which have a serious threat to human health. In recent years, sustainability has drawn increasing attention in the environmental remediation field. Application of natural minerals as a class of iron-containing materials for soil As remediation is meaningful and challenging. In this paper the As sorption ability and soil stabilization of mechanical activated limonite has been studied. Mechanical activation can effectively enhance the adsorption performance of natural limonite. The positive effect of mechanical activation on limonite mainly include: (1) particle size reduction and specific surface area increase; (2) reduction of limonite crystallinity and increase of surface active sites; (3) mineral phase transformation to amorphous iron oxides substances. The average grain size of limonite reduces from 16.8 μm to 0.214 μm after activation while the specific surface area increases from 10.26 m²/g to 56.74 m²/g. The maximum adsorption capacities of mechanically activated limonite (L_m) for As (III) and As (V) were 9.14 mg/g and 8.26 mg/g, respectively at pH 7.0, higher than untreated limonite (L₀). Mechanically activated limonite can effectively stabilize As in soils. When L_m dosage was 10%, the stabilization effects could reach about 78%. Limonite could transform the soil As from non-specifically and specifically sorbed fraction to amorphous iron hydrous oxides bounded fractions. Mechanically activated limonite (L_m) exhibited good adsorption and stabilization performance advantages for As in soils.