Removal and stabilization of As and Cd in water/soil using silicate-supported nano zero-valent iron composites: Preparation, behavior, mechanism and cost analysis

Abstract

A novel silicate-supported nano zero-valent iron composite material (nZVI@SS) for the removal and stabilization of arsenic (As) and cadmium (Cd) in water/soil had been developed through the modification of low-grade oolitic iron ore (OI) by reduction, while refinery sludge (RS) as reductant, manganese carbonate (MC) as additive in this work. The As and Cd adsorption capacity of nZVI@SS reached 93.91 mg·g−1 and 265.81 mg·g−1, respectively. Its specific surface area and pore volume increased by 19.28 m2·g−1 and 0.24 cm3·g−1, respectively when compared with unmodified OI. In the actual soil leaching process, using 2 % nZVI@SS for 30 days, the leaching concentrations of As and Cd decreased by 87.86 % and 85.51 % respectively, while their bioavailable contents were reduced by 15.59 mg·kg−1 and 1.40 mg·kg−1, correspondingly. The formation of chemical precipitates as Fe-As, Ca-As compounds, and Cd(OH)2 was the main mechanism of their adsorption process. Therefore, HMs adsorbed by nZVI@SS were difficult to desorb, making it more suitable for passivation/stabilization of HMs in groundwater/soil. Furthermore, the production cost of nZVI@SS was approximately 50 $/T, below the average market value of comparable adsorption materials. This method made low-grade minerals into environmentally friendly materials with high added value, significantly reduced the environmental risk of HMs in water/soil, and provided a new approach for the development of sustainable environmentally friendly materials using hazardous waste RS as a resource.