Preparation of CaFeAl Layered double hydroxides from polyaluminum chloride residue and adsorption properties of Cr(VI) in water—A new application of a by-product of water treatment reagent production

Polyaluminium chloride as an efficient inorganic polymer water purification material inorganic flocculant which is widely used in China water treatment. About 15% of the waste residue is produced when production of polyaluminium chloride. Traditional treatment technology (landfill or dumping) of waste resiude will cause pollution of non-point source and groundwater. Meanwhile, in the field of water treatment where the polyaluminium chloride are most used widely, drinking water Cr(VI) pollution caused by industrial pollution occurs frequently when the improvement of China’s industrialization. How to remove Cr(VI) pollution in drinking water while increasing the utilization rate of polyaluminium chloride residue has excellent environmental and economic benefits. In this study, the CaFeAl Layered doubled hydroxides was prepared by calcination crystallization method using polyaluminum chloride residue as raw material. The adsorption effect and adsorption mechanism of the new material were characterized. The results showed that the optimal pH value was in the range of 4 to 6; with the increase of adsorbents dosage, the removal rates increased and adsorption capacity decreased of both adsorbents. Based on XRD and SED analyses, the new material not only could provide a larger specific surface area and more active sites, but also could maintain the stability of its structure. According to a comprehensive analysis of the SEM and BET analysis results, the surface area of the new material was almost 6 times higher than polyaluminum chloride residue, which indicated the new material has a high surface area and large pores. The FTIR results could verify the new material has greater adsorption performance and better stability. The second-order adsorption kinetic model and Langmuir adsorption isotherm model could describe the Cr(VI) adsorption process well. The Cr(VI) adsorption by the new material is a spontaneous endothermic process. The regeneration experiment showed that the new material could be regenerated 5 times and maintain a high removal rate, indicating that the material could not only solve the polyaluminium chloride residue problems but also has excellent engineering application potential.