Research progress on treatment of mine wastewater by bentonite composite

Bentonite is widely used in industrial wastewater treatment due to its large reserves and excellent physicochemical properties. In order to further improve the properties of bentonite, natural bentonite needs to be modified before application. The common modification methods of bentonite include thermal activation, acid activation, and microwave activation. In recent years, bentonite composite has been applied to the treatment of the mine wastewater including all kinds of waters influenced by mining activity. In this paper, the main modification methods of bentonite, the preparation methods of bentonite composite materials, and the application of bentonite composite materials in the treatment of the mine wastewater including toxic metals are summarized. Also, these technologies are compared and discussed in depth. All kinds of bentonite calcined at 400 ~ 450 ℃ can better improve the surface area. The structure of bentonite is not damaged, and have enough activity to facilitate the adsorption of organic matter at 400 ~ 450 ℃. The acid concentration of Ca-bentonite acidification process is higher than that of Na-bentonite acidification. The microwave activation method of bentonite has faster reaction rate and better modification effect. The combination of microwave activation and other bentonite activation technologies will significantly improve the activation efficiency. The interlayer spacing of organic bentonite generally increases with the increase of modifier concentration, but it will not increase when the added surfactant dose exceeds the cation exchange capacity of the original bentonite. When the concentration of modifier used in modification is the same, the longer the carbon chain of modifier, the greater the layer spacing of organic bentonite. The magnetic bentonite can adsorb Cu2+, Cd2+, Mn2+, and Cr6+ and can be separated and recovered. The composite of graphene/graphene oxide bentonite can significantly increase the spacing between the bentonite layers, improve the pore structure of the composite obviously, and avoid agglomeration. But the price of graphene is much higher than other adsorption materials, which limits the industrial application of the technology. Investigation and research show that bentonite composites have high removal potential for pollutants in mine wastewater. This paper aims to scientifically summarize and analyze the treatment of mine wastewater with bentonite, and discusses some influencing factors.