Red mud: Abrief review on conventional and unconventional techniques used to characterize this wastematerial

Red mud (RM) is a waste material derived as a residual from the Bayer process by the caustic digestion of crushed bauxite at an elevated temperature. It is chemically characterized by the presence of Si, Al, Fe, Ca, Ti as well as an array of minor constituents such as Na, K, Cr, Ni, Mn, Cu, Zn and Pb. The mineralogical composition shows the presence of iron oxy-hydroxides (i.e., hematite and goethite) with minor aluminium hydroxides (i.e., boehmite). Calcium oxides, titanium oxides, aluminosilicate minerals and sodalite occur on trace in most samples. However, red mud varies in chemical, mineralogical and also physical properties due to differing ore sources and refining processes employed. In the last few years, the increasing number of aluminum plants caused serious environmental problems due to the increasing amount of RM produced. This waste material is in fact generally disposed in the ground, thus causing soil contamination, as well as ground and surface water pollution. However, due to the increasing problems connected with the RM storage, much research has been developed to inertize this material and to convert it into a new raw material. In all of these contexts, an accurate characterization of the RM takes on a fundamental role. This chapter aims to give a brief review of laboratories, in situ and remote sensing techniques applied to characterize the RM waste materials focusing on both standard and novel methods.