Testing the Suitability of Red Mud Based Systems as Permeable Reactive Barrier (PRB) Materials

Abstract

This study involved the investigation of using untreated red mud, acid activated red mud and combined acid and heat treated red mud as Permeable Reactive Barrier (PRB) material by firstly equilibrating the different red mud samples alone and in the presence of some local soils, sand and metallic iron with methylene blue (MB) for up to 60 days. The efficiencies of these systems in discoloration of MB as well as their potentials to release iron to solution were evaluated. Secondly, the three red mud samples were equilibrated with distilled water separately for 60 days, the iron released within this period determined and MB was added to the remaining sample solution for duration of 28 days. The discoloration efficiency and released iron were evaluated. These experiments carried out in batch mode (using test tubes) were without agitation, without filtration and all at room temperature. Red mud samples equilibrated directly with MB showed lower discoloration than those pre-equilibrated with water. However, the latter systems showed higher iron release than the former. The presence of soils, sand and metallic iron used significantly enhances the performance of the different red mud samples. Combined acid and heat treated red mud and its systems had best results with high discoloration and almost zero iron release. These results highlight the long term reactivity of different red muds and their different systems, thus, their suitability as PRB material for contaminant removal from polluted water, hence, limiting environmental impacts from red mud disposal.