Bauxite residue characterization results. (a) Aqua regia digestion - ICP-OES results indicating REEs composition. (b) XRF elemental composition. Error bars represent the standard error of the mean for ten replicates (c) X-ray diffractogram. (d) BSE image of the bauxite residue particle; bright spots are the high atomic number REEs. (e–l) STEM image and EDS elemental mapping of the bauxite residue particle.