Abstract
<title>Abstract</title> <p>The chemical characterization of highly alkaline bauxite residue (red mud) the primary industrial byproduct of the Bayer alumina process presents a severe analytical bottleneck due to its complex, refractory matrix comprising elevated concentrations of iron oxides (Fe₂O₃), titanium dioxide (TiO₂), unextracted alumina, and a highly resilient framework of silicates (SiO₂). This study demonstrates an advanced, orthogonal methodology combining closed-vessel multi-acid microwave dissolution with high-sensitivity Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Suppressed Ion Chromatography (IC). Complete breakdown of the mineral boundaries and siliceous lattices was achieved using a Milestone ETHOS EASY system operating at temperatures up to 220°C and pressures up to 40 bar. Free fluoride ions (F⁻) generated from hydrofluoric acid (HF) digestion were successfully masked using a boric acid (H₃BO₃) complexation mechanism, ensuring safety for quartz sample introduction components and avoiding precipitate-induced analyte loss. Trace Rare Earth Elements (REEs: Sc, Y, La, Ce, Pr, Nd) were quantified using an ICP-MS collision/reaction cell (CRC) pressurized with helium gas to minimize matrix-derived polyatomic spectral overlaps. Orthogonally, soluble inorganic structural anions (F⁻, Cl⁻, Br⁻, PO₄³⁻, SO₄²⁻) were quantified via electrochemical suppressed IC. The analytical methods demonstrated excellent linearity (R² > 0.999) over the target calibration ranges (100–600 ppb for ICP-MS and 100–500 ppm for IC). This dual-instrumental approach offers an efficient, robust framework for trace elemental monitoring and ionic speciation in complex industrial metallurgical matrices.</p>