KTO is a double salt of OA and KHO and comprises two moles of\(\mathrm{C}_{\mathrm{2}}\mathrm{O}_{\mathrm{4}}^{2\mathrm{-}}\) per mole of KTO. Hence, 0.25 M KTO (0.50 M\(\mathrm{C}_{\mathrm{2}}\mathrm{O}_{\mathrm{4}}^{2\mathrm{-}}\)) was used to perform the Al and Fe extraction from NIST SRM 600 bauxite at a 15 g/L S/L ratio. In the KHO study, no significant difference was observed in the rate of metal extraction at higher\(\mathrm{C}_{\mathrm{2}}\mathrm{O}_{\mathrm{4}}^{2\mathrm{-}}\)concentration due to essentially the same pH; therefore, only 0.25 M KTO was studied in detail. In Figure 1a and 1b, the 0.50 M\(\mathrm{C}_{\mathrm{2}}\mathrm{O}_{\mathrm{4}}^{2\mathrm{-}}\)concentration led to an efficient extraction of Fe and Al using 15 g/L S/L ratio of ore; therefore, a higher S/L ratio of 20 g/L with 0.25 M KTO was attempted, as shown in Figure 1c. The Al and Fe extraction kinetics for 20 g/L was slower in comparison to 15 g/L experiments because of the decreased concentration of\(\mathrm{C}_{\mathrm{2}}\mathrm{O}_{\mathrm{4}}^{2\mathrm{-}}\) per metal ion. However, greater than 95% of Al and Fe was extracted in 2.5 h at 20 g/L S/L ratio, which makes this process energy-efficient. An important observation was the rates of Al extraction for OA, KTO, and KHO at the 0.50 M\(\mathrm{C}_{\mathrm{2}}\mathrm{O}_{\mathrm{4}}^{2\mathrm{-}}\)concentration were similar (Figure 1d), which confirms the negligible effect of pH on Al extraction kinetics. To understand this phenomenon in more detail, ore was digested in 0.50 M K₂C₂O_4, and no Al extraction was observed, confirming the importance of acidity to initiate the extraction. The elemental composition shown in Table 2 after the extraction experiments indicates less than 10% of Al and 2% of Fe remain in the solid residue. The typical mass of solid residue recovered was 2.5 g from 15 g of ore digested in 1 L of acid. From the elemental composition of the ore and remaining solid residue shown in Table 2, it can be seen that in addition to Al and Fe, some other metals such as Zr and Mg are also leached into the aqueous phase. The residues recovered in the experiments shown in Figure 1a-1d were also confirmed using PXRD to be primarily quartz (SiO₂). The PXRD patterns for the NIST SRM 600 and the solid residues from the bauxite digestion using 0.50 M OA, 0.50 M KHO, and 0.25 M KTO are shown in Figures S1 and S2, respectively.