Beneficiation of rare‑earth oxides from manganese ores can deliver a commercially viable concentrate (typically 30–45 % RE₂O₃) with recovery rates of 70–90 % while simultaneously upgrading the manganese feedstock for steelmaking. The key to achieving this performance lies in a staged combination of physical separation (gravity, magnetic and electrostatic techniques) followed by selective leaching and solvent‑extraction polishing. Recent pilot‑scale work on lateritic manganese deposits in China, Brazil and India has demonstrated that, when the process is tuned to the mineralogical associations of the light‑ and heavy‑rare‑earth elements (LREEs and HREEs), the overall economics become competitive with dedicated rare‑earth mines, especially when the manganese product is sold as a high‑purity ferro‑manganese alloy. The integrated approach also reduces the volume of tailings, lowers acid consumption, and mitigates the environmental footprint of both manganese and rare‑earth production.
1. Mineralogical context and the need for beneficiation
Manganese ores are predominantly composed of oxides (e.g., pyrolusite MnO₂, hausmannite Mn₃O₄) and silicates (e.g., rhodochrosite, braunite). In many lateritic and sedimentary deposits, REEs are hosted in the same fine‑grained oxide matrix, either adsorbed on Mn‑oxyhydroxide surfaces or incorporated into interlayer sites of birnessite‑type MnO₂. Studies on the Bayan Obo‑type laterite in Inner Mongolia reported total RE₂O₃ contents of 0.12–0.35 % (Zhang et al., 2019), while the Brazilian Carajás laterite contains 0.08–0.22 % RE₂O₃ (Gonçalves et al., 2021). Because the REE distribution is heterogeneous and often associated with Fe‑oxyhydroxides, a simple bulk leach would dissolve large quantities of manganese and iron, leading to low selectivity and high reagent consumption. Therefore, a pre‑concentration step that separates the REE‑bearing fine fraction from the bulk Mn‑oxide is essential..jpg)
2. Physical pre‑concentration
Gravity separation exploits the density contrast between Mn‑oxides (ρ ≈ 4.8–5.0 g cm⁻³) and REE‑bearing silicates or phosphates (ρ ≈ 2.5–3.2 g cm⁻³). Spiral classifiers and shaking tables have been shown to recover 55–65 % of the REE mass in the light‑fraction while delivering a coarse manganese concentrate of > 80 % MnO (Miller et al., 2020).
Magnetic separation is effective because many REE‑bearing phases (e.g., monazite, xenotime) are weakly paramagnetic, whereas Mn‑oxides are strongly ferrimagnetic. High‑intensity wet high‑gradient magnetic separators (HGMS) operating at 2 T can achieve a REE enrichment factor of 3–4 in the non‑magnetic tail (Li & Wang, 2022).
Electrostatic separation further refines the product by charging the fine particles; the less conductive REE‑rich fraction is attracted to the opposite electrode, achieving an additional 10–15 % REE mass gain (Kumar et al., 2023). The combined cascade (gravity → magnetic → electrostatic) typically yields a 2–3 wt % RE₂O₃ concentrate from an ore that originally contained < 0.3 % RE₂O₃.
3. Selective leaching and solution purification
After physical enrichment, the REE‑rich fraction is subjected to a selective acid leach. A dilute sulfuric acid (0.5–1.0 M) at 80–90 °C for 30–45 min dissolves > 85 % of the REEs while leaching < 20 % of Mn²⁺ (Zhang & Zhou, 2020). The selectivity stems from the higher solubility product of REE‑sulfates compared with MnSO₄ under these conditions. In some cases, a carbonate‑buffered leach (0.2 M Na₂CO₃ + 0.1 M H₂SO₄) is employed to suppress Mn dissolution further, achieving REE recoveries of 92 % with Mn losses below 5 % (Silva et al., 2022).
The leachate is then clarified and passed to a solvent‑extraction circuit. Organophosphorus extractants such as di‑(2‑ethylhexyl) phosphoric acid (D2EHPA) in kerosene, combined with a synergist (e.g., 2‑ethylhexyl phosphonic acid, HEHEHP), provide high distribution ratios for both LREEs and HREEs at pH ≈ 2.5. Counter‑current extraction with three stages can strip > 95 % of the REEs into the organic phase, while the aqueous raffinate contains < 0.5 % REE (Wang et al., 2021). Subsequent scrubbing with dilute HCl removes co‑extracted Fe³⁺ and Mn²⁺, and strip‑back with 0.5 M H₂SO₄ yields a purified REE‑rich sulfate solution.
4. Final product recovery and manganese valorisation
The REE sulfate solution is precipitated as oxalates by adding oxalic acid, followed by calcination at 800 °C to obtain a mixed RE₂O₃ powder. When the feed is enriched in LREEs, the final oxide typically contains 70–80 % La₂O₃, 10–15 % CeO₂ and trace HREEs, matching the specifications for phosphor and catalyst feedstocks. .jpg)
Simultaneously, the manganese‑rich streams from the physical and leaching stages are re‑cycled to the ferro‑manganese production line. After neutralisation and filtration, the Mn‑solution is precipitated as MnCO₃, calcined to MnO, and blended into high‑purity ferro‑manganese alloys (≥ 80 % Mn). This dual‑product strategy improves the overall plant margin by 12–18 % compared with a stand‑alone manganese operation (Goon et al., 2014).
5. Environmental and economic considerations
The integrated beneficiation route reduces tailings volume by 35–45 % because the REE‑rich concentrate replaces bulk ore in the leach circuit. Acid consumption is lowered to 0.8 kg H₂SO₄ per tonne of RE₂O₃ produced, roughly half of that required for primary rare‑earth ores (e.g., bastnäsite). Moreover, the recycling of Mn‑bearing solutions eliminates the need for fresh ore mining for ferro‑manganese, conserving land and water resources.
A techno‑economic assessment of a 5 kt yr⁻¹ RE₂O₃ plant co‑located with a 30 kt yr⁻¹ manganese ferro‑alloy facility in Guizhou, China, indicated a net present value (NPV) of US $45 million and an internal rate of return (IRR) of 18 % under a RE₂O₃ price of US $55 kg⁻¹ (Zhang et al., 2023). Sensitivity analysis showed that a 10 % increase in RE₂O₃ price raises the IRR to > 25 %, while a 20 % rise in acid cost reduces the IRR only to 14 %, confirming the robustness of the process.
6. Outlook
Future work should focus on tailored reagents that further discriminate between REEs and Mn/Fe, such as organophosphorus ligands bearing sulfonate groups, and on process intensification through continuous‑flow leaching reactors. The growing demand for light‑rare‑earths in green‑technology applications, combined with the strategic importance of manganese for steel and battery cathodes, makes the joint beneficiation of these resources an attractive pathway for sustainable mineral development.