Highlights

• Brazilian researchers successfully scaled acid mine drainage treatment from 18 liters to 15 cubic meters.
• They achieved the extraction of rare earths at >90% purity while cleaning polluted coal mine water to legal discharge standards.
• The pilot plant demonstrates that toxic mining wastewater can become a continuous secondary source of critical metals like neodymium and dysprosium.
• The process produces approximately 1 gram of REE oxide per 3.6 m³ treated.
• This breakthrough offers Western nations a dual-benefit strategy:
  • Reducing environmental liabilities
  • Creating distributed, low-risk alternatives to China's rare-earth processing monopoly

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A new open-access study led by Vanessa Olivo Viola (opens in a new tab) at the Beneficent Association of the   Santa Catarina Coal Industry (SATC), plus a multidisciplinary team from Brazilian research institutions reports something both surprising and strategically important: toxic acid mine drainage (AMD) from coal mining can be transformed into a secondary source of rare earth elements (REEs)—at pilot scale, under real-world conditions. Published in the Journal of Water Process Engineering (opens in a new tab) (February 2026), the research demonstrates that Brazil’s Santa Catarina coal basin could yield high-purity mixed rare-earth oxides (>90%) while simultaneously cleaning polluted mine water to legal discharge standards.

For readers new to the topic, AMD is the acidic, metal-laden wastewater produced when sulfide minerals are exposed during coal mining. It is typically viewed as a costly environmental liability. This study flips that narrative: AMD is also a dilute but continuous stream of strategically valuable metals—including neodymium, dysprosium, terbium, and yttrium—key inputs for electric vehicles, wind turbines, electronics, and defense systems currently dominated by Chinese processing capacity.

Study Methods: From Lab Bench to Pilot Plant

The researchers sampled AMD from 16 locations across the Santa Catarina coal basin and identified one high-flow, high-REE site as optimal for scale-up. They then tested a sequential precipitation process at three scales:

• Bench scale (18 liters)
• Glass reactor (100 liters)
• Pilot plant (15 cubic meters per batch)

The method relies on controlled oxidation (using hydrogen peroxide) followed by stepwise pH adjustment:

1. pH 4.5–5.0: Iron and aluminum are selectively removed, forming an iron-rich precipitate (P1).
2. pH 8.5–9.0: Remaining metals—including REEs—co-precipitate into a second solid (P2), enriched in rare earths.

This second precipitate is then processed using conventional hydrometallurgy (acid leaching, solvent extraction, and oxalic precipitation) to produce a mixed rare-earth oxide product.

Vanessa Olivo Viola at the Beneficent Association of the   Santa Catarina Coal Industry (SATC), Corresponding Author

Key Results: Modest Grades, Real Scale, High Purity

The findings are notable for their practicality:

• REE pre-concentrate (P2): Up to 2.5% rare earths by mass
• Final product: >90% pure mixed rare-earth oxides
• Yield: ~1 gram of REE oxide per 3.6 m³ of AMD treated
• Metal removal: >95% removal of iron and aluminum; strong reductions in manganese and zinc
• Effluent quality: Final treated water met Brazilian environmental discharge standards

While the REE grades are far lower than mined concentrates, the feedstock is essentially free, continuous, and already requires treatment. The authors show that process performance remained consistent from bench to pilot scale, a critical hurdle that many resource-recovery concepts fail to clear.

Why This Matters Beyond Brazil

This study does not overturn China’s dominance in rare-earth processing—but it challenges the assumption that primary mining is the only path to diversification.

For the U.S., EU, and allies, the implications are clear:

• Secondary sources matter. AMD, mine tailings, and industrial wastewaters could become distributed, low-risk supplements to mined supply.
• Processing know-how is portable. The chemistry demonstrated here—fractional precipitation plus solvent extraction—is well understood and could be deployed near legacy coal and metal sites in Appalachia, Europe, andelsewhere.
• Environmental remediation and supply security can align. Turning cleanup liabilities into revenue streams improves project economics and public acceptance.

In a world where China controls ~90% of rare-earth refining, even incremental non-Chinese supply has strategic value.

Limitations and Open Questions

The authors are careful about what this study does not prove:

• Economics remains site-specific. Profitability depends on AMD flow rates, REE concentrations, reagent costs, and by-product utilization (notably the iron-rich P1 precipitate).
• Not a silver bullet. AMD recovery will never replace large mines, but it can complement them.
• Process optimization is needed. About 20–30% of REEs were still lost to effluent in some pilot runs, suggesting room for improvement.

There is also a broader policy question: will Western regulators and investors support midstream processing at scale, or will promising pilots stall without sustained industrial backing?

Conclusion: Small Streams, Strategic Signal

This Brazilian pilot study sends an important message to policymakers and investors: rare-earth diversification does not start and end with new mines. By recovering critical materials from polluted waters, countries can reduce environmental damage, lower supply-chain risk, and incrementally weaken China’s processing monopoly.

It won’t win the supply-chain war on its own—but it shows how circular economy strategies can become strategic assets.

Citation: Viola, V.O. et al., Journal of Water Process Engineering, Vol. 82 (2026) 109549.