Why magnesium sulfate is becoming the go-to solution for ISR-based rare earth extraction

Magnesium sulfate is quickly gaining attention as the preferred leaching reagent in in-situ recovery (ISR) projects for rare earth elements (REEs), particularly in clay-hosted deposits outside China. Australian-listed Brazilian Critical Minerals Limited has become a notable early adopter of this approach, having validated magnesium sulfate-based ISR in recent field trials at its Ema project in Brazil. With global pressure building to find cleaner and more cost-efficient ways to extract critical minerals, this chemical—best known as Epsom salt—is being repositioned as a key enabler of next-generation REE production.

Why is magnesium sulfate emerging as a preferred leaching solution for ISR rare earth projects globally?

The growing appeal of magnesium sulfate in rare earth mining lies in its chemistry, availability, and environmental profile. Traditional ionic clay REE operations in southern China have long relied on ammonium sulfate, a leaching agent with known environmental drawbacks including groundwater contamination and nitrogen runoff. In contrast, magnesium sulfate provides a far safer ion-exchange mechanism. It displaces rare earth cations from clay particles without generating toxic effluents, and it poses minimal risk to surrounding ecosystems due to its agricultural-grade classification.

At the Ema project, Brazilian Critical Minerals injected a 0.5M magnesium sulfate solution into the clay-rich zones of its ionic adsorption deposit. Field trials demonstrated fast pH reactivity, strong solution flow, and successful recovery of high-value REEs such as neodymium, praseodymium, and dysprosium. Rare earths began mobilizing shortly after pH dropped below threshold levels, confirming both the efficacy and scalability of magnesium sulfate in real geological conditions. Unlike ammonium-based systems, this reagent poses no significant waste disposal challenge and is non-corrosive—cutting down on equipment wear and overall operating costs.

Beyond performance in the ground, magnesium sulfate offers critical logistical advantages. It is widely available, inexpensive, and transportable without significant hazard controls. For ISR developers in remote or infrastructure-light environments, this lowers both the cost and complexity of reagent handling. It also improves the permitting narrative, giving project operators an advantage when negotiating environmental approvals in countries with strict ESG frameworks.

The broader relevance of this shift is hard to ignore. With over 85% of rare earth refining still dependent on Chinese supply chains, Western-aligned producers are under mounting pressure to deploy cleaner and geopolitically independent extraction strategies. Magnesium sulfate-based ISR checks both boxes. It enables localized production of critical magnet metals without relying on high-impact mining or controversial processing chemicals. For policymakers seeking transparent and traceable sources of REEs, magnesium sulfate ISR projects are emerging as viable supply alternatives.

Brazilian Critical Minerals is not alone in exploring this pathway, but it has advanced further than most by transitioning from laboratory testing to field validation. Its early-stage success could pave the way for other explorers in Brazil, Australia, and Africa to rethink their reagent strategies. If magnesium sulfate continues to prove reliable across diverse clay-hosted deposits, it may become the industry’s new standard for ISR-based REE mining.

As rare earth demand accelerates—particularly for EVs, wind turbines, and high-efficiency electronics—efficient and low-impact extraction methods will become increasingly valuable. Magnesium sulfate could play a central role in this transformation, allowing junior explorers and mid-tier developers to deploy ISR with greater community and regulatory alignment. The next phase will depend on scalable feasibility studies and downstream buyer engagement, but the chemistry is already making a compelling case.