Resonant Acoustic Micro-Fracturing for the Selective In-Situ Recovery of Rare Earth Elements

The exploitation of high-yield Rare Earth Element (REE) deposits is frequently bottlenecked by the co-location of radioactive isotopes (e.g., Uranium, Thorium). Classical open-pit mining and explosive hydraulic fracturing necessitate the use of highly corrosive lixiviants (sulfuric acid), which unselectively dissolve the radioactive matrix and generate toxic tailings. This paper proposes a non-destructive, zero-explosive alternative: Macroscopic Resonant Acoustic Micro-Fracturing. By deploying a sub-MHz piezoelectric transducer array—hermetically sealed within a fluid-coupled, heavy-wall titanium sonotrode housing for subterranean durability—into a standard injection well, we generate a continuous acoustic field tuned precisely to the mechanical harmonic resonance of the target ore body. This induces high-density micro-fracturing, exponentially increasing the macroscopic surface area and permeability of the rock matrix. This structural fatigue allows for the use of highly diluted, bio-inert lixiviants (e.g., citric acid) to selectively extract REEs. Due to the differential acoustic impedance and chemical stability of the radioactive isotopes, the benign lixiviant leaves the Uranium and Thorium permanently locked within the solid bedrock. We propose a triaxial core-flooding protocol to empirically validate this ecologically sterile, closed-loop extraction model, suitable for unlocking heavily regulated mineral deposits.