Ligand-induced tetrad effect in coordination leaching of ion-adsorption rare earth ores: enhanced recovery of high-value low-lanthanum rare earth concentrates

Abstract

Conventional in situ leaching techniques for ion-adsorption rare earth ores (IAREOs) using ammonium-based leaching agents present dual challenges of persistent NH₄⁺–N contamination and inefficient La extraction economics. We propose an innovative ammonia-free coordination leaching system that simultaneously enables high-value rare earth concentrate production and environmental remediation. By exploiting ligand-induced tetrad effects, we elucidated quantitative constitutive relationships between leaching agent characteristics (type/concentration) and the extraction efficiency of individual rare earth elements (REEs). Under near-neutral column leaching conditions, differential extraction performance was achieved: high-concentration leaching agents attained exceptional recovery rates of 107.2 ± 7.7% for target REEs, while optimized low-concentration protocols demonstrated selective extraction patterns (<30% for La vs. >107% for other REEs). This strategic separation yielded a premium-grade rare earth concentrate with 15.2% enhanced economic value through lanthanide fractionation. First-principles calculations revealed the mechanistic basis in differential RE³⁺ binding energies with carboxyl groups (ΔE ≥ 222.2 Ha), enabling precise extraction control. Life cycle assessment shows 87.6%, 89.0% and 51.5% reductions in global warming, ozone depletion potential and human toxicity potentials versus the traditional ion exchange process. This molecularly engineered leaching system enables environmentally benign rare earth recovery with precise composition control, providing an innovative solution for demand-oriented rare earth supply systems.