Optimised Recovery of Critical Minerals from Historical Pegmatite Tailings in Rwanda

ABSTRACT Historical pegmatite mining tailings in Rwanda represent a significant but largely unquantified repository of economically recoverable critical minerals. This study presents the results of a comprehensive multi-site beneficiation investigation conducted across five historical tailings deposits — Rutongo and Nyakabingo (North Province), Gifurwe (Northern Province), and Karongi and Rutsiro (Western Province) — encompassing a combined estimated volume of 11.5 million cubic metres. Systematic sampling (618 primary samples) combined with ICP-MS geochemical analysis, XRD mineralogy, and SEM-EDS liberation characterisation established site-specific grade distributions for cassiterite (Sn: 428–1,842 ppm mean), wolframite (WO₃: 142–2,248 ppm mean), columbite-tantalite (Ta₂O₅: 98–612 ppm; Nb₂O₅: 184–948 ppm), lithium (Li: 348–1,284 ppm), gold (Au: 46–284 ppb), and total rare earth oxides (TREO: 542–848 ppm). An integrated beneficiation flowsheet comprising Knelson centrifugal concentration (60G), sequential LIMS-WHIMS magnetic separation (0.10–1.4 T), froth flotation with an octyl hydroxamic acid and styrene phosphonic acid (OHA+SPA) collector blend at pH 5.5, and a roast-leach circuit for lithium recovery achieved primary metal recoveries of 83.8–91.2% across all sites, exceeding the 80% target for all primary minerals. The OHA+SPA blend outperformed conventional fatty acid collectors by 15–20 percentage points in cassiterite recovery, representing a commercially significant finding. A bio-derived flotation collector from locally cultivated Jatropha curcas achieved performance comparable to sodium oleate at approximately 30% lower reagent cost. These results establish, for the first time with site-specific experimental data, the technical amenability of Rwanda's legacy tailings to modern, cost-effective beneficiation, providing an evidence base for investment and policy decisions in Rwanda's emerging tailings reprocessing sector. Keywords: tailings reprocessing; cassiterite; coltan; wolframite; gravity separation; froth flotation; hydroxamic acid collector; Rwanda; Kibaran belt; critical minerals