2025 Schueler Acid leaching of mine tailings flotation fractions

Mine tailings, a substantial global waste stream, often contain recyclable metals with economic and environmental potential. This study focuses on the Rammelsberg mine’s Bollrich tailings pond, where residues from more than 50 years of mining and flotation processes pose contamination risks due to heavy metals. Building on prior projects aimed at recovering valuable metals from these tailings, this study optimizes the leaching of base metals, copper (Cu), zinc (Zn), and lead (Pb), using both inorganic and organic acid approaches. Leaching experiments conducted with sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) demonstrated up to 52% Cu and 77% Zn extraction, with optimal conditions involving controlled acid and solid concentrations and moderate temperatures. The limited solubility of lead (Pb) in H2SO4 prompted additional tests with organic acids (citric, acetic, and gluconic acids), where citric acid achieved the highest Pb leaching efficiency, reaching up to 86% with pH adjustment and H2O2 addition. Subsequent tests with barite fractions showed that citric acid is an effective lixiviant for Pb across different tailing types, achieving high co-extraction of Cu and Zn. A final combined leaching test with H2SO4 followed by citric acid indicated that sulfate compounds from the initial H2SO4 treatment inhibited Pb recovery, underscoring the need for optimized sequential processes. This work demonstrates a practical and sustainable approach to recovering valuable metals from mine tailings by optimizing leaching processes and highlighting the importance of sequential treatments to maximize metal recovery and minimize environmental impact.