Microfluidic-Intensified Two-Stage Tannin Precipitation of Germanium to Reduce Tannin Consumption

To address the challenges of low germanium recovery and high reagent consumption during precipitation from strongly acidic solutions, this study developed a two-stage tannin process intensified by microfluidic mixing and systematically examined the synergistic effects of tannin dosage and pH on coordination chemistry. First-stage recovery rose from 45.23% to 91.28% as the tannin ratio increased from 5- to 15-fold, confirming that sufficient ligand promotes dense chelate formation. Optimising pH to 2.0–2.5 deprotonated tannin hydroxyls, enabling electrostatic–chelation synergy with Ge(OH)3+ and yielding 79.88% recovery—a 20.28% improvement over pH 1.5. The staged second-stage process proved particularly effective: at pH 1.5, a “5-fold primary + 15-fold secondary” scheme achieved 92.04% total recovery with only 13.22-fold cumulative tannin, a 46.81% increase over the single-stage 5-fold treatment; at pH 2.5, a “5-fold + 10-fold” combination reached 95.44% recovery with just 8.67-fold reagent. Microfluidic processing refined particle size and intensified the Ge–O vibration at 864 cm−1, indicating more stable coordination. Economic analysis reveals that efficiency plateaus beyond a 17-fold cumulative dosage, making staged addition the cost-effective choice. By harmonising staged coordination with enhanced mass transfer, this approach resolves the inherent conflict between precipitation depth and reagent overuse, delivering a sustainable strategy for germanium recovery.