Leaching kinetics and mechanisms in efficient chlorination leaching of germanium-rich fume dust

Chlorination distillation is a critical step in the efficient purification of germanium, as it directly influences the quality of the product. However, the current chlorination distillation system still suffers from constrained germanium leaching efficiency and excessive acid consumption, primarily mediated by leaching kinetics. This study establishes an apparent kinetic model for the chlorination leaching system of germanium-rich fume dust within the framework of thermodynamics. The results showed that the leaching efficiency of germanium was as high as 94.43%. The leaching process kinetics of germanium follows the Avrami equation, with all n values less than 0.5 and an apparent activation energy of 8.89 kJ mol^-1, indicating a diffusion-controlled process associated with mass transfer limitations. Meanwhile, impurities were found to preferentially consume hydrochloric acid to reduce the leaching efficiency of germanium, especially at low acid concentrations. Density functional theory (DFT) and sequential chemical extraction analyses indicate that germanium liberation proceeds through proton-assisted cleavage of Ge-O bonds followed by chloride coordination to form Ge-Cl-containing Ge(iv) species, with the leached germanium present as GeCl₄, while unextracted germanium remains in the residue as complex germanosilicate crystalline phases. The elucidation of the leaching kinetics and efficient release mechanisms of germanium provides a theoretical foundation for the optimization of the efficiency and selectivity of chlorination leaching, which are crucial for achieving green recovery of germanium resources.