Recover crystalline germanium thin films from waste optical fibers by leaching-electrodeposition process

• Leaching combined with liquid metal electrodeposition produces germanium thin films • Simplified recovery steps use sodium tetraborate as a leaching agent and electrolyte • Deposition of germanium film can be accomplished efficiently at mild room temperature The current supply-demand imbalance of germanium (Ge) resources is acute, while technologies for recycling and high-value utilization of Ge in waste optical fibers remain underdeveloped. Thereby achieving efficient and high-value recycling of Ge resources is necessary. This study proposes a method for recycling Ge dioxide (GeO 2 ) from waste optical fibers and preparing Ge films via electrochemical liquid-liquid-solid (ec-LLS) technology. The process comprises four stages: pretreatment, leaching Ge with sodium tetraborate (Na₂B₄O₇), salt precipitation for silicon (Si) removal and purification, and solvent-electrochemical deposition of crystalline films using liquid gallium as the conductive substrate. Using Na₂B₄O₇ as both a leaching agent and electrolyte, the combined leaching and liquid metal electrodeposition technique enables simplified recovery steps and efficient preparation of Ge films at mild temperature. Under optimum leaching conditions([GeO 2 ] = 0.1 mol/L, voltage = 1.5 V, reaction temperature = 70°C, time = 2 hours) the Ge leaching rate reaches 71.33%, while the Si removal rate achieves 96.58%. Combined characterization results indicate that the prepared Ge films exhibit a composite microstructure featuring crystalline grains loaded with micro/nanowires. The XRD pattern and the Raman spectrum confirm the excellent crystallinity of the film, with no significant amorphous or impurity phases. SEM indicates that the prepared Ge film exhibits high crystalline quality and a uniform microstructure. Overall, this study provides an environmentally friendly pathway for recycling germanium from optical fibers and preparing germanium thin films.