Sustainable Germanium Recovery From Germanium Dioxide via Halogen-Free Chemical Vapor Transport

Chemical vapor transport (CVT) and its potential for chemical recycling was studied for recovery of Ge from GeO₂ and SiO₂/GeO₂ mixtures using hydrogen, a hydrogen‑argon mixture and natural gas. CVT occurred via the transport species GeO, yielding mixtures of Ge and GeO₂. Natural gas enabled transport but led to deposition of carbon deteriorating separation. Pure hydrogen proved too strong as reducing agent, forming elemental Ge at the source, preventing CVT. Optimal performance was achieved by a hydrogen(10%)‑argon(90%) mixture in combination with water vapor, altogether moderating reduction strength, stabilizing the transport species, improving separation and resulting in a sustainable process. The hydrogen(10%)‑argon(90%)-based CVT achieved a maximum Ge recovery of 86% within 30 min, higher flow rates resulted in 73% in only 10 min. Upscaling was done by a factor of three and maintained high Ge recovery of 83% in 30 min demonstrating scalability. To mimic Ge recovery from optical fibers and thus from SiO₂, a SiO₂/GeO₂ mixture was successfully investigated, resulting in Ge recovery of 76% in 30 min with no simultaneous transport of Si. The process presents significant potential for Ge recovery from oxide feedstocks and could be adapted to secondary resources such as GeO₂-based optical fiber waste.