Recovery of germanium and valuable by-products from lignite: an integrated soluble conversion and chlorination distillation approach

As a strategic semiconductor material, germanium (Ge) is experiencing substantial market demand growth. While lignite serves as a globally significant Ge reservoir, conventional recovery method through lignite combustion generates Ge-rich fly dust with inherent drawbacks of substantial energy loss and elevated carbon emissions. This study presents an innovative low-carbon strategy integrating soluble conversion with chlorination distillation to achieve comprehensive lignite component utilization while recovering Ge. Experimental results demonstrate that the soluble conversion process effectively disrupts the chemical bonding between the carbon matrix and humic acid-bound germanium (HA-Ge) in lignite, facilitating efficient HA-Ge dissociation. This treatment enabled Ge enrichment from an initial concentration of 175.03 mg/kg in raw lignite to 679.01 mg/kg in dissolved solids, representing a 3.88-fold enhancement. Critical process optimization revealed that precise control of reaction duration is essential to maintain Ge in soluble phases and prevent premature flocculation. Subsequent chlorination distillation achieved 85.32 % Ge recovery with 99.89 % purity through vapor phase separation. The methodology concurrently yields two valuable byproducts: purified carbon fuel with combustion potential and humic acid derivatives applicable as agricultural fertilizers. This integrated approach establishes a sustainable paradigm for Ge-bearing lignite utilization that simultaneously addresses three critical aspects: enhanced resource recovery efficiency (85.32 % Ge extraction rate), environmental sustainability (carbon emission reduction through non-combustion processing), and industrial application potential (multi-product outputs).