Extraction of germanium and fixation of arsenic from lignite using pyrolysis

Abstract

The one-step reduction combustion volatilization method of Ge-bearing lignite is the primary technique for extracting germanium (Ge). However, this method generates large amounts of industrial waste, such as fly ash, and releases significant quantities of arsenic (As). This study proposed a pyrolysis method that extracts Ge from lignite while simultaneously immobilizing As. Firstly, by investigating the migration and transformation processes of Ge and As during pyrolysis, it was found that the transformation of aluminosilicates into oxides was the key controlling step for Ge and As volatilization. The addition of carbon sources effectively enhanced Ge volatilization, among which metallurgical coke and coking coal also played roles in As immobilization. The results showed that 1100 °C was a key temperature for Ge volatilization. Under the conditions of a heating temperature of 1100 °C, heating time of 30 min, and 50 % metallurgical coke addition, the Ge volatilization rate reached 84.71 %, while the As volatilization rate was only 9.36 %, increasing the Ge/As ratio from 1.50 to 9.05. Meanwhile, the performance of metallurgical coke remained stable after five cycles of reuse, with a recovery rate of 97.48 %. Finally, the potential mechanisms for Ge volatilization and As fixation during pyrolysis were proposed. This method avoided the generation of large amounts of fly ash and the emission of As associated with traditional processes. It showed potential for improving the separation of Ge and As during subsequent chlorination distillation, providing a novel and environmentally friendly approach for the extraction of germanium from lignite.