Transformation and fate of trace elements during germanium-containing lignite combustion

Studying the migration and transformation behaviors of trace elements during lignite combustion holds significant applied value and strategic importance for guiding the recovery of valuable metals from coal, controlling the emission of toxic pollutants, and supporting the development of clean and efficient utilization for lignite. This study investigates the occurrence characteristics and migration of trace elements (Ge, As, Sb, Pb, Zn and W) during lignite combustion under varying roasting temperatures and oxygen concentrations. Thermodynamic analysis shows that high-valent oxides of trace elements can be readily reduced to low-valent oxides or elemental species by CO or H₂. Experiment results indicate that the volatilization efficiencies of trace elements increase with the increasing combustion temperature, while it decreases with the increasing O₂ concentrations. Under 21 % O₂ concentration, the volatilization efficiencies of Sb and Zn consistently remained above 90 % across combustion temperatures. While the volatilization efficiencies of Ge, As, Pb and W markedly increased from 5.14 %, 3.50 %, 12.36 % and 7.57 % at 773 K to 97.83 %, 97.56 %, 91.93 % and 24.48 % at 1473 K, respectively. Fixed the combustion temperature at 1373 K, the volatilization efficiencies of Ge and Pb moderately decreased from 97.37 % and 93.70 % to 88.52 % and 83.94 %, respectively, with the O₂ concentration increasing from 0 to 21 vol.%. Conversely, the volatilization efficiency of As significantly decreased from 95.31 % to 68.76 %. This finding provides theoretical basis and technical support for the clean and efficient utilization of germanium-containing lignite.