Separation of silicon and germanium from the chlorination distillation residue based on co-precipitation of sodium-aluminum–silicon

Germanium (Ge) is known as a critical metal, and dust from coal burning is an important raw material for the extraction of Ge by the chlorination distillation process. Nevertheless, the residue produced by the chlorination distillation process (RCDP) also contains a considerable amount of Ge. The extraction of Ge from RCDP requires the conversion of Si and Ge into soluble compounds, and the efficient separation of large amounts of Si and Al from small amounts of Ge. In this study, Al, Si and Ge in RCDP were converted to soluble sodium slat by sodium roasting. Under the conditions of roasting temperature of 600 ℃, time of 120 min and the mass ratio of NaOH to RDCP of 3:1, 56.92 % of Al, 87.75 % of Si and 91.20 % of Ge are dissolved into solution. According to the formation mechanism of sodium aluminosilicate, the co–precipitation of Na–Al–Si can be promoted by adjusting the composition of the leaching solution to separate Si and Ge. Noteworthy, 73.97 % of Si have been removed by precipitation, while the precipitation ratio of Ge is only 8.77 %. Moreover, the Ge-containing solution is obtained with low Al–Si concentration (Al 0.37 g/L, Si 0.85 g/L and Ge 0.025 g/L). Overall, the obtained nano-microspherical non-dense cluster zeolite products have great potential for the removal of heavy metal ions from wastewater.