High pressure acid leaching of low germanium bearing silica residue (GRS): Characterization of leach residue and mechanistic details of germanium leaching

This study investigates the leaching behavior of germanium from low germanium bearing silica residue (GRS) with high silicon content by the acid leaching process. The results showed that high-pressure acid leaching process could effectively extract more germanium from the GRS compared with the conventional acid leaching process, and that the leaching of germanium was positively correlated with the leaching temperature. The leaching efficiency of germanium reached 73.8% at 240 degrees C, which is 3.5 times higher than that obtained from the conventional acid leaching process. Further studies demonstrated that the leaching of germanium was directly related to the polymerization and crystallization behavior of silicon. At leaching temperatures below120 degrees C, silicon could transform into amorphous and highly polymeric SiO2, which increased the germanium adsorption capacity of silicon, leading to reduced leaching of germanium. Above 120 degrees C, the depolymerization and poly-condensation reaction of polysilicic acid was enhanced, resulting in the conversion of silicon into dense oligo-meric silica with a low specific surface area. This conversion reduced the adsorption and encapsulation of germanium on silicon, which was conducive to the leaching of germanium.