Selective extraction of germanium from lead slag washing wastewater by tannic acid coordination and precipitation method

With rapid development of the global digital economy and aerospace industry, the recovery of germanium from the “three wastes” (Waste gas, wastewater, and waste residue) is an important way to alleviate resource shortages. This paper proposes a selective extraction method for germanium from lead slag washing wastewater by tannic acid (TA) coordination. The selective mechanism was investigated by analyses using Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra of the precipitate, and the UV spectra of TA-Zn, TA-Fe(II), and TA-Ge. The results indicate that TA exhibits much higher selectivity for Ge compared to Zn and Fe(Ⅱ), with the hydroxyl group of TA phenol reacting with Ge and not with Zn and Fe(Ⅱ). At pH 3∼6, there was no shift in the TA-Zn and TA-Fe(II) titration curve, while the TA-Ge titration curve exhibited a redshift from 275 to 299 nm (the TA characteristic UV absorption peaks), and it was evident that TA selectively coordinates with Ge at a molar ratio of Ge:TA=4:1. The appropriate time for selective extraction of germanium from lead slag washing wastewater is 2 mins, with 96.63% Ge precipitation, and just 1.25% Zn, and 5.08% Fe(Ⅱ) precipitation. Zn mainly precipitates as ZnHSO4, and the main compound of Fe(Ⅱ) is Fe(OH)2. After roasting to remove organic matter from the precipitation, the non-oxide (germanate) was converted to oxide (GeO2) with a Ge content of 32.5%. In addition, the treated wastewater can be reused in the production process.