Ultrasonic enhanced hydrazine sulfate acid leaching of low-grade germanium dust

By studying the principle of ultrasonic-enhanced leaching and the mechanism of reductive acid leaching of valuable metals, a new method of ultrasonic-enhanced hydrazine sulfate leaching of Zn and Ge in zinc oxide dust in the sulfuric acid system has been proved to be very effective. The phase of Ge was determined by the segmented dissolution method, and it was found that insoluble Ge mainly existed in the form of GeS2 and tetragonal phase germanium dioxide. Comparing the solubility of GeS2 and GeS in a hot high-acid system, it was found that GeS was more easily dissolved. And Ge4+ is more prone to hydrolysis at high acid concentration, resulting in germanium precipitation again. In addition, the presence of more Fe3+ in the solution will increase the potential of the system and inhibit the leaching of zinc ferrate. Therefore, the reduction method is used to reduce Ge4+ and Fe3+ to Ge2+ and Fe2+, which can accelerate the dissolution of zinc ferrate and effectively avoid the low leaching rate of zinc and germanium caused by the hydrolytic precipitation of Fe3+ and Ge4+. The valence states of Fe and Ge in the leachate were analyzed by ICP and XPS, and it was found that they mainly existed in the leachate in the divalent form, which indicated that Fe3+ and Ge4+ had been successfully reduced to Fe2+ and Ge2+. Some black substances were formed in the leaching process. EPMA analysis showed that the material was the oxide of silicon and aluminum, and the number of black substances increased gradually with the passage of leaching time, which led to the decreased metal leaching rate. The leaching kinetics is used to study the mechanism of the leaching process. By comparing the fitting degree of multiple models, the final mixed controlled model is determined to control the whole leaching reaction. Therefore, it is finally determined that when the initial acidity of 140 g/L, the liquid–solid ratio of 7 mL/g, the dosage of the reducing agent is 1/3 of the molar mass of Fe in zinc oxide dust, and ultrasonic intensity of 300 W is used to leach for 60 min at 333 K, Zn and Ge have the best leaching efficiency and economic benefits, and the leaching rates are 96.56 % and 94.62 %, respectively. Compared with conventional leaching, the leaching rate of Zn is increased by 6 %, and that of Ge is increased by 11 %.