SO₂ Induced Reductive Leaching Of Germanium-containing Zinc Leaching Residues

Germanium,a rare metal,is known as a modern"high technology element"and is a strategic metal indispensable for new energy,optical fibres,infrared optics and catalysts,and is an important resource for the development of China's strategic emerging industries.At present,over 80%of zinc in China is produced using the main process of boiling roasting-leaching-purification-electrowinning,during which more than 98%of germanium is enriched in the zinc leach residue,with an average content of 200-600 g/t.Therefore,germanium-containing zinc leach residue is an important resource for germanium extraction.To address the problems of long process,poor environmental friendliness and high energy consumption in the current treatment of germanium-containing Zn leach residue,this paper carried out a study on the SO₂-induced reductive leaching of germanium-containing Zn leach residue to achieve efficient leaching of valuable metals Zn and germanium from germanium-containing Zn leach residue.The specific research contents and conclusions are as follows:(1)The zinc and germanium content of the germanium-bearing zinc leach residue is 18.36%and 311.7 g/t respectively,which has a high recovery value.The main phases in the zinc germanium leach residue are zinc ferrate with lead alum,gypsum,gypsum hemihydrate and quartz.(2)The destruction and dissolution of the complex Zn-Fe-H₂O phase is the key to improve the leaching rate of Zn and Ge.Analysis of the potential-p H diagrams of the Zn-Fe-H₂O and Ge-H₂O systems showed that under the effect of SO₂-induced reduction,the high concentration of Fe³⁺in the solution was reduced to Fe²⁺,resulting in a substantial reduction of the Fe³⁺concentration and redox potential in the system,which effectively solved the inhibition of the solution Fe³⁺on the dissolution of zinc ferrate,thus improving the leaching rate of Zn and Ge.(3)A study on the optimization and regulation of the SO₂-induced reduction leaching process of germanium-containing zinc leach residue was carried out.Under the optimized technical conditions of an initial sulphuric acid concentration of 35 g/L,a reaction temperature of 120°C,a reaction time of 120 min,a liquid-solid ratio of 12:1,a stirring speed of 400 r/min and a partial pressure of 0.3 MPa of SO₂,the main complex phases such as zinc ferrate in zinc leach residue containing germanium were almost induced to dissociate,and the decomposition rate of zinc ferrate reached 98%,the leaching rates of zinc and germanium reached 97%and87%,respectively.The SO₂-induced reductive leaching process achieved an efficient dissolution of the germanium-bearing zinc leach residue and an efficient leaching of the valuable elements.The main material phase of the induced leach residue consisted of gypsum,lead alum,quartz and a small amount of sphalerite,of which the contents of zinc and germanium were 1.87%and 116.5 g/t respectively,and the contents of lead and silver were increased from1.9%and 185.9 g/t to 12.56%and 733.8 g/t respectively.The induced reduction leach solution contained Zn²⁺14.9g/L,Ge⁴⁺23.5mg/L,TFe10.8g/L,Fe³⁺<0.1g/L,H₂SO₄32.14g/L,of which Fe²⁺accounted for 99%of the total Fe.A germanium-containing leachate with low acid and low Fe³⁺concentration,which is conducive to the subsequent selective separation and enrichment of germanium,was obtained.(4)The apparent activation energy E of 5.51 k J/mol for zinc leaching and 6.04 k J/mol for germanium leaching was calculated according to the Arrhenius equation,indicating that the leaching of zinc and germanium during SO₂-induced reductive leaching is controlled by diffusion and can be achieved by increasing the reaction temperature and stirring The efficient leaching of zinc and germanium can be achieved by increasing the reaction temperature and stirring speed.(5)The use of SO₂-induced reduction leaching process for zinc leach residue containing germanium not only can significantly increase the leaching rate of zinc and germanium from the raw material,but also achieve the reduction of high concentration of Fe³⁺to Fe²⁺in the leach solution while leaching the valuable metals;the obtained leach solution has Fe³⁺concentration less than 1g/L,H₂SO₄ concentration 32.13g/L and Ge⁴⁺concentration 23mg/L,which provides a favourable condition for the subsequent process of recovering zinc and germanium from solution,which created favourable conditions for the subsequent process to recover Zn and germanium valuable metals and iron from the solution in an efficient and short process.