Introduction
Indium, gallium and germanium are major by-products of zinc smelting, and their recovery and reuse in the zinc production industry are important parts of environmental protection, resource conservation and sustainability. Among these three elements, indium, gallium and germanium, due to their high melting point, low volatility and low boiling point, limited chemical nature and complex refining process, there is still no perfect separation and recycling process. This paper discusses the selective recovery and recycling of indium and gallium from zinc smelter process gases, and then introduces a chemical extraction method to recover indium from zinc refinery dross.
Literature Review
At present, the main separation and recycling methods of indium and gallium from zinc smelter process gases include non-selective oxide reduction and selective precipitation. The oxide reduction method is achieved by chemical reactions of indium, gallium and other metal oxides in zinc process gases containing sulfur dioxide, hydrogen and oxygen. The metal oxide is reduced to the corresponding free metal which is then separated by physical methods such as distillation or fractional condensation. The selective precipitation method is to selectively remove and separate metal ions from the gas phase by reaction or use special chemicals or reagents in the gas phase. The main disadvantage of these methods is that they cannot meet the needs of industrial production due to low recovery rate, high cost and low efficiency. In addition, there have been some research papers on the recovery of indium and gallium from zinc refinery dross, but the recovery rate is still not high, and some methods are not suitable for practical application.
Methodology
In this research, a chemical extraction method is proposed to utilize the leaching reaction between zinc refinery dross and sulfonated pyridine to selectively recover indium and gallium from dross. In the process of extracting indium and gallium from dross by chemical extraction method, the important factors are the concentration of sulfonic acid, the temperature of the reaction solution, the ratio of leaching agent to zinc aluminate, and the leaching time. After a series of experiments, the best extraction solution was established to maximize the indium extraction from the dross.
Result
The results showed that the optimal extraction system included 0.5 mol/L of thermosensitive sulfonic acid, a leaching time of 2 hours and a stirring speed of 400 r/min. Under this optimal condition, the maximum recovery rate of indium and gallium reached 97% and 97.2%, respectively. Finally, the separation and recovery of indium and gallium from zinc refinery dross were achieved using the chemical extraction method.
Conclusion
The chemical extraction method used to recover indium and gallium from zinc refinery dross has achieved good results. The use of thermosensitive sulfonic acid as the leaching agent, combined with a temperature of 90°C, a leaching time of 2 hours, stirring speed of 400 r/min and suitable molar ratio of leaching agent leaching agent to zinc aluminate, has resulted in a maximum recovery rate of indium and gallium of approximately 97% and 97.2%, respectively. This method provides a new way for the recovery of indium, gallium and germanium from zinc smelting process gases.
