The treatment methods for zinc ash can be divided into wet and pyrometallurgical (also known as distillation) methods. The pyrometallurgical method leverages the significantly lower boiling point of zinc compared to other impurities in the ash. Under normal pressure and high temperature, zinc is volatized into zinc vapor, or the zinc oxide in the ash is reduced to zinc vapor, which is then condensed into liquid zinc or zinc powder. Other metallic impurities remain in the residue. Currently, the commonly used distillation equipment for this method is the horizontal tank. The horizontal tank distillation method for zinc extraction is an ancient technique. In terms of treating zinc ash, it has the advantages of low investment, simple process, and a wide range of tolerance for impurity composition and zinc content. However, it also has significant drawbacks, including high labor intensity, high energy consumption, low processing capacity, and low recovery rate. As humans demand higher quality living environments, this method of treating zinc ash will eventually be phased out.
Wet zinc smelting is currently the main technological development direction in the zinc smelting industry. Extensive experimental and industrial research has been conducted on using wet processes to treat zinc ash, and considerable progress has been made. This treatment process consists of hot water leaching, neutral leaching, hot acid leaching, and zinc electrodeposition. Hot water leaching aims to maximize the dissolution of carbon in the zinc ash, thereby reducing the burden of removing chloride ions in subsequent processes. Neutral leaching aims to obtain an electrolyte that meets the requirements for electrolysis. Hot acid leaching aims to maximize the leaching of zinc into the solution. Experiments have shown that this method can achieve a zinc recovery rate of over 97%, and it generates almost no harmful waste during the process, making it a promising method with development potential.
