Abstract
The leaching kinetics of hemimorphite (Zn4Si2O7(OH)2·H2O) in ammonium chloride solution was presented in detail. Effects of stirring speed (150–350 rpm), leaching temperature (75–108 °C), particle size of hemimorphite (45–150 μm), and the concentration of ammonium chloride (3.5–5.5 mol/L) on the zinc extraction rate were studied. The zinc extraction rate enhanced slightly with the increase in stirring speed, but increased significantly with an increase in the leaching temperature and ammonium chloride concentration. Zinc extraction was enhanced significantly in the first 60 min with decreasing particle size, but had little effect on the leaching process after 60 min. Scanning electron microscopy (SEM) analysis showed that some silica gel formed in the leaching process was not separated from the hemimorphite surface, but covered some of the active particle surface. The Elovich equation successfully described the leaching kinetics of hemimorphite in ammonium chloride solution with an apparent activation energy of 405.14 kJ/mol at temperatures of 75–90 °C and 239.61 kJ/mol at temperatures of 95–108 °C, which is characteristic for a chemically-controlled process. Silica gel is generated at temperatures of 75–90 °C and decomposed into silica at temperatures of 95–108 °C.
Highlights
Zinc oxide ores are difficult to use, as these ores are difficult to separate by flotation
Zinc oxide ores are generally found in the form of carbonates and silicates, such as smithsonite, hydrozincite, zincite, willemite, and hemimorphite, etc. [1,2]
The effect of the leaching temperature from 75 to 108 ◦ C on zinc extraction is presented in of that the leaching to 108 °C on zinc extraction is the presented in Thiseffect shows elevatedtemperature temperaturefrom had75 a noticeable enhanced effect on percentage of
Summary
Zinc oxide ores are difficult to use, as these ores are difficult to separate by flotation. With the consumption of zinc sulfide resources and environmental protection requirements, studies are paying more and more attention to zinc oxide ores. Zinc oxide ores are generally found in the form of carbonates and silicates, such as smithsonite, hydrozincite, zincite, willemite, and hemimorphite, etc. High-silicon zinc ore (willemite and hemimorphite) resources are very difficult to use because silicon is hard to dispose of in the current process [3]. To treat high-silicon zinc ores, a large amount of research has been carried out in recent years in pyrometallurgical and hydrometallurgical methods. The hydrometallurgical process is more economically attractive, as the pyrometallurgical method suffers from high energy consumption and capital investment. Acids [4,5], sodium hydroxide [6,7], and ammoniacal solutions are often used as leaching agents [8,9]
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