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Metals 2017, 7(7), 237; doi:10.3390/met7070237

Leaching Kinetics of Hemimorphite in Ammonium Chloride Solution

School of Metallurgy and Environment, Central South University, Changsha 410083, China
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Received: 11 May 2017 / Revised: 21 June 2017 / Accepted: 22 June 2017 / Published: 28 June 2017
(This article belongs to the Special Issue Valuable Metal Recycling)
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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. View Full-Text
Keywords: hemimorphite; ammonium chloride; leaching kinetics; Elovich equation hemimorphite; ammonium chloride; leaching kinetics; Elovich equation
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MDPI and ACS Style

Zhao, D.; Yang, S.; Chen, Y.; Tang, C.; He, J.; Li, H. Leaching Kinetics of Hemimorphite in Ammonium Chloride Solution. Metals 2017, 7, 237.

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