Leaching of low grade zinc oxide ores in NH4Cl–NH3 solutions with nitrilotriacetic acid as complexing agents

Abstract:The leaching kinetics of zinc from zinc oxide-based metal oxide varistors (MOVs) was investigated in H 2 SO 4 at atmospheric pressure. Kinetics experiments were carried out at various agitation speeds, particle sizes, initial H 2 SO 4 concentrations, and reaction temperatures. It was determined that the leaching rate of zinc was independent of agitation speed above 300 rpm and also independent of particle size below 105 µm, whereas it dramatically increased with an increasing H 2 SO 4 concentration. Except for when the H 2 SO 4 concentration was varied, the m-values were almost constant at varying agitation speeds (m-values: 0.554-0.579), particle sizes (m-values: 0.507-0.560) and reaction temperature (m-values: 0.530-0.560) conditions. All of the m-values in these experiments were found to be below 0.580. Therefore, it is proposed that the extraction of zinc is a diffusion-controlled reaction. The leaching kinetics followed the D3 kinetic equation with a rate-controlling diffusion step through the ash layers, and the corresponding apparent activation energy was calculated as 20.7 kJ/mol in the temperature range of 313 K to 353 K.

Section: Effect Of H 2 So 4 Concentrationsupporting

confidence: 79%

Leaching Kinetics of Zinc from Metal Oxide Varistors (MOVs) with Sulfuric Acid

Kim

Lee

2016

“…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].…”

Section: Introductionmentioning

confidence: 99%

Leaching Kinetics of Hemimorphite in Ammonium Chloride Solution

Zhao¹,

Yang²,

Chen³

et al. 2017

The leaching kinetics of hemimorphite (Zn 4 Si 2 O 7 (OH) 2 •H 2 O) 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.

“…In addition, when the solid-liquid phase reaction is simultaneously controlled by the diffusion reaction and the interfacial chemical reaction, the leaching kinetic equation of lead in electrolytic manganese anode mud can be expressed as [36,37]:…”

Section: Kinetic Analysis Of the Leaching Processmentioning

confidence: 99%

Roasting Pretreatment Combined with Ultrasonic Enhanced Leaching Lead from Electrolytic Manganese Anode Mud

Xie

Zhang

et al. 2019

A method of conventional roasting pretreatment combined with ultrasonic enhanced leaching with ammonium acetate was proposed to solve the difficult problem of lead in electrolytic manganese anode mud. The effects of concentration, liquid–solid ratio, temperature, leaching time and rotating speed on the leaching process under conventional and ultrasonic conditions were studied, and the lead leaching rate can be as high as 93.09% under optimized process parameters. A leaching kinetic model under conventional and ultrasonic conditions was established to explore the restrictive links of the leaching process. The results show that the leaching process under both conventional and ultrasonic conditions is controlled by diffusion, and the activation energies are 29.40 kJ/mol and 26.95 kJ/mol for the conventional and ultrasound enhance leaching processes, respectively.