Ju Shaohua

Recent developments in the application of microwave energy in process metallurgy at KUST

ABSTRACT Kunming University of Science and Technology (KUST) has successfully developed, designed, fabricated and installed industrial microwave units for (i) removal of halides, (ii) activation of carbon, (iii) heating of dust laden air in electrostatic precipitators, (iv) drying of water based paints, and (v) heating of the HF pickling solution for cold rolled titanium alloy coils. This review article provides a summary of these process metallurgy applications. It is found that the use of microwave energy can increase the process efficiency, giving advantages, such as lower reaction temperature and shorter reaction time compared to traditional processes. 可显著降低反应温度、缩短时间，具有强化作用

Optimization of Microwave Roasting for Dechlorination of CuCl Residue under Oxygen-Enriched Condition

Abstract The clean utilization of the residue containing chloride, such as zinc oxide dust and CuCl residue, produced from zinc hydrometallurgy is very important for the recycle of valuable metals. In this paper, a new technology for dechlorination of the CuCl residue through thermal treatment with application of microwave and oxygen-enriched air roasting is brought out. And the response surface methodology (RSM) based on five-level, three-variable and central composite design (CCD) was used to optimize the operation parameters for increasing the dechlorination efficiency. The effects of temperature, roasting time and oxygen consumption on the dechlorination efficiency were studied and the optimal process conditions were identified. In addition, X-ray diffraction (XRD), scanning electron microscope (SEM) and Raman spectroscopy were used to characterize the dechlorination process under the optimum condition. The results showed that the experimental data were fitted to a second-order polynomial equation. The optimized process conditions are identified to be a roasting temperature of 451℃, heating duration of 114 min and oxygen consumption of 2.4 times the theoretical oxygen demand. A dechlorination efficiency of 96.4% could be achieved at the optimal process conditions.

Clean Utilization of CuCl Residue by Microwave Roasting under Oxygen-Enriched Condition

Abstract The clean utilization of the CuCl residue containing chloride produced from zinc hydrometallurgy residue is very important for the recycle of valuable metals. A new method of microwave roasting under oxygen enriched condition was put forward to strengthen the process of dechlorination. It was demonstrated that the dechlorination rate of CuCl residue by microwave roasting was higher than that of conventional roasting by tubular resistance furnace under the same conditions (temperature, holding time and atmosphere). After roasting at a temperature of 450°C for 120 min under an oxygen flow rate of 150 mL/min in microwave field, the dechlorination rate of CuCl residue was as high as 97%, increasing 17% compared to that of conventional roasting using tubular resistance furnace. The characterizations of phase variation of CuCl residue in microwave field by means of X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectrometer (SEM-EDS) and Raman spectroscopy indicated that the process of dechlorination by microwave roasting under the oxygen enriched condition was much more efficient than conventional roasting.

Permittivity Study of a CuCl Residue at 13–450 °C and Elucidation of the Microwave Intensification Mechanism for Its Dechlorination

Abstract Permittivity is a vitally important parameter for describing the absorbing and heating characteristics of a material under microwave irradiation, and it is also strongly dependent on temperature. However, the literature contains little information on this topic and even less particular permittivity data at elevated temperatures. In this paper, the permittivity of a CuCl residue at temperatures from 13 to 450 °C at 2.45 GHz was measured using the cavity perturbation method. The relationship of its real part (ε′) and imaginary part (ε″) with temperature (T) was deduced. In addition, the temperature-dependent tangent (tan δ) and the penetration depth (d) of microwaves into the material were calculated. The results of the permittivity study show that the dielectric constant (ε′) of the CuCl residue increased linearly with increasing temperature. In contrast, the dielectric loss factor (ε″) and loss tangent first maintained on a steady value between 13 and 300 °C and then substantially increased from 300 to 450 °C. The positive interaction of the dielectric property and temperature showed the reasonableness of our earlier metallurgy process, where the CuCl residue for dechlorination was roasted at 350–450 °C under microwave irradiation.

Solvent Extraction of Cu2+ with Laminar Flow of Microreactor from Leachant Containing Cu and Fe

Solvent extraction of Cu2+ from the leaching liquor contain Cu and Fe use a microfluidic technology. Currently, the conventional copper extraction process has many problems such as long distance and small driving force of mass transfer. In order to solve the problems, studies are carried out on the extraction process of low grade copper leaching liquid using Lix984N as an extractant with a new microfluidic solvent extraction technology. The effects of flow rate on the separation and extraction efficiency between Cu and Fe are studied, and the results show that a steady liquid-liquid interface of laminar flow is form in the micro-extractor, and extraction efficiency is 78 % and 2.5 % for Cu and Fe at the contact times of 0.84s respectively. Besides, the separation coefficient between Cu and Fe is as high as 140.04. The studied microfluidic technology has the advantages like improving extraction efficiency and reducing reaction time and providing the potential application in the hydrometallurgy extraction of Cu.

Pilot-Scale Dechlorination of CuCl Residue from Zinc Hydrometallurgy by Microwave Roasting

Most Zn hydrometallurgy factories adopt Cu2SO4 as a dechlorination reagent from zinc solution recently, thus much CuCl residue was produced. The present process of treating this residue is washing CuCl residue with water or sodium carbonate solution, which would bring a lot of trouble for water treatment and waste discharge. In this study, a method of roasting the residue with microwave energy is adopted for not only dechlorination of the CuCl residue and also recycle Cl therein as HCl. The pilot-scale equipment system includes a 20 KW microwave roasting equipment, a dust collection and a tail gas adsorption system. The experiments result shown that under following parameters of microwave roasting: 108 Kg CuCl residue with a grain size of −60 mesh, stirring speed at 10 r/min, roasting at 350 °C for 4 h, the dechlorination rate is as high as 78.54 %, and a product of CuO with a Cl concentration of less than 3.7% can be obtained. What’s more, the tail gas was analyzed as air and HCl, which can be absorbed as byproduct of hydrochloride. The power consumption for treating such CuCl residue with microwave energy is only about 488.88kW • h/t.

Optimization on Drying of CuCl Residue by Hot‐Air Using Response Surface Methodology

The clean utilization of the residue containing chloride, CuCl residue, produced from zinc hydrometallurgy is very important for the recycle of valuable metals. And drying is the main process in recycling. In this study, response surface methodology was used to optimize operating conditions of the drying of CuCl residue in a convection oven and desirability function used as the methodology for the optimization. Optimization factors were air temperature (80–100°C), material thickness (10–25mm) and process time (80–120min) while investigated responses was final moisture content. The optimum conditions were found to be the temperature of 95.48°C with the material thickness of 13.47mm for the process time of 89.48 min. Under optimum conditions, the predicted moisture content of CuCl residue was 4.11% while the experimental date was 4.13%. The experimental value after process optimization was found to agree satisfactory with the predicted value. After drying, XRD was used to analyze the main phases of CuCl residue. The CuCl residue is made up of CuCl,Cu2O, ZnS and other compounds.

Dielectric Properties and Microwave Drying Characteristics of CuCl Residue

The basics of microwave drying process of CuCl residue were studied by comparing the dielectric property of the residue with different moisture contents. The dielectric properties were measured by microwave cavity perturbation method. The dielectric constant and dielectric loss factor of the CuCl residue have a linear correlation with the moisture content. With this relationship, we can realize on-line measurement of moisture content of the CuCl residue by dielectric properties. The microwave drying experiments with different thicknesses (1–5cm) of CuCl residue were carried out, and the heating curve of the materials under different microwave powers (250–450W) was made. From these parameters, an optimized operation parameter of microwave roasting technology, the thickness of CuCl residue filter cake to be microwave roasted should be 2cm, was deduced.