Dielectric Characterization and Microwave Roasting of Molybdenite Concentrates at 915 MHz Frequency

The magnetic hysteresis loop was measured to know the magnetic property of molybdenite concentrate.In order to evaluate its microwave absorption capacity, the dielectric properties of molybdenite concentrate was investigated using cavity perturbation method at 915 MHz dependent on densities and temperatures.The parameter data were fitted using regression fit and a model related to the same density and temperature ranges was developed.A nonlinear surface fitting was used to present visually the effect of dielectric parameters on the microwave penetrate depth of molybdnite concentrate.The crystal products of MoO 3 obtained from microwave roasting at different temperatures were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD).The results show both the dielectric constants and loss factors increase in the increase of apparent densities and temperatures with different growth rates in the experimental range.Due to the distinguished trend of dielectric performance dependent on temperatures, two parts in the heating scenario for the molybdenite concentrate samples were divided.The microwave penetration depth is inversely proportional to both apparent densities and temperatures.The nonlinear fitting surfaces indicate the increase of dielectric loss provides an enough decrease in microwave penetration depth.In contrast, the dielectric constant has a positive effect for it.Pure MoO 3 was produced at 800 ℃ by using microwave energy.This work can be helpful to design and simulate microwave system for efficient beneficiation of molybdenite concentrate and to prepare molybdenum products from this concentrate.

Dielectric Properties and Microwave Heating of Molybdenite Concentrate at 2.45 GHz Frequency

Dielectric properties were measured using cavity perturbation method. The temperature rising behaviors of molybdenite concentrate were investigated in the field of microwave. This process was conducted to show the microwave absorption properties of molybdenite concentrate and the feasibility of microwave roasting molybdenite concentrate to prepare high purity MOO3. The dielectric constant,dielectric loss,and loss tangent increase from 3. 51 to 5. 04,0. 22 to 0. 51 and 0. 065 to 0. 102 respectively. They are proportional to the apparent density of molybdenite concentrate in the range of 0. 9-1. 4 g/cm3. The results show that the molybdenite concentrate has good microwave absorption capacity in the conventional density range. The temperature rising curves show that the apparent heating rate of the molybdenite concentrate increases with the increase in microwave power and decreases with the increase in the sample mass and thickness. The temperature of concentrate sample of 100 g reaches approximately 800 ℃ after 5 min of microwave treatment at 0. 5 kW of power. Our findings show that it is feasible to prepare high-purity MOO3from molybdenite concentrate by microwave roasting.

Removing chlorine of CuCl residue from zinc hydrometallurgy by microwave roasting

Most Zn hydrometallurgy factories adopt Cu2SO4 as a dechlorination reagent from zinc solution nowadays, thus much CuCl residue is produced. The existing process of treating this residue is washing with water or sodium carbonate solution, which would cause a lot of troubles to water treatment and waste discharge. A method of microwave roasting was adopted for dechlorination of CuCl residue. A 1.5 kW microwave roasting equipment with dust collection and tail gas adsorption systems was set up and applied during the experiment. By investigating the effect of temperature, heat preservation time, moisture content of raw material and grain size of samples on the dechlorination, the optimal experimental condition is obtained. When the samples with 2% moisture and <150 μm grain size are microwave roasted at 400 °C for 2 h, the Cl content turns from 14.27% to 1.35% and the dechlorination rate is as high as 90%, while that with conventional heating is only 60%-80%. The phase change of the roasting process investigated with X-ray diffraction verifies that CuCl in CuCl residue is removed by being transformed into CuO.

Dechlorination of zinc dross by microwave roasting

Traditional treatments of zinc dross have many disadvantages,such as complicated recovering process and serious environmental pollution.In this work,a new process of chlorine removal from zinc dross by microwave was proposed for solving problem of recycling the zinc dross.With better ability of absorbing the microwave than zinc oxide,the main material in zinc dross,chlorides,can be heated and evaporated rapidly during microwave roasting.Various parameters including roasting temperature,duration time and stirring speed were optimized.The microstructure of roasted materials was characterized by X-ray diffraction(XRD) and scanning electron microscope(SEM).The content of the chloride was analyzed by the method of chlorine ion selective electrode.The experiments indicate that the best duration time is 60 min with a stirring speed of 15 r/min during the microwave roasting process.The dechlorination rate reaches peak value of 88% at 700 ℃.The chlorine is removed as HCl gas when water vapor is used as activating agent,which means that it can be recovered into hydrochloride acid.