Microwave Prepared Synthetic Rutile Research, New Technology And Equipment

Titanium dioxide pigments are manufactured by the chloride or sulfate processes, in which natural rutile or synthetic rutile is used as raw materials. Since available resources of high grade natural rutile tend to diminish, to explore new method to produce synthetic rutile with low energy consumption and less environment pollution is necessary. Thus, producing synthetic rutile from abundantly available high titanium slag becomes a major alternative.Microwave heating has been widely used in research and industrial processes. Compared with conventional heating techniques, the advantage of using microwave heating is that microwave heating is both internal and volumetric heating. Therefore, microwave heating is very rapid, resulting in energy savings and shortening the processing time. Since microwave heating has a high efficiency to convert electricity energy to electromagnetic energy. Additional advantages include greater control of the microwave heating process, no direct contact between the heating source and heated materials and reduced equipment size, which can fulfil the mode of green and clean manufacturing.The work addresses preparation of a new method for high grade synthetic rutile using combined microwave heating and mineral processing technology. The new processing was basically in accordance with the structure and characteristic of high titanium slag from Yunnan Province. The thermal stability, crystal structures, microstructure, surface chemical functional groups and molecular structures of samples were characterized by thermogravimetry and differential thermal analysis (TG/DTA), X-ray diffraction (XRD), scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR) and Raman spectroscopy techniques, respectively. High titanium slag mainly contains iron titanium oxide, FeO, Al2O3, SiO2, MgO, MnO, and minor elements, such as S, P and C. It can be seen from XRD results that anatase TiO2and Fe3Ti2O10(anosovite-type of M3O5) were mainly crystalline compounds in high titanium slag. In addition, a minor amount of rutile TiO2was present. From the SEM-EDAX, the results indicated that the surface structure of primary particles with tighter and smoother surface morphology could be observed in the samples. And more fine cracks could be found on the surface from the SEM image. It has confirmed from FT-IR that the IR bands at493.3cm-1could be ascribed to the bending vibrations of Ti-O and Ti-O-Ti of the TiO2units. The Raman spectrum of the samples showed peaks at155.2,195.8,393.7,515.5and637.3cm-1which were directly attributable to anatase, Ti2O5, and Ti2O3. DTA curve analyses show the exothermic peaks at850.0℃, the thermal analysis results indicate that the anatase TiO2was irreversible conversion to the rutile TiO2in this temperature range. The transformation of anatase TiO2to rutile TiO2was influenced by several experimental conditions, such as temperature, particle size and synthetic method of dioxide.Microwave absorbing properties of high titanium slag were investigated using microwave cavity perturbation technique. By analyzing of the changing behavior and calculating the amplitude of voltage and the shift of frequency of the microwave spectrums, the microwave absorbing properties of samples were obtained. The temperature rise curve of high titanium slag in microwave heating process was acquired. Effects of particle size of high titanium slag and mixtures of high titanium slag with different mass fractions of V2O5on microwave absorbing properties were investigated systematically. The results show that high titanium slag has good microwave absorption property, and it can be heated effectively and efficiently in the microwave field. High frequency shift and low amplitude of voltage make high titanium slag an ideal microwave absorbent.180μm of particle size and10%mass fraction of V2O5were found to be the optimum conditions for microwave absorption, respectively.The effects of microwave heating temperature and holding time on the crystal phase transformation of TiO2, content of TiO2, sulfur content and carbon content were systematically investigated under microwave heating processing. With increasing microwave heating temperature and holding time, the content of TiO2, sulfur content and carbon content decreases, shorten processing time remarkably compared to conventional heating. It can be observed from XRD that the intensity of diffraction peak of the lattice planes (101),(111) and (211) of rutile TiO2were increased and the intensity of diffraction peak of anatase TiO2and Fe2Ti2O1o were decreased. With increasing microwave heating temperature and holding time, the content of TiO2, sulfur content and carbon content decreases, shorten processing time remarkably compared to conventional heating. The intensity of Raman vibrations bands of anatase TiO2at396.8,515.2and637.0cm-1decrease, the intensity of Raman vibrations bands of Ti3O5and the intensity of Raman vibrations bands of Ti2O3at153.2cm-1and197.2cm-1disappears, respectively. And the intensity of Raman vibrations bands of rutile TiO2at244.6,445.6and615.0cm-1increase, and the peaks individually redshifts to low-wave number after microwave irradiation. It can be observed from FT-IR that the most obvious change in the spectrum is that the absorption band the bending vibrations of H-O-H at1697.0cm-1disappears, and the bands of the bending vibrations of O-H at1089.6cm-1become barely visible, and the stretching vibrations of octahedral metal ion in the TiO2units at529.3cm-1individually blueshift to high-wave number. From the SEM image, the results indicated that microwave treated samples appears irregular with a complex acicular structure. The pores of samples surface can be opened through microwave irradiation, which lead to increased surface area. The impurity minerals such as Si, Al, Mg and Mn in the samples have been enriched into the gray granule. They were propitious to the minerals separation processing.Microwave heating temperature, microwave power, and time were the main three dominant factors selected as independent variables. Synthetic rutile content was selected as a dependent variable affected by these factors. Response surface methodology and central composite design were implemented to optimize the experimental conditions for preparing synthetic rutile from high titanium slag by microwave irradiation. By applying least squares method and multiple regression analysis on the experimental results, the second order polynomial equation was found to explain the dependent variable by considering the independent variable. The coefficient of determination (R2) of the model was obtained0.9691, and the value of the adjusted determination coefficient (adj.R2) was0.9382, which suggested that there were excellent correlations between the independent variables. The F-value of the lack-of-fit of3.47implies the lack-of-fit is significant relative to the pure error. In the present case, a very lower value of CV (0.45%) clearly showed a high degree of precision and a good deal of reliability of the experimental values. The optimum experimental conditions of microwave roasting high titanium slag obtained from solving nonlinear regression equation and analyzing response surface and contour. These optimal conditions were microwave temperature of936℃, microwave power of2.5kW, and holding time of48min. Only small deviations were found between the experimental values and the predicted values.In order to improve the quality of TiO2, the minerals separation processing has been proposed for removing the impurity minerals from the microwave roasted production. The effects of milling time, magnetic field strength and flotation reagent on titanium dioxide of microwave roasted samples. Milling time of60min, magnetic field electric current of5A, CMC inhibitor used in flotation separation of250g/t. hydroximic a cid catching agent used in flotation separation of300g/t, the titanium dioxide content of91.25%was obtained, while the synthetic rutile reaches the National Class I Standard.The requirements of the reaction behaviour of microwave high temperature tube reactor during the actual reaction of microwave roasting high titanium slag were studied in this article. According to the classical electromagnetic theory, the sizes of the microwave resonant cavity were designed. In order to make sure that microwave will efficiently transfer into the microwave resonant cavity, the cross-section size of the rectangular waveguide were obtained on the basis of an analysis of calculation results. We can adopt a reasonable choice for the power transmission, it would ensure that microwave were distributed in various patterns in the microwave resonant cavity and obtained a uniform and power microwave field. The microwave power supply for the microwave high temperature tube reactor was made of2magnetrons using the non-coherent power synthesis of power technology, which was cooled by water circulation, at2.45GHz frequency and1.5kW power. The microwave high temperature tube reactor consists of an anode power, a filament power, an electrical systems and a cooling system of the magnetron and the electrical components. Therefore, the microwave high temperature tube reactor can work continuously at high temperature conditions and high power density. Considering the integrated requirements of low dielectric constant, low power consumption and low heat expansion coefficient, the special microwave ceramic tube was selected with different thermal insulation material. The temperature was measured using a Type K thermocouple, placed at the closest proximity to the sample. The thermocouple provides feedback information to the control panel that controls the power to the magnetron, controlling the temperature of the sample during the microwave treatment process in order to prevent the sample from overheating. Modelling, optimization design and simulating assembly of microwave resonant cavity, rectangular waveguide, power transmission and it spare and accessory parts of the microwave high temperature tube reactor using Solid Edge3D design software.In this study, analytic hierarchy process and fuzzy comprehensive evaluation were implemented to the analyzed and assessed for the life cycle assessment of microwave high temperature tube furnace. The effects of the evaluation aspect, such as environmental impact, resource consumption, economy, capability and function, on the mathematical model were systematically investigated. The process involves constructing hierarchical structure, comparing pairwise comparison matrices, establishing assessment criteria, setting weight matrix and fuzzy assessment matrix, and then calculating green degree of microwave high temperature tube furnace by fuzzy mathematical method and statistical technique. The results show that microwave high temperature tube furnace has a good green degree, which can be fulfill with the aim of green manufacture, especially in energy consumption, processing time and environmental protection. Life cycle assessment of microwave high temperature tube furnace using analytic hierarchy process and fuzzy comprehensive evaluation was an easy and practical way to provide a mechanism for improving microwave high temperature tube furnace quality with low resource consumption and less environment pollution.