Clean Microwave Low Temperature Drying Process Panzhihua Titanium Concentrate

Ilmenite concentrate is used to produce titanium dioxide, titanium slag and synthetic rutile as an important raw material, which is usually selected from ilmenite and pseudorutile ores. It was necessary to enrich by gravity, magnetic and flotation separation because of its low grade. However, high moisture is contained in ilmenite concentrate after dressing, and the removal of moisture was an important pre-processing. Conventional drying causes a lot of lust and flotation agent volatilization, which seriously pollutes the environment and goes against production. Thus, there is a critical need for a new drying method.In view of above problem in rotary-kiln drying ilmenite concentrate, the paper puts forward a new process of drying ilmenite at lower temperature based on microwave characteristic of selective heating. The laboratory and pilot test of microwave drying ilmenite at lower temperature were completed and the dielectric property and temperature-rising characteristics of ilmenite in microwave field was measured and analyzed, which lay the foundation for experiment. Study contents, specific works and the conclusions of the paper are as follows.(1) The dielectric property of ilmenite within different moisture was measured in the microwave resonant cavity perturbation method. The relationship between dielectric parameter (dielectric constant ε’,dielectric loss ε", dielectric loss tangent tan5and the penetration depth) and moisture in ilmenite was analyzed and fitted a corresponding regression equation, by which the dielectric parameter of ilmenite could be predicted in the moisture range of1-5%in future. The dielectric constant ε’, dielectric loss ε" and dielectric loss tangent tan8were directly proportional to moisture in ilmenite. The higher the moisture was, the greater their values and the better the absorbing properties of ilmenite. On the contrary, the penetration depth was inversely proportion to moisture. The higher the moisture was, the smaller its values. When the moisture of ilmenite was greater than2%, the penetration depth tends to the constant,0.5cm.(2) The heating rate equation of ilmenite in microwave field was deduced by analyzing the heating curve which includes rapid heating stage, constant temperature stage and continued heating stage. The removal of moisture was little in rapid heating stage and mainly happened in constant temperature stage. The strong absorbing property of ilmenite without moisture led to continued heating stage. By the heating rate equation, the heating rate of ilmenite was not only related to its heat capacity, but its dielectric parameter (dielectric loss ε"). Thus, the absorbing property of ilmenite was qualitatively judged by the heating rate in microwave field.(3) The lab test of microwave drying ilmenite at lower temperature was conducted and optimized with Response surface methodology. The optimum conditions for drying ilmenite has been identified to be a drying temperature of70℃,drying duration of14min and material thickness of2.2cm. The optimum conditions resulted in the average dehydration rate of89.53%and has a relative error of0.523%compared with theoretical value, which shows that the model precision is higher and accurately reflect the relationship between dehydration rate and other factors. Comparing with conventional drying at lower temperature, it shortened the drying duration and improved the drying efficiency in the case of avoiding the flotation agent volatilization.(4) A pilot-scale test of microwave drying ilmenite at lower temperature was carried out by static drying and dynamic drying, respectively, on the basis of lab test. The influence of microwave power and material thickness on dehydration rate and special energy consumption is significant. The experimental results showed that microwave dynamic drying was superior to static drying in term of drying ilmenite. especially improved drying efficiency and reduced special energy consumption in the meantime. The optimum conditions for drying ilmenite has been identified to be a microwave power of36kW, material thickness of1.5cm, drying duration of15min. The optimum conditions resulted in dehydration rate of90.8%.