Characterization Of Nanobubbles And Its Application In Reverse Flotation Of Hematite

Mineral resources are an important material foundation for national economic construction and social development.Iron ore has great influence on national economy,but it is the ore with the highest import dependency(more than 80%).However,with the reduction of China’s iron ore resources and the decline of ore quality,the grinding fineness gradually increases and the flotation difficulty increases.Therefore,it is of great significance to develop efficient iron ore flotation methods to make full use of domestic iron ore resources,relieve the pressure of China’s current import of iron ore,and maintain the supply of high-quality iron ore raw materials.Anshan type(sedimentary metamorphic type)is the most abundant iron ore deposit type in China,accounting for about 50% of the national iron ore resources.Because the dissemination particle size of this kind of ore is too fine(90% is less than 0.038mm),it is difficult to liberate the mineral and fine grinding is necessary to achieve proper liberation degree.Therefore,the flotation feed often contains a large number of fine particles that are only a few microns or even less than one micron.Conventional flotation methods are difficult to separate fine particles and the efficiency is low.The nanobubble flotation technology developed in recent years can significantly enhance the flotation of fine-grained minerals and is suitable for improving the flotation efficiency of Anshan type of hematite.However,most of the previous studies on nano-bubble flotation focus on the application of nanobubbles to flotation.There is much less research on the physical and chemical properties of nanobubbles themselves,particularly the size,surface potential and concentration of nanobubbles generated by different methods and under different conditions,due to lack of appropriate techniques.In this paper,advanced nanobubble characterization technology was used to perform in-depth study of the special physical and chemical properties and surface properties of nanobubbles and the flotation effect of nanobubbles on Anshan-type lean hematite was investigated.The specific research contents are as follows:(1)The bulk phase nanobubbles generated based on the principle of hydrodynamic cavitation are taken as the research objects.The size distribution of nanobubbles and the variation of Zeta potential are studied using dynamic light scattering Malvern Nano ZS 90 nanometer particle size and potential analyzer under the conditions of different surfactant dosage,air flow rate,air pressure,liquid flow rate,solution p H and other parameters.In order to visually verify the measurement results of dynamic light scattering instrument and analyze the influence of different conditions on the concentration of nanobubbles,Olympus BX53 M optical microscope was used to take micro-photographs of the generated nanobubbles.Image J image processing software was used to count the particles in the obtained nanobubble images and the variation of nano-bubble concentration was studied.The experimental results show that the size of nanobubbles decreases with the increase of solution p H,surfactant concentration and liquid flow rate in cavitation tube but increases with the increase of air pressure and air flow rate.The electronegativity of bubble surface is positively correlated with p H value and there is a certain correlation between Zeta potential value and size of nanobubble.The concentration of nanobubbles increases with the increase of frother dosage,solution p H and cavitation tube liquid flow rate,but decreases with the increase of air pressure and air flow rate.This study also found that nanobubbles can exist stably for as long as ten days.(2)With the mixed magnenetic separation concentrate and hematite from Anqian concentrator of An Steel Group as the flotation feed sample,the effects of nanobubbles on the reverse flotation of fine iron ore under different dosages of several reagents(activator Ca O,collector TD-II,depressant starch)were studied by use of the mechanical flotation machine.The experimental results show that use of nanobubbles had significant effects on flotation performance and the degree of improvement depended on the dosage of reagents.When the depressant dosage varied from 0.25-2.0 kg/t,use of nanobubbles improved the Fe grade of concentrate by 1-10% and the recovery by 15-24%.At different activator Ca O dosages ranging from 0.25-2.0 kg/t,the existence of nanobubbles increased the concentrate recovery by 5-10% while the grade was increased slightly.When the collector dosage varied from 0.1-1.0 kg/t,the use of nanobubbles had little effect on concentrate grade,but improved concentrate recovery by 7-21%.Nanobubble flotation also greatly improved the flotation kinetics,reducing the flotation time from 3 min to 0.5 min.