Fundamental And Applied Study Of Fine Bubble Intensified Liquid Phase Oxidation Technology In Sub-molten Salt Medium

Reactive oxygen species(ROS,HO2-,O2-,O22-,etc.)in the sub-molten salt medium are highly reactive and can effective promote the decomposition and oxidization amphoteric metal oxide ores.The reactivity of the sub-molten salt medium is dependent on the amount of the reactive oxygen species generated in the medium.Because fine bubble can efficiently improve the oxygen solubility and promote the formation of ROS in the medium,we have studied the fine bubble intensified oxidation technology to optimize the sub-molten salt technology for the co-extraction of vanadium and chromium vanadium slag,and developed a new method to treat vanadium slag.By manipulation the generation of ROS in the medium,highly efficient recovery of vanadium from high-grade vanadium slag and co-extraction of vanadium and chromium from chromium-containing vanadium slag have been realized.The feasibility,mechanism,process parameters and kinetics of leaching process were systematically studied,providing theoretical support and application guidance for the design of new process and achieving efficiently extract vanadium and chromium from the vanadium slag using sub-molten technology.The thesis achieved the following innovative results:1.A new method for quantitative determination of ROS in high temperature and high alkali concentration sub-molten salt medium was established based on the oxidation of Cr(?).The effect of temperature and alkali concentration on the generation of ROS in the sub-molten salt medium was systematically investigated.The results showed that the amount of ROS in the media was in general governed by the reaction thermodynamics including the OH-concentration,temperature and the oxygen solubility and kinetics including the mass transfer and viscosities of the medium.As the reaction temperature increased,the viscosity of the sub-molten salt medium decreased,improving the mass transfer and consequently the increase of ROS.As the alkali concentration increased,more OH-ions were provided,favoring the generation of ROS thermodynamically;however,solubility of oxygen and the mass transfer coefficient of the medium was reduced significantly,in favor of the ROS generation.The balance of the two controversial effects resulted in the observed initial increase and subsequent decrease of the ROS when alkali concentration increased.2.Experiments have confirmed that fine bubbles could significantly enhance the oxidative decomposition of vanadium iron spinel minerals in sub-molten medium.Using the typical Finnish vanadium slag as an example,highly efficiency leaching of vanadium could be achieved at 110 ? in 40%NaOH solution due to the fine bubble intensification effect.The kinetic study showed that without the fine bubble intensification,the leaching rate of vanadium was controlled by the interface chemical reaction and the activation energy of apparent reaction was 28.88 kJ/mol.In contrast,with the fine bubble intensification,the leaching rate of vanadium was controlled by internal diffusion and the activation energy of the apparent reaction was 20.17 kJ/mol.These results suggested that the fine bubble could promote the generation of ROS in the medium,decrease the reaction activation energy and promote the oxidation of vanadium slag.3.The effect of chromium on vanadium leaching was studied using fine bubble intensified sub-molten salt technology,and the chromium-containing vanadium slag from Chengde Steel and Desheng Steel was investigated.The leaching results showed that the chromium content in vanadium slag had significant effects on the vanadium leaching.Compared with the Finnish vanadium slag,the leaching of vanadium was much more difficult due to the presence of chromium spinel in the slag,and the alkali concentration was 20%higher and the temperature was 20 ? higher in order to leach out the vanadium effectively.The kinetic study showed that the leaching of vanadium was controlled by internal diffusion and the leaching of chromium was controlled by chemical reaction.Further,the increase of chromium content was unfavorable for the leaching of vanadium as evidenced by the increase of the vanadium leaching apparent activation energy as the chromium content increased.4.Experimental results showed that the optimal conditions for vanadium and chromium leaching were also the optimal conditions for the ROS generation,indirectly proving that the ROS in the sub-molten salt medium was critical for the efficient decomposition and oxidation of minerals.The fine bubble intensified sub-molten salt technology could achieve co-extraction of vanadium and chromium under mild reaction conditions,and the technology has been examined in 1,000 ton/a piolet plant test and 50,000 ton/a industrial scale production line.Synergistic extraction of vanadium and chromium from chromium-containing vanadium slag at 150 ? was realized for the first time on industrial production line,suggesting the new technology has great potential and prospects for large scale industrial application.