Applied Fundamental Research On Co-extraction Of Vanadium And Chromium By External Field-assisted Sub-molten Salt Method

The area of western Panzhihua(Sichuan province,China)is rich in vanadium titano-magnetite resources with high chromium content.The reserves attain 3.6 billion tons,in which contains 6 million tons’chromium.It has extremely high mining values.By oxidative blowing the vanadium-containing molten iron which from vanadium titano-magnetite,the high-chromium vanadium slag can be formed.It is an important raw material for vanadium and chromium extraction.However,in the traditional sodium roasting process of vanadium slag,the recovery of vanadium is less than 80%and the chromium can not be extracted.Moreover,roasting process produces a large amount of high-salt ammonia nitrogen wastewater,harmful kiln gas and high-sodium tailings.The end-of-pipe treatment of these wastes is difficult,which seriously restricts the green sustainable development of the vanadium industry.To solve these problems,Institute of Process Engineering of the Chinese Academy of Sciences proposed an efficient and clean extraction method of vanadium and chromium,named sub-molten salt.The vanadium and chromium products can be efficiently separated and obtained.It can avoid the generation of three wastes at the source,which is a green upgrade of the vanadium extraction technology.In order to further realize the application of sub-molten salt technology in high-chromium vanadium slag,this work proposed an external field-assisted sub-molten salt method.Using the external field,the oxygen dissolution and diffusion is intensified,and more reactive oxygen species(ROS)can be generated.The vanadium and chromium in high-chromium vanadium slag can be simultaneously oxidized and leached under mild conditions,which can provide theoretical support for the industrial application and promotion of sub-molten salt clean production technology.The work achieved the following innovative results:(1)A new method of vanadium and chromium co-extraction from vanadium slag by microbubble-reinforced sub-molten salt was proposed.By re-designing and improving the microbubble generating device,the optimal equipment paddle structure for oxygen mass transfer and ROS generation was mastered.And under this condition,the vanadium chromium dissolution rule in high chromium vanadium slag was systematically studied to obtain high chromium.Obtained the optimal reaction conditions:Na OH concentration of 50 wt.%,reaction temperature of 140 ~oC(atmospheric pressure condition).The extraction rates of vanadium and chromium reached 87.48%and 73.00%,respectively.It achieved the simultaneous oxidation of vanadium and chromium in high-chromium vanadium slag under mild conditions,which provided a strong support for the industrial application of microbubble strengthening technology.(2)The effect of oxygen pressure and various reaction parameters on the co-extraction of vanadium and chromium co-extraction from vanadium slag in the pressure field enhanced sub-molten salt medium was systematically studied.For the first time,the high-chromium vanadium slag was efficiently co-extracted under mild conditions(at conditions of 200 ~oC and 50 wt.%Na OH).The leaching rates of vanadium and chromium attained 98.3%and 93.3%,respectively.The kinetic study shows that the vanadium and chromium leaching process obeys the unreacted shrinkage nucleus model and is controlled by the internal diffusion.The apparent activation energies of vanadium and chromium were 27.58 k J/mol and 36.74 k J/mol,respectively.(3)The reaction principle of sodium chromate and low valence metal oxides in vanadium slag within sub-molten salt reaction conditions was intensive studied.By strengthening the oxidation-reduction reaction of oxygen and low valence metal oxides in vanadium slag at low temperature(≤120 ~oC),the phase structure of sodium chromate reduction product can be regulated,which can inhibit the conversion process of sodium chromate to stable anti-spinel phase.It solves the problem of low leaching rate of chromium in the circulating medium,and the conversions of vanadium and chromium were 95%and 90%,respectively.This research work can provide technical support for the industrial application of sub-molten salt technology for high-chromium vanadium slag.