Study On The Extraction Behavior And Mass Transfer Process Of Yttrium Under The Action Of Microfluid

In China,solvent extraction is widely adopted as the dominant process in the single rare earth separation,and this process is mainly carried out in mixer-settler with P507?2-ethylhexylphosphonic acid mono-2-ethylhexyl ester?as the main extractant.The traditional extraction process has some disadvantages,such as long reaction time,high energy consumption,and large space occupation.While microfluidic extraction technology has the advantages of high specific area,short response time,and high mass transfer rate due to its small channel size.Therefore,a new idea of extracting yttrium in microfluidic channel with saponified P507 is proposed in this work so that the extraction process of high efficiency,green,low consumption,and safety can be achieved.In this paper,the aqueous phase and organic phase were yttrium chloride and saponified P507,respectively.The characteristics of the two-phase flow in microchannels were explored to solve the key common problems in microfluidic extraction of rare earths;and the effects of pH,flow rate and channel size on the extraction and mass transfer were studied to obtain the optimal conditions.The mechanism of microchannel action was revealed by comparing extraction efficiency and mass transfer coefficient of Y-type and T-type microchannels.Firstly,the two-phase flow characteristics in the Y-type and T-type microchannels were analyzed.The results showed that desired laminar flow was presented under the low rare earth concentration?[RECl₃]<0.1mol/L?,low extractant concentration?[P507]<1.0mol/L?and flow rate was larger than 1000?L/min.However,slug flow was presented under high rare earth concentrations?[RECl₃]?0.1 mol/L?,high extractant concentrations?[P507]?1.0 mol/L?and flow rates less than 1000?L/min.Comsol Multiphisics software was also used to simulate the multi-physics field under the laminar flow conditions which revealed the process of laminar flow and slug flow pattern.Secondly,the extraction behavior and mass transfer were studied in Y-type microchannels.The results showed that the extraction efficiency increased with an increase of pH and channel length,and decreased with an increase of the two-phase flow rate and channel width.The residence time of microfluidic extraction varied from 2.25 to45 seconds,which was much lower than the conventional extraction time of 10 minutes.The volumetric mass transfer coefficient increased with an increase of pH and flow rate,and decreased with the increase of channel size.The volumetric mass transfer coefficient ranged from 0.218 to 1.642s^-1,which was higher than the conventional mixer-settler(1.01×10^-21.97×10^-2s^-1)and centrifugal extractor(1.55×10^-24.65×10^-2s^-1).Under the conditions:a pH of 1.5,a flow rate of 10?L/min,a chip width of 300?m and a chip length of 25cm,the yttrium extraction efficiency and volumetric mass transfer coefficient?K_L??were 90.5%and 0.333s^-1,respectively.Then the extraction behaviors and mass transfer were studied in T-type microchannels.The results showed that the extraction efficiency increased with an increase of feed solution pH and channel length,and decreased with an increase of the two-phase flow rate and channel width.The volumetric transfer coefficient increased with an increase of pH and flow rate,and decreased with an increase of channel size.Under the conditions:a pH of 1.5,a flow rate of 100?L/min,a chip width of 1/16inch and a chip length of 100cm,the yttrium extraction efficiency and volumetric mass transfer coefficient?K_L??were 90.4%and 0.011s^-1,respectively.Finally,the extraction behavior and mass transfer effect yttrium extraction in the Y-type and T-type microchannels were compared.The results showed that few variations between the extraction efficiencies of the Y-type and T-type microchannels were existed.Additionally both of two extraction processes boasted higher extraction efficiencies than that of conventional extraction,but the volumetric mass transfer coefficient of the Y-type microchannel extraction process was much higher than that of T-type microchannel.Thus the mass transfer effect in Y-type microchannel was much higher than that in T-type microchannel.In addition,the interfacial area and volumetric mass transfer coefficient of microfluidic extraction and conventional extraction were compared.It was found that the microchannel has a higher specific area and volumetric mass transfer coefficient than that of conventional extraction,so the extraction process could be strengthened by microfluidic extraction.In summary,extracting yttrium could be efficiently achieved in microfluidic channel by using saponified P507 as the extractant.These researches provide a theoretical basis for the industrialization of microfluidic extraction in rare earth industries.