| In view of the key scientific problem of lithium and magnesium separation and the high-value utilization of magnesium resources in high Mg/Li ratio brine,a innovation technique for the comprehensive utilization of lithium and magnesium resources by extracting magnesium to separate lithium and magnesium and then direct electrodeposition of magnesium from organic phase was proposed in this thesis.The optimization of parameters for magnesium extraction from high Mg/Li brine and the extraction thermokinetics were carried out first.Subsequently,the electrodes for magnesium electrodeposition was synthesized and optimized,based on which the direct electrodeposition of magnesium from organic phase was conducted.Main conclusions presented in the thesis are summarized as follows:(1)The extraction of magnesium from high Mg/Li brine was carried out using(P204+MIBK+[P4446][NTf2])system,and the parameters were optimized.The optimal conditions are:organic phase composition P204:MIBK:[P4446][NTf2]=8:11:1,saponification rate of P204=70%,extraction ratioR(O/A)=7.5:1,brine pH=4.61,oscillation frequency 250 r/min,oscillation time 20 min,and resting time 10 min.Under these conditions,the single-stage extraction rate of Mg2+ reached 73.8%,the distribution ratios of magnesium and lithium were 3.41 and 0.33,the separation coefficient between magnesium and lithium was 10.33,and the electrical conductivity of the organic system was 235.1 ?S·cm-1.The separation between magnesium and lithium in high Mg/Li brine was successfully realized on the premise of high conductivity of the system.Based on these results,the thermokinetics of magnesium extraction by the(P204+MIBK+[P4446][NTf2])system was carried out using isothermal microcalorimetry.The reaction heat of magnesium extraction by this system at 298.15,313.15,and 328.15 K was obtained,and meanwhile the variations of reaction process and rate with time at different temperatures were simulated and calculated.The results showed that the reaction rate increased significantly with the increase of temperature,but the reaction heat decreased,indicating that high temperature was not conducive to the extraction of magnesium.(2)In order to obtain the electrode system for magnesium electrodeposition from organic phase,three ferrocyanide compounds[K2MFe(CN)6,M=Cu.Co.Ni]were synthesized by the co-precipitation method,and the corresponding electrodes were then prepared.The effects of different conditions on the adsorption and desorption of K+/Na+were investigated and found that the K2CuFe(CN)6 electrode has better performances under the same conditions.When the electrode potential is larger than 0.8 V,the K2CuFe(CN)6 electrode is prone to release K+by losing electrons,while when the potential is within-0.4 V?-0.6 V,the K2CuFe(CN)6 electrode is easy to adsorption K+/Na+by obtaining electrons.That means the K2CuFe(CN)6 electrode has good recycling performance and can be used to equilibrate the electron transfer during the electrodeposition of magnesium in organic phase.(3)The electrodeposition of magnesium from organic phase after magnesium extraction was carried out,and the effects of different electrode systems,electrodeposition conditions on the electrodeposition were investigated.The results showed that the direct electrodeposition of magnesium in organic phase can be realized by using carbon paper or aluminum sheet as the working electrode,K2CuFe(CN)6 as the counter electrode,and Ag/AgCl electrode as the reference electrode,respectively.However,probably resulting from the low conductivity and current efficiency of the organic system,the amount of magnesium obtain by electrodeposition was low.In order to improve the electrodeposition efficiency of magnesium,it is necessary to further study the organic extraction system so as to obtain organic extraction systems with higher conductivity and extraction rate. |
PDF Full Text Request