Synthesis Of Ion-sieve H₄Mn_5-xZr_xO₁₂（X=0～2）by Dual-Template Ion-Sieve And Determine The Selective Exchange Of Li⁺

Sea water, desalinated seawater, salt lake brine contain a large number of low concentrations of lithium, lithium is extracted from these low concentrations of liquid lithium resources by ion exchange method, the key technology is the Ion-sieve must has high selective, high saturation exchange capacity, and solution loss is low.Three-dimensional ordered nanopore ion sieve H4Mn5-xZrxO12is not only an excellent ionic conductivity of lithium-ion battery cathode material, but also as a specific ion memory effect ion exchange material and environment-friendly, could be used for the extraction of lithium from salt lake brine and seawater.The ion sieve of H4Mn5-xZrxO12synthetic steps:Firstly, we should synthesize the hard template poly methyl methacrylate micro balls(PMMA), by using the method of emulsion polymerization, and studied the influence of the particle size of the microsphere size and the particle size distribution range of factors. Then assembled synthetic microspheres with a high-speed centrifugal sedimentation method, obtained PMMA colloidal crystal template. We use triblock copolymer (F-127) as a soft template (or cetyl trimethyl ammonium bromide can be used), lithium nitrate and50%of manganese nitrate as the metal precursor, ethanol as solvent, and used the dual template to synthesis precursor solution, after filtration, drying, roasting after two-stage thermostat, we can get the sieve precursor Li4Mn5ZrxO12. Then with acid modification and low temperature dried, and we can finally get the H4Mn5-xZrxO12ion sieve.By using SEM, XRD, differential thermal gravimetric analysis, saturated exchange capacity, pH titration curves characterized the morphology, decomposition temperature, structure of the material, and ion-exchange properties. The results show that:PMMA microsphere size with monomer general increase in the amount of initiator increases and decreases with the increase of the amount of emulsifier, with the increase of reaction temperature, the speed has little effect on the particle size. The optimum calcinations of lithium ion sieve precursor Li4Mn4.5Zr0.5O12conditions as follows:heating rate of2℃/min, the two-stage thermostat roasting300℃roasting4h, calcined at500℃8-10h. The most suitable acid modification agents were0.7mol·L-1of ammonium persulfate, and it has a good acid stability and the loss rate of Mn is about0.26%, and has a high selectivity of lithium Li+about93%. Simultaneous determination of lithium ion sieve adsorption exchange of Li+ion exchange isotherms at different temperatures, and draw out the H+-Li+exchange system ion exchange isotherms. We can use the Pitzer electrolyte solution theory to calculate the activity coefficient of the ion-exchange system, and then get the H+-Li+exchange thermodynamic equilibrium constants of Li+KLiaH, the standard Gibbs free energy△G0, the thermodynamic parameters of the standard enthalpy△H0and standard entropy change△S0, and so on. According to these we can judge the reaction directional, endothermic or exothermic.