Study On Adsorption Of Rubidium And Cesium Ion By Granular Ammonium Molybdophosphate And Its Composite Ion Exchanger

The salt lake brain in the salt lake of Qinghai province and Tibet is abundant inrubidium/cesium ion, which is an untapped rubidium and cesium resource. Theenrichment, separation and purification of rubidium/cesium ion are still unresolvedtechnical problems. Ammonium molybdophosphate （AMP） has good selectiveadsorption for low concentration of rubidium/cesium ion, but its micro-grain structurelimits its application in industry.In this paper, granular ammonium molybdophosphate and its complex werepapered to change the micro-grain structure of the conventional ammoniummolybdophosphate so that it is suitable for enrichment and separation ofrubidium/cesium ion from salt lake brine. Nucleation mechanism and crystal growthkinetics of granular ammonium molybdophosphate were studied, and the appropriateconditions to prepare granular ammonium molybdophosphate were determined. Theadsorption properties for rubidium/cesium ion from salt lake brine on ammoniummolybdophosphate-titaniumpyrophosphate （AMP-TiP₂O₇） and its analyticity andrecyclability were studied by dynamic adsorptive method. The experimental resultsshow:The suitable conditions for preparing granular AMP crystal with big mean grain,narrow particle size distribution, regular nucleation and high equiaxial degree are thatthe concentration of Mo is0.95mol/L, the dripping time is13.3h, the reactiontemperature is15℃and the aging time is24h. Molecular formula of granular AMPwhich prepared in this condition is （NH₄）₃PMo₁₂O₄₀·0.4H₂O, meanwhile themaximum grain size is45μm. The bigger the grain size of granular AMP is, thestronger its adsorption property for rubidium/cesium ion is. The adsorption propertyis much stronger than it of micro-grain AMP.The linear growth rate of granular AMP crystal is between1.74μm/h and4.15μm/h, and its crystal growth rate ranges between1.17g/L·h and18.6g/L·h. Thenucleation and growing of granular AMP crystal firstly appear in the local solutionwhen touching nitric acid, furthermore, the aging process has little effect on crystalgrowing. The key conditions of preparing AMP crystal with big mean grain, narrowparticle size distribution, regular nucleation and high equiaxial degree are uniformacidification and slow rate acidification. In the composite adsorbent of the prepared granular AMP and TiP₂O₇, granularAMP and TiP₂O₇are combined together firmly by van der waals force. The mainagent for its adsorption for rubidium/cesium ion is granular AMP. The suitablecomposition of the complex for column operation is granular AMP: TiP₂O₇=1:5.42,and its particle size is between0.9mm and1.8mm. After three times of recycling use,this complex still have good adsorption property. There are no loss of granular AMPand generating of molybdenum blue during the process of recycling use.The complex of granular AMP and TiP₂O₇has advantages of simple preparation,character stability and suiting to column operation, and it also has good enrichmentand separation of rubidium/cesium ion from salt lake brine, therefore, it has goodfuture of industrial application.