Preparation Of Phosphoric Acid Activated Chemosynthetic Powder Base Geopolymer Microspheres And Adsorption Properties Of TcO₄^-after Modification By Activated Carbon

In this paper,a kind of high activity geopolymer precursor powder Al₂O₃-2Si O₂is prepared by hydrolytic sol-gel method.The activity of geopolymer precursor powder prepared by different water/ethanol content is compared to determine the optimal ratio of activity.Phosphoric acid-activated geopolymer microspheres （PAAGMs） are prepared by dispersion-suspension-curing method using the geopolymer precursor powder with the optimal ratio of sphericity.Then the ratio is used as binder,and the dispersion-suspension-curing method is adopted to prepare activated carbon modified phosphoric acid-activated geopolymer microspheres（C@PAAGMs）.After determining the optimal loading ratio,the adsorption of ReO₄^-is studied and the optimal adsorption conditions are determined.Geopolymer precursor powder,PAAGMs and C@PAAGMs are characterized by OM,SEM/EDS,PSD,TG/DSC（DTA）,XRD,FTIR,MAS NMR,XPS,BET,Zeta potential,Raman spectroscopy and electrochemical workstation.The water/ethanol ratio on the activity of geopolymer precursor powder,the sphericity of PAAGMs and the adsorption performance of C@PAAGMs for ReO₄^-are investigated（Since all isotopes of Tc are radioactive,in view of the limitation of experimental conditions,the current recognized Re of the same main group was used as a substitute,and ReO₄^-was used to replace TcO₄^-for the adsorption experiment）.The results of this work are as following:（1）The optimal water/ethanol ratio of the prepared geopolymer precursor powder with higher activity is G1-0-35.The sample is mainly amorphous crystalline structure,with a layered structure similar to metakaolin,with a larger amount of penta-coordinated Al[V]and hexacoordinated Al[VI].The experimental results show that the dissolution rate of G1-0-35 in alkali solution is faster,the relative crystallinity of G1-0-35 is the highest（84%）after alkali activation,and it has higher reactivity.The results of Al/Si leaching concentration change and conductivity change of geopolymer reaction at different temperatures show that the leaching concentration change of Al/Si is consistent with the conductivity change,and G1-0-35 conforms to the classical geopolymer theory:depolymerization-polycondensation-curing.In the conductivity variation,the trend of 10℃and 20℃are inconsistent with that of40℃and 60℃,indicating that the influence of low temperature is mainly ion diffusion,and the influence of high temperature is mainly ion concentration.（2）PAAGMs are prepared using G1-0-35 as raw materials by dispersion-suspension-solidification method.The effects of H₃PO₄/Al₂O₃,H₂O/Al₂O₃and rotational speed on the morphology,particle size and sphericity of microspheres are investigated,and the optimal ratio is determined as follows:H₃PO₄/Al₂O₃=1,H₂O/Al₂O₃=9,rotation speed of 1200 r/min,75-300μm particle size ratio of 87.76%,the microspheres have high temperature stability,the main Si O₂phase and Al PO₄phase after calcination,BET is 62.87 m²/g.And the total pore volume is 0.652 cm³/g.（3）Combined with the adsorption experiment,the optimum ratio of C@PAAGMs preparation is 2gC@PAAGMs,which is determined:10 g of synthetic powder（Al₂O₃-2Si O₂）,5.31 g of phosphoric acid,6.50g(3.24_add)of water and 2 g activated carbon.The optimal adsorption conditions of2gC@PAAGMs for ReO₄^-are as follows:p H=3,solid-liquid ratio 0.3 g/100m L,adsorption time 2 h.The results of adsorption experiments are more consistent with the pseudo-second-order model and Freundlich isothermal model,and When the initial concentration reaches 150 mg/L,the maximum adsorption capacity is 65.64 mg/g（calculated by activated carbon loading）.XRD,FTIR and XPS results showed that the C-H bond in 2gC@PAAGMs is converted to C-O bond,and ReO₄^-is reduced to Re O₂,indicating that the adsorption of ReO₄^-includes chemical adsorption and physical adsorption.The effect of competitive ions on adsorption of ReO₄^-is as follows:NO₃^->SO₄^2->Cl^->PO₄^3-,The effect of real water on ReO₄^-adsorption is as follows:tap water（63.62%）>surface water（63.04%）>seawater（50.25%）;Solid-liquid separation experiments shows that 2gC@PAAGMs can achieve solid-liquid separation in 10 s,which is far superior to the performance of activated carbon separation.In addition,it has excellent column separation performance and certain cycle performance.The2gC@PAAGMs in this work have the advantages of simple preparation process,low cost,fast preparation,fast solid-liquid separation,mass preparation,and have potential application prospects in industry.