Study Of The Adsorption Performance And Mechanism Of Attapulgite-based Composite Micro-nano Materials On Uranium-containing Wastewater

Under the guidance of the"double carbon"strategy,nuclear energy has developed rapidly as an efficient and clean energy,and the demand for uranium resources has also increased,resulting in environmental risks such as uranium pollution generated during uranium mining and smelting are becoming more and more prominent.Therefore,the development of uranium-containing wastewater treatment technology has become one of the hot spots in the field of environmental engineering.Compared with membrane separation method,chemical precipitation method,solvent extraction method and biological treatment method,adsorption method has the advantages of economy,high efficiency,convenient operation and wide applicability,and has been widely concerned in uranium-containing wastewater treatment.Nano/micro adsorption materials have shown great potential in the treatment of associated uranium-contaminated wastewater.However,these materials have problems such as easy agglomeration,poor mechanical stability,high preparation cost,low capture efficiency,and weak specific adsorption.In view of this,nano-zero-valent iron（n ZVI）and magnesium-iron layered double hydroxides（Mg-Fe LDHs）materials were used as adsorbed active substances,and attapulgite（ATP）was used as a matrix to synthesize attapulgite composite nano-zero-valent iron adsorbent（ATP@n ZVI）and attapulgite composite magnesium-iron hydrotalcite adsorbent（ATP@Mg-Fe LDHs）in this thesis.The mechanical properties of the composite micro-nano adsorbent wee improved.Taking simulated wastewater as the research object,the adsorption performance of uranium in wastewater was investigated,and the preparation conditions were optimized.Combined with various material characterization methods,the adsorption mechanism was explored,and their economic applicability was analyzed.The main conclusions are as follows:（1）ATP@n ZVI was prepared by sodium borohydride reduction method,and n ZVI particles were successfully dispersed on the surface of rod-like ATP.The Zeta potentials of ATP,n ZVI and composite micro-nano materials were-42.5 m V,1.3 m V and-30.8 m V,respectively,indicating that electrostatic affinity occurred between raw materials and the stability of the composite was excellent.ATP significantly improved the agglomeration defects of n ZVI.The stability index of pure n ZVI was 6.79,and the composite was only 1.69,which proved that the composite material was more evenly distributed in the solution.Under the conditions of p H=5,initial uranium concentration of 3 mg L^-1 and adsorbent dosage of 0.6 g L^-1,ATP@n ZVI can complete the adsorption of uranyl ions within 20 min,and the adsorption efficiency is 95.02%.ATP@n ZVI was greatly affected by PO₄^3-,and the target pollutant competed with PO₄^3-,and the saturated adsorption capacity was only 88.13 mg g^-1.After five cycles of stability experiments,the average adsorption rate of the composite adsorbent reached 88.14%,and the mechanical stability was good.（2）The ATP in the ATP@n ZVI adsorbent is physically adsorbed by the advantage of specific surface area,and the iron oxide contained in the adsorbent has electrostatic interaction,surface complexation and redox effect with uranyl ions.By fitting the isothermal adsorption model with the kinetic adsorption model,the adsorption of uranyl ions by ATP@n ZVI micro-nano adsorbent belongs to an uneven multi-layer adsorption process,and the contribution of physical adsorption and chemical adsorption is equivalent.The treatment effect of ATP@n ZVI adsorbent under many influencing factors was verified by actual wastewater.Especially in the case of high Ca ion concentration,the adsorbent can still reduce the concentration of uranyl ion from 0.12 mg L^-1 to 0.02 mg L^-1,and the final adsorption efficiency reaches 86.39%.（3）ATP@Mg-Fe LDHs micro-nano adsorbents were successfully prepared by hydrothermal method.The original agglomeration of Mg-Fe LDHs was significantly reduced and the effective adsorption sites were increased.The isoelectric points of ATP,Mg-Fe LDHs and ATP@Mg-Fe LDHs were 6.79,1.79 and 4.88,respectively.The surface electrical affinity was formed between the raw materials in weak acid and neutral environment,and the stability of the composite adsorbent was strong.The effects of raw material ratio,preparation p H and preparation temperature on the treatment effect of ATP@Mg-Fe LDHs micro-nano adsorbent were investigated.When the preparation conditions were m ATP:Mg-Fe LDHs=1:2,p H=11,and the temperature was 240°C,the adsorption effect of ATP@Mg-Fe LDHs was the best.When the reaction conditions were p H=5,the initial concentration of uranium was 3 mg L^-1,and the amount of adsorbent was 0.6 g L^-1,the adsorption efficiency of uranyl ions reached97.48%after 20 min of adsorption.The composite adsorbent has strong selective adsorption for uranyl ions and is not affected by coexisting ions such as K⁺,Na⁺and PO₄^3-in the solution.The saturated adsorption capacity under optimal conditions is as high as 670.21 mg g^-1.After eight adsorption/desorption cycle tests,the adsorption efficiency of uranium ions remained high,and the adsorption efficiency was 98.47%,96.92%,96.99%,99.14%,99.15%,99.37%,99.27%and 98.77%,respectively.（4）The adsorption of uranyl ions by ATP@Mg-Fe LDHs micro-nano adsorbents is affected by the complexation of CO₃^2-to uranyl ions,the electrostatic interaction generated by Mg-O bonds,and the redox of reducing substances such as Fe²⁺.The thermodynamic and kinetic model fitting results show that the adsorption behavior of ATP@Mg-Fe LDHs on uranyl ions is more in line with the Langmuir isotherm adsorption model,and physical adsorption and chemical adsorption work together.The preparation costs of the two materials were preliminarily calculated.Compared with ATP@n ZVI adsorbent,ATP@Mg-Fe LDHs adsorbent had lower water treatment price per ton and greater practical application potential.