Indoor PRB Simulation Test Of MoS₂@FeS For Remediation Of Uranium Contaminated Groundwate

With the rapid development of economy,environmental pollution is gradually serious.Heavy metal water pollution has brought huge problems to people’s life and health.The uranium mining and utilization,waste residue treatment have aggravated the pollution of uranium hexavalent[U（Ⅵ）]in groundwater.At present,for the problem of U（Ⅵ）pollution in groundwater,researches mainly focus on material optimization in static water environment,which is quite different from the situation of U（Ⅵ）removal in real groundwater environment,and lacks of practical application.In view of these problems,new nanocomposite material MoS₂@FeS is firstly proposed and prepared for adsorption of U（Ⅵ）in this study,and combined with permeable reactive barrier（PRB）technology.The effect of U（Ⅵ）removal was experimentally studied in static water environment,and a small scale PRB simulation study was carried out with one-dimensional dynamics long-term column test.This research provides theoretical basis and data support for real application of MoS₂@FeS material in the permeable reactive barrier in the later period.In this study,a novel nanocomposite MoS₂@FeS was prepared by loading ferrous sulfide（FeS）onto molybdenum disulfide（MoS₂）by precipitation method.The physical and chemical properties of MoS₂and MoS₂@FeS,microscopic morphology,surface structure and important crystal structure and functional groups of the two materials were analyzed by scanning electron microscopy（SEM）,projected electron microscopy（TEM）,specific surface area and porosity analysis（BET）,Fourier transform spectroscopy（FT-IR）,X-ray diffraction（XRD）and other characterization methods.In addition,the effects of various variables on the uranium removal were studied through batch tests,including p H of solution,initial uranium ion concentration,material dosage,adsorption reaction time and temperature.Meanwhile,the mechanism of U（Ⅵ）removal from water by MoS₂and MoS₂@FeS has been studied and analyzed by kinetic model,isotherm model,thermodynamic analysis and X-ray photoelectron spectroscopy（XPS）.Finally,this study compares the uranium ion concentration before and after U（Ⅵ）contaminated liquid flows through the two materials,to understand the real adsorption situation of the materials in application.The main results of this study are as follows:（1）The technical characterization result of SEM,TEM,BET,FT-IR,XRD,and XPS show that:MoS₂is a sheet structure,FeS has serious reunion phenomenon,and novel material MoS₂@FeS relieve the reunion of FeS,the particle size of FeS is significantly smaller and scattered on the sheet structure of MoS₂.Moreover,the BET surface area and total pore volume of MoS₂@FeS are significantly higher than that of MoS₂,with more adsorption sites.Finally,MoS₂@FeS own rich functional groups,with Mo（IV）,S（-Ⅱ）,Fe（Ⅱ）acting as reducing agents in restoring a fixed U（VI）.（2）Batch experiment results indicate that:the adsorption capacity of nanocomposites MoS₂@FeS to U（VI）is much higher than the individual MoS₂material.In addition,changing the p H of the solution,initial U（VI）concentration,adsorbent dosage,reaction temperature and time can have a significant impact on U（Ⅵ）adsorption.Finally,weak alkaline environment,high initial concentration of U（VI）solution and temperature are beneficial to the removal of U（Ⅵ）ions in water by the two materials.（3）The results of the adsorption models demonstrate that:Freundlich model and Pseudo-second-order model fit MoS₂and MoS₂@FeS adsorption process more appropriately,indicating that the material removes U（VI）mainly by chemical adsorption,and heterogeneous multilayer adsorption;thermodynamic analysis,the enthalpy（ΔH⁰）,entropy（Δ⁰）and Gibbs free energy（Δ⁰）,and the value of temperature increases,these data confirm that MoS₂and MoS₂@FeS in the process of adsorption U（Ⅵ）,is a spontaneous and endothermal absorption reaction.（4）Contrast column test and find that:the adsorption and reduction capacity of MoS₂@FeS is much better than that of MoS₂.Excessive increase of FeS content in the composite material will not improve the adsorption performance and the increase of FeS content in the composite material is more likely to occur reduction reaction with dissolved oxygen in water,resulting in waste of materials.Because of the large amount of quartz sand mixed in the reaction column,the acidic U（Ⅵ）solution flowing through the composite MoS₂@FeS is easier to be adsorbed and fixed,and the service life and adsorption ability of the material are twice that of the alkaline solution environment.