Study On The Reduction Fixation Of Chromium And Rhenium By Several Nano-Ferrous Materials

Nanomaterials are widely used in pollution control of heavy metals,with high specific surface area and activity.Natural pyrite widely exists in nature,in order to improve its reactivity,mechanical ball milling method is used to reduce the size of pyrite,the use of nano natural pyrite in environmental governance,can not only waste utilization,but also improve the treatment effect.Nano zero-valent iron(n ZVI)is an environmental remediation material with high efficiency,low cost and easy operation,which has great advantages in removing pollutants in water or soil.However,agglomeration and oxidation of n ZVI are easy to lead to the loss of effective active sites,and also limit the play of n ZVI in practical application.In order to improve its stability,the modification of n ZVI was initiated.Chromium,widely distributed in the earth’s crust,is a highly toxic and carcinogenic metal.The harm caused by chromium pollution to the soil and water environment should not be ignored.At the same time,it will have adverse effects on the survival of organisms in the soil and water environment,and even threaten human health through the biological chain.Technetium,as a radioactive element with a long half-life,is one of the representative elements in high-level radioactive waste.The study on its repair treatment has long-term significance.Rhenium and technetium have similar properties and are not radioactive,so it is used as a substitute element for technetium in the experiment.In this study,technetium is used as the representative element of radioactive elements in nuclear waste and chromium as the representative element of heavy metal pollution in water.By studying its remediation treatment,the treatment effect of heavy metal pollution can be improved.As an emerging environmental protection material,nanomaterials have attracted wide attention.In the repair treatment of technetium and chromium,nanomaterials can achieve good removal effect.In order to improve the stability of nanomaterials,this study selected pyrite,sodium-bentonite,activated carbon and ZSM-5 as loading materials for the load modification of n ZVI.The specific removal effect of rhenium and chromium by supported composite materials was studied.Meanwhile,pyrite supported n ZVI composite material was taken as the representative of supported composite materials to study the reaction mechanism of fixed heavy metal reduction by nano iron system materials.The specific research contents and results are as follows:1.Nanometer natural pyrite was prepared by mechanical activation method.Meanwhile,n ZVI was prepared by wet chemical reduction method.Pyrite,activated carbon,bentonite and molecular sieve were selected as supporting materials to prepare supported n ZVI composite materials.2.Scanning electron microscopy(SEM),transmission electron microscopy(TEM)and Xray diffractometer(XRD)were used to characterize nanometer natural pyrite,n ZVI and supported n ZVI composites.The results showed that the particle size of natural pyrite reached nanometer level after mechanical ball milling activation,and the crystal structure characteristics of the surface were obvious.After n ZVI is loaded,particles are evenly distributed on the surface of the loaded material,which improves the agglomeration among particles and increases the specific surface area of the material,so as to better contact and remove pollutants.3.Through the batch experiment,the experimental conditions were controlled to compare the experimental results,and it was concluded that the removal rate of Cr(Ⅵ)in water by nano natural pyrite increased with the increase of pyrite dosage.When the temperature was 25-35 ℃,the removal rate of Cr(Ⅵ)in water by nano natural pyrite increased with the increase of temperature.In the range of p H 2～7,the removal ability of Cr(Ⅵ)from water by nanometer natural pyrite decreases with the increase of p H value.The optimal load ratio between the loading material and n ZVI was selected,and the load type n ZVI with pyrite and n ZVI mass ratio of 1:1.5,the load type n ZVI with sodium-bentonite and n ZVI mass ratio of 2:1,the load type n ZVI with activated carbon and n ZVI mass ratio of2:1,and the mass ratio of molecular sieve and n ZVI was 1: The removal effect of the four n ZVI composites with 1 load is the best.By controlling the reaction conditions,it is concluded that the removal effect of rhenium and chromium is better with the increase of temperature and acidity in a certain range.4.In the reaction process of nano natural pyrite reduction of Cr(Ⅵ)in fixed water,the reaction is endothermic,and the temperature rises,which is conducive to the reaction.When the temperature reaches 36℃,the reaction will become spontaneous reaction.The reaction between nanometer natural pyrite and Cr(Ⅵ)in water was analyzed by adsorption thermodynamics theory and kinetic theory.It was found that the reaction could be fitted by quasi second-order kinetics,and the parameters such as reaction rate constant k and activation energy Ea were obtained,which could be used to predict the reaction rate and the removal efficiency of Cr(Ⅵ)in the reaction process.Taking pyrite supported n ZVI composite as the representative of supported n ZVI composite,it is found that the adsorption process can be fitted and analyzed by the quasi second-order kinetic model,and the adsorption process is the joint action of chemisorption and physical adsorption,among which chemisorption may be a ratelimiting process.Through the thermodynamic analysis of the reaction,it is concluded that the reaction is endothermic reaction,and the process of the reaction is the process of entropy increase,the reaction is easy to occur.