In Situ Fixed In Groundwater With Nano Pyrite Cr(Ⅵ) Lm-PRB Experimental Research

As an important raw material for production,heavy metal chromium has a very wide range of applications in many industries（such as leather making,metallurgy,electroplating,textile printing,and batteries）.Among them,hexavalent chromium is easy to migrate and dissolve due to its high toxicity.It cause great harm to the ecological environment,animals and humans.What is more,it is easy to accumulate in the environment whatever in soil or groundwater.With the progress of industrial modernization,the content of heavy metal chromium in the environment continues to increase,the bio-accumulation in the food chain continues to increase,and the resulting ecological impact is also growing.It is urgent to reduce and prevent the pollution of heavy metal chromium.Therefore,research on new functional materials that can effectively adsorb heavy metal chromium and widely exist in nature with low cost to solve the heavy metal chromium pollution among environmental pollution problems in recent decades has become a new research hotspot.Pyrite is a wide range of natural minerals with stable chemical properties.In recent years,pyrite is often used as a material for adsorption and reduction in the field of environmental pollution control.In this study,nano pyrite was prepared by mechanical activation,and the properties of the prepared pyrite nano powder and the surface characteristics of the prepared sample were analyzed.The results showed that the main component of the pyrite prepared in this experiment was Fe S₂;The particle size of pyrite powder can reach the nanometer level.Using nano-natural pyrite as the PRB dielectric material,column experiments were used to investigate whether natural pyrite can effectively exert its reduction and adsorption effect in soil and groundwater for a long time,and its in-situ fixation of Cr（Ⅵ）law.The reaction characteristics of Cr（Ⅵ）in soil and groundwater fixed in situ and application in the field of heavy metal pollution prevention after mechanical activation of nano pyrite as a column experiment reaction medium are comprehensively described.Under the condition of low oxygen,pyrite was used as the reaction medium in the column experiment.In the column experiment,the filling heights of pyrite,filling methods,initial concentrations of heavy metal chromium solution and flow rates were changed.The effect of pyrite removal of heavy metal chromium in soil and groundwater were researched.The paper mainly obtained the following results and conclusions:（1）In the process of column experiment,by comparing mechanically loaded pyrite with blank quartz sand column,in the experiment of fixing heavy metal chromium in situ,it was determined that pyrite has high adsorption of Cr（Ⅵ）effect.Simulated loading of nano-pyrite in soil and groundwater can effectively block the migration and conversion of Cr（Ⅵ）,thereby the concentration of chromium in the environment got decreased.（2）In the effect of the filling height of nano-pyrite on the column experiment,it is obtained that the removal rate of heavy metal Cr（Ⅵ）increases as the filling height of nano-pyrite increases.（3）By changing the filling method of nano-pyrite in the soil column,a conclusion can be drawn that the method of uniformly mixing pyrite and fine quartz sand is better than the method of dispersing pyrite in ethanol and directly injecting it into the soil column.The cumulative removal amount and cumulative removal rate are significantly improved.One possible reason is after the pyrite and quartz sand are mixed into the soil column,the contact area of the reaction between the nano-pyrite and Cr（Ⅵ）increases,and the active site increase.（4）By adjusting the initial concentration of Cr（Ⅵ）solution in the column experiment,the results showed that the lower the initial concentration,the more complete the adsorption and reduction of Cr（Ⅵ）by the nano pyrite,the higher the removal rate,and the better the stability.（5）The flow velocity of pumping the pollutant solution is accelerated,and the adsorption and reduction point of pyrite in the soil column is quickly occupied by the pollutant,so it reaches the stage of stable adsorption equilibrium in a short time.For the continuously flowing Cr（Ⅵ）solution,the pyrite can no longer be adsorbed and fixed,resulting in the faster the flow rate,causing the lower the removal rate of Cr（Ⅵ）.（6）Through a simulated column experiment study,a preliminary theoretical derivation of Cr（Ⅵ）in the soil and groundwater fixed in situ by the nano-pyrite was carried out.As a reaction medium,pyrite not only plays a role of adsorption during the treatment of heavy metal Cr（Ⅵ）,but also undergoes a redox reaction with Cr（Ⅵ）solution.Therefore,the treatment efficiency of Cr（Ⅵ）is greatly improved,and the pollution degree of Cr（Ⅵ）in soil and groundwater is reduced.In the field of environmental pollution control and remediation,pyrite is widely used as a low-cost,high-efficiency material.In this study,nano-natural pyrite was used as the reaction medium in the column experiment to simulate the restoration of Cr（Ⅵ）in the soil and groundwater.A series of experimental investigations were conducted to analyze the experimental results and conclude nano-pyrite’s reaction law and mechanism of the treatment of heavy metal in the soil.This paper provide the theoretical basis and experimental basis for the application of nano-pyrite in the field of environmental remediation.