Study On Removal Of Cr（Ⅵ）in Groundwater By ZVI/Fe₃O₄

Hexavalent chromium（Cr（Ⅵ））in groundwater poses a huge threat to the environment and human health,due to its high toxicity and strong mobility.In the remediation,zero-valent iron is usually used as the reaction medium.Problems such as passivation greatly reduce the reaction efficiency,so it is very important to find more efficient and durable iron-based materials.ZVI/Fe₃O₄ is a potentially efficient reaction medium.However,the optimal use ratio and reaction mechanism of this two-phase mixed system are still undefined.Nitrate is a very common inorganic anion in the chemical composition of groundwater.With the development of agriculture and industry,the pollution of nitrate nitrogen is widespread in China.Excessive nitrate has also been found in Cr（Ⅵ）contaminated sites.In previous studies,it was found that the concentration of nitrate in groundwater has a significant effect on the removal of hexavalent chromium.Therefore,in this paper,we will study the effect of ZVI/Fe₃O₄ on the removal of Cr（Ⅵ）and the influence of nitrate concentration on it through batch experiments.The experimental results in this paper show that:（1）the removal of Cr（Ⅵ）by the two-phase mixed system accords with the first-order reaction kinetics.With the increase of Fe₃O₄:ZVI mass ratio,the removal efficiency of Cr（Ⅵ）in the ZVI/Fe₃O₄ system first increased and then decreased,which mainly affected its reduction process;（2）the inflection points of L-ZVI（large-size zero-valent iron）appeared earlier.In this experiment,the inflection points of S-ZVI（small-size zero-valent iron）and L-ZVI appeared at ZVI-80%and ZVI-95%.Adding an appropriate amount of Fe₃O₄will promote the reduction of Cr（Ⅵ）.If the content of Fe₃O₄ in Fe₃O₄/ZVI is bigger than 40%,Fe₃O₄ will inhibit the removal of Cr（Ⅵ）;（3）Nitrate reduces the maximum adsorption amount of ZVI/Fe₃O₄ to Cr（Ⅵ）,and also reduces the reaction rate.According to the test results,the reduction product is NH₄⁺,High concentration of nitrate lead to the low removal rate of Cr（Ⅵ）.With the increase of the concentration of nitrate,the trend of the decreasing slows down.Nitrate mainly affects the reduction process of Cr（Ⅵ）,Almost no effect on the adsorption process.These research results provide theoretical and technical support for the future use of this two-phase mixed system to efficiently remove Cr（Ⅵ）from groundwater.