The Experimental Study On In Situ Chemical Reduction Remediation Of Cr(?) Contaminated Groundwater By Using Modified Micron Iron

With the rapid development of industrialization,a large amount of heavy metal-containing waste is generated.Due to improper storage and disposal,heavy metals have become the most common pollutants in groundwater.Heavy metal pollution in groundwater poses a threat to the safe use of water resources,human health,and the ecological environment.Remediating toxic heavy metal contaminated soil and groundwater is a huge challenge.Among them,Cr(?)is one of the most common heavy metal contaminants in soil and groundwater.At present,nano-iron is generally regarded as a highly effective in situ chemical reduction remediation agent for groundwater pollution,and has been applied in practical projects.However,injecting nano-iron into the underground environment has uncertain ecological and environmental issues.Some studies have shown that nanoparticles entering the ecological environment system may cause serious toxicological problems,and it is recommended that they should be used with caution.In order to solve the problem that nano-iron has an uncertain impact on the ecological environment,and at the same time can effectively use the reducing power of zero-valent iron,this paper studies the feasibility of micron-level zero-valent iron as an in-situ remediation agent for groundwater.In order to overcome the gravity settlement of micron iron itself and improve the in-situ remediation effect of Cr(?)contaminated groundwater,this experiment changed the type of modifier,system ratio and micron iron particle size to modify the surface of micron iron;systematically studied Stability of modified micron iron slurry and its ability to remove Cr(?);screen out the best modifier and its concentration.Among them,the research focus is on the migration mechanism and characteristics of xanthan gum-modified micron iron slurry,and analysis and grasp of its migration law in the formation medium;on this basis,through simulation experiments,xanthan gum(XG)modification was created Micron iron in situ reduction reaction zone,and comprehensively and systematically study the remediation effect of modified micron iron slurry on contaminated aquifer and monitor the changes of water chemical properties(such as DO,ORP,pH andother related parameters)during the repair process.The research results of this paper are as follows:(1)The experiment modified the surface of the micro-iron by changing the modifier type,system ratio and micro-iron particle size,and finally selected XG as the modifier and the concentration of 6.0 g / L,micro-iron The modification effect is best when the particle size is 1 ?m,and the modified micron iron slurry at this time has the best suspension stability.In the experiment of removing Cr(?),with the increase of XG concentration,the removal rate of Cr(?)also increased.XG can effectively prevent the micro-iron from gravity sedimentation,promote the reduction of micro-iron to Cr(?),and improve the overall removal efficiency of modified micro-iron to Cr(?).(2)Through a one-dimensional simulated column experiment,the migration characteristics of xanthan gum modified micron iron slurry in porous media were studied.The migration ability of micron iron after XG modification is improved.The migration ability of xanthan gum-modified micron iron slurry increases with the increase of the particle size of the aquifer medium,and its migration ability in coarse sand is 2.3 times that in fine sand.At the same time,the migration ability of xanthan gum-modified micron iron slurry is also affected by the injection speed.The migration ability of xanthan gum-modified micron iron slurry increases with the injection rate.In addition,the migration ability of xanthan gum modified micron iron slurry is also affected by its injection concentration.The greater the injection concentration,the worse its migration ability.Therefore,in practical applications,the influence of the formation of the reaction zone and the concentration of the reaction reagent on the remediation effect should be considered comprehensively,and the appropriate injection concentration should be selected to ensure the formation of an effective reaction zone.(3)Injecting the xanthan gum modified micron iron slurry into the Cr(?)contaminated aquifer through the injection well to carry out the simulation experiment of the remediation of the contaminated aquifer.After the slurry injection,a stable in-situ reaction zone was formed near the injection well and in the downstream area toeffectively remove Cr(?)pollution from groundwater.Its DO and ORP fell below 2mg / L and-200 mV,respectively.The ORP then stabilized around-100 mV.The transformation of ORP from oxidizing environment to reducing environment provides very favorable conditions for the reduction of Cr(?).At the same time,the pH value increased and stabilized in the range of 8.2 to 8.8,which shows that the injection of xanthan gum modified micron iron slurry has no significant effect on the increase of the system pH value,so it is environmentally friendly.As the xanthan gum-modified micron iron slurry was consumed to remove Cr(?)pollutants,the reaction zone gradually attenuated until it disappeared,and the water chemistry parameters of groundwater slowly returned to the original level.(4)The research in this paper shows that micron zero-valent iron can be used for in-situ chemical reduction and repair of Cr(?)polluted aquifer with better permeability through proper modification.In this experiment,the modified micron iron has a certain effect on the removal of Cr(?).Due to the low cost and low health risk of micron iron,it has broad prospects in the remediation of in-situ reduction reaction zone of groundwater pollution.