Study On The Enhancement Mechanism Of PNP Degradation By Iron Mineral Fenton In Shallow Aquifer Media In The Jingjinji Plain

With the acceleration of urbanization and the rapid development of industry,many environmental issues have gradually attracted attention.Organic pollution of groundwater is persistent,difficult to degrade,and highly toxic.Long-term retention in groundwater will cause greater harm to ecology and human health.Due to the concealment of groundwater,the difficulty of monitoring,and the dynamic change,the remediation and treatment of organic pollution of groundwater is always a thorny issue.And the problem of secondary pollution after repair is also a major problem in the repair project.At present,a variety of in-situ remediation technologies have been applied to the remediation of organic pollutants in groundwater（such as chemical remediation,physical extraction,electric remediation,phytoremediation,etc.）.Among them,Fenton oxidation technology is due to its fast remediation,low pollution,The advantages of simple facilities and low cost have generally attracted people’s attention.Fenton oxidation technology is an advanced oxidation technology that uses hydroxyl radicals generated by Fenton reagent to degrade pollutants.It is widely used in sewage treatment and groundwater remediation,and it has the characteristics of wide application range and mild conditions.However,this technology currently has some problems in terms of catalytic materials.The main reason is that most iron-based catalytic materials are large-particle solid-phase materials,which are easily blocked by soil and aquifer media during the injection process,and most of them will be intercepted or Adsorbed in the soil or aquifer,not only is it difficult to truly exert its effectiveness,but also the risk of secondary pollution will increase with the injection of a large amount of iron-based materials.In this paper,the Beijing-Tianjin-Hebei region is used as the research area,and the shallow aquifer medium in 5 typical Beijing-Tianjin-Hebei regions is adopted,and the chelating agent（CA）is used as the strengthening reagent to construct the CA/medium iron mineral/H₂O₂ system and explore the system The effect on the degradation efficiency of organic pollutants（p-nitrophenol,PNP）and environmental p H,and reveals its degradation mechanism.The specific research contents of this paper are as follows:（1）The enhancement efficiency of chelating agent on Fenton system of medium iron mineral was studied.The typical area of Beijing Tianjin Hebei was selected to collect shallow groundwater medium samples,and the enhancement efficiency of different chelating agents（glutamic acid,citric acid,oxalic acid,ascorbic acid,hydroxylamine hydrochloride）on Fenton oxidation degradation of PNP of medium iron mineral was explored.（2）The enhancement mechanism of chelating agent on the Fenton system of medium iron minerals was studied.The composition of iron minerals on the medium surface and the change of iron content in the reaction process before and after the addition of chelating agent were compared and analyzed,and the main iron species and the location of Fe²⁺/Fe³⁺cycle were determined;Combined with the detection results of free radicals,the types of free radicals in the reaction system were identified,and the free radicals that play a major role in the degradation were identified.The strengthening mechanism of chelating agent on the medium iron mineral Fenton system was revealed.（3）Study on the environmental limiting conditions of medium iron mineral Fenton oxidation degradation of PNP,study the influence of groundwater p H and other conditions on the efficiency of chelating agent enhanced medium iron mineral Fenton oxidation degradation of PNP,and explore the change of material content in the system before and after the reaction,Combined with the actual hydrogeological conditions and hydrochemical environment in Beijing,Tianjin and Hebei,the applicability of Fenton oxidation technology for medium iron minerals was evaluated.research shows:（1）Taking the Beijing-Tianjin-Hebei region as an example,comprehensively considering the regional groundwater system zoning,geological type and geological age,5 typical areas of shallow aquifer media were collected,and the test medium composition and element distribution were analyzed using XRF,SEM and XRD techniques According to the situation,it was found that the medium phase composition of the five aquifers is complex,and they are mineral composite materials,and their surfaces all contain a certain amount of iron minerals,which have certain potential in constructing an in-situ Fenton system to repair the organic pollution of groundwater.（2）The aquifer medium has poor adsorption performance for PNP,and the maximum adsorption removal rate of PNP in the five media systems is not more than 12%;natural reducing agent/ligand-ascorbic acid is used as a strengthening reagent for various aquifer media/H₂O₂ The system has the best degradation efficiency for PNP,and the strengthening effect of the medium mainly based on feldspar is better.The removal rate of PNP can reach more than 89.00%within 40 hours,which is 6.82 times higher than that of the system without ascorbic acid.（3）In the ascorbic acid/aquifer medium/H₂O₂system,H₂O₂ is mainly catalyzed and decomposed by the ferrous complex formed by the reaction with ascorbic acid in the liquid phase.·OH is the main functional free radical for oxidative degradation of PNP;ascorbic acid/water The layered medium/H₂O₂system can slowly and continuously produce·OH under the strengthening of ascorbic acid,ensuring a long-term strong oxidizing environment in the system,and is more suitable for in-situ remediation of organic pollution of groundwater.（4）Ascorbic acid effectively broadens the applicable p H range of the aquifer medium Fenton system.When the initial p H is in the range of 5-10,the removal rate of PNP in each system does not change much with the initial p H,even when the initial p H is 11,the PNP removal rate The highest removal rate is still 62.66%,which has great application potential in the in-situ remediation of organic pollution in groundwater.