Study On The Degradation Of Pyrene In Groundwater Of Coking Plant By Ferrous Activated Sustained Release Persulfate

There are a large number of polycyclic aromatic hydrocarbons in the soil and groundwater of the coking site,which are often repaired by in-situ chemical oxidation,but the sustainability is insufficient.Aiming at the problem of excessive consumption of oxidants during the repair process,sodium persulfate（PDS）and ferrous sulfate（Fe SO₄）were selected as active substances,and stearic acid（SA）was used as binder.Granular sodium persulfate-stearic acid sustained-release material（PDS@SA）and ferrous sulfate-stearic acid sustained-release material（Fe SO₄@SA）were prepared by melt-casting condensation method.The effects of mass ratio and particle size of PDS to SA on the release of PDS from PDS@SA were discussed.The effect and influencing factors of pyrene degradation by Fe SO₄@SA activated PDS@SA were investigated.The main conclusions are as follows:（1）The results of PDS@SA release batch experiments showed that the higher the proportion of PDS,the smaller the size of the sustained-release material,the faster the release rate and the shorter the release period.However,it is difficult to form when PDS:SA≥1:2,and the release rate is too fast when PDS:SA=1:2,which has a’burst release’effect.Therefore,the optimal ratio of PDS and SA is 1:3.When D=5 mm,PDS:SA=1:3,the release cycle can reach 35 d,and the release rate can reach94%.One-dimensional column experiments also confirmed that the sustained-release materials can achieve long-term and stable release.The release cycles of the three sustained-release materials with PDS:SA=1:3,D=5,7.5,and 10 mm reached 21,28,and 40 d,respectively.（2）The release of PDS in PDS@SA was more in line with the pseudo-first-order kinetic equation（0.9521<R²<0.99）,and the reaction rate constant k1decreased with the increase of diameter.SEM characterization results show that the pores on the surface and cross-section of the material after leaching change from the original flat and dense to porous and loose.Combined with the Bhasker and Rigter-Peppas models,it is inferred that the release of PDS is affected by the internal diffusion of PDS in PDS@SA,the external diffusion in solution,and the dissolution of SA,among which the dissolution of SA is the most critical.（3）Based on the experimental results,the PDS release model in PDS@SA was established.The model was tested by the experimental results.Whether it is the slow-release life or the slow-release rate,the predicted data and the experimental results are highly coincident.On this basis,it is predicted that the slow-release life of four slow-release materials with PDS:SA=1:3,D=15,20,30,40 mm is expected to be 90,119,173,295 d when the release amount reaches 90%.（4）In the experiment of pyrene degradation by Fe SO₄@SA activated PDS@SA,the removal rate was only 35.11%after adding PDS@SA and 15mg/L pyrene for 2h under static conditions.After adding Fe SO₄@SA:PDS@SA=1:3,D=5mm sustained-release material and different concentrations of pyrene（5,10,15,20mg/L）for 2h,the removal rate can reach more than 90%.Under dynamic conditions,the average removal rate of 15mg/L pyrene by adding Fe SO₄@SA:PDS@SA=1:3,D=5mm sustained-release material in the first 7～15d reached 89.3%.In addition,the presence of anions such as Cl^-and HCO₃^-also inhibited the degradation of pyrene.In summary,the composite sustained-release material prepared in this thesis can release active substances stably and has a good repair effect on polycyclic aromatic hydrocarbons in groundwater.This thesis has 58 figures,23 tables and 114 references.