The Performance And Mechanism Of Pyrite-activated Persulfate Degradation Of Organophosphates

Organophosphates?OPEs?are one kind of highly effective flame retardants which are widely applied in a variety of consumer products.It was released to the environment from the processes of production,use and disposal of the products.Due to the difference in substituents,the chemical properties of various substances in OPEs are different.Among them,the chlorinated OPEs appear more frequently in the report,and the toxicity is larger.Because of the weak ultraviolet absorption capacity,it is difficult to directly photolyze,which makes the natural degradation difficult.Therefore,tris?2-chloroethyl?phosphate?TCEP?was selected as the research object.The advanced oxidation method based on SO₄^·-has attracted much attention for many years.This paper chooses pyrite with wide distribution,large reserves,low cost and high efficiency as activator of activated persulfate.We explored the mechanism of pyrite?FeS₂?activation of persulfate?PS?and the effectiveness of TCEP degradation,the effects of various environmental factors on the TCEP degradation in FeS₂-PS system and its intrinsic factors,as well as the degradation products and pathways of TCEP.The main findings are as follows:?1?In the FeS₂-PS system,the degradation rate of TCEP is close to 100%in 120 minutes and not more than 30%in single pyrite/PS system.Therefore,pyrite can effectively activate PS to generate radical degradation of TCEP.The introduction of Fe²⁺into single PS system confirmed that Fe²⁺plays an important role in the activation mechanism.When methanol and tert-butyl alcohol were added to the system,TCEP hardly degraded,and the degradation was terminated due to the capture of free radicals.Therefore,the radical oxidation is the main cause of degradation of TCEP.The presence of·OH and SO₄^·-was detected by an electron paramagnetic resonance?EPR?.Therefore,pyrite activated persulfate can produce SO₄^·-and·OH to degrade pollutants,and the degradation of TCEP in FeS₂-PS system accords with pseudo-first-order kinetic model.?2?We explored the effects of pyrite content,PS concentration,pH,inorganic ions and humic acid?HA?on the FeS2-PS system.It is found that the degradation rate increases with the increase of the dosage of pyrite,while the amount of PS has a threshold.The acidic environment is more conducive to the generation of radicals.Due to the acidification of pyrite,the system can be applied to a wider pH range.The effects of eight inorganic ions(HCO₃^-,Cl^-,H₂PO₄^-,NO₃^-and Fe³⁺,NH₄⁺,Ca²⁺,Cu²⁺)on the FeS₂-PS system were also investigated.The result indicated that Cl^-and Fe³⁺can promote the degradation efficiency of TCEP,while HCO₃^-and H₂PO₄^-are severely inhibited.In addition,the degradation rate of TCEP in FeS²-PS system decreases with increasing HA concentration,which indicated that Fe²⁺was easily complexed with four metal chelators such as?-cyclodextrin,oxalic acid,sodium citrate and edetate disodium,resulting in a decrease in active substances.In general,these influence factors mainly reduce the yield of radicals or shield their effects by acting with radicals.This conclusion was supported by the result of electron paramagnetic resonance?EPR?spectra.?3?Besides,two oxidation products,C₄H₉Cl₂O₄P and C₂H₆ClO₄P were identified by UPLC-Q-TOF,which suggest that hydroxylation was probably the main mechanism.The total organic carbon in the solution was also determined and only 40%of the organics were removed from the solution.Therefore,only a small portion of the TCEP was completely mineralized,and the remainder may not have completely degraded or converted to stable small molecular organics.According to the molecular formula and structural formula of the product,a feasible degradation path for TCEP is proposed:TCEP?C₄H₉Cl₂O₄P?C₂H₆ClO₄P.Finally,the TCEP molecules may be completely mineralized to CO₂,H₂O,Cl^-and PO₄^3-,and oxidation of hydroxylation and C-O bond is the main degradation mechanism.