Degradation Of Atrazine By Natural Pyrite Activated Persulfate And Influencing Factors

Atrazine（ATZ）,a chemical herbicide widely used in agricultural production,has a high detection rate in the environment due to its easy residue and difficult degradation.In recent years,advanced oxidation technology based on the activation of SO₄^-·by Fe²⁺has been widely used for the degradation and removal of organic matter in the environment.However,this technology also has obvious drawbacks,such as demanding p H reaction conditions and easy formation of large amounts of iron sludge.It is good to overcome these disadvantages by using natural iron-ore slow-release Fe²⁺.Natural pyrite（Fe S₂）as a tailing for mineral environment,it is widely available and inexpensive.Based on this,this paper chose natural pyrite activated persulfate（PS）to degrade ATZ in water and carried out the following points:the effectiveness of pyrite/PS system in degrading ATZ and the pathway of free radical generation and its contribution;the effect of reaction conditions on the degradation of ATZ in pyrite/PS system;the effect of environmental factors on the degradation of ATZ in pyrite/PS system;the degradation products and the degradation pathway of ATZ degradation in pyrite/PS system.Through the above research,the following main results are obtained:（1）Pyrite oxidation retards the release of Fe²⁺to provide a continuous Fe²⁺activation for the pyrite/PS system to effectively degrade ATZ.free radical burst experiments and electron paramagnetic resonance（EPR）confirm that·OH and SO₄^-·generated by pyrite activated PS are key substances for the degradation of ATZ,among which the oxidative degradation by SO₄^-·is dominant.（2）Under the reaction conditions of pyrite concentration of 0.4 g/L,PS concentration of2 mmol/L and temperature of 30℃,5 mg/L ATZ was almost completely degraded after 50min of reaction.The rate and efficiency of ATZ degradation by pyrite/PS could be improved by appropriately increasing the pyrite dosage,PS initial concentration,temperature and decreasing the pyrite particle size within a certain range.In addition,the acidic environment can promote the dissolution of Fe²⁺and more stable free radicals,which are favorable to the degradation of ATZ.Therefore,the oxidation of pyrite to produce acid leads to the pyrite/PS system can sustain the efficient degradation of ATZ in a broader p H range.（3）Except for Fe³⁺which accelerated the degradation of ATZ,NH₄⁺,Cu²⁺,Mn²⁺,HCO₃^-,CO₃^2-,H₂PO₄^-,NO₃^-and Cl^-all inhibited the degradation of ATZ to different degrees,and the three inorganic ions with the strongest inhibitory effect were ranked as CO₃^2->HCO₃^->H₂PO₄^-.The degradation of ATZ was slightly inhibited by humic acid（HA）,and the degree of inhibition increased with the increase of HA concentration.Common metal chelators such as EDTA,sodium citrate and oxalic acid readily complexed with Fe²⁺produced by pyrite,significantly reducing the performance of pyrite-activated PS and thus severely inhibiting ATZ degradation.Finally,EPR assays revealed that these environmental factors inhibit the production of free radicals in pyrite/PS systems and are directly responsible for the inhibition of ATZ degradation.（4）Mass spectrometry analysis showed that six intermediate products could be formed in the pyrite/PS system.Based on the molecular and structural formulas of the products,this study suggested that the effective degradation of ATZ was achieved mainly through dealkylation,dechlorination and hydroxylation attacking ethyl and isopropyl on the branched chains.