Preparation Of Fe₃O₄/Kaolin Complex And Its Performance In Activation Of Persulfate To Degrade Typical Organic Micro-Pollutants

The organic micro-pollutants（OMPs）in the environment are stable and accumulate easily.It is difficult to remove them by routine treatment processes.When OMPs remain in water and soil,they will not only cause toxicological problems,but also threaten public health and food security The advanced oxidation processes which based on sulfate radical(SO₄^·-)can remove organic micro-pollutants effectively in the environment.Using heterogeneous catalyst with loaded iron is an effective method to activate persulfate.It is very meaningful to develop a highly-efficient catalyst of persulfate with low cost,recyclable and good stability,and investigate the efficacy and mechanism of this oxidation system.The purpose of this study is to use kaolinite and Fe₃O₄ to prepare Fe₃O₄/Kaolin complex which is highly efficient and magnetic.First,the physicochemical properties of Fe₃O₄/Kaolin complex was investigated.Second,the efficiency of Fe₃O₄/Kaolin-PDS system when it is degrading typical OMPs was studied.Third,the stability and reusability of complex in the oxidation system was investigated.Then,the contribution of different free radicals in this system was studied.Finally,this project reveal the mechanism of activation and the degradation of OMPs,as well as the underlying pathways of OMPs.The results show that:Fe₃O₄/Kaolin material has high purity and large surface area.It can be recycled from water because of its strong magnetism.Fe₃O₄/Kaolin-PDS system can degrade the typical OMPs effectively（CIP and AMT）.When 11μm kaolin is used as a support material,the Fe₃O₄/Kaolin₁₁ complex has the most effective activation compared with 2.5μm and 5.0μm kaolin.Increasing the concentration of PDS and catalyst will stimulate the degradation of OMPs.However,alkaline conditions（p H>8）may inhibit OMPs degradation.After reacting for 120 min,the degradation rate of CIP and AMT reached 90.2%and 71.3%respective when OMPs initial concentration was 7.0 mg·L^-1,PDS concentration is 3.5 m M,the dosing amount of catalytic is 1.0 g·L^-1 and temperature is 20℃.It is worth noting that Fe₃O₄/Kaolin-PDS system can clean up co-pollute water which is polluted by CIP and AMT.As well as PDS can also be activated by Fe₃O₄/Kaolin complex in soil and then remove AMT.The efficient activation of complex is attribute to the electron transfer of the element Fe from Fe₃O₄ and the hydroxyl groups on kaolinite.Free radicals play major roles in this system.Experiment and ESR research show that SO₄^·-and HO^·are the major free radicals in the system.The mineralize rate of OMPs in water can reach 52.2%.The degradation intermediates of OMPs were analysed and the underlying degradation pathway of OMPs were identified.This project provides a new activation material of AOPs which based on SO₄^·-in the field of environmental remediation.