| Chemical pollution of pesticides has become one of the most urgent environmental problems.Atrazine（2-chloro-4-ethylamine-6-isopropylamine-1,3,5-triazine）is a widely used herbicide worldwide that effectively inhibits the growth of broad-leaf weeds in sugarcane,wheat,sorghum,nut and maize fields.The sprayed atrazine herbicide enters the surface water and groundwater system through surface runoff or soil leaching.It remains for a long time and is difficult to be degraded by nature.Long-term exposure to atrazine will have adverse effects on animal reproduction and human health.It is urgent to develop green and efficient pollution control technology to eliminate atrazine pollution in water environment.The activation of persulfate by iron minerals is an advanced oxidation technology with a promising application at present.However,its degradation efficiency is limited by the formation of Fe（Ⅱ）ions and the conversion rate between Fe（Ⅲ）and Fe（Ⅱ）.Cysteine is a natural iron reducing agent widely existing in nature and exists in natural water bodies.The sulfhydryl functional groups contained in it have the function of complexing dissolved iron minerals to release Fe（Ⅱ）ions,and can promote the reduction of Fe（Ⅲ）to Fe（Ⅱ）.The aim of this study was to investigate the effect of cysteine on the degradation of atrazine by activated persulfate of iron minerals（magnetite,hematite and pyrite）and its mechanism.The research contents include:the effect of different iron minerals on the degradation of atrazine;The effects of different factors on the degradation rate of atrazine;Study on mechanism of cysteine promoting persulfate activation by different iron minerals;Atrazine degradation pathway;Analysis of mineral physical properties.The main conclusions are as follows:（1）Cysteine can significantly promote the degradation efficiency of three iron minerals（magnetite,hematite and pyrite）by activating persulfate,but the degradation performance of atrazine is different among different systems.When no cysteine was added,the degradation efficiency of atrazine by Fe3O4/PS,Fe2O3/PS and Fe S2/PS was 9.3%,7.7%and 31.4%,respectively.When cysteine was added,the degradation efficiency of Atrazine by Fe3O4/PS,Fe2O3/PS and Fe S2/PS reached 75.3%,45.8%and 68.2%respectively.The dosage of iron minerals,persulfate and cysteine all increased the degradation rate of atrazine in a certain range,but excessive dosage would inhibit the degradation of atrazine.Both Cl-and HCO3-can significantly inhibit the degradation of atrazine,and the inhibition effect of HCO3-is more obvious.The degradation efficiency of atrazine under acidic condition is obviously better than that under alkaline condition.（2）The main species of persulfate activated by cysteine/iron minerals are iron bivalent,but the process mechanism of persulfate activation by cysteine and different iron minerals is different.Ferrobivalent in magnetite can directly activate persulfate,and sulfhydryl（-SH）in cysteine can reduce the oxidized ferrotrivalent and the ferrotrivalent in magnetite to ferrobivalent,forming an iron cycle.-SH loses electrons to form-S·,and the two-S·quickly form-SS-,making cysteine cystine.Subsequently,cystine is reduced to cysteine by·OH to form a cysteine/cystine cycle.Unlike magnetite,hematite does not activate persulfate directly.Cysteine first reduces the ferric iron in hematite to ferrous iron,which then activates persulfate to degrade atrazine.Pyrite can also activate persulfate directly through its own iron bivalent content.But unlike magnetite,pyrite itself contains S22,which works with cysteine in the iron cycle.（3）The main active species of Atrazine were SO4·-and·OH activated by cysteine and different iron minerals for persulfate degradation,but the degradation paths of Atrazine were different.There are three degradation paths of atrazine in Fe3O4/PS/Cys system.The first path is that Atrazine reacts with SO4·-to deethylate,and then undergoes substitution reaction with·OH to remove amino group.Path two is to oxygenate Atrazine ethyl,and then there will be two different paths to generate different degradation products,through the deisopropyl,or the reaction with·OH to dechlorine-hydroxylation,then demethylation;Path three is only through dechlorine-hydroxylation;There is only one Fe2O3/PS/Cys system.Atrazine first reacts with SO4·-for deethylation,and then deamination with·OH at the same time.The Fe S2/PS/Cys system has two paths:one is the deethylation of atrazine through reaction with SO4·-,and the second is the deisopropyl through chelation reaction with SO4·-.Route two is to oxygenate atrazine ethyl and then deisopropyl. |
