| Hexachlorocyclohexene (HCH) has been phased out for decades as a kind of typical environmental pollutant, though, the isomers of it can be found ubiquitously in the lake, the river, the ocean, the soil and the sediment. In order to understand the environmental behavior of HCH, a series of experiments were designed in the lab. y-HCH as the target compounds, the anoxic seawater environment withpH 8.30 and ion strength 0.1N as the solution condition, our task is to study the kinetics, the products and the pathways transformed both in homogenous water system and heterogeneous FeS-water system, and to explore factors to control the condition in this system.Ampoule-shaker system was employed for the kinetic study. The results of homogeneous hydrolysis of y-HCH showed that pentaclorocyclohexene (PCCH) was the intermediate product, the three isomers of trichlorbenzene (TCB) were the final products, and 1,2,4-TCB is the predominant one. Pseudo-first-order rate reaction was proposed as the kinetic of hydrolysis, based on which, the half-life of hydrolysis was determined as 122 days at 25癈 and pH 8.30. According to the experiment consequence, hydrolysis of y-HCH is pH-dependent and the first-order rate reaction versus [OH'] when pH > 7.4, while pH-independent and the zeroth-order rate reaction versus [OH"] when pH < 7.4. The kinetics equations provided in this paper having a good correlation with the evolution trend of the intermediate and final products in varied aqueous solutions proved them to be appropriate model for the reaction.Being much more complex in the heterogeneous FeS-water system, hydrolysis, physical adsorption and reduction are involved in the transformation of y-HCH. Two to twenty times' increase can be found for the disappearance of the reactant in this system than that in water at pHs from 6 to 9. Similarly. PCCH and TCBs was found in the system as the transformation products. However, the appearance of isomers of DCB and CB in this aqueous solution, andgammathe reductive intermediates: techchlorocyclohexene (TeCCH) and dichlorocyclohexadiene (DCCD), is much different from in the homogeneous water system. Among the products, the formation of TCBs and DCBs is selective. Four pathways are suggested in the paper based on the species and distribution of products in the FeS system. As the focus in the paper, the proposed pathways are tested and proved from the following aspects. Dehydrochlorination and dichloroelimination are proposed as the mechanism for the reaction. The possible dechlorination or hydrogenolysis is excluded from the system by both experimental data and the theory analysis. In addition, the facts in the subsequent experiments give a more clear scenario about the process: branching pathways and more than one kind of product coexisted in the system. As a result, PCCH. TeCCH and DCCD are determined as the detectable intermediate, the isomers of TCB and DCB and CB are the final products. Benzene is also proposed as one products in this system.The experimental results also show that pH is an important factor for the transformation rate of y-HCH by FeS suspension. The combined rate constants increase with pH growth, however, high pH benefits hydrolysis while low pH being proper for reduction process relatively. The concentration of FeS, include the physi-chemical properties and the mass concentration, is also a critical factor for the transformation.The influences of organic components, inorganic ions and temperature on the transformation of y-HCH in both systems are also discussed in the paper. The base-catalytic constants and the neutral-catalytic constants at different temperature, as well as the active energy in different solutions listed here are much more useful to understand the evolution of y-HCH at various environment. The lower active energy in FeS-water system is responsible for the fast transformation of y-HCH.The changes of X-ray photoelectron spectroscopy (XPS) of FeS versus different reaction time, showed at the last paragraph of the paper, is hopefully a valu...
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