【作者】 张凯；

【导师】 洪梅；

【作者基本信息】 吉林大学 ， 环境工程， 2021， 硕士

【摘要】 高氯代烯烃,如四氯乙烯（PCE）和三氯乙烯（TCE）,是地下水和土壤中常见的挥发性有机污染物,在缺氧/厌氧条件下会被还原脱氯,但高氯代烯烃的不完全还原脱氯会导致中间产物顺-二氯乙烯（Cis-DCE）和氯乙烯（VC）的大量积累。氯代烯烃（PCE>TCE>Cis-DCE>VC）中氯取代基团的含量越低,还原脱氯的难度越大;同时与母体污染物高氯代烯烃相比,Cis-DCE和VC具有更强的毒性和持久性,因此给环境修复工作带来了很大的困难。截至目前,Cis-DCE的还原脱氯处理方法主要有两类,分别是微生物方法和化学方法。其中化学还原修复方法中,目前主要使用的还原材料是金属铁基材料,包括零价铁、硫铁矿、硫改性铁材料等;而同铁基还原材料相比,在环境中广泛存在的另一种还原试剂—非金属硫化物(包括H₂S,HS^-,S^2-,S_x^2-等),具有更好的水溶性、迁移性、还原性及碱性条件下的亲核性,因此理论上,硫化物还原氯代烯烃类污染物从热力学的角度是可行的,但动力学极其缓慢,而利用某些催化剂有望加速氯代烯烃的降解。为验证上述科学假设,本论文拟利用生物质炭为催化材料,加速硫化物还原降解Cis-DCE。主要研究内容包括:（1）以农林废弃物苜蓿秸秆作为原材料,对其进行无氧高温处理,并采用硝酸对其进行改性处理,根据无氧热解温度不同将制备的三种生物质炭命名为MXBC-400、MXBC-600和MXBC-800。（2）使用扫描电子显微镜（SEM）、透射电子显微镜（TEM）、氮气吸脱附实验（BJH、BET）、光电子能谱（XPS）、傅里叶红外光谱（FTIR）等技术对三种MXBC进行表征分析,获悉材料的理化特性。（3）通过对比三种MXBC对Cis-DCE的吸附和降解能力,确定最优催化剂。（4）考察了MXBC-800投加量、硫化物（Na₂S）浓度、初始p H、反应温度和Cis-DCE初始浓度等因素对Cis-DCE去除效果的影响。（5）对反应中间产物进行了气质测试,探究反应途径与机理。（6）考察了溶解性腐殖酸、地下水中部分常见阴离子对Cis-DCE去除效果的影响;同时根据材料的循环使用实验,验证其催化稳定性。结果表明:3种材料对Cis-DCE均具有一定的吸附作用,但只有MXBC-600和MXBC-800可以催化硫化物还原处理Cis-DCE,其中800℃制备的生物炭催化性能最佳,可以将Cis-DCE完全降解为乙炔;当MXBC-800的投加量为500mg/L、硫化物浓度为10m M、反应温度为80℃,反应72 h后,一定初始浓度的Cis-DCE（5-20ppm）的去除率能达到95%以上;在一定范围内,材料投加量、硫化物浓度、反应温度以及溶液初始p H的增加都对反应具有促进作用;Cis-DCE降解的主要反应为β消除反应（消除氯化氢分子）,反应链条为:顺-二氯乙烯→氯乙炔→乙炔;溶解性腐殖酸的存在会抑制体系内Cis-DCE的去除效果,阴离子的存在会对体系内Cis-DCE的去除效果产生轻微的抑制作用;重复利用性实验结果表明MXBC-800具有一定的催化稳定性。本论文的实验研究证明,新提出的基于苜蓿基生物炭/硫化物体系的Cis-DCE处理技术不仅可以实现Cis-DCE的绿色无害化处理,而且受地下水中常见组分的影响较小。研究内容可为实际场地Cis-DCE污染地下水的处理提供参考。更多还原

【Abstract】 Perchlorinated alkenes,such as Tetrachloroethylene（PCE）and Trichloroethylene（TCE）,are very common volatile organic pollutants in groundwater and soil,and are reduced to dechlorination under anoxic/anaerobic conditions,but incomplete reduced dechlorination of Perchlorinated alkenes leads to the accumulation of intermediate Cis-Dichloroethylene（Cis-DCE）and vinyl chloride（VC）.The lower the content of chloro-substituted groups in Chlorinated alkenes（PCE>TCE>Cis-DCE>VC）,the more difficult the reduction and dechlorination is.At the same time,Cis-DCE and VC have stronger toxicity and durability compared with the parent pollutants of Perchlorinated alkenes,which brings great difficulties to the environmental remediation work.Up to now,reductive dechlorination methods of Cis-DCE mainly fall into two categories,namely microbial methods and chemical methods.In the chemical reduction of repair method,the main use of raw material is ferrous metal materials,including zero-valent iron,iron pyrite,sulfur modified materials,however,compared with iron-based raw material,non-metallic sulfides(including H₂S,HS^-,S^2-,S_x^2-,etc.)is an another kind of reductive reagent widespread in the environment,which have better solubility in water,migration,reductive and nucleophilic in alkaline conditions.Therefore,from the perspective of thermodynamics,the reduction of chlorinated alkenes pollutants by sulfides is theoretically feasible,but the kinetics is extremely slow.However some catalysts are expected to accelerate the degradation of chlorinated alkenes.To verify the scientific hypothesis,this paper intends to use biochar as catalytic materials to accelerate the sulfide reduction degradation of Cis-DCE.The main research contents include:（1）the alfalfa straw which is agricultural and forestal waste was used as raw materials,by high-temperature anaerobic treatment,and with nitric acid on the modified treatment,according to different anaerobic pyrolysis temperature,the three biochar prepared were named as MXBC-400,MXBC-600 and MXBC-800.（2）Scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,nitrogen adsorption and desorption experiments（BJH,BET）,photoelectron spectroscopy（XPS）,Fourier infrared spectroscopy（FTIR）and other techniques were used to characterize the three kinds of MXBC,and the physical and chemical properties of the materials were obtained.（3）The optimal catalyst was determined by comparing the adsorption and degradation capacities of three kinds of MXBC for Cis-DCE.（4）Examines the MXBC-800 dosing quantity,concentration of sulfide（Na₂S）,initial p H value,reaction temperature and Cis-DCE initial concentration on Cis-DCE removal effect.（5）On the GC-MS test of system intermediate,the reaction pathway and mechanism was explored.（6）The effects of some common anions and dissolved humic acid in groundwater on the removal efficiency of Cis-DCE were investigated.At the same time,its catalytic stability was verified according to the recycling experiment of the material.The results showed that the three materials all had certain adsorption effect on Cis-DCE,but only MXBC-600 and MXBC-800 could catalyze the reduction of Cis-DCE.The biochar prepared under 800℃had the best catalytic performance,which could completely degrade CIS-DCE into acetylene.When the dosage of MXBC-800 is 500mg/L,the sulfide concentration is 10m M,the reaction temperature is 80℃,and the reaction time is 72 h,the removal rate of Cis-DCE（5-20ppm）at a certain initial concentration can reach more than 95%.In a certain range,the increase of material dosage,sulfide concentration,reaction temperature and initial p H of solution can promote the reaction.The main reaction of Cis-DCE degradation isβ-elimination reaction（elimination of hydrogen chloride molecule）,and the reaction chain is Cis-Dichloroethylene→Chloroacetylene→Acetylene;the presence of dissolved humic acid will inhibit the removal effect of Cis-DCE in the system,and the presence of anions will slightly inhibit the removal effect of Cis-DCE in the system.The results of reusability experiments show that MXBC-800 has certain catalytic stability.The experimental study in this paper proves that the new Cis-DCE treatment technology based on alfa-biochar/sulfide system can not only realize the green and harmless treatment of Cis-DCE,but also be less affected by common components in groundwater.The research content can provide reference for the treatment of Cis-DCE contaminated groundwater in the actual site.更多还原