Batch-test study on the dechlorination of 1,1,1-trichloroethane in contaminated aquifer material by zero-valent iron

Chlorinated aliphatic hydrocarbons are common groundwater contaminants. One possible remediation option is in-situ reductive dechlorination by zero-valent iron, either by direct injection or as reactive barriers. Chlorinated ethenes (tetrachloroethene: PCE; trichloroethene: TCE) have received extensive attention in this context. However, another common groundwater pollutant, 1,1,1-trichlorethane (TCA), has attracted much less attention. We studied TCA reduction by three types of granular zero-valent irons in a series of batch experiments using polluted groundwater, with and without added aquifer material. Two types of iron were able to reduce TCA completely with no daughter product concentration increases (1,1-dichloroethane: DCA; chloroethane: CA). One type of iron showed slower reduction, with intermediate rise of DCA and CA concentrations. When evaluating the formation of daughter products, the tests on the groundwater alone showed different results than the groundwater plus aquifer batches: DCA did not temporarily accumulate in the batches with added aquifer material, contrary to the batches without added aquifer material. 1,1-dichloroethene (DCE, also present in the groundwater as an abiotic degradation product of TCA) was also reduced slower in the batches without added aquifer material than in the batches with aquifer material. Redox potentials gradually decreased to low values in batches with aquifer material without iron, while the batches with groundwater alone maintained a constant higher redox potential. Either adsorption processes or microbiological activity in the samples could explain these phenomena. Polymerase Chain Reaction (PCR: a targeted gene probe technique) for chlorinated aliphatic compound (CAH)-degrading bacteria confirmed the presence of Dehalococcoides sp. (chloroethene-degraders) but was negative for Desulfobacterium autotrophicum (a known co-metabolic TCA degrader). DCA reduction was rate determining: first-order half-lives of 300-350 h were observed. TCA was fully removed within hours. CA is resistant to reduction by zero-valent iron but it is known to hydrolyze easily. Since CA did not accumulate in our batches, it may have disappeared by the latter mechanism or it may not have formed as a major daughter product.     

Remediation of alachlor and atrazine contaminated water with zero-valent iron nanoparticles

Zero-valent iron nanoparticles (nZVI, diameter < 90 nm, specific surface area = 25 m² g^?1) have been used under anoxic conditions for the remediation of pesticides alachlor and atrazine in water. While alachlor (10, 20, 40 mg L^?1) was reduced by 92–96% within 72 h, no degradation of atrazine was observed. The alachlor degradation reaction was found to obey first-order kinetics very closely. The reaction rate (35.5 × 10^?3–43.0 × 10^?3 h^?1) increased with increasing alachlor concentration. The results are in conformity with other researchers who worked on these pesticides but mostly with micro ZVI and iron filings. This is for the first time that alachlor has been degraded under reductive environment using nZVI. The authors contend that nZVI may prove to be a simple method for on-site treatment of high concentration pesticide rinse water (100 mg L^?1) and for use in flooring materials in pesticide filling and storage stations.     

Influence of hydrogeochemical processes on zero-valent iron reactive barrier performance: a field investigation

Geochemical and mineralogical changes were evaluated at a field Fe0-PRB at the Oak Ridge Y-12 site concerning operation performance during the treatment of U in high NO3- groundwater. In the 5-year study period, the Fe0 remained reactive as shown in pore-water monitoring data, where increases in pH and the removal of certain ionic species persisted. However, coring revealed varying degrees of cementation. After 3.8-year treatment, porosity reduction of up to 41.7% was obtained from mineralogical analysis on core samples collected at the upgradient gravel-Fe0 interface. Elsewhere, Fe0 filings were loose with some cementation. Fe0 corrosion and pore volume reduction at this site are more severe due to the presence of NO3- at a high level. Tracer tests indicate that hydraulic performance deteriorated: the flow distribution was heterogeneous and under the influence of interfacial cementation a large portion of water was diverted around the Fe0 and transported outside the PRB. Based on the equilibrium reductions of NO3- and SO4(2-) by Fe0 and mineral precipitation, geochemical modeling predicted a maximum of 49% porosity loss for 5 years of operation. Additionally, modeling showed a spatial distribution of mineral precipitate volumes, with the maximum advancing from the interface toward downgradient with time. This study suggests that water quality monitoring, coupled with hydraulic monitoring and geochemical modeling, can provide a low-cost method for assessing PRB performance.     

金属铁还原脱氯处理有机氯化物的研究进展

本文对金属铁在还原降解六氯乙烷、四氯化碳、氯仿、三氯乙烯、四氯乙烯、二氯乙烯、氯乙烯、五氯酚、多氯联苯等有机氯化物中的应用作了评述 ,讨论了金属铁降解有机氯化物的反应机理及动力学。     

Arsenic stabilization by zero-valent iron,bauxite residue,and zeolite at a contaminated site planting Panax notoginseng

Panax notoginseng (Burk.) F.H. Chen, a rare traditional Chinese medicinal herb, is a widely used phytomedicine used all over the world. In recent years, the arsenic contamination of the herb and its relative products becomes a serious problem due to elevated soil As concentration. This study aimed to evaluate the effects of different types and dosages of amendments on As stabilization in soil and its uptake by P. notoginseng. Results showed that comparing to control treatment, the As concentrations of P. notoginseng declined by 49–63%, 43–61% and 52–66% in 0.25% zero-valent iron (Fe(0)), 0.5% bauxite residue, and 1% zeolite treatment, respectively; whereas the biomasses were elevated by 62–116%, 45–152% and 114–265%, respectively. The As(III) proportions of P. notoginseng increased by 8%, 9%, and 8%, and the transfer factors of As from root to shoot increased by 37%, 42% and 84% in the optimal treatments of Fe(0), bauxite residue, and zeolite. For soil As, all the three amendments could transform the non-specifically adsorbed As fraction to hydrous oxides Fe/Al fractions (by Fe(0) and red mud) or specifically adsorbed As fraction (by zeolite), therefore reduced the bioavailability of soil As. With a comprehensive consideration of stabilization efficiency, plant growth, environmental influence, and cost, Fe(0) appeared to be the best amendment, and zeolite could also be a good choice. In conclusion, this study was of significance in developing As contamination control in P. notoginseng planting areas, and even other areas for medicinal herb growing.     

超声波/零价铁降解对硝基苯胺的试验研究

对在超声波、零价铁和超声波/零价铁(U/Fe0)等体系中对硝基苯胺的降解规律进行了研究。研究结果表明,对硝基苯胺在超声波作用下,降解规律符合一级反应动力学模型,但超声波对高浓度的对硝基苯胺降解效果较差。在U/Fe0体系中,超声波和零价铁对降解对硝基苯胺具有协同作用,对硝基苯胺降解速率显著提高。降解机理显示,对硝基苯胺在零价铁表面上发生原电池反应,被还原为对苯二胺,在超声波作用下进一步降解。在U/Fe0体系中添加Cu2+,形成Fe/Cu原电池,可进一步促进对硝基苯胺的降解速率,降解效率优于铸铁屑形成的Fe/C原电池。     

纳米零价铁处理冶炼废水

多年的理论和机制研究发现,纳米零价铁（NZVI）作为还原剂及吸附剂,可处理水溶液中的多种重金属及类金属物质;而高效处理含高浓度重金属且成分复杂的冶炼废水是一项技术难题。本研究针对特定的冶炼废水（高浓度重金属及砷、高浓度氨氮、低pH、高含盐量）,研究了pH及NZVI投加量对砷、铜、锌、铅、镍的处理效果,并考察了连续流反应器中水力停留时间（HRT）及NZVI投加量对处理效果的影响。实验通过电感耦合等离子体发射光谱仪（ICP-OES）进行水样测试,扫描电子显微镜（SEM）、X射线衍射仪（XRD）进行固相表征。实验表明,通过NZVI处理,砷、铜、锌、铅、镍去除率均达99%以上,出水浓度均小于0.1 mg/L,达到废水排放标准（GB 8978-1996）。通过连续流反应器的应用发现,适当增大HRT、增加NZVI投加量,有利于更长时间保证出水水质的良好,延长NZVI消耗时间,提高废水处理量。结果显示,NZVI对复杂冶炼废水有极好的处理效果,在废水处理领域有着独特的优势,为后续研究及实际应用提供借鉴。     

Influences of redox transformation, metal complexation and aggregation of fulvic acid and humic acid on Cr(VI) and As(V) removal by zero-valent iron

This study investigated the removal kinetics and mechanisms of Cr(VI) and As(V) by Fe(0) in the presence of fulvic acid (FA) and humic acid (HA) by means of batch experiments. The focus was on the involvements of FA and HA in redox reactions, metal complexation, and iron corrosion product aggregation in the removal of Cr(VI) and As(V) removal by Fe(0). Synthetic groundwater was used as the background electrolyte to simulate typical groundwater. The results showed faster Cr(VI) removal in the presence of HA compared to FA. Fluorescence spectroscopy revealed that no redox reaction occurred in the FA and HA. The results of the speciation modeling indicate that the free Fe(II) concentration was higher in the presence of HA, resulting in a higher removal rate of Cr(VI). However, the removal of As(V) was inhibited in the HA solution. Speciation modeling showed that the concentration of dissolved metal-natural organic matter (metal-NOM) complexes significantly affected the aggregation of the iron corrosion products which in turn affected the removal of As(V). The aggregation was found to be induced by gel-bridging of metal-NOM with the iron corrosion products. The effects of metal-NOM on the aggregation of the iron corrosion products were further confirmed by TEM studies. Larger sizes of iron corrosion products were formed in the FA solution compared to HA solution. This study can shed light on understanding the relationships between the properties of NOM (especially the content of metal-binding sites) and the removal of Cr(VI) and As(V) by Fe(0).     

不同阳离子对Fe~0还原硝酸盐的影响

由于水中硝酸盐污染的普遍性、难去除性和对人体健康的潜在危害性而引起人们的广泛关注。通过批实验,考察了不同阳离子(Fe2+、Fe3+和Cu2+)对Fe0还原硝酸盐的影响。结果表明,由于加入阳离子可直接或间接地增加溶液中的Fe2+而都能促进硝酸盐的还原,作用顺序为Fe3+Fe2+Cu2+;Fe2+对硝酸盐的还原具有重要作用,并随着反应的进行,转化为铁氧化物附着在铁表面而降低铁的活性;硝酸盐还原的主要产物为氨氮,亚硝酸盐只在反应初期有少量积累,尤其是加Cu2+的体系中,但随后都很快降低;在所有体系中,检测到的三氮(NO3--N、NO2--N和NH4+-N)之和只占理论总氮的51.5%~82.6%;动力学分析表明,硝酸盐的还原在不加阳离子的体系中更符合一级反应,而加了阳离子的处理更符合Lo-gistic模型。本研究结果阐明了Fe2+对Fe0还原硝酸盐的重要性。     

土壤中零价铁还原3-氯硝基苯的作用

利用零价铁在常温常压下对土壤中的3-氯硝基苯的还原,对反应物和产物随时间的变化及反应的各个影响因素进行了研究。实验结果表明,零价铁能够有效地将3-氯硝基苯还原为3-氯苯胺,反应过程中没有检测到脱氯产物。其反应速率随铁粉用量、反应体系含水量的增加以及反应温度的升高而升高,随土壤初始pH值的升高而降低。在土壤中3-氯硝基苯含量约为2.5×10^-6 mol/g,铁粉使用量为25 mg/g,反应体系中含水量为0.75 mL/g,pH值为6.8时,在恒温生化培养箱(25±1)℃反应5 h后,3-氯硝基苯的还原率达到92.75％。     

Microbial reduction of nitrate in the presence of nanoscale zero-valent iron

Microbial reduction of nitrate in the presence of nanoscale zero-valent iron (NZVI) was evaluated to assess the feasibility of employing NZVI in the biological nitrate treatment. Nitrate was completely reduced within 3 d in a nanoscale Fe(0)-cell reactor, while only 50% of the nitrate was abiotically reduced over 7 d at 25 °C. The removal rate of nitrate in the integrated NZVI-cell system was unaffected by the presence of high amounts of sulfate. Efficient removal of nitrate by Fe(II)-supported anaerobic culture in 14 d indicated that Fe(II), which is produced during anaerobic iron corrosion in the Fe(0)-cell system, might act as an electron donor for nitrate. Unlike abiotic reduction, microbial reduction of nitrate was not significantly affected by low temperature conditions. This study demonstrated the potential applicability of employing NZVI iron as a source of electrons for biological nitrate reduction. Use of NZVI for microbial nitrate reduction can obviate the disadvantages associated with traditional biological denitrification, that relies on the use of organic substrates or explosive hydrogen gas, and maintain the advantages offered by nano-particle technology such as higher surface reactivity and functionality in suspensions.     

纳米铁去除水中硝酸盐的动力学研究

实验中采用了液相还原法制备新型吸附剂纳米铁。在纳米铁低投放量的条件下,采用间歇实验,分别从初始硝酸盐浓度、溶液pH值和温度的不同外界条件下研究了纳米铁对硝酸盐的去除情况。实验结果表明,硝酸盐初始浓度对反应速率有影响,但对去除率影响不大;溶液pH值为2.0时纳米铁对硝酸盐的去除效果最好;随着温度的升高,纳米铁对硝酸盐的去除率有所增加。以t时刻已反应掉的硝酸盐浓度为切入点,提出拟二级动力学方程。进而确定不同温度下的反应速率常数k。实验中k在50℃时最大,为0.014 mg/（L·min）。反应活化能Ea为17.18 kJ/mol,该反应以质量传递为控制因素。溶液中性条件下硝酸盐氮的还原产物为氨氮。     

超声波／零价铁降解水中双酚A

研究了超声波／零价铁（US／Fe^0）工艺对水中双酚A（BPA）的降解效果及影响因素。结果表明,US／Fe^0工艺可以有效降解水中的BPA,具有协同作用,且降解过程符合一级动力学规律;Fe^0具有促进和抑制的双重作用;超声功率越大,越有利于BPA的降解;初始浓度较低时,BPA的降解效果较好;弱酸性条件有利于BPA的降解;加入一定量的自由基捕获剂（正丁醇）可以抑制BPA的降解;联合作用2h后,TOC的去除率较低,说明其矿化程度不完全。     

超声波-零价铁协同降解废水中活性深蓝M-2GE的研究

研究了超声波-零价铁对废水中活性深蓝M-2GE的协同降解,探讨了铁粉添加量、超声波功率、介质pH和染料的浓度等对活性深蓝M-2GE降解效率的影响。结果表明,零价铁的存在可显著提高废水中活性深蓝M-2GE的超声降解效率,其降解率随着铁粉添加量的增多而升高。介质pH对活性深蓝M-2GE的降解有显著影响,pH=3时降解率最高。另外增大超声功率有利于有机污染物的降解,有机染料的浓度越低,降解率越高。     

生物炭负载纳米零价铁对湖泊底泥镉污染的修复效果

制备了生物炭负载纳米零价铁(nZVI/BC)复合材料,采用SEM、TEM、FTIR、EDS、XPS等手段对其表面形貌、粒径大小、官能团结构、表面元素及化学形态进行了表征和分析。通过镉(Cd)形态、浸出毒性、生物可利用性、上覆水中溶解态Cd质量浓度及底泥理化性质等指标评价了nZVI/BC对湖泊底泥中Cd的修复效果。结果表明,相比于对照组,经56 d修复后nZVI/BC处理组中Cd的残渣态质量分数增加了29.73%,有效降低了Cd的移动性;Cd的浸出质量浓度从4.65 μg·L⁻¹降至0.38 μg·L⁻¹,Cd的生物可提取态质量浓度从5.08 μg·L⁻¹降至2.13 μg·L⁻¹,其浸出质量浓度和生物可提取态质量浓度分别下降了91.83%和58.07%。同时,经过56 d的修复,nZVI/BC使上覆水中溶解态Cd的质量浓度比对照组降低了67.53%。此外,nZVI/BC的添加提高了底泥的pH和有机质,根据这2个指标的变化进一步分析了nZVI/BC复合材料对Cd的稳定机制。以上研究结果可为重金属污染底泥的修复提供参考。     

超声强化Fe0去除阳离子红GTL的研究

采用US/Fe0系统去除阳离子红GTL,考察了pH值、Fe0用量、超声功率及活性炭、H2O2、盐分添加对阳离子红GTL去除率的影响,利用紫外-可见吸收光谱变化查明阳离子红GTL在不同条件下的去除差异性,利用SEM解析铁的形态与染料去除的相关性。结果表明： pH≥5.0时超声和Fe0具有协同效应,Fe0用量2 g/L,pH=7.0,超声功率135 W,阳离子红GTL去除率达到96.07%;一定量的活性炭、H2O2、盐分添加会加速染料去除,US加速Fe0反应速度,但不改变染料降解机理,添加活性炭能够彻底降解阳离子红GTL,添加H2O2提供的氧化环境抑制苯胺类化合物生成;铁的形态及与染料的接触是影响染料去除效果的重要原因。     

Detoxification of hexachlorobenzene by dechlorination with potassium-sodium alloy

Dechlorination of hexachlorobenzene (HCB) was achieved by a liquid potassium–sodium (K–Na)-alloy. HCB in a cyclohexane/benzene solution (22 mmol/l, 4.67 g/l as chlorine) was dechlorinated by almost 100% after a 30-min reaction, indicating high reactivity of K–Na alloy and high proton donating power of cyclohexane. Decreasing orders of chlorobenzenes identified after a 15-min reaction, by amount were 1,2,3,4- > 1,2,3,5- > 1,2,4,5- for tetrachlorobenzenes, 1,2,4- > 1,2,3- > 1,3,5- for trichlorobenzenes, and 1,4- > 1,3- > 1,2- for dichlorobenzenes. It was hypothesized that once one chlorine atom in HCB was replaced with a proton, the adjacent chlorine atom to the proton tended to be replaced with another hydrogen atom. A total of 63 PCBs formed via the Wurtz–Fittig reaction were identified as by-products in the sample after a 15-min reaction. Among PCBs found, 2,3^′,4^′,5-tetrachlorobiphenyl, which was a product from 1,2,4-trichlorobenzene formed via the Wurtz–Fittig reaction, was detected in relatively high concentration (48.9 nmol/ml). The sample obtained from a reaction mixture after 30 min contained only 14 PCBs in trace amounts, indicating that the PCBs formed were also further dechlorinated by K–Na alloy. Non-chlorinated compounds––such as methylbenzene, dimethylbenzene, dimer of tetrahydrofuran, and dicyclohexyl (dimer of cyclohexane)––were also identified in the samples. A method using K–Na alloy developed in the present study dechlorinated satisfactorily HCB at room temperature.     

几种印染助剂对壳聚糖稳定纳米铁去除酸性品红的影响

以氯化铁为铁源,硼氢化钠为还原剂,壳聚糖为稳定剂,采用液相还原法制备壳聚糖稳定纳米铁（CS-nZⅥ）;研究了印染废水中常见助剂NaNO₃、Na₂SO₄、NaH₂PO₄、K₂Cr₂O₇、EDTA二钠盐存在下,超声波辅助CS-nZⅥ对酸性品红（AF）降解的影响。结果表明,反应15 min,0.01 g CS-nZⅥ对25 mL、100 mg/L AF的去除率高达99.9%;各种助剂的存在使得纳米铁表面不同程度失活,阻碍反应的进行,使得AF的去除率下降。NaNO₃、K₂Cr₂O₇、EDTA二钠盐与纳米铁发生反应,与AF存在明显的竞争作用。重复利用实验表明,CS-nZⅥ重复利用7次仍具有一定的反应活性。此外,CS-nZⅥ对加标（50 mg/L）实际废水中AF的去除率达到99%以上,表明CS-nZⅥ是一种潜在的环境修复材料。     

零价铁/过硫酸钾降解对氯苯酚模拟废水

以对氯苯酚（4-CP）为目标污染物,研究了零价铁（ZVI）活化过硫酸钾（KPS）氧化降解4-CP模拟废水的影响因素,对照了单独零价铁、单独过硫酸钾和联合体系的降解性能,检测了降解过程的氯离子和TOC的变化。结果表明,在pH值为5,零价铁投加量为0.3 g·L-1,过硫酸钾浓度为1.6 mmol·L-1,常温条件时,4-CP的去除率10 min可达87%。对照实验表明,体系中4-CP的降解不是零价铁或者过硫酸钾单独作用,而是联合体系产生的自由基的作用,其中硫酸根自由基起主要作用。体系中氯离子浓度随反应进行提高较快而TOC的去除率低于降解率,说明氧化脱氯作用明显,4-CP没有完全矿化。     

有机配体对纳米零价铁还原硝基苯的影响与机理

通过FeSO4·7H2O与NaBH4反应,采用液相还原法制备纳米级零价铁(NZVI),并用XRD,SEM对其性能进行表征。研究了纳米零价铁还原硝基苯(NB)的动力学规律及柠檬酸、草酸、柠檬酸钠、草酸钠、乙二胺四乙酸二钠(EDTA二钠盐)几种有机小分子对其还原效率的影响,并对其机理进行了初步探讨。结果表明,纳米零价铁去除硝基苯反应符合准一级动力学方程,并且当硝基苯浓度一定时,增加NZVI投加量,去除率会显著增大;当NZVI浓度一定时,硝基苯浓度越低,去除率越高;柠檬酸和EDTA二钠盐在较低浓度时抑制还原反应进行,而在3 mmol/L左右时,具有促进还原反应进行的作用,而草酸、柠檬酸钠和草酸钠则为抑制作用。