【作者】 王倩；

【导师】 徐新华；

【作者基本信息】 浙江大学 ， 环境工程， 2010， 博士

【摘要】 采用PRB(Permeable Reactive Barrier,可渗透反应墙)技术修复受污染地下水或土壤的过程中,零价铁或纳米级零价铁会被逐渐氧化为Fe203等含铁氧化物(类似于含铁矿物),同时各种含铁矿物也在土壤中广泛存在。本文考察了自然界中常见的铁矿石——黄铁矿、褐铁矿、磁铁矿、赤铁矿和磁黄铁矿,以及微生物对水中Cr(Ⅵ)的去除效果,并将铁矿石和微生物有机结合,初步研究了铁矿石-微生物协同体系对水中Cr(Ⅵ)的去除效果及机理,探讨了在纳米级零价铁的制备中加入稳定剂CMC(羧甲基纤维素),使制备的纳米级零价铁或反应后形成的含铁氧化物高度分散,有效提高对Cr(Ⅵ)去除能力的情况,同时CMC可为后续的微生物处理提供碳源。结果表明：1、黄铁矿可以有效去除水中的Cr(Ⅵ),去除效率主要受颗粒大小、投加量、初始pH值和反应温度等影响,水中Cl-和SO42-等离子对Cr(Ⅵ)去除效率影响不大,而H2P04-的添加会抑制反应的进行。在Cr(Ⅵ)初始浓度为10 mgl-1、100～200目黄铁矿投加量为20 gl-1、室温的条件下,当pH=3.0时,30 mmin即反应完全；pH=5.5时,120 min后Cr(Ⅵ)去除率可达到91.82%,而在pH=9.0时,反应120 min后Cr(Ⅵ)的去除率仅为52.73%。在与前述相同的反应条件下,当pH=5.5时,黄铁矿对Cr(Ⅵ)的去除能力约为1.53 mg Cr(Ⅵ)g-1。在反应过程中,水中的Cr(Ⅵ)主要与黄铁矿表面的FeS2进行反应,Cr(Ⅵ)被还原成Cr(Ⅲ),形成了类似Fe304结构的Cr2S3和CrS的混合物Cr3S4,及少量的Cr02,并在黄铁矿表面形成覆盖层,使黄铁矿的表面逐渐钝化而失去反应能力。同时,FeS2中的Fe(11)也被氧化为Fe(Ⅲ),从而失去还原去除Cr(Ⅵ)的能力。2、褐铁矿也可有效去除水中的Cr(Ⅵ)。褐铁矿的颗粒大小、投加量和初始pH值对Cr(Ⅵ)去除效率也有显著的影响,而温度对反应的影响不大。水中Cl-和NO3-对Cr(Ⅵ)去除的影响不大,而MgO的添加在反应初期对反应有抑制作用。在反应过程中,水中的Cr(Ⅵ)与褐铁矿表面的FeS2等反应,Cr(Ⅵ)被还原成Cr2S3和CrS的混合物Cr3S4,并产生了部分Cr5Si3,主要沉积在褐铁矿的表面,使褐铁矿表面逐渐钝化并失去反应能力。室温下,当pH=5.5时,100～200目的褐铁矿对Cr(Ⅵ)的去除能力约为10.03 mg Cr(Ⅵ)g-1。3、在中性条件下,磁铁矿去除水中Cr(Ⅵ)的能力较差,赤铁矿则具有一定的去除能力。在酸性条件下,两者对水中Cr(Ⅵ)的去除能力均有提高,磁铁矿的去除能力提高较为明显。而磁黄铁矿在酸性和中性条件下对Cr(Ⅵ)均具有较好的去除效果,Cr(Ⅵ)还原产物Cr(Ⅲ)主要以FeCr2O4的形式存在于磁黄铁矿的表面。在碱性条件下,三种铁矿石的去除能力均较差。4、利用城市污水处理厂厌氧消化池中的污泥接种,加入低浓度含Cr(Ⅵ)废水进行驯化,筛选出对Cr(Ⅵ)具有较强还原去除能力的微生物,微生物对Cr(Ⅵ)的去除反应为酶促反应。乙酸钠是较为合适的碳源,pH值是影响反应的重要因素,在中性条件下,反应效果最佳。在短暂的饥饿状态下,微生物仍具有还原Cr(Ⅵ)的能力。经11h反应后,5 mgl-1的Cr(Ⅵ)废水浓度即降至0。5、利用铁矿石-微生物联合体系去除水中的Cr(Ⅵ)时,发现铁矿石与微生物之间存在一定的协同效果,去除能力明显优于两者单独反应。在使用0.2 g褐铁矿和2.0 g离心后污泥分别及联合去除30 mgl-1 Cr(Ⅵ)时,78 h后褐铁矿仅将Cr(V1)浓度降至29.6 mgl-1,单独微生物作用可将Cr(Ⅵ)浓度降至5.07 mgl-1,而两者联合作用下,Cr(Ⅵ)浓度可降至3.68 mgl-1。协同体系还原去除Cr(Ⅵ)的反应主要有三条途径：一是铁矿石对Cr(Ⅵ)的吸附与还原,二是微生物对Cr(Ⅵ)的还原降解,三是微生物将铁矿石表面和液相中的Fe(Ⅲ)还原为Fe(Ⅱ),并通过Fe(Ⅱ)间接还原Cr(Ⅵ)。6、利用纳米级零价铁处理水中Cr(Ⅵ)的过程中,零价铁被逐渐氧化为Fe203等类似于铁矿石的含铁化合物。加入稳定剂CMC可提高纳米级零价铁及被氧化后纳米级含铁化合物的分散度,以保持好的反应活性,同时投加的CMC还可作为后续生物处理过程中微生物的营养物质(碳源),研究为稳定化纳米级零价铁-微生物协同修复Cr(Ⅵ)进行前期的探索。更多还原

【Abstract】 Iron particles and nanoparticles could be used to remediate Cr(Ⅵ)-polluted soils and underground waters with PRB (Permeable Reactive Barrier) and would be oxidized to Fe2O3 gradually while many kinds of minerals which containing iron oxides exist in soils.This article researched on Cr(Ⅵ) removal by pyrite, limonite, magnetite, hematite, pyrrhotite and bacteria and synergistic removal of Cr(Ⅵ) by iron ores and bacteria was studied. Besides, Carboxymethyl Cellulose (CMC), a nontoxic and biodegradable stabilizer, was used to stabilize the nanoscale zero-valent iron and maintain Cr(Ⅵ) removal rate in Cr(Ⅵ) reduction. It could also be used as a carbon source in synergistic removal of Cr(Ⅵ) by iron ores and bacteria.The results are as follows:1. Cr(Ⅵ) could be removed from water by pyrite and the removal efficiency was affected by pyrite size and dose, initial pH and temperature. Cl- and SO42- did not affect the reaction obviously but H2PO4- could inhibit the reaction. At room temperature,10 mg l-1 Cr(Ⅵ) could be removed completely after 30 min by 20 g l-1 pyrite (100～200 mesh) with pH of 3.0, while Cr(Ⅵ) removal rate could reach 91.82% after 120 min at pH 5.5 with other conditions the same as before, and only 52.73% of Cr(Ⅵ) could be removed at pH 9.0. At pH 5.5 and room temperature, reaction capability of pyrite (100～200 mesh) to reduce Cr(Ⅵ) was 1.53 mg Cr(Ⅵ) g-1. FeS2 from the surface of pyrite reacted with Cr(Ⅵ) in the solution and Cr(Ⅵ) was reduced to form Cr3S4, composed of Cr2S3 and CrS, while some CrO2 was produced. They appeared on the surface of pyrite and covered it, which made pyrite lose the ability to reduce Cr(Ⅵ) gradually. Meanwhile, Fe(Ⅱ) in FeS2 was oxidized to Fe(Ⅲ) and could not reduce Cr(Ⅵ) any more.2. Cr(Ⅵ) could also be removed from water by limonite and the removal efficiency was affected by limonite size and dose, initial pH. Temperature did not play an important role in reaction, just like the addition of Cl- and NO3-. But MgO could inhibit the reaction at the beginning of the reaction. FeS2 from the surface of limonite reacted with Cr(Ⅵ) in the solution and Cr(Ⅵ) was reduced to form Cr3S4, composed of Cr2S3 and CrS, while some Cr5Si3 was produced. They appeared on the surface of limonite and covered it, which made limonite lose the ability to reduce Cr(Ⅵ) gradually. At pH 5.5 and room temperature, reaction capability of limonite (100～200 mesh) to reduce Cr(Ⅵ) was 10.03 mg Cr(Ⅵ) g-1.3. In neutral condition, magnetite could hardly remove Cr(Ⅵ) while hematite had the ability. In acid condition, the Cr(Ⅵ) removal abilities of magnetite and hematite were all improved, especially magnetite. In comparison, pyrrhotite had good abilities to remove Cr(Ⅵ) in aquous solution in neutral and acid conditions and FeCr2O4 produced in the reaction would exist on the surface of pyrrhotite. In basic condition, all three iron ores had bad results in removal.4. Indigenous bacteria from Sewage Treatment Plant could be acclimated and screened, and then used in hexavalent chromium reduction in aqueous solution. The microbial reduction of Cr(Ⅵ) was an enzyme catalysis reaction. NaAc was the suitable carbon resource. pH played an important roles in reactions and best results appeared in neutral condition. After short starvation the bacteria still had the ability to removal Cr(Ⅵ).5. A synergistic mechanism was found in Cr(Ⅵ) removal by iron ore and bacteria and better results could be obtained by them together than by them seperately. After 78 h,30 mg l-1 Cr(Ⅵ) could only be reduced to 29.6 mg l-1 by 0.2 g limonite and could be reduced to 5.07 mg l-1 by 2.0 g bacteria. At the same condition,30 mg l-1 Cr(Ⅵ) could be reduced to 3.68 mg l-1 by limonite and bacteria. The synergistic reaction had three reaction pathways. First, Cr(Ⅵ) was adsorbed and reduced by iron ores. Second, bacteria reduced Cr(Ⅵ). Third, Fe(Ⅲ) which exists on the surface of iron ores and in the solution was reduced to Fe(Ⅱ) by bacteria and then Fe(Ⅱ) reacted with Cr(Ⅵ).6. Iron particles and nanoparticles could be used to remove Cr(Ⅵ) and would be oxidized to Fe2O3 gradually. Carboxymethyl Cellulose could disperse iron nanoparticles and iron oxides which were producted from iron nanoparticles to maintain the reaction activity. It could also be used as a carbon source in synergistic removal of Cr(Ⅵ) by iron ores and bacteria and the results could be regarded as the basic researches results in Cr(Ⅵ) removal synergistic reaction of iron nanoparticles and bacteria.更多还原