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苯系物是苯及其衍生物的统称,地下水层中的苯系物主要来自于原油开采、储运过程中的溢漏事故以及化工焦化废水排放等[1]。苯系物会对人类产生致癌、致畸和致突变等毒性作用,被美国环境保护署列为优先控制环境污染物[2]。而苯酚和苯胺作为基本的有机化工原料,被广泛用于药物合成、合成橡胶以及染料、炼油等工业生产活动,具有较强的挥发性和环境破坏性,对生物具有明显的毒害作用[3]。因此寻找高效的去除地下水中苯酚苯胺的方法具有重要意义。
苯系物的去除方法包括吸附法[4-5]、原位化学氧化法 (in-situ chemical oxidation,ISCO) [6-7]、生物修复法[8]以及自然衰减法[9]。其中,ISCO技术操作简单、去除效果好且修复成本较低,因此在地下水苯系物的修复方面得到了广泛应用[10-11],是去除苯系物污染最具前景的技术之一[12]。ISCO技术是通过向污染区域注入特定氧化剂,使氧化剂和有机物反应,将其降解为水、CO2和毒性较低的小分子化合物[13]。然而,在实际运用中,当氧化剂以溶液形式直接注入时,往往会与地下水体中的有机质、无机颗粒成分或其它的还原性物质产生非选择性消耗,造成氧化剂浪费、利用效率低[14]以及修复效果差等问题[15-16]。因此,为了达到氧化剂的控制释放、有效传输和高效修复的目的[17-18],专家学者提出了缓释氧化技术以达到长期高效的修复效果。
常用的缓释材料有KMnO4、碱土金属过氧化物、过硫酸盐缓释氧化剂,各类缓释氧化材料均有其优缺点。碱土金属过氧化物缓释氧化剂的制备条件更为苛刻,要求完全的无水环境[19];过硫酸盐缓释氧化剂使用过程需要特定的条件来激活和维持有效的氧化反应[20],并且会产生硫酸盐沉淀等副产物;KMnO4缓释材料的最终产物MnO2可能会影响缓释材料的渗透性等[21]。相比之下,KMnO4是目前缓释氧化材料最常用的氧化剂。制备KMnO4缓释材料重要的是选择合适的结合材料[22],结合材料应具有环境友好,无毒无害且易于回收利用等优点,目前应用最多的结合材料为石蜡。KANG等[23]制备了KMnO4-石蜡缓释颗粒,释放时间长达472 d。ZENG等[24]使用石蜡和硅砂制备了复合型KMnO4缓释体,实现了缓释剂的可控和持久释放。但KMnO4复合材料使用之后会生成氧化锰涂层,从而降低多孔介质的孔隙度和渗透率,最终影响KMnO4向水相的传质速率[25],降低缓释材料的缓释性能。因此,寻找合适的添加剂来有效降低反应产物MnO2对材料渗透性的影响是目前KMnO4缓释材料需要解决的问题之一。有研究表明在KMnO4缓释材料中添加活性炭可以增大多孔材料的渗透率[26],显著提高材料的孔隙度和耐酸碱腐蚀性能[27]。ZHANG等[27]以活性炭做造孔剂,制备了陶瓷膜支撑体,活性炭质量分数从0~18%,支撑体的孔隙率从25%提高到37.5%,并具有良好的耐化学腐蚀性能,证明了活性炭能显著提高复合材料的孔隙率和渗透压率。
基于此,本研究通过制备添加活性炭的KMnO4缓释材料,通过清水缓释实验研究了缓释材料的缓释性能,在此基础上开展了二维砂槽中KMnO4缓释材料降解苯酚苯胺的研究;鉴于目前缓释材料大多只进行清水缓释实验,并未考虑实际地下水中阴离子和有机物对材料使用过程中的影响,本研究深入考察了地下水中常见离子及有机质对苯酚苯胺降解的影响,研究结果可为于解决实际地下水中苯系物污染的问题提供一定的指导。该研究不仅可以解决氧化剂浪费、利用效率低以及修复效果差等问题,还能通过定期更换缓释氧化剂来实现持续降解污染物的目的,从而节省经济的投入并降低工作安全风险,可为地下水含水层高效修复提供一种新的思路。
KMnO4缓释氧化剂降解地下水中的苯酚和苯胺
Degradation of phenol and aniline in groundwater by KMnO4 slow-release oxidant
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摘要: 为了达到氧化剂控制释放、有效传输和高效修复的目的,采用缓释技术实现氧化剂对地下水含水层的长期高效修复。实验通过熔化成型法制备了添加活性炭的高锰酸钾 (KMnO4) 缓释材料,并通过释放动力学确定缓释材料的最佳配比和尺寸。此外,对KMnO4缓释材料降解苯酚苯胺的动力学进行了研究,并考察了地下水水质对苯酚苯胺降解的影响。最后开展了二维砂槽中缓释材料降解苯酚苯胺的实验。结果表明:石蜡、高锰酸钾、活性炭以及硅砂质量比为3∶3∶2∶1的1 cm立方体的KMnO4缓释氧化剂缓释效果最好。释放动力学研究显示,30 d后缓释材料的释放率为64.17%,表明其具有优异的缓释特性,并且采用一级动力学方程对实验数据拟合时相关性较好。并且缓释后的KMnO4缓释材料表面出现大量孔洞和缝隙,且表面Mn、O、Si和K元素含量明显增加,说明KMnO4缓释材料在水中的释放原理是以溶解扩散为主。在缓释氧化剂作用下,二维砂槽中苯酚和苯胺的浓度变化形成以缓释材料为中心的锥形修复区域,且纵向苯酚苯胺的浓度下降较快。这一实验结果为实际地下水含水层污染修复提供了理论支撑。
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关键词:
- KMnO4缓释氧化剂 /
- 苯酚 /
- 苯胺 /
- 降解
Abstract: In order to achieve the purpose of controlled release, effective transport and efficient remediation of the oxidant, the slow-release technology is used to realize the long-term and efficient remediation of the groundwater aquifer by the oxidant. The potassium permanganate (KMnO4) slow-release materials with the addition of activated carbon were experimentally prepared by melt molding method, and the optimal ratios and sizes of slow-release materials were determined by release kinetics. In addition, the phenol-aniline degradation kinetics by KMnO4 slow-release materials and the effect of groundwater quality on phenol-aniline degradation were also investigated. Finally, an experiment was conducted on the degradation of phenol and aniline using slow-release materials in a two-dimensional sand tank. The results showed that the slow-release effect of KMnO4 slow-release material with a mass ratio of 3∶3∶2∶1 for paraffin, potassium permanganate, activated carbon, and silica sand, which was a 1 cm cube, was the best. The release kinetics study showed that the release rate of the sustained-release material after 30 d was 64.17%, indicating that it had excellent sustained-release properties, and the first-order kinetics equation was used to fit the experimental data with good correlation. And there were numerous holes and gaps appeared on the surface of KMnO4 retarded material after retardation, and the content of Mn, O, Si, and K elements on the surface increased significantly. This indicating that the release principle of KMnO4 slow-release material in water was mainly dissolution diffusion. Under the action of the slow-release oxidant, the concentration changes of phenol and aniline in the two-dimensional sand tank form a conical repair area centered on the slow-release material, and the concentration of phenol and aniline in the longitudinal direction decreased rapidly. This experimental result provides theoretical support for the remediation of actual groundwater aquifer pollution.-
Key words:
- KMnO4 slow-release oxidant /
- phenol /
- aniline /
- degradation
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表 1 不同高锰酸钾缓释材料的质量配比
Table 1. Mass ratios of different potassium permanganate slow release materials
材料编号 石蜡/g 硅砂/g 高锰酸钾/g 活性炭/g 石蜡∶高锰酸钾 A1 12 4 6 0 2∶1 A2 12 4 12 0 1∶1 A3 12 4 24 0 1∶2 B1 12 4 6 4 2∶1 B2 12 4 12 4 1∶1 B3 12 4 24 4 1∶2 表 2 浸提液更换周期
Table 2. Leaching solution replacement cycle
浸出阶段 浸提液更换时间 累计时间/d 间隔时间/h 1 0.25 6 2 1 18 3 2.25 30 4 4 42 5 9 120 6 16 168 7 36 480 8 64 672 表 3 各影响因素梯度设置方案
Table 3. Setting scheme of each factor in the experimental group
因素 梯度设置 pH 3 5 7 9 NO3−/(mg·L−1) 0 140 700 3 500 SO42−/(mg·L−1) 0 140 700 3 500 HCO3−/(mg·L−1) 0 140 700 3 500 Cl−/(mg·L−1) 0 140 700 3 500 腐殖酸/(mg·L−1) 0 10 30 100 表 4 降解动力学参数值及其方程
Table 4. Degradation of kinetic parameter values and their equations
污染物 $ {k}_{\text{obs}} $ $ r=-\dfrac{\text{d}{c}}{\text{d}{t}}={k}_{\text{obs}}{c} $ R2 苯酚 0.019 4 0.019 4c 0.976 1 苯胺 0.009 0 0.009 0c 0.969 5 -
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