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氟污染是一个全球性问题,特别是在发展中国家[1],其中钢铁冶金、铝电解、铅锌冶炼、铜冶炼、光伏产业、锂离子电池等冶金行业是氟污染的主要来源[2]。过量摄入氟化物将会对人体产生有害影响,阻碍儿童生长发育[3]。我国对地表水体及生活饮用水中的氟化物质量浓度有严格的限值,也不断强化关于氟化物排放的管控。目前,水体中氟化物的去除技术主要有沉淀絮凝法、膜处理法、离子交换法、吸附法[4-7],其中吸附法具有产生无害废物数量少、材料成本低、操作简便等优点,被认为是最有前途的除氟方法。
生物炭具有较大的比表面积,表面含有丰富的含氧官能团,且相对廉价,可作为新型吸附材料用于环境修复领域[8-9]。近年来,已有关于不同生物质来源(改性)生物炭除氟应用的研究报道。汤家喜等[10]利用花生壳、玉米秸秆制备的生物炭,最大吸附容量为1.18 mg·g−1;邱会华等[11]制备的氢氧化钾活化的荷叶基生物炭,最大吸附容量为0.85 mg·g−1;张涛等[12]制备了铁改性猪粪生物炭,最大吸附容量为4.4 mg·g−1;徐凌云等[13]制备了铝负载酒糟生物炭,最大吸附容量为18.05 mg·g−1;FENG等[14]利用城市污水处理厂污泥合成的改性污泥生物炭最大吸附容量高达30.49 mg·g−1。显然,不同原料衍生的生物炭吸附除氟能力不尽相同,其中由于污泥含有更高含量的亲氟矿物,其衍生的污泥生物炭对氟的吸附能力最强。但是,未经改性的污泥生物炭直接除氟效果并不理想,一般需要通过铝、铁等金属的负载以提高其吸附性能。近年来发现镧[15]、铈[16]、钇[17]等稀土金属有更好的亲氟性,可用于氟化物的去除,但是单独使用成本较高,如与铁或铝复合使用,有望发挥协同作用并降低成本。另外,我国污泥产量巨大,据统计2021年我国含水率80%的城市污泥产量已超过6 000×104 t[18]。当前污泥的主流处置方式包括干化焚烧、污泥堆肥和卫生填埋,都可能产生二次污染,对环境造成巨大的风险[19-20]。因此,研发基于污泥生物炭的复合改性除氟材料,拓展污泥资源化利用途径,实现以废治废,具有较好的开发前景。
本研究以南通市政污泥为原料,通过缺氧热解-醋酸钾活化-铝铈改性工艺,制备了铝铈改性污泥生物炭(Al/Ce-CSBC),运用SEM、EDS、BET、XRD及XPS等技术对材料吸附前后的表面形态和结构特征进行了表征和分析,探究了Al/Ce-CSBC对模拟废水中氟离子的吸附行为和吸附机理,以期为污泥生物炭在除氟的资源化利用研究提供参考。
负载铝铈污泥生物炭对模拟废水的强化除氟作用
Enhanced fluoride removal from simulated wastewater by aluminum-cerium loaded sludge biochar
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摘要: 以市政污泥为原料,通过热解、活化及共沉淀工艺制备了铝铈负载污泥生物炭复合材料(Al/Ce-CSBC),运用多种分析技术表征了材料形貌、比表面积及结构特征,通过模拟废水的批量吸附实验,考察了pH、初始氟离子质量浓度及吸附时间对Al/Ce-CSBC吸附氟性能的影响,最后探究了其除氟机制。结果表明,活化和改性均提高污泥生物炭的比表面积,其中Al/Ce-CSBC具有丰富的狭缝形介孔,比表面积为176.36 m2·g−1,pHPZC为9.5。负载于材料表面的无定形铝/铈氧化物是主要吸附组分,且发挥了双金属协同作用,在pH=4.0~9.0内其可保持较高的吸附容量。吸附动力学符合伪二级模型,吸附等温线符合Freundlich模型。最大吸附容量可达到41.74 mg·g−1,显著优于其他常见生物炭材料。其吸附机理主要包括静电吸附、离子交换和表面络合。本文可为污泥的资源化利用提供重要的参考。Abstract: In this study, sewage sludge was taken as raw material, and a novel Al/Ce loaded sludge biochar composite (Al/Ce-CSBC) was prepared by pyrolysis, activation and co-precipitation. Its morphology, specific surface area and structure were characterized by various advanced instrumental analysis techniques. Batch adsorption experiments were conducted in simulated wastewater, the effects of pH, initial fluoride concentration and adsorption time on fluoride adsorption by Al/Ce-CSBC were investigated, and finally the fluoride removal mechanism was explored. The results showed that both activation and modification could increase the specific surface area of sludge biochar. Al/Ce-CSBC had rich slit mesopores, and its specific surface area and pHPZC were 176.36 m2·g−1 and 9.5, respectively. Amorphous aluminum/cerium oxide loading on the material surface was the main active component for adsorption, and also played a bimetallic synergistic role, which could maintain a high adsorption capacity within pH range of 4.0~9.0. The adsorption kinetics conformed to the pseudo-second order model, the adsorption isotherm conformed to the Freundlich model. The maximum adsorption capacity of Al/Ce-CSBC could reach 41.74 m2·g−1, which was significantly over the conventional biochar adsorption materials. The adsorption mechanism mainly included electrostatic adsorption, ion exchange and surface complexation. This work can provide an important reference for the resource utilization of sludge.
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Key words:
- sludge /
- biochar /
- aluminum cerium loading /
- defluoridation /
- adsorption
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表 1 样品元素含量变化
Table 1. Changes in the element content of the samples
% 样品 O C Ca Fe Al Si P Mg K Ce SBC 39.9 28.0 16.4 4.0 3.7 3.4 1.1 1.0 0.8 0 Al/Ce-CSBC 35.1 46.8 0.2 1.8 1.7 10.9 0 0.2 0.6 2.3 表 2 样品的孔隙结构
Table 2. Pore structure of the studied samples
样品 BET比表面积/(m2·g−1) 总孔体积/(cm3·g−1) 平均孔径/nm SBC 25.59 0.114 4 13.454 CSBC 69.78 0.144 0 11.395 Al/Ce-CSBC 176.36 0.174 8 6.610 表 3 不同吸附剂的氟离子吸附性能对比
Table 3. Comparison of fluorine ion adsorption performance of different adsorbents
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