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据统计,我国纺织工业废水年排放量超过20.0亿t,印染作为纺织品加工的关键环节,废水排放量占全行业的70%—80%[1]. 印染废水中含有多种致癌染料化合物,具有较高生物毒性,严重影响地表水水环境和人类健康[2]. 染料是印染废水中的主要污染物,按其结构可分为多种类型,如偶氮类、三苯基甲烷类和噻嗪类. 其中偶氮类染料约占世界上染料总量的70%[3],而甲基红(methyl red,MR)是最常用的偶氮染料之一,因其结构稳定,可生化性差,常规技术较难处理[4];孔雀石绿(malachite green,MG)是一种典型的三苯基甲烷类染料,广泛用于印染、皮革、酿酒和水产养殖等行业的杀菌和防腐[5 − 6],现有研究表明孔雀石绿可能会诱发人体和动物细胞肿瘤的形成[7];同样,亚甲基蓝(methylene Blue,MB)作为典型的噻嗪类染料,在印染、化工等行业应用广泛,体现出较高的生物毒性[8].
目前,印染废水常用的处理方法有高级氧化法、生化法、吸附法、离子交换法等多种方法[9]. 吸附法具有操作简便、成本低廉等优势,适合处理色度高、成分复杂的印染废水,但存在效率不高等缺点. 生物炭具有疏松多孔结构、比表面积较大、表面含有羧基、羟基、酯和酸酐等官能团的特点[10],因此被开发成各种吸附剂. 然而,原始的生物炭材料对污染物去除效果欠佳,需改性后才能获得更高价值. 常见的改性方法可对生物炭进行金属负载改性或二次热解改性. 金属负载的方式又分为浸渍热解法、液相还原法、生物沥滤法等. 浸渍热解法[11]改性效率低,液相还原法[12]药剂浪费严重,能耗高,容易产生二次污染. 生物沥滤法[13]又称微生物湿法冶金法,能将固相中某些不溶性成分(如重金属、硫及其它金属)有效分离和浸提出来,工艺简单,快捷有效,在新型催化材料合成领域具有较好的应用前景. 对生物炭进行二次热解可进一步增加其孔隙度和活性点位,改善其吸附能力. 因此,将某些金属离子经生物沥滤负载后再进行二次热解,理论上可大幅提高材料的吸附降解性能. 本论文通过生物沥滤法和二次热解制备了铁改性生物炭材料,探讨了对几种染料的吸附能力和去除机理.
铁改性生物炭对几种染料的吸附机理研究
Study on the adsorption mechanism of several dyes by iron-modified biochar
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摘要: 本文以生物炭为原料,经氧化亚铁硫杆菌生物沥滤,将离子态的铁负载到生物炭上再进行二次热解,制备出铁改性生物炭材料(FeBC). 开展该材料对三苯基甲烷、偶氮和噻嗪类染料等典型染料进行吸附试验,考察材料投加量、染料浓度以及温度因素对染料去除的影响,利用XRD、FT-IR、XPS和BET等分析方法对FeBC进行表征并做吸附动力学模型和等温吸附模型拟合. 结果表明,FeBC负载了Fe3O4后表面官能团和孔隙结构更加丰富. FeBC对几种染料的吸附结果符合一阶动力学方程和Langmuir等温吸附模型,证明FeBC对染料的去除是以物理吸附为主的单分子层吸附过程;染料去除率与初始浓度呈极显著负相关(P<0.01),与温度呈极显著正相关(P<0.01). 本文初步揭示了该材料对几种染料的去除机理,是以孔隙吸附、氢键、π—π电子共轭吸附以及静电吸附等方式去除,改性后对不同染料吸附量提高达302.2%—409.5%. 该研究为新型炭改性材料在染料废水中的处理提供了新思路.Abstract: In this paper, iron-modified biochar material (FeBC) was prepared by biolestrating by thiobacter ferrooxidans and loading ionic iron onto biochar for secondary pyrolysis. The adsorption tests on several typical dyes, such as triphenylmethane, azo and thiazine dyes, were carried out to investigate the effects of material dosage, dye concentration and temperature on dye removal. FeBC was characterized by XRD, FT-IR, XPS and BET, and the adsorption kinetics model and isothermal adsorption model were fitted. The results show that FeBC loaded with Fe3O4 has more functional groups and pore structures. The adsorption results of FeBC on several dyes conform to the first-order kinetic equation and Langmuir isothermal adsorption model, which proves that the removal of dyes by FeBC is a single-molecule layer adsorption process based on physical adsorption. The dye removal rate was negatively correlated with initial concentration (P<0.01), and positively correlated with temperature (P<0.01). In this paper, the removal mechanism of several dyes by the material was preliminically revealed, including pore adsorption, hydrogen bond, π—π electron conjugated adsorption and electrostatic adsorption. After modification, the adsorption capacity of different dyes was increased to 302.2% — 409.5%. This study provides a new idea for the treatment of new carbon modified materials in dye wastewater.
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Key words:
- iron-modified biochar /
- dye wastewater /
- adsorption.
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表 1 BC、MBC和FeBC的BET结果
Table 1. BET results of BC, MBC and FeBC
比表面积 /(m2·g−1)
Surface area平均孔径/nm
Average pore diameter总孔容 /(cm3·g−1)
Total pore volumeBC 52.7430 4.8348 0.063751 MBC 45.6641 5.4489 0.053971 FeBC 12.7462 6.2280 0.019846 表 2 染料的性质
Table 2. Properties of dyes
名称
Name分子式
Molecular formula分子结构
Molecular structures相对分子质量
Molecular weight孔雀石绿 Cu2(OH)2CO3 239 甲基红 C15H15N3O2 269 亚甲基蓝 C16H18N3ClS 319.5 表 3 三种染料的准一阶动力学模型、准二阶动力学模型拟合参数
Table 3. The fitting parameters of quasi-first-order kinetic model and quasi-second-order kinetic model of three dyes were obtained
染料名称
Dye of name准一阶动力学模型
Pseudo-first-order kinetic model准二阶动力学模型
Pseudo-second-order kinetic modelk1/h−1 qe/(mg·g−1) R2 K2/(g·mg−1·min−1) qe/(mg·g−1) R2 MG 7.68 298.91 0.9793 9.6293 302.11 0.9770 MR 16.40 80.77 0.9721 74.0740 87.71 0.9457 MB 12.97 298.71 0.9955 2.6761 313.48 0.9686 表 4 三种染料吸附等温线Freundlich模型和Langmuir模型拟合参数
Table 4. Fitting parameters of the Freundlich model and Langmuir model for three kinds of dye adsorption isotherms
染料
Dye of nameFreundlich模型 Langmuir模型 KF/(mg·g−1)·(L·mg−1)1/n 1/n R2 qm/(mg·g−1) kL/(L·mg−1) R2 MG 1.8776 0.7668 0.9881 221.239 0.004 0.9962 MR 78.7195 0.1332 0.9772 76.394 0.014 0.9988 MB 6.8895 0.0026 0.9555 6.3291 0.102 0.9861 -
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