生物炭负载羧甲基纤维素钠稳定化纳米铁对水中六价铬的去除

闫奇; 郑乾送; 周江敏; 陶月良; 杨旭; 袁孝康; 陈华林

doi:10.12030/j.cjee.201905066

温州大学生命与环境科学学院，温州 325035

作者简介: 闫奇(1993—)，男，硕士研究生。研究方向：水中重金属污染防治。E-mail：1035412565@qq.com

通讯作者: 陈华林(1971—)，男，博士，副教授。研究方向：水污染化学等。E-mail：hualin2100@126.com

基金项目:

浙江省国际产业联合研发计划基金资助项目(2019C54002)；浙江省自然科学基金资助项目(LY17D010003)

中图分类号: X52

Removal of hexavalent chromium from water by biochar supported with sodium carboxymethyl cellulose-stabilized nano-iron

College of Life and Environmental Sciences, Wenzhou University, Wenzhou 325035, China

Corresponding author: CHEN Hualin, hualin2100@126.com

摘要: 利用液相还原法，通过先负载再包裹的方式制备了4种不同炭铁质量比的生物炭负载羧甲基纤维素钠稳定化纳米铁(BC-nZVI-CMC)材料，并将其用于对水中Cr(Ⅵ)的去除，使用扫描电镜、X射线衍射和傅里叶红外等技术对BC-nZVI-CMC的结构与性质进行了表征。结果表明：BC-nZVI-CMC具有较好的分散性，粒径为纳米级且被CMC完全包覆，抗氧化能力得到较大提升，可有效去除水中Cr(Ⅵ)；投加1 g·L⁻¹的BC-nZVI-CMC对含有30 mg·L⁻¹的Cr(Ⅵ)去除率达99.83%；pH越小，越有利于BC-nZVI-CMC对水中Cr(Ⅵ)的去除，最高去除率可达100%；BC-nZVI-CMC的抗氧化能力明显高于商品纳米铁和生物炭负载纳米铁；含有8 g·L⁻¹ C/Fe=1∶1的BC-nZVI-CMC对电镀废水中Ni、Zn、Cu、总铬、Cr(Ⅵ)的去除率可达39.60%、91.70%、100%、91.69%、100%。上述研究结果对水中Cr(Ⅵ)去除新技术的开发有重要的参考价值。

Abstract: In this study, biochars supported with sodium carboxymethyl cellulose-stabilized nano-iron (BC-nZVI-CMC) with four different carbon-iron mass ratios was prepared though liquid-phase reduction method and first supporting and then covering way, which were used to remove Cr(Ⅵ) from water. The structure and properties of BC-nZVI-CMC were characterized by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The results showed that BC-nZVI-CMC presented good dispersion, nano-sized distribution, complete CMC coating and greatly improved anti-oxidation ability, it could effectively remove Cr(Ⅵ) from water. At the dosage of 1 g·L⁻¹ BC-nZVI-CMC, 99.83% Cr(Ⅵ) could be removed from water with the initial concentration of 30 mg·L⁻¹. The lower the pH, the higher removal efficiency of Cr(Ⅵ) by BC-nZVI-CMC, and the highest removal efficiency could reach 100%. The anti-oxidation ability of BC-nZVI-CMC was significantly superior to that of commercial nano-iron and biochar-loaded nano-iron. At the dosage of 8 g·L⁻¹ BC-nZVI-CMC with C/Fe=1∶1, the removal efficiencies of Ni, Zn, Cu, total chromium and Cr(Ⅵ) in electroplating wastewater could reach 39.60%, 91.70%, 100%, 91.69% and 100%, respectively. The result provides important reference for the development of new Cr(Ⅵ) removal technology from water.

Key words:

纳米铁类型

准一级动力学

准二级动力学

k₁/min⁻¹

R²

k₂/min⁻¹

R²

C/Fe=1:0.5

0.006 3

0.821 1

0.000 31

0.999 9

C/Fe=1:1

0.007 7

0.929 5

0.002 06

0.998 5

C/Fe=1:5

0.007 6

0.863 4

0.001 89

0.997 7

C/Fe=1:10

0.006 4

0.674 9

0.001 46

0.998 6

生物炭负载羧甲基纤维素钠稳定化纳米铁对水中六价铬的去除

通讯作者: 陈华林(1971—)，男，博士，副教授。研究方向：水污染化学等。E-mail：hualin2100@126.com

作者简介: 闫奇(1993—)，男，硕士研究生。研究方向：水中重金属污染防治。E-mail：1035412565@qq.com
温州大学生命与环境科学学院，温州 325035

收稿日期: 2019-05-12

录用日期: 2019-10-17

网络出版日期: 2020-03-25

基金项目:

浙江省国际产业联合研发计划基金资助项目(2019C54002)；浙江省自然科学基金资助项目(LY17D010003)

关键词:

Removal of hexavalent chromium from water by biochar supported with sodium carboxymethyl cellulose-stabilized nano-iron

Corresponding author: CHEN Hualin, hualin2100@126.com

College of Life and Environmental Sciences, Wenzhou University, Wenzhou 325035, China

Received Date: 2019-05-12

Accepted Date: 2019-10-17

Available Online: 2020-03-25

Keywords:

全文HTML

自然界中铬主要以Cr(Ⅲ)和Cr(Ⅵ) 2种形式存在^[1]，Cr(Ⅲ)比较稳定，是人体必需的微量元素之一，而Cr(Ⅵ)以其高毒性引起了人们的广泛关注。Cr(Ⅵ)的毒性是Cr(Ⅲ)的100倍左右，因其易溶于水而可迁移到深层地下水和土壤中^[2]。Cr(Ⅵ)被国际公共卫生组织列为一级致癌物，对生态系统具有严重的危害^[3]。目前国内外常见的含铬废水处理方法主要有活性炭吸附、离子交换、电渗析以及生物吸附等^[4]，但这些方法都存在一定的局限性，如能耗大、Cr(Ⅵ)去除率低、运行维护费用高等。

近年来，纳米铁已经成为环境中Cr(Ⅵ)污染修复的研究热点。纳米铁因具有较大的比表面积和较高的反应活性而被广泛应用于环境重金属污染修复中^[5]。对水中Cr(Ⅵ)的去除，相比吸附、沉淀、离子交换和膜分离等方法^[6-7]，纳米零价铁(nZVI)处理具有成本低、固废产生量少、易于从水体中分离等优点^[8-9]，但同时具有易氧化和团聚的缺点^[10-11]。生物炭(BC)在土壤中具有永久的存在性、较大的比表面积和大量的含氧活性官能团等优点^[12]，从而进入研究人员的视野^[13]。羧甲基纤维素钠(CMC-Na)因其无毒和来源广泛，是十分理想的nZVI稳定材料^[14]。目前，已经有相关研究报道了BC负载纳米铁、CMC稳定纳米铁的一些优势，但BC负载的纳米铁抗氧化能力较弱，CMC稳定化纳米铁材料对纳米铁的分散性改良较弱，无法发挥纳米铁的还原优势。本研究利用液相还原法制备了生物炭负载羧甲基纤维素钠稳定化纳米铁(BC-nZVI-CMC)，且探究了BC-nZVI-CMC去除水中Cr(Ⅵ)的效率及主要影响因素，为高效处理重金属废水提供参考。

1. 材料与方法

1.1. 实验材料

1)试剂。FeSO₄·7H₂O购于西陇科学股份有限公司，NaHB₄购于上海凌峰化学试剂有限公司，无水乙醇购于安徽安特食品股份有限公司，以上试剂纯度均为分析纯。羧甲基纤维素钠(CMC)购于国药集团化学试剂有限公司，纯度为化学纯。

2) BC。水稻秸秆用蒸馏水洗净，在105 ℃下烘至恒重，粉碎磨细，过200目筛，放于马弗炉中，在恒温缺氧的条件下，以5 ℃·min⁻¹升温至700 ℃，恒温热解4 h，冷却后密封保存。将制备好的BC放入1.0 mol·L⁻¹ 盐酸中，搅拌处理2 h，用去离子水洗至pH中性，烘干，避光保存备用。

3) BC-nZVI-CMC。采用质量比为1∶0.5、1∶1、1∶5、1∶10生物炭/铁来制备BC-nZVI-CMC。将50 mL 0.4 mol·L⁻¹的FeSO₄溶液和上述炭/铁质量比的生物炭和50 mL乙醇置于1 L三角瓶中，不断搅拌和超声分散0.5 h，然后匀速滴入0.4 mol·L⁻¹的NaHB₄，直至反应完全，过滤，用乙醇和超纯水分别清洗2次，以去除多余的反应液，整个过程在氮气保护下进行。清洗完成后，加入CMC/BC质量比为1∶2的CMC溶液，搅拌混合。将混合体系置于−80 ℃冷冻8 h后，于冷冻干燥仪上冻干，得最终产物。

1.2. 实验方法

采用二苯碳酰二肼分光光度法(GB 7467-1987)测定溶液中Cr(Ⅵ)，玻璃电极法测pH^[15]。按BC-nZVI-CMC的含量为0.5、1、2、4、8 g·L⁻¹取适量BC-nZVI-CMC于离心管中，加入30 mg·L⁻¹ Cr(Ⅵ)溶液50 mL，在25 ℃、240 r·min⁻¹条件下进行水浴振荡，12 h后测定Cr(Ⅵ)含量。分别取一系列50 mL浓度为50 mg·L⁻¹的Cr(Ⅵ)溶液于离心管中，调整溶液pH分别为 2.0、4.0、6.0、8.0、10.0，各管加入BC-nZVI-CMC，使其含量为1 g·L⁻¹，在25 ℃、240 r·min⁻¹条件下，进行水浴振荡，12 h后，测定溶液中的Cr(Ⅵ)含量。将商品纳米铁、BC-nZVI-CMC、BC-nZVI及CMC-nZVI(CMC/nZVI=1∶10)置于空气中暴露7 d，之后各取适量，按1 g·L⁻¹的量加入50 mg·L⁻¹ Cr(Ⅵ)溶液中，同时以新鲜CMC-Na作对照，在25 ℃、240 r·min⁻¹条件下进行水浴振荡，12 h后，测定溶液中Cr(Ⅵ)含量。将2、4、8 g·L⁻¹的BC-nZVI-CMC投加入50 mL含铬电镀废水中，在25 ℃、240 r·min⁻¹条件下进行水浴振荡，12 h后取样，测定废水中重金属的含量。

1.3. 材料表征

采用美国ThermoFisher Scientific公司Verios G4型扫描电镜对样品进行微观结构及表面形态的观察，分析纳米铁颗粒的大小。采用美国Bruker公司D8 Advance型X射线衍射仪对样品进行晶相分析，工作电压为40 kV，电流为40 mA，2 $\theta$ 为10°~90°。采用Bruker Optik GmbH德国公司的TRENSOR27型傅里叶红外光谱仪对样品进行FT-IR谱图测定，使用KBr压片，扫描范围为350~4 000 cm⁻¹。

3. 结论

1)合成的BC-nZVI-CMC颗粒为纳米单质零价铁，CMC对BC-nZVI能起到抗氧化的保护作用；与其他纳米铁相比，BC-nZVI-CMC有更强的还原和抗氧化能力。

2)在pH较低、投加量较多时，BC-nZVI-CMC对Cr(Ⅵ)的去除率较高；BC-nZVI-CMC对Cr(Ⅵ)的去除机理主要为Cr(Ⅵ)被还原，并与Fe(Ⅲ)以共沉淀的形式存在于生物炭表面。

3)吸附动力学数据表明，BC-nZVI-CMC对Cr(Ⅵ)的去除符合准二级动力学模型，吸附过程为以离子交换和螯合反应为主的化学吸附。

参考文献 (32)

[1]	LYU H, ZHAO H, TANG J, et al. Immobilization of hexavalent chromium in contaminated soils using biochar supported nanoscale iron sulfide composite[J]. Chemosphere, 2018, 194: 360-369. doi: 10.1016/j.chemosphere.2017.11.182
[2]	NICKENS K P, PATIERNO S R, CERYAK S. Chromium genotoxicity: A double-edged sword[J]. Chemical Biology Interact, 2010, 188(2): 276-288. doi: 10.1016/j.cbi.2010.04.018
[3]	XIAO R, WANG J J, LI R H, et al. Enhanced sorption of hexavalent chromium Cr(VI) from aqueous solutions by diluted sulfuric acid-assisted MgO-coated biochar composite[J]. Chemosphere, 2018, 208: 408-416. doi: 10.1016/j.chemosphere.2018.05.175
[4]	WU B, PENG D H, HOU S Y, et al. Dynamic study of Cr(VI) removal performance and mechanism from water using multilayer material coated nanoscale zerovalent iron[J]. Environmental Pollution, 2018, 240: 717-724. doi: 10.1016/j.envpol.2018.04.099
[5]	QIU X Q, FANG Z Q, YAN X M, et al. Emergency remediation of simulated chromium (VI)-polluted river by nanoscale zero-valent iron: Laboratory study and numerical simulation[J]. Chemical Engineering Journal, 2012, 193-194(25): 358-365.
[6]	GU P, ZHANG S, LI X, et al. Recent advances in layered double hydroxide-based nanomaterials for the removal of radionuclides from aqueous solution[J]. Environmental Pollution, 2018, 240: 493-505. doi: 10.1016/j.envpol.2018.04.136
[7]	SUN J T, ZHANG Z P, JI J, et al. Removal of Cr⁶⁺ from wastewater via adsorption with high-specific-surface-area nitrogen-doped hierarchical porous carbon derived from silkworm cocoon[J]. Applied Surface Science, 2017, 405: 372-379. doi: 10.1016/j.apsusc.2017.02.044
[8]	ZHANG W, ZHANG S L, WANG J, et al. Hybrid functionalized chitosan-Al₂O₃@SiO₂ composite for enhanced Cr(VI) adsorption[J]. Chemosphere, 2018, 203: 188-198. doi: 10.1016/j.chemosphere.2018.03.188
[9]	ZHU S S, HUANG X C, WANG D W, et al. Enhanced hexavalent chromium removal performance and stabilization by magnetic iron nanoparticles assisted biochar in aqueous solution: Mechanisms and application potential[J]. Chemosphere, 2018, 207: 50-59. doi: 10.1016/j.chemosphere.2018.05.046
[10]	XUE W J, HUANG D L, ZENG G M, et al. Performance and toxicity assessment of nanoscale zero valent iron particles in the remediation of contaminated soil: A review[J]. Chemosphere, 2018, 210: 1145-1156. doi: 10.1016/j.chemosphere.2018.07.118
[11]	XIE Y K, DONG H R, ZENG G M, et al. The interactions between nanoscale zero-valent iron and microbes in the subsurface environment: A review[J]. Journal of Hazardous Materials, 2017, 321: 390-407. doi: 10.1016/j.jhazmat.2016.09.028
[12]	DONG H, DENG J, XIE Y, et al. Stabilization of nanoscale zero-valent iron (nZVI) with modified biochar for Cr(VI) removal from aqueous solution[J]. Journal of Hazardous Materials, 2017, 332: 79-86. doi: 10.1016/j.jhazmat.2017.03.002
[13]	ZHAO X, LIU W, CAI Z Q, et al. An overview of preparation and applications of stabilized zero-valent iron nanoparticles for soil and groundwater remediation[J]. Water Research, 2016, 100: 245-266. doi: 10.1016/j.watres.2016.05.019
[14]	AMBIKA S, NAMBI I M, SENTHILNATHAN J. Low temperature synthesis of highly stable and reusable CMC-Fe²⁺(-nZVI) catalyst for the elimination of organic pollutants[J]. Chemical Engineering Journal, 2016, 289: 544-553. doi: 10.1016/j.cej.2015.12.063
[15]	奚旦立, 孙裕生, 刘秀英. 环境监测[M]. 北京: 高等教育出版社, 2003.
[16]	ZHOU Y M, GAO B, ZIMMERMAN A R, et al. Biochar-supported zerovalent iron for removal of various contaminants from aqueous solutions[J]. Bioresource Technology, 2014, 152(1): 538-542.
[17]	QIAN L B, ZHANG W Y, YAN J C, et al. Effective removal of heavy metal by biochar colloids under different pyrolysis temperatures[J]. Bioresource Technology, 2016, 206: 217-224. doi: 10.1016/j.biortech.2016.01.065
[18]	RONGBING F, YINGPIN Y, ZHEN X, et al. The removal of chromium (VI) and lead (II) from groundwater using sepiolite-supported nanoscale zero-valent iron (S-NZVI)[J]. Chemosphere, 2015, 138: 726-734. doi: 10.1016/j.chemosphere.2015.07.051
[19]	QIAN L B, ZHANG W Y, YAN J C, et al. Nanoscale zero-valent iron supported by biochars produced at different temperatures: Synthesis mechanism and effect on Cr(VI) removal[J]. Environmental Pollution, 2017, 223: 153-160. doi: 10.1016/j.envpol.2016.12.077
[20]	DONG H R, ZHAO F, HE Q, et al. Physicochemical transformation of carboxymethyl cellulose-coated zero-valent iron nanoparticles (nZVI) in simulated groundwater under anaerobic conditions[J]. Separation & Purification Technology, 2017, 175: 376-383.
[21]	QIAN L B, CHEN B L. Dual role of biochars as adsorbents for aluminum: the effects of oxygen-containing organic components and the scattering of silicate particles[J]. Environmental Science & Technology, 2013, 47(15): 8759-8768.
[22]	YAN J, HAN L, GAO W, et al. Biochar supported nanoscale zerovalent iron composite used as persulfate activator for removing trichloroethylene[J]. Bioresource Technology, 2015, 175: 269-274. doi: 10.1016/j.biortech.2014.10.103
[23]	刘勇, 黄超, 翁秀兰, 等. 绿色合成纳米铁去除水中铬离子[J]. 环境工程学报, 2016, 10(8): 4118-4124. doi: 10.12030/j.cjee.201601146
[24]	WANG T, JIN X Y, CHEN Z L, et al. Greensynthesis of Fe nanoparticles using eucalyptus leaf extracts for treatment of eutrophic wastewater[J]. Science of the Total Environment, 2014, 466-467: 210-213. doi: 10.1016/j.scitotenv.2013.07.022
[25]	SU H J, FANG Z Q, TSANG P E, et al. Stabilisation of nanoscale zero-valent iron with biochar for enhanced transport and in-situ remediation of hexavalent chromium in soil[J]. Environmental Pollution, 2016, 214: 94-100. doi: 10.1016/j.envpol.2016.03.072
[26]	薛嵩, 钱林波, 晏井春, 等. 生物炭携载纳米零价铁对溶液中Cr(VI) 的去除[J]. 环境工程学报, 2016, 10(6): 2895-2901. doi: 10.12030/j.cjee.201501155
[27]	WANG Y, HONG C S. Effect of hydrogen peroxide, periodate and persulfate on photocatalysis of 2-chlorobiphenyl in aqueous TiO₂ suspensions[J]. Water Research, 1999, 33(9): 2031-2036. doi: 10.1016/S0043-1354(98)00436-9
[28]	GUO N, LIANG Y M, LAN S, et al. Uniform TiO₂-SiO₂ hollow nanospheres: Synthesis, characterization and enhanced adsorption-photodegradation of azo dyes and phenol[J]. Applied Surface Science, 2014, 305(12): 562-574.
[29]	ZAHEER K, THABAITI A L, SHAEEL A, et al. Nanoscale water soluble self-assembled zero-valent iron: Role of stabilizers in their morphology[J]. Research Advances, 2016, 9(6): 7267-7278.
[30]	JANG I, YOU K E, KIM Y C, et al. Surfactant-assisted preparation of core-shell-type TiO₂-Fe₂O₃ composites and their photocatalytic activities under room light irradiation[J]. Applied Surface Science, 2014, 316: 187-193. doi: 10.1016/j.apsusc.2014.07.204
[31]	LU H L, ZHANG W H, YANG Y X, et al. Relative distribution of Pb²⁺ sorption mechanisms by sludge-derived biochar[J]. Water research, 2012, 46(3): 854-862. doi: 10.1016/j.watres.2011.11.058
[32]	LI M, LIU Q, GUO L J, et al. Cu(II) removal from aqueous solution by Spartina alterniflora derived biochar[J]. Bioresource Technology, 2013, 141: 83-88. doi: 10.1016/j.biortech.2012.12.096