原质及改性生物炭对土壤重金属污染物影响的研究进展

引用本文

赵帅, 蔡雄飞, 王济, 李晓燕, 李丁, 赵士杰, 郁鑫杰, 徐蝶. 原质及改性生物炭对土壤重金属污染物影响的研究进展[J]. 中国水土保持科学, 2021, 19(2): 135-150. DOI: 10.16843/j.sswc.2021.02.017.

ZHAO Shuai, CAI Xiongfei, WANG Ji, LI Xiaoyan, LI Ding, ZHAO Shijie, YU Xinjie, XU Die. Research progress on the effects of raw and modified biochar on soil heavy metal pollutants[J]. Science of Soil and Water Conservation, 2021, 19(2): 135-150. DOI: 10.16843/j.sswc.2021.02.017.

项目名称

贵州省科技支撑计划项目"喀斯特地区蔬菜地农业系统中重金属减控关键技术研究"（[2017]2580）

第一作者简介

赵帅(1997-), 男, 硕士研究生。主要研究方向: 生物炭修复治理土壤重金属污染。E-mail: 1217771794@qq.com

通信作者简介

王济(1975-), 男, 博士, 教授。主要研究方向: 土壤重金属污染治理与修复。E-mail: wangji@gznu.edu.cn

文章历史

收稿日期：2020-07-20
修回日期：2021-02-04

Contents Abstract Full text Figures/Tables PDF

原质及改性生物炭对土壤重金属污染物影响的研究进展

赵帅 ^1,2, 蔡雄飞 ^1,2, 王济 ^1,2, 李晓燕 ^1,2, 李丁 ^1,2, 赵士杰 ^1,2, 郁鑫杰 ^1,2, 徐蝶 ^1,2

1. 贵州师范大学地理与环境科学学院, 550025;
2. 贵州省喀斯特山地生态环境国家重点实验室培育基地, 550025:贵阳

收稿日期：2020-07-20; 修回日期：2021-02-04

项目名称：贵州省科技支撑计划项目"喀斯特地区蔬菜地农业系统中重金属减控关键技术研究"（[2017]2580）

第一作者简介：赵帅(1997-), 男, 硕士研究生。主要研究方向: 生物炭修复治理土壤重金属污染。E-mail: 1217771794@qq.com

通信作者简介：王济(1975-), 男, 博士, 教授。主要研究方向: 土壤重金属污染治理与修复。E-mail: wangji@gznu.edu.cn

摘要：土壤重金属污染问题日益突出，已经对土壤生态环境造成严重危害。生物炭材料来源广泛、成本较低，在环境污染治理中应用较多，已成为当前环境污染功能材料中的研究热点。笔者介绍制备生物炭所需的生物质来源和制备技术，以及生物质原料和制备温度对生物炭性质的影响；讨论生物炭对重金属的吸附机理，并探析生物炭对土壤重金属污染物的修复效果；总结生物炭的改性方法以及改性后结构变化，阐述改性生物炭的性能提升和对重金属的修复效果。目前多数研究旨在探究生物炭对土壤中重金属污染物的修复效果和作用机制，但对生物炭的最终去向、循环利用和对土壤环境的负面影响等方面缺乏研究，未来的研究趋势应该着重于完善生物炭的选取标准和制备体系，避免生物炭对土壤环境造成二次污染。

关键词：生物炭改性重金属污染修复效果

Research progress on the effects of raw and modified biochar on soil heavy metal pollutants

ZHAO Shuai ^1,2, CAI Xiongfei ^1,2, WANG Ji ^1,2, LI Xiaoyan ^1,2, LI Ding ^1,2, ZHAO Shijie ^1,2, YU Xinjie ^1,2, XU Die ^1,2

1. School of Geography and Environmental Science, Guizhou Normal University, 550025;
2. The State Key Laboratory Incubation Base for Karst Mountain Ecology Environment of Guizhou Province, 550025:Guiyang, China

Abstract: [Background] Duo to the rapid development of modern society, soil heavy metal pollution becomes increasingly prominent, which seriously threatens the security of ecological environment. Biochar comes from a wide range of biological sources and of a low cost. It has a huge specific surface area, complex pore structure and abundant functional groups. With its excellent performance, it can effectively renovate soil heavy metal pollution, making it a research hotspot in a variety of environmental functional materials. With the complexity of soil heavy metal pollution types, it is necessary to modify biochar to achieve the purpose of improving the remediation effect. [Methods] In view of this research hotspot, numerous literature retrieval were carried out with "biochar", "soil heavy metal pollution", "passivation remediation" and "modified biochar" as keywords. These keywords appeared very frequently in relevant fields. Representative literatures were selected for analysis and integration. The characteristic and applications of biochar were briefly described, the remediation effects of biochar on heavy metal pollutants were summarized, and the modified biochar was emphatically discussed, and the properties of modified biochar and the changes of its effects on heavy metals were discussed. [Results] Biochar comes from a wide range of sources (agricultural wastes, sludge, fruit shells, and poultry dung), it is mainly prepared by low-temperature anoxic slow-speed pyrolysis technology. Its properties mainly depend on the types of biomass raw materials and pyrolysis conditions. The adsorption mechanism of biochar for heavy metals can be divided into surface adsorption (physical adsorption), surface complexation or precipitation, ion exchange and electrostatic attraction, which can effectively reduce the availability and migration of heavy metal pollutants in soil. After modification, the application performance of biochar is enhanced, for example, functional groups are introduced, impurities are removed and surface performance is improved. Remediation effect of heavy metal pollutants in soil is significantly improved. [Conculsions] The treatment of heavy metal contaminated soil by modified biochar has been quite effective, but at present, it is mainly in the laboratory stage or small-scale test stage, and there is a lack of large-scale in-situ experiments. The aging and final flow direction of biochar are not studied deeply enough. The selection of raw materials of biochar should follow the principle of taking local materials, and the secondary pollution of soil environment should be avoided in the process of treatment. Green environmental protection and efficiency is the development trend of biochar field.

Keywords: biochar modification heavy metal contamination remediation effects

随着现代社会的快速发展，工矿业和农业生产过程中排放的大量重金属(heavy metals, HMs)污染物进入土壤环境，严重危害土壤生态环境和生物健康^[1-2]。生物质材料在缺氧、相对低温的条件下热解制备的高含碳固体物质称之为生物炭(biochar, BC)^[3]。生物炭材料因其具有来源广泛、绿色环保、成本低廉等性质，成为治理HMs污染土壤的研究热点^[4-5]；BC具有高度芳香化和杂环化结构，这使它具备良好的吸附能力，可以有效地修复土壤环境中的HMs污染；它还具有复杂的孔隙结构、巨大的比表面积和丰富的表面基团，可为土壤中的微生物提供一定所需栖息环境和所需元素，提升微生物的活性和繁殖效率，对土壤HMs污染治理起到正面调节作用^[6-7]。但当前土壤HMs污染情况复杂多样，原质BC不能满足现有需求且达不到研究效果，因此需要对原质BC材料进行改性处理，提升原质BC某方面性能，例如增大比表面积、孔隙复杂程度和改变表面的官能团物质类别，以此对HMs污染土壤达到更好的治理效果^[8]。笔者介绍制备BC所需的生物质来源和生物炭制备技术，以及生物质原料和制备温度对BC性质的影响；讨论BC对HMs的吸附机制，并探析BC对土壤HMs污染物的修复效果；总结BC的改性方法以及改性后结构变化，阐述改性BC的性能提升和对HMs的修复效果。最后对BC修复HMs污染土壤的发展方向和情况进行总结和展望，希望为BC修复HMs污染土壤领域的研究和发展提供借鉴。

1 生物炭来源与制取 1.1 原料来源和制备过程

可用于制备BC的材料来源广泛，其中包含农林废弃物、污泥、果壳、家禽粪便等几种类型，不同研究采用的生物质原料和制备过程也有较大差别，表 1对一些研究中所涉及到的BC原料来源和制备过程进行总结。

表 1 生物炭的原料来源和制备 Tab. 1 Raw materials sources of biochar and preparations

	原料来源 Raw material source	制备过程 Preparation process
农林废弃物 Forestry and agricultural residues	松针Pine needle	在700 ℃下热解制备Prepared by pyrolysis at 700 ℃
	花椰菜根、叶Cauliflower root, leaf	在500 ℃下限氧裂解制得Obtained by cracking under oxygen restriction at 500 ℃
	玉米秸秆Maize straw	在550 ℃下限氧热解制备Prepared by pyrolysis under oxygen restriction at 550 ℃
	小麦秸秆Wheat straw	分别在300、500和700 ℃下进行热解制备Prepared by pyrolysis at 300, 500 and 700 ℃, respectively
	水稻秸秆Rice straw	在500 ℃下热解制备Prepared by pyrolysis at 500 ℃
	槐树皮、梧桐锯末Locust bark, Chinese parasol sawdust	在550 ℃高温下热解制备Prepared by pyrolysis at high temperature 550 ℃
	桉树叶Eucalyptus leaves	在3个温度梯度下(300、500和700 ℃)制备桉树叶生物炭Eucalyptus leaves biochar were prepared at 3 temperature gradients (300, 500 and 700 ℃)
	锯末屑Sawdust	在400、500、600、700和800 ℃下快速热解8 h，并持续通入氩气(0.5 L/min) Fast pyrolysis at 400, 500, 600, 700 and 800 ℃ for 8 h with continuous argon (0.5 L/min)
	稻谷Rice grain	在多个温度梯度下(300~900 ℃，每100 ℃为1个梯度)分别制备稻谷生物炭Rice biochar was prepared under several temperature gradients (300 ℃-900 ℃, with one gradient for every 100 ℃)
	稻杆Rice straw	分别在400和700 ℃厌氧120 min热解制得稻杆生物炭Rice straw biochar was obtained by pyrolysis at 400 ℃ and 700 ℃ anaerobic for 120 min, respectively
	稻草Straw	在限氧条件下热解，温度从25 ℃升高到500 ℃(速度为10 ℃/min)制备稻草生物炭Straw biochar was prepared by pyrolysis under the condition of oxygen restriction, and the temperature increased from 25 ℃ to 500 ℃ (at a speed of 10 ℃/min)
	柳枝和木屑混合Willow twigs and sawdust	在500 ℃下热解2 h制备生物炭Biochar was prepared by pyrolysis at 500 ℃ for 2 h
	棉籽壳和棉籽混合Cottonseed shell and cottonseed	分别在200、350、500、650和800 ℃条件下热解4 h制备生物炭Biochar was prepared by pyrolysis for 4 h at 200, 350, 500, 650 and 800 ℃, respectively
	麦秸和木针片Wheat straw and wood needles	在500 ℃下维持30 min制备混合生物炭Mixed biochar was prepared at 500 ℃ for 30 min
污泥 Sludge	污水厂污泥Sewage sludge	通入氮气4 h条件下热解制备污泥生物炭Sludge biochar was prepared by pyrolysis under nitrogen for 4 h
	污水厂污泥Sewage sludge	分别在250、300、350、400、450和500 ℃下低温慢热解制备生物炭Biochar was prepared by low temperature slow pyrolysis at 250, 300, 350, 400, 450 and 500 ℃, respectively
	市政污泥Civil sludge	生物-物理干化后, 通过快速热解制备污泥生物炭After bio-physical drying, sludge biochar was prepared through rapid pyrolysis
	市政污泥Civil sludge	在20 ℃/min的升温速率下达到500 ℃, 并在此热解温度下保持6 h制备污泥生物炭Sludge biochar was prepared at a heating rate of 20 ℃/min to 500 ℃ and kept at this pyrolysis temperature for 6 h
果壳 Shell	向日葵渣Sunflower slag	在550 ℃热解并且恒温1 h制备向日葵渣BC Sunflower slag biochar was prepared by pyrolysis at 550 ℃ and constant temperature for 1 h
	花生壳Peanut shell	在350、550和750 ℃条件下限氧热解制备花生壳废物生物炭Peanut shell waste biochar was prepared by oxygen-restricted pyrolysis at 350, 550 and 750 ℃
	核桃青皮Walnut green seedcase	在500 ℃条件下限氧裂解6 h制得核桃皮生物炭The walnut peel biochar was prepared by oxygen-restricted pyrolysis at 500 ℃ for 6 h
	杏壳Apricot shell	于358 K烘箱中烘干至恒重制备杏壳生物炭Apricot shell biochar was prepared by drying to constant weight in a 358 K oven
家畜粪便 Livestock manure	牛粪Cow dung	在 < 500 ℃的条件下热解制备牛粪生物炭Cow manure biochar was prepared by pyrolysis under the condition of < 500 ℃
	羊粪Sheep manure	以20 ℃/min的升温速率分别加热至350、450、550和650 ℃后恒温3 h制备羊粪生物炭Sheep dung biochar was prepared by heating to 350, 450, 550 and 650 ℃ at a heating rate of 20 ℃/min for 3 h after constant temperature
	牛粪Cow dung	在600 ℃下低氧炭化2 h制备牛粪生物炭Cow manure biochar was prepared by hypoxic carbonization at 600 ℃ for 2 h
	猪粪Pig manure	分别在300和500 ℃下热解1 h制备猪粪生物炭(通氮气) Pig manure biochar was prepared by pyrolysis for 1 h at 300 ℃ and 500 ℃ respectively(nitrogen-purified)

表 1 生物炭的原料来源和制备 Tab. 1 Raw materials sources of biochar and preparations

1.2 制备工艺和影响性质的主要因素

BC由生物质原料通过热化学过程(缺氧或无氧条件下)制备。制备BC的工艺可分为快速热裂解、慢速热裂解、气化、水热炭化等几类。由表 2可知，几种制备方法的温度区间在175~1 500 ℃左右，气化法所需温度较高，制备过程须达到700~1 500 ℃高温和较高气压，且BC产率较低，只有10%左右，但是停留时间较短，只需几秒钟到几分钟，此法主要用于获取气相产物；而水热炭化法所需制备温度较低，且BC产量较高，可达到30%~60%，缺点是停留时间较长，需要几个小时时间，含水量高的生物质材料使用此方法进行BC的制备；大多数研究中采用慢速热裂解手段制备所需BC。

表 2 生物炭制备方法^[15] Tab. 2 Biochar preparation methods^[15]

BC的物化性质包括产率、灰分、挥发分、表面积、孔径、阳离子交换量等，受原料种类和热解条件影响较大^[9-11]。动物粪便和植物秸秆的BC产率相差较大，因为其中的灰分和HMs含量差异显著，挥发分和灰分之间呈正相关关系^[7]。研究发现，水葫芦、杨树枝和玉米秸秆BC的表面性质差异较大，水葫芦BC表面积更大，对Pb的吸附效率最高。温度是热解BC时的关键工艺参数，较高温度裂解制备的BC具有较高的pH、灰分含量、生物学稳定性和碳含量，BC的表面积、微孔量及疏水性也较高；较低温度裂解下吸附容量较高^[12]。不考虑原料差异所带来的影响，热解温度决定了BC的比表面积和阳离子交换量(cation exchange capacity, CEC)，只有在一定的温度范围内热解BC^[13]，才能使BC的表面积、孔径及阳离子交换量获得最大值^[14]，提高HMs污染物的去除效率。

2 生物炭对重金属的吸附机理和修复效果 2.1 吸附机理

为了研究BC对HMs的去除效果，需要明确其吸附过程的基本机制。一般可分为表面吸附(物理吸附)、表面络合或沉淀、离子交换和静电引力作用^[7]。BC对HMs离子的表面吸附效果取决于BC对HMs离子的化学键力强度，也与HMs离子本身的性质有关，比表面积和孔隙结构也是影响BC吸附能力的关键因素，通常情况下，较大的比表面积和复杂的孔隙结构会强化BC的表面吸附能力；表面络合或沉淀则与BC表面的官能团种类和数量有直接关系，且BC表面的金属和矿物组分(CO₃^2-、SiO₃^2-和PO₄^3-)也会对其产生影响；离子交换作用效果与BC表面的金属种类和性质相关；静电引力作用可分为2种情况：当HMs带负电荷时，会被BC表面带正电的官能团吸引；但带正电荷时就会被BC表面带负电的官能团吸引；详见图 1。

图 1 生物炭对重金属吸附机理^[7] Fig. 1 Mechanism of heavy metal adsorption by biochar^[7]

2.2 对污染土壤中重金属的修复效果

土壤中HMs具有迁移性、不可降解性、稳定性和毒害性。BC孔隙结构复杂且发达，拥有巨大的比表面积和丰富的官能团，可以有效吸附土壤中的HMs并且降低其在土壤中的迁移性和生物有效性^[15-16]。陈再明等^[13]发现水稻秸秆BC中的有机碳和无机矿物组分对Pb²⁺可产生吸附作用，其最大的吸附量可达85.7 mg/g；实验表明，牛粪和稻杆BC可以降低Pb、Zn和Cd的TCLP形态含量^[17]，其中牛粪BC和稻杆对Pb的作用效果优良，可分别降低56.0%和35.8%的TCLP形态Pb含量，降低Pb的迁移性。在HMs污染土壤中施加BC，不仅可以提高土壤pH、增加CEC和土壤表面可变负电荷，还可降低土壤电动电位(zeta)，HMs离子与BC发生键合作用后形成金属氢氧化物、碳酸盐或磷酸盐沉淀^[18]，明显降低某些HMs的有效态含量^[19]，减弱HMs生物有效性和毒性^[20]；徐楠楠等^[21]在研究中得到与上述一致的结果，在施加玉米秸秆BC后土壤pH升高，Cd²⁺与OH^-结合形成沉淀物Cd(OH)₂；Xu等^[22]通过研究发现也得到相似的结果，粪便BC可与大部分Cd形成金属磷酸盐和碳酸盐沉淀。BC还可以强化阳离子的吸附能力，抑制Pb的解吸并促进Pb₃(CO₃)₂(OH)₂、Pb₂OF₂沉淀产生；Dong等^[23]通过研究发现BC中的P含量较高，其中溶解产生的可溶性P与Pb能够形成Ca₂Pb₈(PO₄)₆(OH)₂和Pb₁₀(PO₄)₆(OH)₂沉淀；郭文娟等^[24]热解棉花秸秆制备BC，在吸附Cd过程中加入电解质钠盐和钾盐(NaCl、NaNO₃和KNO₃)后，对BC与Cd²⁺的离子交换产生竞争，抑制BC对Cd²⁺的吸附，通过FTIR分析BC，发现水葫芦BC吸收Cd²⁺的量等于释放其他几种阳离子的量(K⁺、Ca²⁺、Na⁺和Mg²⁺)，Cd²⁺与BC上的O—H和—CH₂中含有的H⁺也可发生离子交换^[25]；袁启慧等^[26]发现BC与HMs可形成络合物，BC中的CO可与Cd²⁺络合；因为BC种类繁多，且性质差异较大，所以研究效果存在差异性，在此基础上针对不同土壤环境和污染类型，深入研究BC的制备条件，提高BC性能和修复效率。

3 改性生物炭研究和对重金属修复效果 3.1 改性方法和结构变化

不同类型的BC性质有较大差异，从环境污染的角度出发，人们常通过物理、化学2类改性方法来提升BC自身性能。其中化学改性方法应用较为广泛，主要包括酸改性、碱改性、氧化剂改性、金属氧化物改性和碳质材料改性；物理改性主要包括蒸汽和汽化(图 2)。酸改性可以去除BC表面的金属等杂质，并且引入酸性官能团物质，常用到盐酸、硫酸、硝酸、磷酸、草酸和柠檬酸^[27]；碱改性可以提升BC的表面积，引入含氧官能团，常见的碱性改性剂有NaOH和KOH；通过加入不同的氧化剂，如H₂O₂、HNO₃或KMnO₄^[28]，也能起到引入含氧官能团的作用，还可以活化BC表面官能团并增加其活性点位；而金属氧化物改性可提升BC磁性，磁化介质能够长时间稳定存在于BC中，修复完成后BC和被修复对象易于分离，表面性能和吸附能力得到增强，一般采用金属Fe、Mg、Al和Mn作为金属氧化物；利用碳质材料改性可以提高BC的表面积；利用蒸汽和汽化改性BC，可提高BC的pH和比表面积，使其表面的孔隙结构复杂化，拥有更大的孔隙体积，增强其吸附能力^[29]。

图 2 生物炭改性方法^[30] Fig. 2 Modification methods of biochar^[30]

大多数研究发现，BC的结构如表面形态、孔径分配、表面积和表面官能团是影响BC吸附能力的关键性质，改性的目的是使BC获得更加突出的结构性能，以便在实际运用中发挥最大效力^[31]。无论是化学改性还是物理改性，几乎都能改变原有BC的表面结构，使其表面塌陷或出现褶皱，从而提高BC的比表面积，但是少数研究发现在BC改性后，其孔洞被改性物质堵塞造成孔径和比表面积减小的情况(表 3)。因此对于不同的生物质原料应该选取不同的改性方法，尽量避免出现负面效应。

表 3 改性后生物炭结构性质变化 Tab. 3 Changes in structures and properties of biochar after modification

生物炭原料 Raw material of biochar	改性方法 Modification method	结构性质变化 Structural change	参考文献 Reference
松针 Pine needle	盐酸Hydrochloric acid	通过FTIR和SEM分析发现表面活性官能团增加、表面疏松和不平滑，颗粒物破碎程度加深，孔隙结构复杂化，吸附效果得到提升Through FTIR and SEM analysis, it was found that the surface active functional groups increased, the surface was loose and uneven, the degree of particle breakage deepened, the pore structure was complicated, and the adsorption effect was improved	[32]
玉米秸秆 Maize straw	碳酸氢钠和三聚氰胺活化Activation of sodium bicarbonate and melamine	在比表面积、孔隙结构丰富度、芳香性、亲水性、极性、表面官能团丰富度和含氧官能团等方面均有提升Specific surface area, pore structure richness, aromaticity, hydrophilicity, polarity, surface functional group richness and oxygen-containing functional group were all improved	[33]
橘皮 Orange peel	Fe³⁺和Fe²⁺联合沉淀改性Combined precipitation of Fe³⁺ and Fe²⁺	孔隙直径增大Pore diameter increased	[34]
甘蔗渣 Bagasse	消化处理Digestive treatment	pH升高、比表面积变大、CEC和表面负电荷含量增加pH increased, specific surface area increased, CEC and surface negative charge content increased	[35]
小麦秸秆 Wheat straw	硝酸Nitric acid	表面凹凸度增加，孔隙增多并且孔洞更加粗糙，吸附位点增多Surface concavity increased, the pores increased and the pores became rougher, and the adsorption sites increased	[36]
棉花秸秆 Cotton straw	加入氯化锌和氯化铝Adding zinc chloride and aluminum chloride	改性后棉花秸秆生物炭孔壁上出现小孔，吸附位点和比表面积得到提升After modification, pores appeared on the biochar wall of cotton straw, and the adsorption site and specific surface area were improved	[37]
小麦秸秆 Wheat straw	载铁Iron-loading	pH为2.4，比表面积增大，Fe—O官能团含量增加pH was 2.4, specific surface area increased, and Fe—O functional group content increased	[38]
柚子皮 Shaddock peel	磁化Magnetization	灰分和挥发分增加，比表面积和总孔容增大，pH升高Ash content and volatiles increased, specific surface area and total pore volume increased, and pH increased	[39]
稻壳 Rice husk	氯化钙Calcium chloride	呈现多孔炭架结构，孔道轮廓清晰，孔径和比表面积增大(8.15倍) Structure of poly-porous carbon frame presented, clear tunnel contour, the pore diameter and specific surface area increased (8.15 times)	[40]
木屑 Bits of wood	氢氧化钠Sodium hydroxide	呈蜂窝状，微孔和粗糙度增加，比表面积得到提升Honeycomb, micropores and roughness increased, and the specific surface area was improved	[41]
玉米芯和秸秆混合 Mixed corn cob with the straw	氢氧化钾Potassium hydroxide	表面孔隙增多，孔隙结构丰富，粗糙度和比表面积增大Surface pores increased, the pore structure was rich, and the roughness and specific surface area increased	[42]
水稻秸秆 Rice straw	硅烷偶联剂Silane coupling agent	表面光滑，团聚性较好Surface was smooth and the agglomeration was good	[43]
浒苔 Ulva	氢氧化钠Sodium hydroxide	2 mol/L的NaOH改性提高了浒苔生物炭的比表面积和表面微孔结构，增加氧元素含量The specific surface area and surface microporous structure of Ulva biochar and the content of oxygen element increased by NaOH modification of 2 mol/L	[44]
米糠 Rice bran	氢氧化钠浸渍Sodium hydroxide impregnation	比表面积扩大4.6倍，总孔隙体积提升3.9倍，碳含量增加Specific surface area expanded by 4.6 times, the total pore volume increased by 3.9 times, and the carbon content increased	[45]
菠萝叶子 Pineapple leaf	十六烷基三甲基溴化铵Hexadecyl trimethyl ammonium bromide	改性后生物炭样貌变化不大，但平均孔径增加The appearance of biochar changed little after modification, while the average pore size increased	[46]
油菜秸秆 Rape straw	磷酸Phosphoric acid	孔体积和比表面积显著提升，孔隙度升高Pore volume and specific surface area increased significantly, and porosity increased significantly	[47]
榴莲壳 Durian shell	磷酸活化Phosphoric acid activation	比表面积、总孔体积、微孔体积有着明显的增加，85%磷酸活化的生物炭表面积增加500倍，总孔体积提升45倍Specific surface area, total pore volume and micropore volume increased obviously. The biochar activated by 85% phosphoric acid increased the surface area by 500 times and the total pore volume by 45 times	[48]
玉米秸秆 Maize straw	盐酸和氯化锌Hydrochloric acid and zinc chloride	孔径细小紧密，微孔结构明显，表面积和孔隙率增大Pore size was small and compact, the micropore structure was obvious, and the surface area and porosity increased	[49]
木薯秸秆 Tapioca stalks	氯化镁Magnesium chloride	表面粗糙度、比表面积、总孔径和平均孔径增加Surface roughness, specific surface area, total aperture and average aperture increased	[50]
芦苇秸秆 Reed straw	氧化镁Magnesium oxide	改性后表面粗糙，比表面积和总孔容提升Surface roughness, specific surface area and total pore volume improved after modification	[51]
花生壳 Peanut shell	铁Iron	显著增加生物炭的比表面积和孔容，分别提升了12、16和5倍，结构有序性增加Specific surface area and pore volume of biochar increased by 12, 16 and 5 times, respectively, and the structure order increased	[52]
沙棘果残渣 Seabuckthorn fruit residue	微波硝酸Microwave nitric acid	表面粗糙度增加，小颗粒物和孔隙变多，孔穴排列紧密且不规则Surface roughness increased, the number of small particles and pores increased, and the pore arrangement was compact and irregular	[53]
松木屑 Pine sawdust	磷酸Phosphoric acid	总体积和内孔数量明显提高，比表面积急剧增大Total volume and the number of inner pores increased obviously, and the specific surface area increased sharply	[54]
椰子壳 Coconut shell	磷酸修饰Phosphoric acid modification	比表面积和孔隙度提高，孔容可达到0.146 cm³/g Specific surface area and porosity were improved, and the pore volume reached 0.146 cm³/g	[55]
蔗糖 Sucrose	La和Me纳米杂化La and Me nano hybridization	蜂窝结构，孔隙度增大Honeycomb structure with increased porosity	[56]
玉米秸秆 Maize straw	Fe(NO₃)₃·9H₂O修饰Fe(NO₃)₃·9H₂O	表面粗造度增加，比表面积明显提升Surface roughness increased and the specific surface area increased obviously	[57]
木屑 Bits of wood	氯化镁Magnesium chloride	表面覆盖熔融物质，比表面积和总孔径体积明显增加Specific surface area and total pore volume increased obviously when the surface was covered with molten material	[58]
稻壳 Rice straw	硫酸亚铁磁化Ferrous sulfate magnetization	平均粒子表面积下降Average particle surface area decreased	[59]
玉米秸秆 Maize straw	蒙脱石修饰Montmorillonite trim	改性后呈片状结构，表面积增大The surface area increased and the structure was flaky after modification	[60]
浒苔 Ulva	氯化铁Ferric chloride	气孔数量和大小均有提升，氧含量增加，碳含量降低Number and size of stomata increased, oxygen content increased and carbon content decreased	[61]
小麦秸秆 Wheat straw	Fe(NO₃)₃	氮和氧含量的增加，吸附容量得到提升With the increase of nitrogen and oxygen content, the adsorption capacity was improved	[62]

表 3 改性后生物炭结构性质变化 Tab. 3 Changes in structures and properties of biochar after modification

3.2 对重金属修复效果

相比于原质BC，改性BC施加进入HMs污染土壤后，对HMs的修复效果会得到不同程度的加强，提高HMs稳定形态含量，降低植物根际有效态HMs浓度。利用磷酸盐改性竹子生物炭，发现对Cd的吸附能力提升将近10倍，其去除效率可达到85.78%；由表 4可知，利用磷酸改性小麦秸秆，可以提升土壤pH，使Pb沉淀从而达到固定效果；而用聚乙烯亚胺改性玉米秸秆生物炭后，对Cr⁶⁺的最大吸附量可达到386.3 mg/g，对Cr⁶⁺的最大吸附效率达到95.94%，有着非常优良的吸附效果；通过大量研究结果表明，纳米零价铁BC性能优良，采用羧甲基纤维素来稳定纳米零价铁BC，当制备比例为2.5 g/kg时，对Cr⁶⁺的修复效率可达100%。

表 4 改性生物炭对重金属的修复效果 Tab. 4 Remediation effects of modified biochar on heavy metals

改性材料 Modifying material	重金属 Heavy metals	修复效果 Remediation effect	参考文献 Reference
水稻秸秆载Fe Rice straw carrying Fe	As	可降低水稻根部As浓度Reducing the concentration of As in the root of rice	[63]
牛粪载磷Cow dung carrying phosphorus	Pb、Cd	提高土壤中Pb、Cd的可氧化态、残渣态含量，有效钝化重金属Increasing the content of Pb and Cd in soil oxidizable state and residue state, and effectively passivating heavy metals	[64]
小麦秸秆载Fe Wheat straw carrying Fe	Cd、Cu、As	降低酸雨淋溶下几种重金属的淋失，对几种重金属的形态转化有积极效应Reducing the leaching loss of some heavy metals in acid rain and having a positive effect on the morphological transformation of some heavy metals	[36]
尿素改性甘蔗Sugarcane modified by urea	Pb	改变了甘蔗生物炭表面极性和电子结构，增强对Pb的吸附能力The surface polarity and electronic structure of sugarcane biochar were changed to enhance the adsorption capacity of Pb	[65]
磷酸盐改性竹炭Bamboo charcoal modified by phosphate	Cd	吸附Cd的能力增加近10倍，去除效率达85.78% The adsorption capacity of Cd increased nearly tenfold and the removal efficiency reached 85.78%	[66]
磷酸改性小麦秸秆Wheat straw modified by phosphoric acid	Pb	石灰污染的碱性土壤pH降低，碳酸盐和氧化态Pb会溶解释放，改性生物炭释放的PO₄^3-与Pb生成磷酸Pb盐沉淀或者直接被吸附Carbonate and oxidized Pb were dissolved and released when the pH of alkaline soil polluted by lime decreased. PO₄^3- released by modified biochar was deposited with Pb to form Pb phosphate salts or be directly adsorbed	[67]
磷酸二氢钾改性枣树Date tree modified by potassium dihydrogen phosphate	Cu、Fe、Mn、Pb、Zn	载磷改性生物炭用量3%时，在土壤溶液中金属和磷可产生沉淀，固定重金属Cu、Fe、Mn、Pb、Zn表现较好The metal and phosphorus in the soil solution produced precipitation when the phosphorus carrying modified biochar content was 3%, and the fixing heavy metals Cu, Fe, Mn, Pb and Zn performed well	[60]
氧化锰改性玉米秸秆Corn stalk modified by manganese oxide	As	能够降低水稻不同部位的含As浓度，Mn氧化物氧化As(Ⅲ)变为As(Ⅴ)，与Mn氧化物对As(Ⅴ)的强吸附作用有关Reducing the As concentration in different parts of rice, Mn oxide oxidizing As (Ⅲ) into the As (Ⅴ), and being related to the strong adsorption of Mn oxide to the As(Ⅴ)	[68]
零价铁改性生物炭Biochar modified by zero-value iron	As、Cd	降低了水稻中As、Cd的吸水性、生物利用度，且在不同植株部位的浓度也有降低的趋势Reducing absorbency and bioavailability of As and Cd in rice, and the concentrations in different plant parts also tending to decrease	[69]
硫改性麦秸生物炭Wheat straw biochar modified by sulfur	Cd	原始生物炭施加到土壤中后，可以降低15.86%~22.10%的Cd浓度，改性后可降低22.72%~27.90% The Cd concentration was reduced by 15.86%-22.10% when the original biochar was applied to the soil, and reduced by 22.72%-27.90% when modified biochar was applied	[70]
ZnCl₂改性胶渣生物炭Colloidal residue biochar modified by ZnCl₂	Cd	最大吸附量可以达到325.54 mg/g，最高去除率可达98%，再生能力强，6次循环后对Cd的去除能力仍能达到90% Maximum adsorption capacity reached 325.54 mg/g, the highest removal rate reached 98%, the regeneration ability was strong, and Cd removal ability still reached 90% after 6 cycles	[71]
AMD铁絮体改性水稻秸秆生物炭Rice straw biochar modified by AMD iron floc	Pb²⁺	对Pb²⁺的最大拟合吸附量为278 mg/g，未改性时仅为35.16 mg/g Maximum fitting adsorption capacity of Pb²⁺ was 278 mg/g, and was only 35.16 mg/g without modification	[72]
MnOx改性水稻秸秆生物炭Rice straw biochar modified by MnOx	Cu²⁺、Zn²⁺	投加3 g/L的改性生物炭时，对Cu²⁺、Zn²⁺的去除效率高达90% The removal efficiency of Cu²⁺ and Zn²⁺ was as high as 90% when adding 3 g/L modified biochar	[73]
聚乙烯亚胺改性玉米秸秆生物炭Corn stalk biochar modified by polyethylene imine	Cr⁶⁺	对Cr⁶⁺的最大吸附量为386.3 mg/g，对Cr⁶⁺的最大吸附效率达到95.94% Maximum adsorption capacity of Cr⁶⁺ was 386.3 mg/g, and the maximum adsorption efficiency of Cr⁶⁺ was 95.94%	[74]
CaCl₂改性稻壳生物炭Rice hull biochar modified by CaCl₂	Cd	添加后土壤中有效态Cd的含量降低12.0%~30.2%，Cd形态由高活性可交换态和可还原态向残渣态转变The content of available Cd in the soil decreased by 12.0%-30.2%, and the Cd form changed from the highly active exchangeable and reducible state to the residue state after addition	[75]
酸洗负载零价铁柳枝生物炭Pickling load zero-valent iron willow twig biochar	Cr⁶⁺	可以显著促进Cr⁶⁺还原以及总Cr向残渣态转化，提高土壤中残渣态含量11.58% Significantly promoting the reduction of Cr⁶⁺ and the transformation of total Cr into residue state, and increasing the residue state content in soil by 11.58%	[76]
负载纳米零价铁鸡骨生物炭Nano-supported zero-valent iron chicken bone biochar	Cr⁶⁺	对Cr⁶⁺的最大吸附量为153.60 mg/g Maximum adsorption capacity of Cr⁶⁺ was 153.60 mg/g	[77]
聚乙二醇稳定纳米零价铁生物炭Nanometer zero-valent iron biochar stabilized by polyethylene glycol	Cr⁶⁺	去除率高达97.38% Removal rate was as high as 97.38%	[78]
羧甲基纤维素稳定纳米零价铁生物炭Nanometer zero-valent iron biochar stabilized by carboxymethyl cellulose	Cr⁶⁺	当羧甲基纤维素纳米铁和生物炭的制备比例为2.5 g/kg时，修复率可达到100% The remediation rate reached 100% when the preparation ratio of carboxymethyl cellulose nano-iron and biochar was 2.5 g/kg	[79]
铈锰改性生物炭Biochar by cerium manganese	As	在红壤、黄壤和紫色土中添加改性生物炭，添加比例为10%时，对3种土壤中有效As的固定率达到95%以上，As向稳定态转变，土壤中As的迁移性降低When modified biochar was added to red soil, yellow soil and purple soil with an added ratio of 10%, the fixed rate of effective As in the three soils reached> 95%, As changed to a stable state, and the migration of As in the soil reduced	[80]

表 4 改性生物炭对重金属的修复效果 Tab. 4 Remediation effects of modified biochar on heavy metals

研究发现，在BC的结构中引入N、P和S基团能提高BC碱性和表面极性，使其电子结构发生改变，引入基团位点可以产生局部电荷累积的离域效应，局部的电荷密度对电子转移有重要作用，配位机制促进了分子的解离或吸附，可以增强对HMs离子的吸附效果^[81]。在杨兰等^[82]的研究中，原状Cd污染土壤中，几种改性BC都可以降低Cd的有效态和可交换态含量；在外源高含量Cd污染土壤中，也可以起到同样的效果，说明改性BC对于重金属迁移转化产生积极效应。目前，大多数改性BC应用在水中污染物的吸附或者去除，对土壤中HMs污染物的钝化研究相对较少^[83]，虽然BC治理土壤HMs污染物有着不错的效果，但对改性BC在热解后是否会产生有害毒素并对土壤造成二次污染的研究不足，是否会破坏土壤中原有的生态系统动态平衡也还不够清楚，未来应建全BC在HMs污染土壤中的应用规范，以期改性BC材料在土壤HMs污染原位修复领域中更加实用。

4 总结及展望

1) 原质BC在HMs污染土壤的修复治理中或许不够有效、高效和长效，针对不同类型的BC材料，通过适当的改性方法提升BC的自身性能，并尽可能控制成本和环境影响，提高HMs污染土壤治理成效。

2) 目前多数关于BC治理修复HMs污染土壤的研究还停留在实验室阶段或者小规模实验阶段，缺乏大规模原位实验，实验室条件与大田实验环境差异较大，缺乏自然环境因素对实验的影响。BC施加到土壤后长期暴露在自然环境中会出现老化的现象，老化后BC的修复效果可能会降低，还应探究老化带来的负面效果以及BC的流向问题。

2) BC材料来源广泛且类型和范围无专业划分标准，针对不同材料选取适当制备方法，探究不同类型BC材料的最佳热解条件将会决定BC修复治理土壤HMs的功效最大化能否实现。针对现有研究阶段的不足，利用当地特有的生物质原材料，探析当地主要的HMs污染类型，选取合适的生物质原料进行产业化推广应用，坚持绿色环保的理念合理运用BC材料，以免对环境造成二次污染。

5 参考文献

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