生物炭吸附水體中重金屬機理與工藝研究進展

韓魯佳 李彥霏 劉 賢 韓婭紅

(中國農(nóng)業(yè)大學工學院， 北京 100083)

生物炭吸附水體中重金屬機理與工藝研究進展

韓魯佳 李彥霏 劉 賢 韓婭紅

(中國農(nóng)業(yè)大學工學院， 北京 100083)

生物炭因其良好的表面特性和孔隙結構，廣泛的原料來源和廣闊的產(chǎn)業(yè)化發(fā)展前景，已成為當今環(huán)境、農(nóng)業(yè)和能源等領域的研究熱點。針對生物炭對水體重金屬的吸附研究，本文基于生物炭原料和制備工藝的多樣性，綜合分析了國內外生物炭重金屬吸附機理的研究成果，詳細闡述、分析了5種吸附作用機制(物理吸附、靜電作用、離子交換、絡合反應和化學沉淀)及其相關表征手段；同時評述了吸附工藝條件和重金屬種類對生物炭吸附重金屬的影響；指出生物炭重金屬吸附領域未來的研究中，應開展針對重金屬吸附的生物炭原料特性及吸附產(chǎn)物的多維、微納尺度表征方法研究。

生物炭； 水體重金屬； 吸附機理； 表征

引言

重金屬在環(huán)境中無處不在，危及人類健康[1]。由于人類各種生產(chǎn)活動：冶煉加工、礦山開采、化工生產(chǎn)等，將含有重金屬的廢水排放到水環(huán)境中，造成了嚴重的水體重金屬污染。重金屬污染與其他有機化合物污染不同，許多有機化合物可以通過自然界本身物理的、化學的或生物的方式凈化，使有害性降低或解除。重金屬具有持久性和富集性，很難在環(huán)境中降解，對人類及動植物危害極大[2]。環(huán)境中的鉛、銅含量超標會顯著抑制動植物生長，嚴重時甚至導致其死亡[3]; 同時，重金屬還會通過食物鏈進入人體，干擾人體正常的生理功能進而對其健康造成危害[4-5]。因此，水體中重金屬污染物的治理問題刻不容緩。

目前，移除和回收水體中重金屬的方法主要有化學沉淀、氧化還原、離子交換、生物過濾、活性污泥法和吸附法等[6-11]。其中，吸附法具有凈化效果好、操作簡便、不會造成二次污染等優(yōu)點，被視為一種有效且高效的處理方式[12-13]，被廣泛應用于城市廢水、工業(yè)污水中重金屬的去除[14]。而決定其吸附效果和成本的核心因素是吸附劑[15-16]。因此，研制低廉高效的吸附劑是當前水體污染物吸附處理問題的研究熱點。

生物炭(biochar)是生物質在一定溫度和缺氧條件下熱裂解形成的一類高度芳香難熔性固體物質[17-18]。通常生物炭具有一定的比表面積和豐富的極性官能團，例如羧基、酚羥基和氨基，且孔隙結構發(fā)達[19-21]，其作為一種潛在的新型重金屬生物吸附材料已成為科技工作者的研究熱點[22]。與目前水體污染物吸附常用的活性炭吸附劑[14]相比，生物炭未經(jīng)活化處理，成本低，且來源更為廣泛。生物炭的吸附應用是一個多贏策略，在治理水體中污染物的同時消除了焚燒、腐爛處理對環(huán)境造成的破壞[23]，并且生物炭生產(chǎn)過程中產(chǎn)生的生物油(bio-oil)和混合氣(syngas)有助于緩解能源短缺[24]。

國內外研究表明生物炭可用于吸附水溶液中的Pb(Ⅱ)、Cu(Ⅱ)、Zn(Ⅱ)、Ni(Ⅱ)、U(Ⅵ)、Ag(Ⅱ)、Cr(Ⅴ)和Cd(Ⅱ)等金屬離子[25-29]，但由于生物質原料特性迥異[30-32]，炭化工藝與轉化過程復雜[33-35]，從而導致生物炭特性多變，可控性較弱。同時，生物炭的特性[36-37]和不同的吸附條件[38-39]以及目標重金屬種類[40-41]均顯著影響其吸附行為和效果。由此可見，生物炭吸附水中重金屬的影響因素眾多，并存在復雜的吸附機理。

1 生物炭原料種類、制備工藝及其特性

生物炭的來源非常廣泛，主要包括農(nóng)林業(yè)廢棄物如秸稈、草本、果殼、果皮果渣等，工業(yè)和城市生活中產(chǎn)生的有機廢棄物如生活垃圾、污泥等，養(yǎng)殖廢棄物如畜禽糞便等。這些生物質都已被熱轉換為各種理化特性的生物炭并應用于水體、土壤等環(huán)境修復和改良。不同種類生物質制備的生物炭在元素組成、工業(yè)組成、礦質元素、比表面積、孔容、孔徑、灰分含量、羧酸酯化、芳香化、脂肪族鏈狀結構等理化性質上存在差異。

2 生物炭重金屬吸附效果分析

生物炭原料和炭化溫度顯著影響其重金屬吸附的能力，同一生物炭對不同重金屬的吸附效果不同。研究顯示，目前用于水體中重金屬吸附的生物炭原料來源可分為秸稈類、畜禽糞便類、果殼類、果皮果渣類、木本類、草本類、泥類、水生植物類、骨類。用于吸附水體中重金屬離子涉及Pb(Ⅱ)、Cu(Ⅱ)、Zn(Ⅱ)、Cr(Ⅲ)、Cr(Ⅵ)、Cd(Ⅱ)、As(Ⅴ)、Ni(Ⅱ)、Hg(Ⅱ)等[52-56]，其中對Pb(Ⅱ)、Cu(Ⅱ)、Zn(Ⅱ)、Cd(Ⅱ)的吸附量較大[57-59]。對Pb(Ⅱ)有較好吸附效果的是畜禽糞便類生物炭、秸稈類生物炭和骨類生物炭，例如400℃碳化的豬糞生物炭對Pb(Ⅱ)最大吸附量為230.7 mg/g[60](表1); 對Cu(Ⅱ)具有良好吸附效果的是畜禽糞便類生物炭、秸稈類生物炭和草本類生物炭，例如400℃炭化豬糞生物炭對Cu(Ⅱ)最大吸附量為88.23 mg/g[60]；對Zn(Ⅱ)具有良好吸附效果的是畜禽糞便類生物炭、果殼類生物炭、秸稈類生物炭和水生植物類生物炭，例如豬糞在400℃制備條件下對Zn(Ⅱ)的最大吸附量為79.62 mg/g[60]; 對Cd(Ⅱ)具有良好吸附效果的是畜禽糞便類生物炭、秸稈類生物炭、水生植物類生物炭和骨類生物炭，例如豬糞在400℃制備條件下對Cd(Ⅱ)的最大吸附量為117.01 mg/g[60]。綜上所述，畜禽糞便類和秸稈類生物炭是極具潛力的重金屬生物吸附劑。但值得注意的是最大吸附量不僅與生物炭原料、制備條件相關，同時也受到吸附條件(初始pH值、溫度、吸附劑濃度、吸附質濃度)等因素的影響。表1中的吸附量均是在特定制備和吸附條件下所得，可比性較差，后續(xù)應將生物質特性與其吸附效果進行相關性分析。

3 生物炭重金屬吸附機制

由于生物炭結構組成復雜，其對水體中重金屬的吸附機理也十分復雜。如圖1所示，生物炭重金屬吸附機制主要表現(xiàn)為：物理吸附、靜電作用、離子交換、絡合反應和化學沉淀[52-53,85]。生物炭的理化性質差異，吸附條件和重金屬離子類型的變化都會造成吸附機理的不同，具體表現(xiàn)為每種機理對吸附過程的貢獻不同。

表1 生物炭原料、炭化溫度及重金屬最大吸附量Tab.1 Maximum adsorption of heavy metals in water bybiochar with different raw materials and pyrolysis temperature

圖1 生物炭對水體中重金屬的吸附機理示意圖Fig.1 Conceptual illustration of heavy metal sorption mechanisms on biochar

3.1 物理吸附

物理吸附是由吸附質與吸附劑之間范德華力產(chǎn)生的，結合力較弱，屬于可逆過程。生物炭粒子有著各種不同的比表面積和微孔，當制備溫度在500～700℃時，更容易形成較高的比表面積和孔隙體積[86]。這些結構可以與重金屬離子發(fā)生物理吸附[36,53,87-88]。

SHEN等[89]研究表明英國當?shù)氐挠材旧锾康牧斤@著影響Pb(Ⅱ)的吸附，0.15 mm和2 mm生物炭對Pb(Ⅱ)的最大吸附量分別為47.66 mg/g和30.04 mg/g。生物炭在一定范圍內，粒徑減小，其比表面積會增加，進而提高對Pb(Ⅱ)的吸附能力。但是比表面積大小并不是決定吸附強弱的重要理化參數(shù)[10,61,90]。例如，畜禽糞便生物炭的比表面積隨著炭化溫度的升高而升高，但對重金屬Pb(Ⅱ)的吸附卻未隨比表面積的升高而增加。水稻秸稈生物炭比表面積為73.40 m2/g，小于木屑生物炭的比表面積391.12 m2/g，但對Pb(Ⅱ)吸附量是水稻秸稈生物炭(126.58 mg/g)大于木屑生物炭(47.62 mg/g)，對Cd(Ⅱ)的吸附量也是水稻秸稈生物炭(60.61 mg/g)大于木屑生物炭(6.67 mg/g)。橡木生物炭的比表面積為1～3 m2/g，其對Cr(Ⅵ)的移除效果與比表面積約為1 000 m2/g的活性炭相當[10]。因此，生物炭表面的物理吸附占重金屬吸附機理的比重較弱；同樣的結果也被SHEN等[89]和ZHOU等[37]研究得到。

生物炭內部孔道也會發(fā)生物理吸附。LIU等[68]通過2種制備方式：300℃水熱炭化和700℃熱解分別制得2種松木生物炭，標記為H300和P700。測定了比表面積、平均孔直徑和微孔體積差異。 H300和P700的平均孔徑分別為0.86、1.48 nm。戴靜等[61]分別測定了米糠、木屑、稻稈、玉米秸稈生物炭的平均孔徑分別為2.15、2.03、3.56、2.33 nm。而金屬離子Pb(Ⅱ)、Cu(Ⅱ)、Al(Ⅲ)、Cr(Ⅲ)、Cr(Ⅵ)、Ni(Ⅱ)、Cd(Ⅱ)、Zn(Ⅱ)的直徑分別為0.238、0.146、0.107、0.123、0.088、0.138、0.19、0.148 nm。這些重金屬離子直徑均小于生物炭的平均孔徑。因此，在生物炭與重金屬離子接觸時，會有部分重金屬離子進入到生物炭的孔隙中，不斷填充孔隙，形成生物炭對重金屬離子的物理吸附。一般來說，重金屬的直徑越小，滲透到生物炭孔徑中越多，從而提高吸附量[91-92]。

3.2 絡合反應

除了物理吸附之外，其他化學吸附機制如表面絡合反應也參與重金屬離子的吸附[5,21,93-94]。與重金屬離子相結合的主要官能團有羧基、磷酰基、羥基、硫酸酯基、氨基和酰胺基，其中氮、氧、磷、硫可作為配位原子與重金屬離子配位絡合。絡合反應在秸稈類生物炭吸附重金屬機制中有重要的作用。PAN等[95]發(fā)現(xiàn)4種秸稈生物炭(花生秸稈、大豆秸稈、油菜秸稈、水稻秸稈)對Cr(Ⅲ)的吸附量與其含氧官能團含量成正比，并且利用紅外光譜分析吸附重金屬前后的生物炭表面官能團，發(fā)現(xiàn)吸附前后出現(xiàn)了不同程度的官能團位點的遷移，說明這些含氧官能團均參與了生物炭對重金屬離子的吸附過程。

值得注意的是，表面絡合主要是含氧官能團尤其是羧基和酚羥基[37,82,96]，會與重金屬形成絡合物從而參與吸附反應[85,97]。在LU等[85]的研究中，通過FTIR對吸附前后的污泥生物炭進行光譜分析，發(fā)現(xiàn)羧基和羥基官能團含量發(fā)生變化，而羰基的量幾乎沒有變化。SHEN等[89]在研究中指出，硬木生物炭含有大量的羧基，會形成重金屬絡合物。以上研究結果說明羧基和酚羥基在與重金屬的絡合反應中起到了重要作用。

3.3 離子交換

離子交換反應需要在適宜的pH值條件下才能發(fā)生。酸性生物炭表面電離的質子與重金屬離子發(fā)生離子交換反應[98-99]。可以與重金屬離子發(fā)生交換的電離質子包括Ca2+、K+、Mg2+、Si+、Na+[61]，見圖1。這些無機礦物成分參與了生物炭吸附重金屬的反應。LU等[85]對Pb2+吸附完成后的溶液進行檢測，發(fā)現(xiàn)有大量的Ca2+、K+、Mg2+、Na+離子被釋放出來，并且釋放的離子總量越高時，Pb(Ⅱ)的吸附量越大。這說明在生物炭與重金屬接觸時，溶液中的重金屬離子會與生物炭表面電離的質子發(fā)生交換，造成電離的質子被釋放到溶液中。但同時，若電離質子Ca2+、K+、Mg2+、Si+、Na+在溶液中存在量過大，則會對重金屬的吸附造成抑制[65]，并且隨離子濃度的增大，對吸附反應的抑制作用也越強。這是由于溶液中的這些離子會與重金屬目標物競爭生物炭表面的離子交換位點[100]，直至達到吸附平衡。

生物炭的這些離子多存在于其表面的含氧官能團中，含氧官能團增多會增加生物炭與重金屬離子發(fā)生離子交換的可能性。LIU等[68]采用300℃水熱炭化和700℃熱解兩種方式制備松木生物炭，將其進行表征并應用于水體中Cu(Ⅱ)的吸附。結果顯示，與松木原料相比，水熱炭相比于原料提高了95%的含氧官能團，而熱解炭降低了56%的含氧官能團。盡管水熱炭的比表面積較低，但對Cu(Ⅱ)的吸附能力遠高于熱解炭，這是因為水熱炭吸附機理中離子交換反應占據(jù)主導地位。

3.4 化學沉淀

值得注意的是，不可溶的P含量與吸附重金屬無關，這是因為形成的P-Ca-Mg結構穩(wěn)定的晶體物質(如磷鈣礦(Ca,Mg)3(PO4)2)不會與重金屬離子發(fā)生沉淀反應[90]。畜禽糞便生物炭的可溶性P含量在25～200℃時隨著熱解溫度的升高而升高，原因可以歸結為可溶性P質量幾乎不變但生物炭總量降低；在200～500℃時隨著熱解溫度的升高，可溶性P含量下降，是因為不可溶P-Ca-Mg晶體物質逐漸形成；在500℃可以觀察到磷鈣礦的存在。在200℃熱解溫度下得到的牛糞生物炭與Pb(Ⅱ)反應后會沉積β-Pb9(PO4)6晶體；在350℃熱解溫度下得到的牛糞生物炭與Pb(Ⅱ)反應后除了沉積β-Pb9(PO4)6晶體外還有Pb3(CO3)2(OH)2的形成，這是因為隨著熱解溫度的升高，生物炭堿性和方解石(CaCO3)含量逐漸增強[90]。因此，化學沉淀作用是有關組分共同作用的結果。

3.5 靜電吸附

靜電吸附作用多發(fā)生在適宜的pH值條件下。當溶液pH值大于生物炭零電荷點(pHpzc)時，生物炭表面攜帶的負電荷能與帶正電荷的重金屬離子發(fā)生靜電吸附作用[95,98,104-105]。當溶液pH值小于生物炭pHpzc時，生物炭表面會電離出質子，與帶負電荷的重金屬離子發(fā)生靜電吸附作用。因此，靜電吸附作用與重金屬離子電動勢，在水溶液中的存在形式以及生物炭表面的電荷量密切相關，而生物炭表面負電荷量又與生物炭表面含氧官能團，包括羧基(—COO-)、羰基(—CO-)和羥基(—OH)[106]、溶液pH值緊密相關[53]。

SHEN等[89]將制備的硬木生物炭用于水體中4種重金屬的吸附，通過Langmuir吸附模型計算不同重金屬離子吸附能力，由大到小分別為Pb(Ⅱ)、Cu(Ⅱ)、Ni(Ⅱ)、Zn(Ⅱ)，其中對Pb(Ⅱ)的吸附遠高于其他3種重金屬離子的原因是，Pb(Ⅱ)的電負性常數(shù)遠高于其他3種(Pb(Ⅱ)、Cu(Ⅱ)、Ni(Ⅱ)和Zn(Ⅱ)的電負性常數(shù)分別為2.33、1.90、1.93、0.69)[93]，因此硬木生物炭對Pb(Ⅱ)有很強的靜電吸附作用。果樹枝生物炭[21]對Pb(Ⅱ)和Cr(Ⅲ)的吸附遠大于Cu(Ⅱ)，這是因為Pb(Ⅱ)和Cr(Ⅲ)有著很高的電荷密度，遠高于Cu(Ⅱ)，因此，Pb(Ⅱ)和Cr(Ⅲ)與生物炭之間的庫倫引力更大[93]。

靜電吸附在秸稈生物炭吸附重金屬機理中占的比重小于化學沉淀。TONG等[63]通過慢速熱解制備得到花生秸稈、大豆秸稈和油菜秸稈生物炭，雖然油菜秸稈生物炭表面負電荷最多，但是P含量小于花生和大豆生物炭，造成了油菜秸稈生物炭對Cu(Ⅱ)的吸附小于花生和大豆生物炭。

4 生物炭重金屬吸附工藝條件

對于特定生物炭而言，影響生物炭重金屬吸附效果的重要因素包括吸附溶液pH值、溶液溫度、吸附劑用量、吸附平衡時間和吸附質初始濃度等。除生物炭原料、制備條件以外，吸附工藝條件對吸附效果的影響也不容忽視。

4.1 吸附溶液pH值

4.2 溶液溫度

溫度主要是通過影響生物炭吸附熱力學過程和吸附熱容等因素來進一步影響吸附效果。一般來說，吸附過程是吸熱反應，可通過控制體系溫度來提高吸附量[66,107,112-114]。MOHAN等[10]將橡木和橡樹生物炭應用于水體中重金屬離子吸附，研究結果表明，溶液的溫度越高生物炭對重金屬吸附能力越強。張雙圣等[115]研究污泥生物炭吸附劑對Pb(Ⅱ)的吸附效果隨溶液溫度的升高而增強，當溶液溫度超過30℃，吸附效果增強不明顯。LIU等[66]發(fā)現(xiàn)重金屬離子被吸附到生物炭表面需要足夠的能量完成這一遷移過程，即生物炭吸附重金屬的過程是吸熱反應，因而溶液溫度升高有利于吸附反應的發(fā)生。KOODYSKA等[60]研究結果也證明了這一點。

4.3 吸附時間

當生物炭吸附重金屬時，只有保證吸附時間的充裕，才能使吸附達到平衡，充分利用生物炭吸附性能。通常生物炭重金屬的吸附過程可以分為兩個階段[116-118]：第一階段，在生物炭與重金屬接觸的前幾分鐘，吸附率和吸附量都快速增加，這是因為吸附位點幾乎完全暴露；隨著吸附位點被占據(jù)，吸附率變慢隨即進入吸附的第二階段，一般持續(xù)時間較長，隨后達到吸附平衡，多為1～4 h[85,60,118]；當吸附時間超過24 h后，吸附量基本保持穩(wěn)定。因此，在實際研究中，同時考慮時間效率和吸附效果，通常選用平衡時間作為吸附時間。

同一種材料吸附不同重金屬時，吸附平衡時間也不盡相同。KOODYSKA等[60]在研究豬糞和牛糞對4種重金屬(Pb、Cd、Zn、Cu)的吸附行為時，發(fā)現(xiàn)對Cu和Zn的吸附平衡時間是30～60 min，對Cd和Pb的吸附平衡時間為120～180 min。平衡時間除了與生物炭和目標重金屬性質相關，還與它們的初始濃度密切相關[119]。

4.4 吸附劑用量與重金屬的初始濃度

在吸附實驗中，經(jīng)常通過加大生物炭的量來増加與重金屬離子接觸的吸附點位，進而提高對重金屬的去除效果[120]。然而,吸附劑增加過量后,由于吸附劑本身官能團對重金屬的競爭吸附能力飽和或者吸附位點達到飽和，不僅造成浪費，還影響單位質量吸附劑的吸附能力。

PELLERA等[118]研究了稻殼、橄欖渣、橘子皮、糞便生物炭對Cu(Ⅱ)的吸附，4種生物炭的用量在2.5～25 g/L時，隨著用量的增加，吸附量增加。生物炭用量從2.5 g/L增加到5 g/L時的吸附率遠大于5 g/L增加到25 g/L，研究最終選擇5 g/L的吸附劑用量。CHEN等[112]在研究玉米秸稈生物炭吸附重金屬Cu(Ⅱ)時也發(fā)現(xiàn)相同規(guī)律，優(yōu)化的生物炭用量也是5 g/L。

重金屬初始濃度和吸附劑濃度對吸附量的影響有著相似的規(guī)律[118,120-121]。AMAN等[121]研究了馬鈴薯皮生物炭對Cu(Ⅱ)的吸附，當Cu(Ⅱ)的初始質量濃度在150～400 mg/L增加時，吸附速率逐漸降低。相同的規(guī)律也被PELLERA等[118]和EL-ASHTOUKHY等[120]得到。因此，實驗中往往需要找到同時滿足吸附率和吸附量的吸附劑和重金屬濃度。

5 不同目標重金屬吸附能力比較分析

特定種類生物炭在吸附不同種重金屬時，對每種重金屬的吸附能力也有差異[60]。INYANG等[5]采用消解甘蔗渣(DWSBC)通過熱解方式制備生物炭應用于水體中Pb(Ⅱ)、Cu(Ⅱ)、Ni(Ⅱ)和Cd(Ⅱ)的吸附，DWSBC對4種重金屬吸附能力由小到大依次為Pb、Cu、Cd、Ni。UCHIMIYA等[98]分別在350℃和700℃條件下慢速熱解制備了雞糞生物炭，結果顯示，對Pb(Ⅱ)、Cu(Ⅱ)、Ni(Ⅱ)和Cd(Ⅱ) 4種重金屬吸附能力由小到大依次為Pb、Cu、Cd、Ni。RAFATULLAH等[122]研究發(fā)現(xiàn)，柳桉木生物炭對不同重金屬的吸附能力由小到大為Pb、Ni、Cu、Cr。PARK等[40]制備的芝麻秸稈生物炭對5種重金屬的最大吸附量由小到大依次為Pb (102 mg/g)、Cd(86 mg/g)、Cr (65 mg/g)、Cu (55 mg/g)、Zn (34 mg/g)。MOHAN等[119]制備了橡木樹皮生物炭，其單位表面積上對水中Pb(Ⅱ)、Cd(Ⅱ)的吸附量分別為0.515 7、0.213 mg/m2。根據(jù)目前已有研究表明，相較于其他重金屬，生物炭對Pb(Ⅱ)表現(xiàn)出較高的吸附能力。

6 總結與展望

生物炭作為一種新型的吸附材料，具有綠色環(huán)保、價格低廉、來源廣泛、吸附性能強等特點，使得其在重金屬吸附方面表現(xiàn)出良好的潛力和前景。目前，雖然針對生物炭重金屬的吸附研究取得了不少進展，但未來的研究工作還應側重以下幾方面。

(1)在生物炭特性及其吸附產(chǎn)物方面，針對最優(yōu)吸附能力的物料選擇和工藝參數(shù)缺乏研究[123]，因此，應開展針對重金屬吸附的生物炭原料特性及吸附產(chǎn)物的多維、微納尺度表征方法研究，以期為生物炭重金屬吸附劑的定向生產(chǎn)奠定基礎。

(2)在生物炭的吸附特性方面，由于生物炭的制備原料和制備條件不同，吸附也多在不同初始pH值、溫度、吸附劑濃度、吸附質濃度等工藝條件下展開，所揭示的吸附效果均是在特定制備條件和吸附條件下，可比性較弱[124]。應將生物炭特性結合其吸附效果進行相關性分析。

(3)在吸附機理研究方面，已有研究工作尚處于定性描述階段，對生物炭吸附重金屬過程中，各個吸附機制對吸附過程的貢獻以及生物炭表面官能團對吸附貢獻的比重還不系統(tǒng)、詳細。研究僅停留在實驗室的模擬與分析上。應采用多維、微納尺度表征手段分析吸附機制和吸附過程。

(4)已有研究多局限于生物炭對單一重金屬溶液體系的吸附，而實際污染水體多為復合重金屬污染[123]。當多種重金屬同時被吸附時，是否產(chǎn)生相互作用，以及在重金屬復合污染物體系中，吸附復雜機理研究應是未來的一個研究重點。

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ReviewofBiocharasAdsorbentforAqueousHeavyMetalRemoval

HAN Lujia LI Yanfei LIU Xian HAN Yahong

(CollegeofEngineering,ChinaAgriculturalUniversity,Beijing100083,China)

Biochar has a bright prospect due to its good surface properties, pore structure and broad raw materials of its production. It has already been a hotspot in the fields of environment, agriculture and energy. It can be produced from a variety of biomass feedstock, such as agricultural residues, manures, wood, bone and so on, under oxygen-limited conditions. It has great potentials for heavy metal remediation and waste water treatment due to its unique properties, low price, easy processing and wide range of preparation material. The existing literature was incorporated to understand the overall sorption research of heavy metals on biochar adsorbents. However, there was still lack of information on the roles of different sorption mechanisms for biochar. The effects of feedstock materials and pyrolysis temperature on biochar characteristics and metal adsorption capacity were discussed. The interaction mechanisms between biochar and heavy metals, such as ion exchange, complexation, physical sorption, precipitation and electrostatic interactions were analyzed in detail. The influence of adsorption conditions and heavy metal species on heavy metals adsorbed by biochar was also included. At the end, the future research directions on sorption of heavy metals by biochar were proposed. The review would help to build important theory and methodology foundation for directly controlling production and scientific utilization of biochar.

biochar; heavy metal; adsorption mechanism; characterization

10.6041/j.issn.1000-1298.2017.11.001

S216

A

1000-1298(2017)11-0001-11

2017-09-21

2017-10-09

國家自然科學基金項目(31271611)

韓魯佳(1964—)，女，教授，博士生導師，主要從事生物質與生物處理工程研究，E-mail: hanlj@cau.edu.cn