化(hua)學(xue)(xue)固化(hua)是(shi)改變土(tu)壤(rang)(rang)重金(jin)屬賦存狀(zhuang)態、降(jiang)低重金(jin)屬生物有效性(xing)、提(ti)高農產(chan)品質量的(de)(de)(de)重要(yao)途徑，是(shi)一種廉價(jia)高效的(de)(de)(de)化(hua)學(xue)(xue)處理(li)方(fang)法，應用前景廣闊(kuo)。本文就土(tu)壤(rang)(rang)重金(jin)屬污(wu)染治(zhi)理(li)的(de)(de)(de)技術、土(tu)壤(rang)(rang)重金(jin)屬化(hua)學(xue)(xue)固化(hua)的(de)(de)(de)原(yuan)理(li)及其影響因素、存在的(de)(de)(de)問(wen)題及發展方(fang)向進行了探討，期望能為土(tu)壤(rang)(rang)重金(jin)屬污(wu)染治(zhi)理(li)提(ti)供(gong)參考(kao)。  

圖為受重金屬污染的水果  

重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)在土(tu)(tu)(tu)壤(rang)(rang)(rang)中理(li)化(hua)(hua)(hua)性質(zhi)相對穩(wen)定(ding)并且遷移性差，重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)污(wu)(wu)(wu)染(ran)(ran)會破(po)壞(huai)土(tu)(tu)(tu)壤(rang)(rang)(rang)結構，影(ying)響(xiang)(xiang)土(tu)(tu)(tu)壤(rang)(rang)(rang)理(li)化(hua)(hua)(hua)性質(zhi)和微生物群落結構，降低(di)土(tu)(tu)(tu)壤(rang)(rang)(rang)生態平(ping)衡的(de)穩(wen)定(ding)性。統(tong)計顯示，我國約(yue)140萬hm2的(de)污(wu)(wu)(wu)水(shui)灌(guan)區(qu)中，約(yue)有(you)64.8%的(de)土(tu)(tu)(tu)壤(rang)(rang)(rang)遭(zao)受重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)污(wu)(wu)(wu)染(ran)(ran)，每年被(bei)重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)污(wu)(wu)(wu)染(ran)(ran)的(de)糧食(shi)達1200萬t，直接經濟損失超過200億元。我國有(you)130萬hm2的(de)農(nong)業(ye)土(tu)(tu)(tu)地因(yin)為(wei)遭(zao)受嚴重(zhong)(zhong)(zhong)鎘污(wu)(wu)(wu)染(ran)(ran)而(er)棄耕，極(ji)大影(ying)響(xiang)(xiang)了(le)糧食(shi)產(chan)量(liang)與安全。土(tu)(tu)(tu)壤(rang)(rang)(rang)重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)污(wu)(wu)(wu)染(ran)(ran)來源主要包括采(cai)礦(kuang)、金(jin)(jin)屬(shu)(shu)(shu)冶(ye)(ye)煉(lian)、化(hua)(hua)(hua)工(gong)制造(zao)、燃煤、電(dian)子、制革染(ran)(ran)料、污(wu)(wu)(wu)水(shui)灌(guan)溉及(ji)(ji)農(nong)用物資(zi)施用。其(qi)中有(you)色金(jin)(jin)屬(shu)(shu)(shu)礦(kuang)采(cai)選業(ye)、有(you)色金(jin)(jin)屬(shu)(shu)(shu)冶(ye)(ye)煉(lian)及(ji)(ji)壓(ya)延(yan)加工(gong)業(ye)、化(hua)(hua)(hua)學原(yuan)料及(ji)(ji)化(hua)(hua)(hua)學制品制造(zao)業(ye)、黑色金(jin)(jin)屬(shu)(shu)(shu)冶(ye)(ye)煉(lian)及(ji)(ji)壓(ya)延(yan)加工(gong)業(ye)位(wei)列2008年重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)(Hg、Cd、Cr、Pb、As)排(pai)放量(liang)的(de)前(qian)4位(wei)，這4個行(xing)業(ye)重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)排(pai)放量(liang)為(wei)483.3t，占重(zhong)(zhong)(zhong)點(dian)調查統(tong)計企(qi)業(ye)排(pai)放量(liang)的(de)84.5%。化(hua)(hua)(hua)學固化(hua)(hua)(hua)方(fang)(fang)法是(shi)一種經濟可行(xing)、前(qian)景廣闊的(de)土(tu)(tu)(tu)壤(rang)(rang)(rang)重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)污(wu)(wu)(wu)染(ran)(ran)治理(li)方(fang)(fang)法。本文重(zhong)(zhong)(zhong)點(dian)探討了(le)土(tu)(tu)(tu)壤(rang)(rang)(rang)重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)污(wu)(wu)(wu)染(ran)(ran)治理(li)的(de)技(ji)術、土(tu)(tu)(tu)壤(rang)(rang)(rang)重(zhong)(zhong)(zhong)金(jin)(jin)屬(shu)(shu)(shu)化(hua)(hua)(hua)學固化(hua)(hua)(hua)的(de)原(yuan)理(li)及(ji)(ji)其(qi)影(ying)響(xiang)(xiang)因(yin)素(su)、存在的(de)問(wen)題及(ji)(ji)發展方(fang)(fang)向。  

土壤重金屬污染修復技術  

土(tu)(tu)(tu)壤(rang)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)污(wu)染(ran)(ran)是(shi)(shi)(shi)指由(you)于(yu)人類活動將(jiang)(jiang)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)引(yin)入到(dao)土(tu)(tu)(tu)壤(rang)中(zhong)(zhong)(zhong)，致使(shi)土(tu)(tu)(tu)壤(rang)中(zhong)(zhong)(zhong)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)含量(liang)(liang)明顯高(gao)(gao)于(yu)原有含量(liang)(liang)，并(bing)造(zao)成生(sheng)(sheng)態環(huan)境惡化(hua)(hua)(hua)(hua)(hua)的(de)(de)(de)(de)現象(xiang)。土(tu)(tu)(tu)壤(rang)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)污(wu)染(ran)(ran)具(ju)有隱蔽性、潛伏(fu)性、積累(lei)性和(he)(he)長期性的(de)(de)(de)(de)特點(dian)。重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)污(wu)染(ran)(ran)的(de)(de)(de)(de)治(zhi)理(li)(li)(li)(li)的(de)(de)(de)(de)有兩(liang)條思路：一(yi)是(shi)(shi)(shi)直接將(jiang)(jiang)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)從(cong)土(tu)(tu)(tu)壤(rang)中(zhong)(zhong)(zhong)去(qu)除(chu)，削(xue)減(jian)土(tu)(tu)(tu)壤(rang)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)總量(liang)(liang);二(er)是(shi)(shi)(shi)降(jiang)低重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)的(de)(de)(de)(de)遷(qian)移(yi)(yi)性和(he)(he)生(sheng)(sheng)物(wu)(wu)有效(xiao)性，削(xue)減(jian)有效(xiao)態重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)含量(liang)(liang)。修復(fu)技(ji)術(shu)(shu)包(bao)括物(wu)(wu)理(li)(li)(li)(li)、化(hua)(hua)(hua)(hua)(hua)學(xue)、生(sheng)(sheng)物(wu)(wu)和(he)(he)工程(cheng)技(ji)術(shu)(shu)。物(wu)(wu)理(li)(li)(li)(li)技(ji)術(shu)(shu)主要(yao)是(shi)(shi)(shi)通過(guo)(guo)電熱和(he)(he)土(tu)(tu)(tu)壤(rang)淋洗(xi)等途(tu)徑將(jiang)(jiang)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)從(cong)土(tu)(tu)(tu)壤(rang)中(zhong)(zhong)(zhong)去(qu)除(chu)，這種治(zhi)理(li)(li)(li)(li)方法(fa)較為(wei)徹底(di)，但是(shi)(shi)(shi)效(xiao)率低，成本高(gao)(gao)，應用范圍受到(dao)限制(zhi)(zhi)。生(sheng)(sheng)物(wu)(wu)技(ji)術(shu)(shu)主要(yao)是(shi)(shi)(shi)通過(guo)(guo)植(zhi)(zhi)物(wu)(wu)(植(zhi)(zhi)物(wu)(wu)提取(qu)，植(zhi)(zhi)物(wu)(wu)揮(hui)發，植(zhi)(zhi)物(wu)(wu)固(gu)(gu)(gu)(gu)定)、動植(zhi)(zhi)物(wu)(wu)殘體和(he)(he)微生(sheng)(sheng)物(wu)(wu)來固(gu)(gu)(gu)(gu)化(hua)(hua)(hua)(hua)(hua)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)，這種方法(fa)較為(wei)環(huan)保，但是(shi)(shi)(shi)富(fu)集(ji)植(zhi)(zhi)物(wu)(wu)篩選復(fu)雜(za)，固(gu)(gu)(gu)(gu)定效(xiao)率低，并(bing)且收割后的(de)(de)(de)(de)植(zhi)(zhi)物(wu)(wu)焚燒后產生(sheng)(sheng)的(de)(de)(de)(de)灰分(fen)怎樣處理(li)(li)(li)(li)，在業界頗(po)有爭(zheng)議。工程(cheng)技(ji)術(shu)(shu)主要(yao)是(shi)(shi)(shi)通過(guo)(guo)客(ke)土(tu)(tu)(tu)，覆(fu)土(tu)(tu)(tu)和(he)(he)深耕翻土(tu)(tu)(tu)等途(tu)徑將(jiang)(jiang)土(tu)(tu)(tu)壤(rang)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)轉移(yi)(yi)到(dao)別處，或者(zhe)覆(fu)蓋到(dao)植(zhi)(zhi)物(wu)(wu)根(gen)系不(bu)能(neng)觸及(ji)的(de)(de)(de)(de)深層(ceng)土(tu)(tu)(tu)，但是(shi)(shi)(shi)其工程(cheng)里(li)大、成本高(gao)(gao)，難以(yi)(yi)推廣。重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)化(hua)(hua)(hua)(hua)(hua)學(xue)固(gu)(gu)(gu)(gu)化(hua)(hua)(hua)(hua)(hua)技(ji)術(shu)(shu)主要(yao)是(shi)(shi)(shi)通過(guo)(guo)向(xiang)土(tu)(tu)(tu)壤(rang)中(zhong)(zhong)(zhong)添加(jia)固(gu)(gu)(gu)(gu)化(hua)(hua)(hua)(hua)(hua)制(zhi)(zhi)劑或材(cai)料，使(shi)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)的(de)(de)(de)(de)生(sheng)(sheng)物(wu)(wu)可(ke)利用性降(jiang)低，甚至完全不(bu)能(neng)被(bei)生(sheng)(sheng)物(wu)(wu)吸收，成為(wei)沉淀狀態。同時，固(gu)(gu)(gu)(gu)化(hua)(hua)(hua)(hua)(hua)材(cai)料來源(yuan)廣泛，許多行業的(de)(de)(de)(de)廢棄(qi)物(wu)(wu)都可(ke)以(yi)(yi)作為(wei)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)固(gu)(gu)(gu)(gu)化(hua)(hua)(hua)(hua)(hua)材(cai)料，這樣既能(neng)治(zhi)理(li)(li)(li)(li)污(wu)染(ran)(ran)，又能(neng)變(bian)廢為(wei)寶。例如，施用紙廠(chang)濾泥，石灰，鐵尾渣，粉煤灰等工業廢棄(qi)物(wu)(wu)作為(wei)固(gu)(gu)(gu)(gu)化(hua)(hua)(hua)(hua)(hua)材(cai)料，不(bu)僅材(cai)料來源(yuan)廣泛，而且可(ke)以(yi)(yi)有效(xiao)降(jiang)低稻田土(tu)(tu)(tu)壤(rang)中(zhong)(zhong)(zhong)的(de)(de)(de)(de)Pb，Cd含量(liang)(liang)。化(hua)(hua)(hua)(hua)(hua)學(xue)固(gu)(gu)(gu)(gu)化(hua)(hua)(hua)(hua)(hua)技(ji)術(shu)(shu)治(zhi)理(li)(li)(li)(li)重(zhong)(zhong)(zhong)金(jin)(jin)(jin)屬(shu)污(wu)染(ran)(ran)表現出潛能(neng)和(he)(he)重(zhong)(zhong)(zhong)要(yao)性，已引(yin)起學(xue)者(zhe)和(he)(he)應用者(zhe)愈來愈廣泛的(de)(de)(de)(de)重(zhong)(zhong)(zhong)視。  

土壤重金屬化學固化的原理  

向土壤中加入固化(hua)劑(ji)，調節和(he)(he)改(gai)變(bian)土壤的理化(hua)性(xing)質，通過(guo)沉淀(dian)作(zuo)用(yong)、吸附作(zuo)用(yong)、配(pei)位作(zuo)用(yong)，有機絡合和(he)(he)氧化(hua)還原(yuan)作(zuo)用(yong)等改(gai)變(bian)重金(jin)屬在土壤中的賦存形(xing)態(tai)和(he)(he)化(hua)學(xue)形(xing)態(tai)，降低其(qi)遷移性(xing)和(he)(he)生(sheng)物有效(xiao)性(xing)，達到修復受污染載體的目(mu)的。  

(1)沉(chen)淀作(zuo)用  

固化(hua)材(cai)料(liao)(liao)通(tong)過(guo)(guo)自身溶解(jie)作(zuo)用(yong)(yong)所產生的(de)陰離子(zi)與重(zhong)(zhong)金(jin)(jin)屬(shu)元(yuan)素產生沉(chen)淀(dian)作(zuo)用(yong)(yong)，從而降(jiang)(jiang)低(di)(di)重(zhong)(zhong)金(jin)(jin)屬(shu)的(de)遷移性和(he)(he)生物有(you)效性。以(yi)石(shi)(shi)灰(hui)石(shi)(shi)為代表的(de)堿性鈍(dun)化(hua)修復劑(ji)主(zhu)要(yao)是(shi)通(tong)過(guo)(guo)提高土(tu)(tu)壤溶液pH，促使(shi)土(tu)(tu)壤中(zhong)重(zhong)(zhong)金(jin)(jin)屬(shu)形成(cheng)氫氧化(hua)物沉(chen)淀(dian)。石(shi)(shi)灰(hui)石(shi)(shi)能(neng)夠有(you)效地降(jiang)(jiang)低(di)(di)土(tu)(tu)壤中(zhong)交換態Pb、Cd、Cu、Zn的(de)含量，并且明(ming)顯減少了土(tu)(tu)壤中(zhong)相應(ying)重(zhong)(zhong)金(jin)(jin)屬(shu)的(de)毒(du)性浸出量，使(shi)重(zhong)(zhong)金(jin)(jin)屬(shu)固定下(xia)來(lai)。有(you)研究證實，向受(shou)污(wu)染的(de)稻田土(tu)(tu)壤中(zhong)添(tian)加鈣鎂磷肥(fei)，石(shi)(shi)灰(hui)和(he)(he)硅肥(fei)等肥(fei)料(liao)(liao)，亦可降(jiang)(jiang)低(di)(di)稻田中(zhong)Cd含量。對沸石(shi)(shi)、磷酸鹽(yan)和(he)(he)鐵氧化(hua)物對作(zuo)物吸收重(zhong)(zhong)金(jin)(jin)屬(shu)Pb，Cd的(de)影響及其(qi)(qi)機(ji)理的(de)研究表明(ming)，低(di)(di)劑(ji)量的(de)沸石(shi)(shi)和(he)(he)磷酸鹽(yan)配合使(shi)用(yong)(yong)能(neng)使(shi)Pb，Cd轉化(hua)成(cheng)沉(chen)淀(dian)或難溶狀(zhuang)態化(hua)合物，顯著降(jiang)(jiang)低(di)(di)作(zuo)物對Pb，Cd的(de)吸收。在淹水條件(jian)下(xia)，土(tu)(tu)壤中(zhong)的(de)硫酸根(gen)離子(zi)被還原成(cheng)S2-，其(qi)(qi)與重(zhong)(zhong)金(jin)(jin)屬(shu)Zn2+結合生成(cheng)沉(chen)淀(dian)，降(jiang)(jiang)低(di)(di)了重(zhong)(zhong)金(jin)(jin)屬(shu)鋅的(de)遷移性和(he)(he)生物有(you)效性。沉(chen)淀(dian)作(zuo)用(yong)(yong)是(shi)土(tu)(tu)壤重(zhong)(zhong)金(jin)(jin)屬(shu)固化(hua)的(de)一(yi)種重(zhong)(zhong)要(yao)方式。  

(2)吸(xi)附作用  

固(gu)化材料對(dui)重(zhong)(zhong)金(jin)(jin)屬(shu)的(de)(de)(de)(de)吸(xi)(xi)(xi)(xi)(xi)附(fu)作用(yong)(yong)(yong)實(shi)際上(shang)是(shi)吸(xi)(xi)(xi)(xi)(xi)附(fu)劑(ji)對(dui)吸(xi)(xi)(xi)(xi)(xi)附(fu)質(zhi)(zhi)質(zhi)(zhi)點的(de)(de)(de)(de)吸(xi)(xi)(xi)(xi)(xi)引作用(yong)(yong)(yong)，分為物理吸(xi)(xi)(xi)(xi)(xi)附(fu)作用(yong)(yong)(yong)和(he)(he)化學吸(xi)(xi)(xi)(xi)(xi)附(fu)作用(yong)(yong)(yong)。沸石(shi)具(ju)有(you)特殊(shu)的(de)(de)(de)(de)Si-O四面(mian)體結(jie)構(gou)，這(zhe)種特殊(shu)的(de)(de)(de)(de)結(jie)構(gou)使(shi)其(qi)具(ju)有(you)良好的(de)(de)(de)(de)吸(xi)(xi)(xi)(xi)(xi)附(fu)性(xing)能(neng)，通過物理吸(xi)(xi)(xi)(xi)(xi)附(fu)作用(yong)(yong)(yong)可將(jiang)重(zhong)(zhong)金(jin)(jin)屬(shu)Pb，Cd吸(xi)(xi)(xi)(xi)(xi)附(fu)在表(biao)面(mian)，從而將(jiang)重(zhong)(zhong)金(jin)(jin)屬(shu)固(gu)定下來。柿單寧是(shi)柿子(zi)中含(han)有(you)的(de)(de)(de)(de)一(yi)種使(shi)其(qi)呈澀感(gan)的(de)(de)(de)(de)多(duo)酚(fen)類天然(ran)高分子(zi)物質(zhi)(zhi)，其(qi)分子(zi)結(jie)構(gou)中的(de)(de)(de)(de)B環含(han)有(you)豐(feng)富(fu)的(de)(de)(de)(de)鄰位(wei)酚(fen)羥基，對(dui)貴金(jin)(jin)屬(shu)金(jin)(jin)(Au)和(he)(he)鈀(Pd)，以及放(fang)射(she)性(xing)重(zhong)(zhong)金(jin)(jin)屬(shu)鈾(U)、釷(Th)等具(ju)有(you)很強(qiang)的(de)(de)(de)(de)化學吸(xi)(xi)(xi)(xi)(xi)附(fu)能(neng)力，將(jiang)其(qi)固(gu)定下來，用(yong)(yong)(yong)于貴金(jin)(jin)屬(shu)回(hui)收和(he)(he)放(fang)射(she)性(xing)重(zhong)(zhong)金(jin)(jin)屬(shu)污染治理。柿單寧對(dui)Au3+的(de)(de)(de)(de)吸(xi)(xi)(xi)(xi)(xi)附(fu)過程(cheng)(cheng)分為3個步(bu)驟：Au3+和(he)(he)羥基(主要(yao)是(shi)鄰位(wei)酚(fen)羥基)發生配體交換反(fan)應;Au3+被(bei)還原為Au0;柿單寧凝膠吸(xi)(xi)(xi)(xi)(xi)附(fu)生成的(de)(de)(de)(de)Au0，是(shi)一(yi)個復雜(za)的(de)(de)(de)(de)化學反(fan)應過程(cheng)(cheng)。吸(xi)(xi)(xi)(xi)(xi)附(fu)作用(yong)(yong)(yong)是(shi)土壤(rang)重(zhong)(zhong)金(jin)(jin)屬(shu)化學固(gu)化的(de)(de)(de)(de)一(yi)個重(zhong)(zhong)要(yao)形式，在重(zhong)(zhong)金(jin)(jin)屬(shu)污染治理中低位(wei)特殊(shu)。  

(3)配位作用  

粘(zhan)(zhan)土(tu)(tu)(tu)礦物(wu)羥基(ji)(ji)(ji)化(hua)表面(mian)可以通過靜電作(zuo)(zuo)用(yong)(yong)于溶液中的(de)(de)離(li)子(zi)發(fa)(fa)生(sheng)表面(mian)配(pei)位反(fan)應。粘(zhan)(zhan)土(tu)(tu)(tu)礦物(wu)層(ceng)與層(ceng)之(zhi)間(jian)是分子(zi)引力相聯接，重(zhong)(zhong)金屬(shu)(shu)離(li)子(zi)可以進入層(ceng)間(jian)與SiO-發(fa)(fa)生(sheng)晶(jing)間(jian)配(pei)合(he)(he)作(zuo)(zuo)用(yong)(yong)。向污染(ran)土(tu)(tu)(tu)壤中添加粘(zhan)(zhan)土(tu)(tu)(tu)礦物(wu)，利用(yong)(yong)其對重(zhong)(zhong)金屬(shu)(shu)的(de)(de)配(pei)合(he)(he)作(zuo)(zuo)用(yong)(yong)降低(di)重(zhong)(zhong)金屬(shu)(shu)的(de)(de)遷(qian)移性(xing)和(he)生(sheng)物(wu)有(you)效(xiao)性(xing)，可實現污染(ran)土(tu)(tu)(tu)壤的(de)(de)化(hua)學修復。骨粉和(he)凹凸棒等粘(zhan)(zhan)土(tu)(tu)(tu)礦物(wu)作(zuo)(zuo)為土(tu)(tu)(tu)壤改良(liang)劑可以通過與重(zhong)(zhong)金屬(shu)(shu)離(li)子(zi)的(de)(de)配(pei)位作(zuo)(zuo)用(yong)(yong)有(you)效(xiao)減少(shao)煙草對重(zhong)(zhong)金屬(shu)(shu)Pb，Cd的(de)(de)吸收[7,20]。酚(fen)羥基(ji)(ji)(ji)上(shang)的(de)(de)氧基(ji)(ji)(ji)由于存(cun)在非(fei)鍵合(he)(he)電子(zi)對，通常被(bei)認為是一種很(hen)強(qiang)的(de)(de)路易(yi)斯堿,可與路易(yi)斯酸金屬(shu)(shu)離(li)子(zi)發(fa)(fa)生(sheng)配(pei)位作(zuo)(zuo)用(yong)(yong),形成配(pei)合(he)(he)物(wu)。有(you)研究證實鉻酸鹽(Cr6+)與兒(er)茶(cha)酚(fen)發(fa)(fa)生(sheng)酯化(hua)作(zuo)(zuo)用(yong)(yong)，實質上(shang)是CrO22+(硬(ying)酸)與兒(er)茶(cha)酚(fen)(硬(ying)堿)結(jie)合(he)(he)，Cr6+被(bei)吸附并被(bei)固定(ding)。  

(4)有機絡合作用  

土(tu)(tu)壤有(you)(you)機(ji)(ji)質在微(wei)生(sheng)(sheng)物作(zuo)(zuo)用下(xia)，通(tong)過生(sheng)(sheng)物和(he)化(hua)學(xue)作(zuo)(zuo)用使一(yi)些(xie)分(fen)解的(de)中間(jian)產物重(zhong)新合成(cheng)復(fu)雜高分(fen)子(zi)聚合物，與重(zhong)金(jin)(jin)屬(shu)離子(zi)發生(sheng)(sheng)有(you)(you)機(ji)(ji)絡(luo)合作(zuo)(zuo)用形成(cheng)絡(luo)合物，從(cong)而(er)使重(zhong)金(jin)(jin)屬(shu)離子(zi)固化(hua)下(xia)來(lai)。施用農家肥能顯著降(jiang)低淋(lin)洗液中Cd和(he)Zn的(de)濃(nong)度，廄(jiu)肥降(jiang)低有(you)(you)效(xiao)(xiao)態Cd和(he)Zn的(de)含量(liang)主要(yao)是(shi)由于(yu)游離的(de)鎘、鋅離子(zi)與有(you)(you)機(ji)(ji)質的(de)絡(luo)合作(zuo)(zuo)用。蚯蚓糞一(yi)方面可(ke)以(yi)改善土(tu)(tu)壤肥力，另一(yi)方面可(ke)以(yi)提高土(tu)(tu)壤對(dui)Pb，Hg，Co，Cd等重(zhong)金(jin)(jin)屬(shu)的(de)遷(qian)移性(xing)和(he)生(sheng)(sheng)物有(you)(you)效(xiao)(xiao)性(xing)。堆肥可(ke)降(jiang)低重(zhong)金(jin)(jin)屬(shu)的(de)遷(qian)移性(xing)和(he)生(sheng)(sheng)物有(you)(you)效(xiao)(xiao)性(xing)，但具體效(xiao)(xiao)果(guo)因土(tu)(tu)壤，金(jin)(jin)屬(shu)，堆肥性(xing)質不(bu)同而(er)有(you)(you)很(hen)大差異。另外，部(bu)分(fen)細(xi)菌及真(zhen)菌細(xi)胞壁上含有(you)(you)大量(liang)巰(qiu)基，羧基，羥基等活性(xing)基團，對(dui)重(zhong)金(jin)(jin)屬(shu)離子(zi)產生(sheng)(sheng)很(hen)強的(de)絡(luo)合能力，從(cong)而(er)使重(zhong)金(jin)(jin)屬(shu)污染物的(de)生(sheng)(sheng)物可(ke)利用性(xing)降(jiang)低。在有(you)(you)機(ji)(ji)質豐富的(de)土(tu)(tu)壤中，有(you)(you)機(ji)(ji)絡(luo)合是(shi)重(zhong)金(jin)(jin)屬(shu)化(hua)學(xue)固化(hua)的(de)一(yi)種主要(yao)形式。  

(5)氧化還原(yuan)作(zuo)用  

對(dui)(dui)于(yu)變價重(zhong)金屬(shu)而(er)言，在不(bu)同(tong)價態下，其毒性(xing)，遷(qian)移性(xing)和生(sheng)物有(you)效性(xing)的(de)差異(yi)很大。一些微生(sheng)物對(dui)(dui)As5+、Se4+、Cr6+、Fe3+、Hg2+等元素(su)有(you)還(huan)(huan)原(yuan)作(zuo)用(yong)，而(er)另(ling)一些微生(sheng)物對(dui)(dui)Fe2+、Fe、As3+等元素(su)具有(you)有(you)氧化作(zuo)用(yong)。在厭氧條件下，微生(sheng)物可(ke)(ke)以講Hg2+還(huan)(huan)原(yuan)成揮發性(xing)較強的(de)Hg，將(jiang)Cr6+還(huan)(huan)原(yuan)成毒性(xing)較低(di)的(de)Cr3+，降低(di)重(zhong)金屬(shu)的(de)毒害作(zuo)用(yong)。硫(liu)酸(suan)鹽還(huan)(huan)原(yuan)細菌可(ke)(ke)通過氧化還(huan)(huan)原(yuan)作(zuo)用(yong)將(jiang)硫(liu)酸(suan)根(gen)離子還(huan)(huan)原(yuan)成S2+，而(er)S2+可(ke)(ke)與重(zhong)金屬(shu)Pb、Cd發生(sheng)反應生(sheng)成沉淀(dian)，從而(er)起到(dao)固化作(zuo)用(yong)。  

土壤重金屬化學固化的影響因素  

化(hua)學固化(hua)是指通過加入固化(hua)材料(liao)在污染(ran)場地就地處理重金屬的一種方法。但是，固化(hua)過程受到土壤生物、理化(hua)性質和外(wai)部環境的影響與制約(yue)。  

影(ying)響重金屬(shu)化學(xue)固化穩(wen)定化的主(zhu)要因素(su)包括(kuo)酸堿度(pH)、氧(yang)化還原(yuan)電位(Eh)、陽(yang)離子(zi)交換量(CEC)、有機質(zhi)(OM)、重金屬(shu)離子(zi)種(zhong)類(lei)與濃度、礦物質(zhi)組成、植物和微生物種(zhong)類(lei)等(deng)。  

土(tu)(tu)壤(rang)(rang)(rang)(rang)(rang)pH影響(xiang)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)離(li)(li)(li)(li)子(zi)(zi)(zi)在土(tu)(tu)壤(rang)(rang)(rang)(rang)(rang)中(zhong)的(de)(de)存(cun)在形態(tai)，以(yi)石灰(hui)或碳(tan)酸鈣為代(dai)表(biao)的(de)(de)堿性(xing)(xing)鈍(dun)化(hua)(hua)(hua)(hua)修復(fu)劑主要是通過提高(gao)土(tu)(tu)壤(rang)(rang)(rang)(rang)(rang)pH，促使Pb、Cd等重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)離(li)(li)(li)(li)子(zi)(zi)(zi)形成氫氧(yang)化(hua)(hua)(hua)(hua)物(wu)或碳(tan)酸鹽(yan)結合(he)態(tai)沉(chen)淀。然(ran)(ran)而，有(you)些(xie)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)如Pb和(he)Cu在強堿條下(xia)由于(yu)和(he)OH-絡(luo)合(he)形成了Cu(OH)3-和(he)Pb(OH)3-，溶解度反而增大(da)，移(yi)動性(xing)(xing)增強。對(dui)于(yu)變價(jia)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)而言，氧(yang)化(hua)(hua)(hua)(hua)還原(yuan)電位(wei)(wei)對(dui)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)的(de)(de)毒性(xing)(xing)、遷移(yi)性(xing)(xing)和(he)生(sheng)物(wu)有(you)效(xiao)性(xing)(xing)影響(xiang)很(hen)大(da)。土(tu)(tu)壤(rang)(rang)(rang)(rang)(rang)氧(yang)化(hua)(hua)(hua)(hua)原(yuan)電位(wei)(wei)降低會促進Cr6+還原(yuan)成毒性(xing)(xing)較小(xiao)的(de)(de)Cr3+并生(sheng)成較穩定的(de)(de)沉(chen)淀。陽(yang)離(li)(li)(li)(li)子(zi)(zi)(zi)交(jiao)換量(liang)影響(xiang)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)的(de)(de)固(gu)化(hua)(hua)(hua)(hua)作(zuo)(zuo)用(yong)，例如沸石的(de)(de)硅氧(yang)四面(mian)體(ti)結構中(zhong)鋁離(li)(li)(li)(li)子(zi)(zi)(zi)取代(dai)硅離(li)(li)(li)(li)子(zi)(zi)(zi)所造成的(de)(de)負(fu)電荷由Na+，K+,Ca2+，Mg2+等平衡，這(zhe)些(xie)陽(yang)離(li)(li)(li)(li)子(zi)(zi)(zi)極易與(yu)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)Pb、Cd陽(yang)離(li)(li)(li)(li)子(zi)(zi)(zi)發(fa)生(sheng)離(li)(li)(li)(li)子(zi)(zi)(zi)交(jiao)換作(zuo)(zuo)用(yong)，從而將(jiang)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)鉛、鎘(ge)固(gu)定下(xia)來。有(you)機(ji)質(zhi)和(he)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)離(li)(li)(li)(li)子(zi)(zi)(zi)發(fa)生(sheng)絡(luo)合(he)作(zuo)(zuo)用(yong)生(sheng)成不(bu)溶性(xing)(xing)復(fu)合(he)物(wu)，起(qi)到固(gu)定重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)的(de)(de)作(zuo)(zuo)用(yong)。農(nong)家(jia)肥中(zhong)的(de)(de)有(you)機(ji)質(zhi)與(yu)游離(li)(li)(li)(li)的(de)(de)Cd2+、Zn2+發(fa)生(sheng)絡(luo)合(he)作(zuo)(zuo)用(yong)，能顯著降低淋洗(xi)液中(zhong)Cd和(he)Zn的(de)(de)濃度。然(ran)(ran)而有(you)機(ji)質(zhi)也(ye)可(ke)以(yi)起(qi)到活化(hua)(hua)(hua)(hua)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)作(zuo)(zuo)用(yong)，例如蚯蚓糞(fen)可(ke)以(yi)提高(gao)土(tu)(tu)壤(rang)(rang)(rang)(rang)(rang)對(dui)Pb，Hg，Co，Cd等重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)的(de)(de)遷移(yi)性(xing)(xing)和(he)生(sheng)物(wu)有(you)效(xiao)性(xing)(xing)，有(you)潛力成為重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)污(wu)染土(tu)(tu)壤(rang)(rang)(rang)(rang)(rang)修復(fu)劑。各種重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)離(li)(li)(li)(li)子(zi)(zi)(zi)之間存(cun)在著點(dian)位(wei)(wei)競爭，重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)離(li)(li)(li)(li)子(zi)(zi)(zi)的(de)(de)種類和(he)數量(liang)影響(xiang)其固(gu)化(hua)(hua)(hua)(hua)作(zuo)(zuo)用(yong)。土(tu)(tu)壤(rang)(rang)(rang)(rang)(rang)中(zhong)含有(you)大(da)量(liang)粘土(tu)(tu)礦(kuang)物(wu)，這(zhe)些(xie)粘土(tu)(tu)礦(kuang)物(wu)存(cun)在空腔或羥(qian)基(ji)化(hua)(hua)(hua)(hua)表(biao)面(mian)，使重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)離(li)(li)(li)(li)子(zi)(zi)(zi)發(fa)生(sheng)吸(xi)附或配位(wei)(wei)作(zuo)(zuo)用(yong)，而固(gu)定下(xia)來。另(ling)外(wai)，土(tu)(tu)壤(rang)(rang)(rang)(rang)(rang)中(zhong)微生(sheng)物(wu)或植物(wu)也(ye)對(dui)重(zhong)(zhong)(zhong)(zhong)金(jin)(jin)(jin)(jin)(jin)(jin)(jin)(jin)屬(shu)(shu)(shu)固(gu)定起(qi)著重(zhong)(zhong)(zhong)(zhong)要作(zuo)(zuo)用(yong)。  

存在的問題及發展方向  

國內土(tu)壤重(zhong)金(jin)(jin)屬化學(xue)固(gu)化研(yan)究側重(zhong)于實踐應(ying)用(yong)，對(dui)固(gu)化效(xiao)果關注較(jiao)多，對(dui)化學(xue)作用(yong)過程及作用(yong)機(ji)理(li)研(yan)究偏(pian)少。同時，實踐中固(gu)化材料或固(gu)化方(fang)(fang)法綜合(he)應(ying)用(yong)研(yan)究偏(pian)少。國外在重(zhong)金(jin)(jin)屬化學(xue)固(gu)化研(yan)究方(fang)(fang)面起(qi)步較(jiao)早，更加重(zhong)視固(gu)化機(ji)理(li)與(yu)重(zhong)金(jin)(jin)屬的遷移與(yu)轉化過程，這(zhe)(zhe)些基(ji)礎性研(yan)究也(ye)正是根治(zhi)土(tu)壤重(zhong)金(jin)(jin)屬污染(ran)的關鍵所在。土(tu)壤重(zhong)金(jin)(jin)屬化學(xue)固(gu)化技術有其他處(chu)(chu)理(li)方(fang)(fang)法不可比擬的優(you)勢，但是這(zhe)(zhe)種處(chu)(chu)理(li)方(fang)(fang)法也(ye)有其固(gu)有的弱(ruo)點(dian)，有些問題還有待深入研(yan)究。  

(1)重金(jin)屬化學(xue)固化效果的穩定性  

化(hua)(hua)學固化(hua)(hua)減少重金(jin)屬的有效態(tai)或可遷移態(tai)含(han)量，總量不發生變(bian)化(hua)(hua)。但是，當土壤環境發生變(bian)化(hua)(hua)時(shi)，被(bei)固化(hua)(hua)的重金(jin)屬可能重新釋放(fang)。例如當土壤的pH由堿性變(bian)為中性或酸(suan)性時(shi)，被(bei)固定的重金(jin)屬Pb，Cd離子可能重新釋放(fang)出(chu)來。當土壤中的透氣性較(jiao)好，氧(yang)氣充足(zu)，呈(cheng)現氧(yang)化(hua)(hua)環境時(shi)，Cr3+可能重新被(bei)氧(yang)化(hua)(hua)成毒性較(jiao)大的Cr6+。  

對重金(jin)屬離子化(hua)學固(gu)化(hua)的過(guo)程與機理進行(xing)研究，分析影響化(hua)學固(gu)化(hua)過(guo)程的因素，并對固(gu)化(hua)效果進行(xing)實時監測，并對固(gu)化(hua)方法(fa)進行(xing)修正和改進，以保證固(gu)化(hua)效果的穩(wen)定性。  

(2)固化材料及(ji)配(pei)套應用技(ji)術(shu)  

一些固化(hua)(hua)(hua)材料(liao)(liao)吸附或固化(hua)(hua)(hua)效果并不顯著;固化(hua)(hua)(hua)材料(liao)(liao)自身的(de)化(hua)(hua)(hua)學(xue)穩(wen)定性和生物降解(jie)性差;能(neng)應對多種重金屬復合污(wu)染的(de)固化(hua)(hua)(hua)材料(liao)(liao)研(yan)究有待加強。  

首先(xian)，加(jia)(jia)強(qiang)改(gai)性固(gu)(gu)(gu)化(hua)(hua)材料(liao)的研制和開發。有(you)些天(tian)然沸石固(gu)(gu)(gu)化(hua)(hua)效(xiao)(xiao)果不好，經(jing)過(guo)酸化(hua)(hua)或鹽化(hua)(hua)處理，其固(gu)(gu)(gu)化(hua)(hua)性能成倍(bei)提高。其次(ci)，重金屬(shu)復(fu)合污染(ran)風險加(jia)(jia)大，多(duo)種固(gu)(gu)(gu)化(hua)(hua)材料(liao)按照合適(shi)比例配施(shi)能極(ji)大提高固(gu)(gu)(gu)化(hua)(hua)修復(fu)效(xiao)(xiao)果。最后，與生物技術和耕作(zuo)環境結合，加(jia)(jia)強(qiang)對固(gu)(gu)(gu)化(hua)(hua)材料(liao)本身及其應用(yong)技術的研究。  

(3)重金屬(shu)化學(xue)固化理論研究  

與國(guo)外相比，國(guo)內土壤重(zhong)(zhong)金(jin)屬污染修復起步(bu)較晚，由(you)于(yu)實(shi)驗條件和(he)試驗設備所限，對重(zhong)(zhong)金(jin)屬固(gu)化機理研究的還(huan)有待深入。射線特別是X射線吸收光譜分析有助(zhu)于(yu)了解固(gu)化金(jin)屬離子的價態，配(pei)位形(xing)式(shi)和(he)賦存形(xing)態，有助(zhu)于(yu)判斷吸附還(huan)是沉淀，內層(ceng)絡(luo)(luo)合還(huan)是外層(ceng)絡(luo)(luo)合，能夠為重(zhong)(zhong)金(jin)屬的配(pei)位形(xing)態和(he)微觀結構提供最直接的證(zheng)據。  

繼(ji)續加強(qiang)基礎理論研究，弄清(qing)重(zhong)金屬的化(hua)學(xue)固化(hua)過程與(yu)機理，對重(zhong)金屬固化(hua)修復尤為(wei)迫切，具有重(zhong)要的現(xian)實意(yi)義。

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