PVC濃度對(duì)熱處理過(guò)程中Pb遷移轉(zhuǎn)化的影響

程翔翔,章 驊,2,邵立明,2,何品晶,2

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PVC濃度對(duì)熱處理過(guò)程中Pb遷移轉(zhuǎn)化的影響

程翔翔1,章 驊1,2*,邵立明1,2,何品晶1,2

(1.同濟(jì)大學(xué)固體廢物處理與資源化研究所,上海 200092；2.住房和城鄉(xiāng)建設(shè)部村鎮(zhèn)建設(shè)司,農(nóng)村生活垃圾處理技術(shù)研究與培訓(xùn)中心,上海 200092)

生活垃圾熱處理過(guò)程中含氯化合物的存在會(huì)使重金屬轉(zhuǎn)化為顆粒更小、更易揮發(fā)的重金屬氯化物,擴(kuò)大其環(huán)境影響.本文采用熱分析和管式爐模擬法,研究在不同氣氛下城市生活垃圾中典型有機(jī)氯化物——聚氯乙烯(PVC)對(duì)重金屬Pb遷移轉(zhuǎn)化的影響.結(jié)果表明,PVC和PbO共存的體系中,PVC在250℃左右熱分解產(chǎn)生HCl,并與PbO反應(yīng)生成PbCl2(501℃左右開(kāi)始揮發(fā))而促進(jìn)Pb遷移進(jìn)入煙氣.當(dāng)Cl:Pb物質(zhì)的量比為2,3,5和10時(shí),在空氣氣氛下PVC濃度的增加對(duì)Pb的揮發(fā)沒(méi)有顯著影響,而在氮?dú)鈿夥障?Cl:Pb=3時(shí),Pb揮發(fā)率最大,達(dá)到88.19%,Cl:Pb=2時(shí),Pb揮發(fā)率最小,為68.60%.

熱處理；聚氯乙烯；氯化鉛；遷移

熱處理具有減量化、回收能源、完全分解有機(jī)物、徹底殺害病原菌等優(yōu)點(diǎn),因此在生活垃圾處理工藝中占據(jù)的比例越來(lái)越高.2017年我國(guó)城市生活垃圾焚燒量已達(dá)到8463.3萬(wàn)t,同比增長(zhǎng)了14.7%[1].但是隨著國(guó)家污染排放標(biāo)準(zhǔn)日益嚴(yán)格以及人們對(duì)生活環(huán)境要求日益提高,焚燒等熱處理過(guò)程帶來(lái)的重金屬和二噁英污染問(wèn)題也受到廣泛關(guān)注.

重金屬在焚燒等熱處理過(guò)程中的遷移轉(zhuǎn)化途徑主要有3種[2]:重金屬及其化合物不參與熱轉(zhuǎn)化反應(yīng),或反應(yīng)生成不易揮發(fā)的產(chǎn)物,最終留在底渣中;部分粒徑在1~100μm之間的含重金屬顆粒被高溫?zé)煔鈯A帶進(jìn)入煙氣進(jìn)而被捕集在飛灰中,如含Ni和Cr等的顆粒;重金屬及煙氣經(jīng)過(guò)同相吸附或異相吸附過(guò)程進(jìn)入飛灰.

研究表明,生活垃圾焚燒過(guò)程中,47%~73%的Cd和60%~100%的Hg會(huì)進(jìn)入飛灰中,而74%~94%的Zn和46%~79%的Pb富集在爐渣中,飛灰中Hg、Cd、Pb、Zn等重金屬的濃度顯著高于爐渣[3].重金屬Pb、Cu和Zn等在熱處理過(guò)程中和含氯化合物反應(yīng),生成更易揮發(fā)、顆粒更小的重金屬氯化物,從而遷移至煙氣中[4].其中冷凝形成的亞微米顆粒能夠穿過(guò)尾氣處理裝置,進(jìn)入到空氣、水體或富集在食物鏈中,造成環(huán)境危害[5].Pb是一種毒性很大的重金屬,長(zhǎng)時(shí)間暴露于Pb環(huán)境中會(huì)造成人體中樞神經(jīng)系統(tǒng)、造血功能以及肝腎功能紊亂,嚴(yán)重時(shí)會(huì)導(dǎo)致腦缺氧死亡[6].生活垃圾中Pb含量約為10~50mg/kg[7-9],易發(fā)生氯化反應(yīng)而遷移至煙氣或飛灰中[10]而引起較大的環(huán)境影響,因此是生活垃圾焚燒處理最受關(guān)注的重金屬污染物之一[11-13].本文以Pb為對(duì)象,研究其在熱處理過(guò)程中的遷移轉(zhuǎn)化行為.

研究者們采用熱平衡計(jì)算法[14-15]、熱分析法[16-17]、管式爐模擬法[14,18-19]、流化床法[20-21]和水泥窯共處置模擬法[22]等方法,對(duì)重金屬在熱處理過(guò)程中的氯化反應(yīng)途徑進(jìn)行了一系列研究.結(jié)果表明,除氯化劑種類[15,23]外,反應(yīng)條件如停留時(shí)間[24-25]、反應(yīng)溫度[24-27]、反應(yīng)物濃度[17,28-29]、氣體流速[25]、水蒸汽含量[16,28]等均對(duì)重金屬的遷移轉(zhuǎn)化有顯著的影響.利用重金屬氯化反應(yīng),還可進(jìn)行資源回收和污染控制.如Nowak等[23,25-26]采用不同種類的無(wú)機(jī)氯化物處理城市生活垃圾焚燒飛灰,回收重金屬;Vogel等[24,30]利用聚氯乙烯(PVC)和HCl去除污泥灰中的重金屬,并通過(guò)添加MgO提高P的生物可利用性,實(shí)現(xiàn)污泥中P資源的回收.

目前的研究主要采用真實(shí)垃圾或根據(jù)垃圾組成配制樣品,熱處理過(guò)程中多種宏量金屬、微量重金屬、不同氯源同時(shí)存在,重金屬揮發(fā)和固定反應(yīng)之間的競(jìng)爭(zhēng)作用共同影響重金屬的遷移和轉(zhuǎn)化規(guī)律,從而限制了重金屬氯化反應(yīng)機(jī)理解析.Wang等[31-32]以簡(jiǎn)單體系模擬關(guān)鍵反應(yīng)物,研究了4種重金屬氧化物(PbO、CdO、ZnO和CuO)的氯化反應(yīng).但并未對(duì)影響重金屬氯化反應(yīng)的重要因素——氯濃度進(jìn)行研究.熱處理過(guò)程中有機(jī)氯比無(wú)機(jī)氯對(duì)于重金屬揮發(fā)的促進(jìn)作用更大[32-33],Watanabe等[34]將生活垃圾中可燃氯歸為有機(jī)氯,其含量為2.7mg/g,而含氯量在50%~60%之間的PVC被廣泛應(yīng)用于日用品、管材、線纜等塑料制品,是廢棄物中有機(jī)氯的主要成分(含量波動(dòng)大),在熱處理過(guò)程中易和重金屬反應(yīng)而促進(jìn)其揮發(fā).因此本研究采用熱分析系統(tǒng)和管式爐結(jié)合的方法模擬熱處理過(guò)程,以垃圾中典型有機(jī)氯PVC和主要的重金屬污染物Pb為對(duì)象,研究Pb的氯化機(jī)理和氯化物濃度對(duì)重金屬Pb揮發(fā)的影響.

1 實(shí)驗(yàn)方法

1.1 樣品制備

將黃色PbO(分析純,國(guó)藥集團(tuán)化學(xué)試劑有限公司)置于105℃烘箱中干燥24h后,與PVC(分析純,西格瑪奧德里奇上海貿(mào)易有限公司,分子量48000,粒徑75~150μm),按Cl:Pb物質(zhì)的量比為2:1,3:1,5:1和10:1(PVC質(zhì)量百分比見(jiàn)表1)配制樣品(2PVC、3PVC、5PVC和10PVC),在瑪瑙研缽中研磨,使樣品混合均勻.實(shí)際生活垃圾中Cl和Pb物質(zhì)的量比一般大于300,但鑒于有機(jī)氯的占比(波動(dòng)較大)、其它重金屬的競(jìng)爭(zhēng)反應(yīng),本研究考查了適量(2PVC)和過(guò)量(3~10PVC)的情況.

表1 實(shí)驗(yàn)樣品中PVC與PbO的質(zhì)量分?jǐn)?shù)和摩爾分?jǐn)?shù)(%)

1.2 熱分析實(shí)驗(yàn)

采用熱重(TG)和差示掃描量熱(DSC)聯(lián)用的同步熱分析儀(德國(guó)Netzsch公司,STA449F5),連接傅里葉紅外光譜儀(FTIR,德國(guó)Bruker公司, TENSOR 37),在空氣或氮?dú)鈿夥?流速100mL/min)中測(cè)試樣品(13mg左右),每個(gè)樣品2個(gè)平行.升溫程序設(shè)置成50~900℃,升溫速率10℃/min,停留時(shí)間為60min.

1.3 管式爐模擬實(shí)驗(yàn)

將盛有(2.00±0.01)g樣品的剛玉舟置于管式爐的石英管中,在空氣或氮?dú)鈿夥障?流速均為1L/ min),從室溫加熱至900℃,升溫速率和終點(diǎn)溫度停留時(shí)間分別為6℃/min和60min.石英管末端放置石英冷凝環(huán)用以收集冷凝產(chǎn)物.根據(jù)美國(guó)環(huán)保署Method 29[35],石英管末端連接6個(gè)吸收瓶,第1個(gè)為空瓶,第2~5個(gè)吸收瓶?jī)?nèi)裝有100mL 5% HNO3(/)和10% H2O2(/)的混合溶液,用于吸收重金屬,第6個(gè)吸收瓶?jī)?nèi)加入硅膠,所有吸收瓶置于裝有冰水混合物的容器中.實(shí)驗(yàn)設(shè)置2個(gè)平行.

1.4 產(chǎn)物分析

采用X射線衍射儀(XRD,德國(guó)Bruker公司, D8Advance),分析管式爐模擬實(shí)驗(yàn)中冷凝環(huán)收集的冷凝產(chǎn)物和剛玉舟中的底渣產(chǎn)物.工作電流40mA,電壓40kV,步長(zhǎng)為0.02°,每步掃描時(shí)間0.1s.

固相底渣采用四酸消解法(HCl、HNO3、HF和HClO4)消解,消解后用等離子體發(fā)射光譜儀(ICP- OES,美國(guó)Agilent公司,720ES)測(cè)試Pb濃度.

2 結(jié)果與討論

2.1 PVC-PbO反應(yīng)機(jī)理

如圖1所示,PVC熱分解經(jīng)歷了2個(gè)階段.第一階段PVC失重溫度范圍分別為228~358℃(空氣)、239~381℃(氮?dú)?,失重量分別為62.85%(空氣)和64.12%(氮?dú)?,該階段2種氣氛下PVC分解過(guò)程相似:PVC脫除HCl形成共軛雙鍵,并生成少量H2O和苯等芳香烴化合物(圖2的FTIR圖譜),與其他研究結(jié)果一致[17,31,36-37].該過(guò)程為吸熱反應(yīng),在280℃左右出現(xiàn)吸熱峰.第二階段空氣和氮?dú)鈿夥障碌腜VC熱分解有明顯區(qū)別.空氣氣氛下失重溫度范圍為419~600℃,失重量為36.58%,DSC曲線在550℃左右有很強(qiáng)的放熱峰,因?yàn)樵摐囟认職埩舻腜VC分解產(chǎn)物被迅速氧化,釋放出大量的熱量.如圖2所示,此過(guò)程的產(chǎn)物主要是CO2、H2O以及少量的CO和苯.而氮?dú)鈿夥障碌氖е販囟确秶鸀?02~552℃,失重量為29.98%,DSC曲線在440,500℃左右出現(xiàn)吸熱峰,分別對(duì)應(yīng)于第一階段生成產(chǎn)物的縮合反應(yīng)(生成多環(huán)芳烴)[36]和焦油揮發(fā).溫度大于500℃時(shí),焦油和揮發(fā)性物質(zhì)從液相中脫離,殘?zhí)恳怨潭ㄌ嫉男问搅粼诘自衃37].

圖1 PVC的熱重(TG)和差示掃描量熱(DSC)曲線

箭頭表示DSC放熱峰方向

圖2 特征溫度下PVC熱分解氣相產(chǎn)物的傅里葉紅外光譜(FTIR)圖譜

PVC-PbO體系在空氣和氮?dú)鈿夥障碌臒岱治鼋Y(jié)果分別如圖3、4所示,也顯示為2個(gè)階段.空氣氣氛下第一階段(280~330℃)PVC-PbO體系失重峰值和放熱峰值溫度范圍為300~320℃,比純PVC(280℃)高20~40℃左右.2PVC、3PVC、5PVC和10PVC在第一階段的失重率見(jiàn)表2,均低于樣品所含PVC在該階段的理論失重率(由式1計(jì)算,分別為22.56%、28.69%、36.66%和46.31%),純PVC的DSC曲線在280℃左右為吸熱峰,而PVC-PbO體系在該溫度下出現(xiàn)放熱峰,表明PVC和PbO在該階段發(fā)生了反應(yīng).而且隨著PVC濃度增加,放熱峰的面積逐漸減小,表明釋放的熱量也在相應(yīng)減小,這是反應(yīng)物的相對(duì)比例減小了的緣故.

根據(jù)FTIR結(jié)果(圖5),PVC-PbO體系檢測(cè)到HCl的時(shí)間和HCl達(dá)到峰值的時(shí)間均比純PVC體系晚2~3min,管式爐模擬實(shí)驗(yàn)中PVC與PbO反應(yīng)的冷凝產(chǎn)物中檢測(cè)到PbCl2的存在(圖6、8),說(shuō)明PVC是通過(guò)分解產(chǎn)生HCl然后和PbO發(fā)生反應(yīng)生成PbCl2(熔點(diǎn)為501℃)和H2O,從而使PVC-PbO體系第一階段的失重量比PVC體系小. PVC剛開(kāi)始分解時(shí)產(chǎn)生的HCl量較少,全部與PbO反應(yīng)生成PbCl2,隨著溫度升高,H2O產(chǎn)生及HCl產(chǎn)生量增多而逸出,體系開(kāi)始失重.

圖3 空氣氣氛下PVC-PbO體系的熱重(TG)和差示掃描量熱(DSC)曲線

箭頭表示DSC放熱峰方向

箭頭表示DSC放熱峰方向

圖5 空氣氣氛下PVC-PbO體系特征產(chǎn)物HCl的FTIR圖譜

2.2 PVC濃度對(duì)重金屬Pb揮發(fā)的影響

2.2.1 熱分析實(shí)驗(yàn)結(jié)果 在空氣氣氛下,PVC-PbO體系總失重率為93%~97%(圖3),且隨著PVC濃度的增大而增大.2PVC、3PVC、5PVC和10PVC在第一階段的失重率分別為10.07%、18.48%、25.45%和40.44%,在第二階段的失重量分別為80.71%、70.15%、67.32%和54.80%(表2),失重溫度范圍為430~690℃,DSC曲線顯示為2個(gè)放熱峰,分別位于480℃和570℃左右.第二階段2PVC、3PVC、5PVC和10PVC體系所含PVC理論失重率(由式1計(jì)算)為13.13%、16.70%、21.34%和26.96%,遠(yuǎn)小于體系在該階段的實(shí)際失重率,是因?yàn)槌薖VC脫HCl后的產(chǎn)物在空氣中氧化生成CO2和H2O之外,還有第一階段的氯化產(chǎn)物PbCl2在溫度達(dá)到熔點(diǎn)(501℃)后揮發(fā)導(dǎo)致的.

PVC-PbO體系熱處理后的殘?jiān)M分為未完全反應(yīng)的PbO和源自PVC的少量殘余物質(zhì)(氧氣氣氛下為PVC中的極少量灰分;氮?dú)鈿夥障聻闅執(zhí)亢突曳?,生成的PbCl2可全部揮發(fā).假設(shè)PbO的存在對(duì)PVC熱處理殘余物質(zhì)的量沒(méi)有影響,則可以通過(guò)式2、3計(jì)算在此過(guò)程中Pb的揮發(fā)率,結(jié)果如表2、3所示.

計(jì)算結(jié)果表明空氣氣氛下PVC的濃度對(duì)Pb揮發(fā)影響不大,2PVC、3PVC、5PVC和10PVC中Pb的揮發(fā)率均在90%左右.

氮?dú)鈿夥障翽VC-PbO的總失重率約為85%, PVC濃度的改變對(duì)于體系的總失重幾乎沒(méi)有影響,總失重率低于空氣氣氛是因?yàn)榈獨(dú)鈿夥障翽VC熱解有殘?zhí)可?2PVC、3PVC、5PVC和10PVC在第一階段的失重分別為9.14%、14.65%、27.05%和41.62%,失重溫度范圍為290~350℃;在第二階段的失重分別為69.16%、61.43%、48.59%和42.19%,失重溫度范圍為430~690℃.通過(guò)式2、3計(jì)算Pb的揮發(fā)率,結(jié)果如表3所示.2PVC、3PVC、5PVC和10PVC的Pb揮發(fā)率分別為83.60%、76.72%、66.02%和67.40%.Pb的揮發(fā)率隨著PVC濃度的增加(Cl:Pb從2增至5)而降低.因?yàn)樵诘獨(dú)鈿夥障翽VC產(chǎn)生的殘?zhí)靠珊蚉bO反應(yīng)生成CO或CO2逸出,且PVC含量越高,產(chǎn)生的殘?zhí)吭蕉?逸出的CO和CO2越多,使計(jì)算得到的Pb揮發(fā)率也越低,式3計(jì)算方法會(huì)低估樣品的Pb揮發(fā)率.Cl:Pb繼續(xù)增大至10時(shí),由于樣品中PbO的含量低(只有5PVC時(shí)的63%),殘?zhí)繉?duì)Pb揮發(fā)率的影響較小,因此5PVC和10PVC的揮發(fā)率統(tǒng)計(jì)上無(wú)顯著性差異.

圖6 空氣氣氛下PVC-PbO體系冷凝產(chǎn)物的XRD

圖7 氮?dú)鈿夥障翽VC-PbO體系殘?jiān)a(chǎn)物的XRD

圖8 氮?dú)鈿夥障翽VC-PbO體系冷凝產(chǎn)物的XRD

2.2.2 管式爐模擬實(shí)驗(yàn)結(jié)果 管式爐模擬實(shí)驗(yàn)通過(guò)測(cè)量剛玉舟上底渣中Pb的含量,利用差值法計(jì)算Pb的揮發(fā)率.如圖9所示,2PVC、3PVC、5PVC和10PVC在空氣氣氛下的Pb揮發(fā)率分別為(91.47±1.23)%、(95.32±1.45)%、(87.48±2.32)%和(89.77±1.38)%,與熱分析實(shí)驗(yàn)理論計(jì)算結(jié)果相似;在氮?dú)鈿夥障翽b的揮發(fā)率分別為(68.60±3.51)%、(88.19±0.75)%、(76.56±3.01)%和(83.10±1.85)%,均低于在空氣氣氛下的Pb揮發(fā)率,在PVC含量相對(duì)較少(2PVC)時(shí)尤其明顯.這是因?yàn)檠鯕鈪⑴c了HCl向Cl2的轉(zhuǎn)化[29],提高了重金屬氯化反應(yīng)效率[25].采用單因素方差分析研究PVC濃度對(duì)Pb揮發(fā)率影響的顯著性,結(jié)果表明空氣氣氛下PVC濃度的改變對(duì)Pb揮發(fā)不具有顯著性影響,而氮?dú)鈿夥障翽VC濃度的改變對(duì)Pb揮發(fā)有顯著性影響.這可能是因?yàn)樵诳諝鈿夥障卵鯕獾拇嬖趯?dǎo)致Pb揮發(fā)率相對(duì)較高,所以PVC濃度的提高對(duì)于Pb揮發(fā)率的影響不是很顯著.對(duì)氮?dú)鈿夥障虏煌琍VC濃度下Pb揮發(fā)率進(jìn)行t-test顯著性檢驗(yàn),結(jié)果表明Pb揮發(fā)率3PVC>10PVC≈5PVC> 2PVC,5PVC和10PVC之間不具有顯著性差異,氯濃度的適當(dāng)過(guò)量能夠促進(jìn)熱解過(guò)程中Pb的揮發(fā),但是PVC濃度過(guò)高反而會(huì)導(dǎo)致Pb揮發(fā)率的下降,這可能是因?yàn)槁然镌跍囟雀哂谄淙埸c(diǎn)時(shí)熔化形成液體屏障或潤(rùn)濕樣品形成小顆粒,阻礙傳質(zhì)過(guò)程的進(jìn)行[23].當(dāng)Cl:Pb>5時(shí),氮?dú)鈿夥障翽VC濃度的增加對(duì)于Pb的揮發(fā)則沒(méi)有顯著性影響.

底渣和冷凝產(chǎn)物的XRD分析結(jié)果如圖6、7、8所示(空氣氣氛下樣品失重率幾乎達(dá)到95%以上,收集不到底渣,故沒(méi)有底渣的XRD測(cè)試結(jié)果).空氣和氮?dú)鈿夥障滤袠悠返睦淠a(chǎn)物均為PbCl2,表明PbO和PVC發(fā)生氯化反應(yīng),產(chǎn)物為PbCl2,且氯濃度的變化不會(huì)改變氯化反應(yīng)的產(chǎn)物.在氮?dú)鈿夥障?底渣組成均為PbO和Pb2O,說(shuō)明一部分PbO沒(méi)有和PVC分解產(chǎn)生的HCl反應(yīng),而是被殘?zhí)窟€原生成了Pb2O,這也是氮?dú)鈿夥障翽b揮發(fā)率相對(duì)較低的原因之一.

上述研究表明,焚燒和熱解過(guò)程中,Pb與PVC分解的含氯產(chǎn)物均不可避免地發(fā)生氯化反應(yīng).實(shí)際生活垃圾焚燒過(guò)程中,Cl:Pb物質(zhì)的量比通常是過(guò)量的.源頭上減少生活垃圾中的PVC是最有效的熱處理過(guò)程重金屬污染控制的方法.本研究加深了對(duì)重金屬Pb氯化遷移機(jī)理的了解,可為生活垃圾熱處理過(guò)程中Pb污染控制和回收方法發(fā)展提供參考.

圖9 管式爐模擬實(shí)驗(yàn)PVC-PbO體系的Pb揮發(fā)率

表2 空氣氣氛下樣品失重率和Pb揮發(fā)率(%)

表3 氮?dú)鈿夥障聵悠肥е芈屎蚉b揮發(fā)率(%)

3 結(jié)論

3.1 PVC-PbO體系在熱處理過(guò)程中的反應(yīng)可以分為2個(gè)階段.第一階段溫度范圍280~320℃(空氣)或290~350℃(氮?dú)?,PVC先脫氯產(chǎn)生HCl, 然后和PbO發(fā)生氯化反應(yīng)生成PbCl2.第二階段溫度范圍為430~690℃,該階段下PVC進(jìn)一步失重,第一階段生成的PbCl2也開(kāi)始受熱揮發(fā).

3.2 利用殘?jiān)视?jì)算熱分析過(guò)程Pb的理論揮發(fā)率.結(jié)果表明空氣氣氛下Pb揮發(fā)率在90%左右,PVC濃度的改變對(duì)于Pb的揮發(fā)率沒(méi)有顯著影響;氮?dú)鈿夥障掠捎诓糠諴bO被熱解殘?zhí)窟€原,使體系失重率增加,通過(guò)殘?jiān)视?jì)算的Pb揮發(fā)率被低估.

3.3 管式爐模擬實(shí)驗(yàn)結(jié)果表明,空氣氣氛下PVC濃度的改變對(duì)于Pb的揮發(fā)并沒(méi)有顯著的影響,與熱分析實(shí)驗(yàn)結(jié)果一致.在氮?dú)鈿夥障?3PVC具有最大的失重率和Pb揮發(fā)率.空氣氣氛下Pb的揮發(fā)率比氮?dú)鈿夥障赂?PVC濃度的變化不會(huì)改變Pb和PVC的反應(yīng)途徑,氣相冷凝產(chǎn)物均為PbCl2,氮?dú)鈿夥障碌牡自a(chǎn)物則為PbO和Pb2O.

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Effect of PVC concentration on the transformation and migration of Pb during thermal treatment.

CHENG Xiang-xiang1, ZHANG Hua1,2*, SHAO Li-ming1,2, HE Pin-jing1,2

(1.Institute of Waste Treatment and Reclamation, Tongji University, Shanghai 200092, China；2.Centre for the Technology Research and Training on Household Waste in Small Towns & Rural Area, Ministry of Housing and Urban-Rural Development, Shanghai 200092, China)., 2019,39(4)：1645~1653

The migration and release of heavy metals during thermal treatment of municipal solid waste (MSW) is an environmental issue of great concern. Chlorine-containing compounds present in MSW could convert heavy metals into smaller particles and volatile chlorides during thermal treatment, thus cause serious environmental pollution. In this study, thermogravimetric analysis and tube furnace were used to investigate the effect of polyvinyl chloride (PVC) on the transformation and migration of Pb under different atmosphere. The results showed that PVC decomposed at 250°C, and then the released HCl reacted with PbO to form PbCl2(melting point: 501°C), which promoted the migration of Pb into the flue gas. The concentration of PVC (at the molar ratios of Cl:Pb = 2, 3, 5, and 10) had no significant effect on the volatilization of Pb under air atmosphere. While under N2atmosphere, the highest volatility of Pb could reach 88.19% at the molar ratio of Cl:Pb=3; the lowest volatility of Pb was 68.60% at the molar ratio of Cl:Pb=2.

thermal treatment；polyvinyl chloride；lead chloride；migration

X799.3

A

1000-6923(2019)04-1645-09

2018-09-27

國(guó)家自然科學(xué)基金資助項(xiàng)目(21577102)

*責(zé)任作者, 教授, 06120@#edu.cn

程翔翔(1994-),男,江西上饒人,同濟(jì)大學(xué)碩士研究生,主要從事固體廢物熱處理研究.