飛灰螯合劑中揮發(fā)性污染物的釋放

章 驊,曾佳瑋,呂 凡,邵立明,何品晶*

飛灰螯合劑中揮發(fā)性污染物的釋放

章 驊1,2,曾佳瑋1,呂 凡1,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.上海污染控制與生態(tài)安全研究院,上海 200092)

采集了4個(gè)市售飛灰螯合劑樣品,分析其在20,40℃下?lián)]發(fā)性污染物的釋放規(guī)律.結(jié)果表明,釋放的揮發(fā)性污染物主要有甲醛、乙醛、苯、異戊醛/異丙醇、甲硫醇、乙硫醇等;其中3個(gè)螯合劑樣品甲醛的釋放濃度在20 ℃為748~1325 μg/L-螯合劑,占釋放的易揮發(fā)污染物的68%~96%(質(zhì)量比),在40 ℃為4282~6822 μg/L-螯合劑,占釋放的易揮發(fā)污染物的87%~95%(質(zhì)量比).隨著溫度升高,釋放的揮發(fā)性污染物種類變多,部分污染物濃度增加,40 ℃時(shí),4個(gè)螯合劑樣品釋放的易揮發(fā)污染物濃度比20 ℃時(shí)增加了142%~444%.元素分析、拉曼光譜和熱重分析結(jié)果表明,4個(gè)螯合劑的主要有效成分相似,為二硫代氨基甲酸鹽類物質(zhì).因此,推測(cè)這種飛灰螯合劑在稀釋和飛灰穩(wěn)定化過(guò)程中,對(duì)工作人員的健康可能有潛在的危害風(fēng)險(xiǎn),應(yīng)收集釋放的氣體并進(jìn)行處理;且在飛灰填埋過(guò)程中,可能會(huì)導(dǎo)致滲濾液中NH4+-N等物質(zhì)的濃度升高,增加滲濾液的處理難度.

飛灰；螯合劑；二硫代氨基甲酸鹽；揮發(fā)性污染物；空氣污染

由于快速城市化、人口增長(zhǎng)和工業(yè)化,全球產(chǎn)生的城市固體廢物數(shù)量持續(xù)增加[1-2].據(jù)世界銀行估計(jì),到2025年,全球產(chǎn)生的城市固體廢物量將達(dá)到610萬(wàn)t/d[2].由于填埋容量有限,生活垃圾焚燒發(fā)電以其無(wú)害化、減量化、穩(wěn)定化和能源利用的優(yōu)點(diǎn)[3-5],越來(lái)越被全世界所重視和采用.目前,全世界的生活垃圾焚燒廠已超過(guò)2100座,焚燒生活垃圾量約為2.3億t/a,其中發(fā)達(dá)國(guó)家生活垃圾焚燒量最多的日本、美國(guó)、德國(guó),焚燒量分別為3490,2700,2500萬(wàn)t/a[6].據(jù)統(tǒng)計(jì),從2004~2017年,中國(guó)垃圾焚燒廠的數(shù)量由54座增至286座,焚燒處理量由449萬(wàn)t/a增至8463萬(wàn)t/a[7].

城市固體廢物焚燒處理過(guò)程中,會(huì)產(chǎn)生顆粒物、氮氧化物、硫氧化物、氯化氫以及重金屬等污染物,需通過(guò)煙氣凈化系統(tǒng)(APC)去除這些污染物,從而產(chǎn)生焚燒飛灰.如,我國(guó)爐排爐和流化床生活垃圾焚燒廠煙氣凈化系統(tǒng)產(chǎn)生的飛灰分別占其焚燒垃圾質(zhì)量的3%~5%和10%~20%[8].隨著城市固體廢物焚燒量的增加,飛灰的產(chǎn)生量也相應(yīng)地增加.由于含有重金屬(Pb、Zn、Cr、Cu、Ni、Cd等)、可溶性鹽(NaCl、KCl、CaCl2等)以及痕量劇毒有機(jī)化合物(二噁英、呋喃)[9],飛灰屬于需要特殊處理處置的危險(xiǎn)廢物[10-11].飛灰處理方法通?？煞譃槿怺9,11-12]:固化/穩(wěn)定化、分離(如水洗、酸洗)、熱處理(如熔融、燒結(jié)).其中,水泥固化(添加水泥和水將飛灰轉(zhuǎn)化為低滲透性的塊狀固體[13])和化學(xué)藥劑穩(wěn)定化(添加化學(xué)藥劑將有毒有害污染物轉(zhuǎn)變?yōu)榈腿芙庑浴⒌头磻?yīng)性、低遷移性及低毒性物質(zhì))使用最普遍.已有研究者使用可溶性磷酸鹽[14-22]、螯合劑[14,23-24]、硫酸亞鐵[25-28]、膠體鋁酸鹽[29]、可溶性硅酸鹽[30-32]和硫化鈉[33],研究了飛灰穩(wěn)定化處理效果.由于螯合劑穩(wěn)定化工藝具有室溫下運(yùn)行、操作靈活、絡(luò)合重金屬能力強(qiáng)、無(wú)需預(yù)處理(如pH值控制)[24,33-34],以及比無(wú)機(jī)試劑用量少等優(yōu)點(diǎn),因此在實(shí)際飛灰穩(wěn)定化處理工程中被廣泛使用[35].

乙二胺四乙酸和硫代二乙醇酸、硫脲、二硫代氨基甲酸鹽(DTC)、吡咯烷、亞胺、氨基甲酸酯和硫醇等螯合劑被用于飛灰的固化/穩(wěn)定化[13,29,33,36-39],投加量一般為處理飛灰質(zhì)量的2%~5%[33].其中,DTC對(duì)重金屬的絡(luò)合能力強(qiáng),且處理過(guò)的產(chǎn)物在寬pH值范圍內(nèi)顯示出較高的還原能力和金屬的固定能力,因此在許多國(guó)家和地區(qū)被廣泛使用,例如日本、中國(guó)[13-14].

由于多胺或聚乙烯亞胺分子的氮原子上存在活性氫原子,可以被二硫化碳取代,因此理論上可與二硫化碳反應(yīng)形成二硫代氨基甲酸酯的官能基團(tuán)[23].但是,DTC在水溶液中會(huì)緩慢分解,形成二硫化碳和甲胺或其他胺,且在酸性條件下會(huì)加速其分解,當(dāng)被加熱時(shí)可能會(huì)分解釋放出二硫化碳、硫氧化物、氮氧化物、硫化氫、氨、甲胺等有毒氣體[40].部分飛灰處理車間發(fā)現(xiàn),某些螯合劑在儲(chǔ)存和處理飛灰的過(guò)程中會(huì)散發(fā)出刺激性氣味.螯合劑在儲(chǔ)存和使用的過(guò)程中是否會(huì)釋放有毒有害的揮發(fā)性污染物,如硫化氫、二硫化碳等,對(duì)周圍環(huán)境以及工作人員健康的影響尚不清楚[41-42],需開(kāi)展相應(yīng)的檢測(cè)和研究.

目前關(guān)于螯合劑的研究主要側(cè)重于其與飛灰混合后,飛灰中重金屬的浸出毒性變化情況;與其他種類的穩(wěn)定化方法相比,螯合劑絡(luò)合飛灰重金屬能力的強(qiáng)弱;螯合劑穩(wěn)定后飛灰的長(zhǎng)期穩(wěn)定性[14-15,23-24,27,29,33,35-36,43],而對(duì)螯合劑使用過(guò)程可能存在危害的研究極少.考慮到儲(chǔ)存狀態(tài)下環(huán)境溫度變化的影響,以及與飛灰反應(yīng)過(guò)程的放熱使體系溫度升高的影響,本文采集了4個(gè)市售飛灰螯合劑樣品,分析其在20,40℃下?lián)]發(fā)性污染物釋放情況,從而為飛灰螯合劑穩(wěn)定化過(guò)程可能的氣相污染風(fēng)險(xiǎn)與污染控制提供理論參考.

1 材料與方法

1.1 材料

實(shí)驗(yàn)所用市售螯合劑樣品(A、B、C、D)分別來(lái)自于4家常見(jiàn)的螯合劑生產(chǎn)廠家,為液態(tài)產(chǎn)品.樣品均密封、避光陰涼處保存.所用試劑氧化鈣、濃硝酸、三水合二乙基二硫代氨基甲酸鈉(DDTC)均為分析純.

1.2 螯合劑中揮發(fā)性污染物的釋放

根據(jù)《固定污染源廢氣揮發(fā)性有機(jī)物的采樣氣袋法》(HJ 732-2014)[44]和《水質(zhì)揮發(fā)性有機(jī)物的測(cè)定吹掃捕集氣相色譜法》(HJ 686-2014)[45],測(cè)試螯合劑中揮發(fā)性污染物的釋放.用橡膠軟管將玻璃吸收瓶的首尾段分別與充滿氮?dú)獾臍獯蜐崈魺o(wú)氣體氣袋相連后,取螯合劑5mL置于吸收瓶(水浴恒溫,=20,40℃)內(nèi),隨后啟動(dòng)蠕動(dòng)泵,控制氮?dú)獾臍怏w流速為40mL/min,吹掃時(shí)間為11min.螯合劑吹掃收集的氣體和空白樣品(氮?dú)?分別注入預(yù)濃縮儀(Model 7100A, Entech,美國(guó)),經(jīng)三級(jí)冷阱濃縮后送入GC(Bruker 450GC, Varian,美國(guó)),先用FID檢測(cè)器測(cè)試氣體中醛類、醇類、酮類、苯系物等非硫有機(jī)物,后用PFPD檢測(cè)器測(cè)試硫化氫、二硫化碳以及含硫有機(jī)物.所有氣袋使用前,均先用高純氮?dú)鉀_洗,用預(yù)濃縮儀-GC-FID/PFPD檢測(cè)確認(rèn)氣袋已經(jīng)清洗干凈.吹掃和氣體分析實(shí)驗(yàn)平行開(kāi)展4次.

1.3 螯合劑物理性質(zhì)與基本結(jié)構(gòu)分析

使用pH計(jì)(PXSJ-216F,雷磁,中國(guó))測(cè)量螯合劑樣品的pH值.使用電子天平稱量一定體積的螯合劑,計(jì)算螯合劑樣品的密度.將螯合劑用超純水稀釋1000倍,經(jīng)0.22μm微孔濾膜過(guò)濾后,立即用TOC儀(TOC-VCPH, SHIMADZU,日本)測(cè)定濾液的TOC值.

采用拉曼光譜儀分析螯合劑分子結(jié)構(gòu)(Horiba Jobin Yvon XploRA, HORIBA,法國(guó)),儀器的激發(fā)激光波長(zhǎng)為532nm,功率為50mW,單個(gè)數(shù)據(jù)點(diǎn)的采集時(shí)間為10s.

螯合劑用HNO3法消解后,采用電感耦合等離子體原子發(fā)射光譜儀(Optima 2100DV, PerkinElmer, 美國(guó))測(cè)定金屬濃度.

上述性質(zhì)分析測(cè)試平行開(kāi)展3次.

將螯合劑樣品放入真空冷凍干燥儀(FD-1C,北京博醫(yī)康實(shí)驗(yàn)儀器有限公司,中國(guó))中冷凍干燥至恒重,記錄干燥前后的質(zhì)量變化,用于后續(xù)的元素含量換算.螯合劑冷凍干燥后的固體粉末,以及DDTC藥劑,采用元素分析儀(Vario EL III, Elementar, 德國(guó))測(cè)定元素C、H、N、S含量,采用熱重分析儀(NETZSCH STA 449F5, NETZSCH, 中國(guó))測(cè)量樣品在升溫過(guò)程(50℃上升至900℃,升溫速率為10℃/min;保護(hù)氣氮?dú)獾耐馑俾蕿?0mL/min,載氣空氣或氮?dú)獾耐馑俾蕿?0mL/min)中的失重和吸/放熱,元素分析和熱重分析測(cè)試平行開(kāi)展2次.

2 結(jié)果與討論

2.1 螯合劑易揮發(fā)污染物釋放潛力

2.1.1 螯合劑易揮發(fā)污染物的釋放 4個(gè)螯合劑樣品在不同溫度下(=20,40℃)釋放的易揮發(fā)污染物如圖1所示,能夠檢測(cè)到乙醛、異丁醛、乙酸乙酯、甲醛、丁酮、乙醇、異戊醛/異丙醇(GC出峰位置相同,無(wú)法區(qū)分)、苯、甲苯、乙苯、二甲苯、苯乙烯、硫化氫、羰基硫、甲硫醇、甲硫醚、乙硫醇、二硫化碳和噻吩.這些物質(zhì)如果釋放到環(huán)境中,可能會(huì)給周圍環(huán)境以及工作人員造成危害,如引起鼻炎、咽喉炎等疾病[41,46],長(zhǎng)期暴露于高濃度環(huán)境中甚至可能會(huì)有畸變、癌變等風(fēng)險(xiǎn)[42].

不同螯合劑樣品釋放的易揮發(fā)污染物種類大致相似,釋放濃度也大都比較相近.樣品B、C和D釋放的易揮發(fā)污染物中,甲醛的釋放濃度最高,是螯合劑釋放的主要污染物;=20℃時(shí),甲醛的釋放濃度為748~1325μg/L-螯合劑,占釋放的易揮發(fā)污染物的68%~96%(質(zhì)量比);=40℃時(shí),甲醛的釋放濃度為4282~6822μg/L-螯合劑,占釋放的易揮發(fā)污染物的87%~95%(質(zhì)量比);這也導(dǎo)致不含硫揮發(fā)性有機(jī)污染物的濃度遠(yuǎn)大于含硫揮發(fā)性有機(jī)污染物.在4個(gè)樣品中,樣品D所釋放的易揮發(fā)污染物濃度最高,溫度從20℃上升到40℃時(shí),釋放的甲醛濃度從1325μg/L-螯合劑上升至6822μg/L-螯合劑;乙醛、甲醛和異戊醛/異戊醇這3種物質(zhì)的濃度分別比其他3個(gè)樣品高-62%~2360%、4%~11000%和120%~ 3800%.

不同螯合劑樣品中易揮發(fā)污染物的釋放隨溫度變化的規(guī)律大致一致.=40℃時(shí),樣品A、B、C、D釋放的易揮發(fā)污染物濃度比=20℃時(shí)分別增加了142%、270%、306%、444%.其中,樣品A、B、C、D釋放的乙醛、甲醛等不含硫揮發(fā)性有機(jī)污染物分別增加了46%、267%、299%和443%,這可能是由于溫度的升高導(dǎo)致這些易揮發(fā)物質(zhì)能夠更多地?fù)]發(fā)出來(lái).并且,在=40℃下,收集到的易揮發(fā)物質(zhì)中含硫物質(zhì)的種類變多,H2S、COS、甲硫醚、乙硫醇、CS2和噻吩被檢測(cè)出;4個(gè)樣品的含硫揮發(fā)性污染物釋放的濃度也相應(yīng)地變高,分別增加了375%、536%、3567%、1480%.同時(shí),可以看出部分揮發(fā)性污染物為致臭物質(zhì),例如,H2S、甲硫醇、乙硫醇在濃度極低的情況下,仍具有強(qiáng)烈的惡臭氣味.因此,溫度升高會(huì)導(dǎo)致螯合劑釋放的易揮發(fā)污染物的惡臭強(qiáng)度相應(yīng)增強(qiáng).

不同螯合劑樣品醛類物質(zhì)釋放濃度的差異,可能是因?yàn)轵蟿┑闹苽浜铣煞椒ɑ蛟洗嬖诓町愃鶎?dǎo)致的.由2.2節(jié)螯合劑性質(zhì)分析可知,4個(gè)螯合劑的主要成分均屬于DTC類物質(zhì).而DTC可以甲醛作為交聯(lián)劑[47]進(jìn)行合成,樣品D中DTC類有效組分可能就是通過(guò)這種方式合成,從而導(dǎo)致了樣品D中甲醛的濃度遠(yuǎn)高于樣品A.

a,b為醇/醛類物質(zhì);c,d為苯類物質(zhì);e,f為含硫類物質(zhì)

2.1.2 螯合劑易揮發(fā)污染物的潛在危害 根據(jù)螯合劑樣品的氣相污染物釋放結(jié)果,可以看出部分易揮發(fā)組分為致臭物質(zhì),例如,H2S、甲硫醇、甲硫醚.因此,將致臭物質(zhì)的嗅閾值[48]作為基準(zhǔn),根據(jù)各樣品易揮發(fā)污染物的氣體濃度與其嗅閾值的比值,評(píng)估各污染物的潛在危害程度,結(jié)果如圖2所示.在20℃下,樣品A、B的易揮發(fā)污染物中,甲硫醇與其嗅閾值的比值最大,樣品C、D的易揮發(fā)污染物中,乙醛與其嗅閾值的比值最大.在40℃下,樣品B、C和D的易揮發(fā)污染物中,乙硫醇與其嗅閾值的比值最大,且各揮發(fā)性污染物與其嗅閾值的比值之和比20℃時(shí)增加了450%~1300%;而樣品A的易揮發(fā)污染物中,與嗅閾值比值最大的仍是甲硫醇,但與20℃時(shí)相比,降低了56%,其它3個(gè)樣品釋放的甲硫醇與其嗅閾值的比值也均有所降低,說(shuō)明溫度升高不會(huì)增加甲硫醇釋放.由上述結(jié)果可知,在螯合劑樣品釋放的致臭性污染物中,應(yīng)該重點(diǎn)關(guān)注乙硫醇、乙醛和甲硫醇的釋放情況.

將4個(gè)螯合劑樣品釋放的易揮發(fā)污染物濃度與《工作場(chǎng)所有害因素職業(yè)接觸限值化學(xué)有害因素》(GBZ 2.1-2007)[49]中相應(yīng)物質(zhì)的限值濃度進(jìn)行對(duì)比,如表1所示,發(fā)現(xiàn)樣品B、C、D釋放的甲醛氣體濃度遠(yuǎn)大于標(biāo)準(zhǔn)中最高容許濃度(0.5mg/m3).表明螯合劑中甲醛的釋放可能會(huì)引起職業(yè)健康危害角度,需引起重視.

因此,在螯合劑儲(chǔ)存、配制和穩(wěn)定化處理飛灰過(guò)程中,應(yīng)注意這些致臭性(乙硫醇、乙醛和甲硫醇)和有害污染物(甲醛)揮發(fā)釋放帶來(lái)的健康與環(huán)境污染風(fēng)險(xiǎn).工作人員需要做好充分的保護(hù)措施;同時(shí)對(duì)于周圍環(huán)境的污染情況,也需要采取相應(yīng)的措施,如及時(shí)通風(fēng)、或局部抽氣收集氣體后進(jìn)行相應(yīng)的處理等.

圖2 4個(gè)螯合劑樣品揮發(fā)性污染物濃度與嗅閾值的比值

2.2 螯合劑物理性質(zhì)與基本結(jié)構(gòu)

4個(gè)螯合劑樣品的性質(zhì)如表2所示,可以看出4個(gè)螯合劑的元素組成相近,根據(jù)元素分析結(jié)果可推測(cè)螯合劑的化學(xué)式為:C3.0H7.5-8.3NS1.6-1.7Na0.3-0.4.

通過(guò)拉曼光譜儀,對(duì)螯合劑的官能團(tuán)結(jié)構(gòu)進(jìn)行檢測(cè)(圖3),并參照分析化學(xué)手冊(cè)[50]對(duì)主要的特征拉曼峰進(jìn)行指認(rèn)和比對(duì),結(jié)果見(jiàn)表3.

900~800cm-1范圍內(nèi)為—C—C—的伸縮振動(dòng)帶,420~150cm-1和970~960cm-1范圍內(nèi)為—C—C—的扭曲振動(dòng)帶;3550~3350cm-1和3450~3300cm-1范圍內(nèi)分別為官能團(tuán)RNH2的N—H不對(duì)稱和對(duì)稱伸縮振動(dòng)帶;2820~2763cm-1范圍內(nèi)為官能團(tuán)N—CH2的CH2對(duì)稱伸縮振動(dòng)帶;1420~1260cm-1和1140~ 940cm-1范圍內(nèi)分別為官能團(tuán)N—C=S的C=S和C—N振動(dòng)之間強(qiáng)烈偶合的振動(dòng)帶.從圖3可以看出4個(gè)螯合劑的分子結(jié)構(gòu)相似,且均含有上述官能團(tuán)的特征拉曼位移.同時(shí),將樣品A原液與標(biāo)準(zhǔn)樣品((C2H5)2NCS2Na×3H2O)配制的溶液的拉曼光譜圖進(jìn)行比較,發(fā)現(xiàn)在相同拉曼位移范圍內(nèi),兩者具有相似的拉曼光譜圖,推測(cè)這4個(gè)螯合劑的官能團(tuán)與標(biāo)準(zhǔn)樣品((C2H5)2NCS2Na×3H2O)相似,均屬于DTC類物質(zhì).

表1 測(cè)試螯合劑中部分易揮發(fā)污染物的氣體濃度及其在工作場(chǎng)所空氣中的容許濃度

注:"OELs"表示職業(yè)接觸值,"MAC"表示最高容許濃度,"PC-TWA"表示時(shí)間加權(quán)平均容許濃度,"PC-STEL"表示短時(shí)間接觸容許濃度,"-"表示未檢測(cè)到(低于檢測(cè)限).

表2 測(cè)試螯合劑的基本性質(zhì)

由圖3可知,樣品A冷凍干燥后獲得的固體樣品與原液的拉曼光譜圖基本一致,可以看出固體樣品的分子結(jié)構(gòu)并沒(méi)有受到破壞,可以用于熱重分析.4個(gè)螯合劑冷凍干燥后的固體樣品和標(biāo)準(zhǔn)樣品((C2H5)2NCS2Na×3H2O)的熱重、熱流分析結(jié)果如圖4~5所示.可以看出,4個(gè)螯合劑和標(biāo)準(zhǔn)樣品的失重和吸放熱情況相似.在氮?dú)鈿夥障?=90~130℃時(shí),4個(gè)螯合劑和標(biāo)準(zhǔn)樣品均存在一個(gè)吸熱峰,前者的失重率約為20%,后者的失重率約為30%,此階段應(yīng)為脫水階段;4個(gè)螯合劑樣品分別在=290~300℃和=340~360℃時(shí)各存在一個(gè)吸熱峰,總失重率約為46%,而標(biāo)準(zhǔn)樣品在=320~360℃時(shí)存在一個(gè)吸收峰,失重率約為40%,此時(shí)4個(gè)螯合劑和標(biāo)準(zhǔn)樣品應(yīng)發(fā)生了分解反應(yīng).在空氣氣氛下,=80~120℃時(shí),4個(gè)螯合劑和標(biāo)準(zhǔn)樣品均存在一個(gè)吸收峰,4個(gè)螯合劑樣品的失重率約為14%,標(biāo)準(zhǔn)樣品的失重率約為28%,此階段應(yīng)也為脫水階段;4個(gè)螯合劑樣品分別在= 260~290℃、=300~330℃和=400~500℃時(shí)各存在一個(gè)放熱峰,總失重率約為45%,而標(biāo)準(zhǔn)樣品在=300~330℃和=440~500℃時(shí)各存在一個(gè)放熱峰,總失重率約為28%,此時(shí)4個(gè)螯合劑和標(biāo)準(zhǔn)樣品應(yīng)發(fā)生了氧化反應(yīng).在空氣氣氛下的總失重率小于氮?dú)鈿夥障碌目偸е芈?且空氣氣氛下的樣品均在=840℃附近存在一個(gè)熔融峰,說(shuō)明氧化反應(yīng)生成了Na2SO4,在該溫度下熔融.

綜合上述分析推斷,4個(gè)螯合劑的主要成分均屬于DTC類物質(zhì).同時(shí),根據(jù)DTC的相關(guān)資料[39],可以看出螯合劑釋放的易揮發(fā)污染物不僅來(lái)自于螯合劑制備過(guò)程中生成的副產(chǎn)物;也來(lái)自于螯合劑本身的緩慢分解釋放,且這種分解釋放速率會(huì)受到溫度等環(huán)境因素的影響.這也相應(yīng)地印證了2.1中的部分測(cè)試結(jié)果,如,在=40℃時(shí)檢測(cè)到了在=20℃未檢測(cè)到的二硫化碳.

并且,根據(jù)螯合劑的主要有效成分可知,螯合劑除了會(huì)釋放出上述所測(cè)得的易揮發(fā)污染物外,也應(yīng)會(huì)釋放出氨、甲胺等含氮類物質(zhì).這些含氮類物質(zhì)可能不僅有毒有害,也可能會(huì)在飛灰填埋過(guò)程中通過(guò)浸出的方式進(jìn)入滲濾液中,造成滲濾液氨氮濃度升高等污染.

表3 相關(guān)分子基團(tuán)及其對(duì)應(yīng)的特征拉曼位移

圖3 4個(gè)螯合劑和標(biāo)準(zhǔn)樣品的拉曼光譜

3 結(jié)論

3.1 飛灰螯合劑釋放的易揮發(fā)組分含有乙醛、甲醛、異戊醛/異丙醇、苯、甲硫醇、乙硫醇等,且隨著溫度升高,易揮發(fā)污染物濃度增加、種類增多.

3.2 隨著溫度升高,螯合劑釋放的甲硫醇、乙醛、乙硫醇等致臭物質(zhì)的惡臭強(qiáng)度相應(yīng)地增強(qiáng);且其中3個(gè)螯合劑釋放的甲醛濃度高,可能會(huì)導(dǎo)致其揮發(fā)至氣相中的濃度超過(guò)工作場(chǎng)所空氣中的容許濃度.因此,在螯合劑儲(chǔ)存、配制和穩(wěn)定化處理飛灰過(guò)程中,應(yīng)注意其揮發(fā)釋放帶來(lái)的健康與環(huán)境污染風(fēng)險(xiǎn),在整個(gè)飛灰穩(wěn)定化處理處置的操作過(guò)程中,工作人員需要做好相應(yīng)的防護(hù)措施.

3.3 由螯合劑樣品與標(biāo)準(zhǔn)樣品((C2H5)2NCS2Na?3H2O)的組成、拉曼光譜、熱重分析比較可知,這些螯合劑樣品均屬于二硫代氨基甲酸鹽類物質(zhì).可能會(huì)分解釋放出氨、甲胺等含氮類物質(zhì),而這些物質(zhì)可能會(huì)在飛灰填埋過(guò)程中導(dǎo)致滲濾液中氨氮濃度升高,影響后續(xù)的滲濾液處理處置.

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Release of volatile pollutants from four chelating agents used for stabilization of fly ash.

ZHANG Hua1,2, ZENG Jia-wei1, Lü Fan1, SHAO Li-ming1,2, HE Pin-jing1,2*

(1.Institute of Waste Treatment and Reclamation, Tongji University, Shanghai 200092, China；2.Institute of Pollution Control and Ecological Safety, Shanghai 200092, China)., 2019,39(12)：5182~5190

Four commercially available chelating agents used for fly ash stabilization were collected and used to study the releasing characteristic of volatile pollutants at 20℃ and 40℃. The results showed that the released volatile pollutants were composed of formaldehyde, acetaldehyde, benzene, isovaleraldehyde/isopropanol, methyl mercaptan, ethyl mercaptan and so on. Among the volatile pollutants released from three chelating agent samples, the concentration of formaldehyde was the highest; at 20°C, the concentration of formaldehyde was 748~1325 μg/L-chelating agent, accounting for 68%~96%(mass ratio) of the released volatile pollutants; at 40℃, the concentration of formaldehyde was 4282~6822 μg/L-chelating agent, accounting for 87%~95% (mass ratio) of the released volatile pollutants. With the increase of temperature, more types of volatile pollutants were released from the chelating agents, and the concentrations of some pollutants increased. At 40℃, the concentrations of the volatile pollutants released from the four chelating agent samples increased by 142% to 444% compared with those at 20℃. Elemental analysis, Raman spectroscopy and thermogravimetric analysis showed that these four chelating agents had similar active ingredients of dithiocarbamates. It suggested that, during the storage, dilution, and fly ash stabilization processes, the pollutants released from this type of chelating agents might be harmful to the health of the operators. Emitted air pollutants should be collected for further treatment. In addition, during the fly ash landfill process, the residual chelating agents in the fly ash may increase the concentration of ammonia and other substances in the leachate, which would increase the difficulty for leachate treatment.

fly ash；chelating agents；dithiocarbamates；volatile pollutants；air pollution

X705

A

1000-6923(2019)12-5182-09

章 驊(1978-),女,浙江桐廬人,教授,博士,主要從事固體廢物管理全過(guò)程重金屬及微量有機(jī)污染物的遷移規(guī)律與控制機(jī)理.發(fā)表論文50篇.

2019-05-06

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

* 責(zé)任作者, 教授, xhpjk@#edu.cn