大氣中汞的來源
1 主要來源
大(da)氣中(zhong)(zhong)主(zhu)要(yao)汞(gong)污染源(yuan)為燃(ran)(ran)煤(mei)電廠(chang)(chang)(chang)、水(shui)泥(ni)廠(chang)(chang)(chang)以及有關礦物材料的開(kai)采和(he)加工。甲基(ji)汞(gong)同時可從城市(shi)廢物充(chong)填和(he)污水(shui)處理廠(chang)(chang)(chang)直接排出(chu)。燃(ran)(ran)煤(mei)電廠(chang)(chang)(chang)是汞(gong)向大(da)氣排入的最(zui)主(zhu)要(yao)來源(yuan)。上海市(shi)對空(kong)氣中(zhong)(zhong)細粒(li)徑顆粒(li)態(tai)汞(gong)的分析(xi)表明，大(da)氣中(zhong)(zhong)汞(gong)的顆粒(li)物來源(yuan)燃(ran)(ran)煤(mei)約占(zhan)80％左右。
2 燃煤電廠生(sheng)產過程汞的遷移轉化
電廠燃煤(mei)中的(de)汞(gong)(gong)(gong)(gong)經燃燒(shao)通(tong)過煙(yan)氣(qi)(qi)、飛灰(hui)(hui)和灰(hui)(hui)渣以及沖灰(hui)(hui)水(shui)的(de)排放進入大氣(qi)(qi)、土壤(rang)和水(shui)體。由于(yu)(yu)汞(gong)(gong)(gong)(gong)具有揮發(fa)性，電廠用(yong)煤(mei)在粉(fen)碎過程(cheng)中已有部(bu)分(fen)揮發(fa)。煤(mei)粉(fen)進入爐內，隨(sui)著(zhu)溫度升(sheng)高，揮發(fa)出的(de)氣(qi)(qi)態汞(gong)(gong)(gong)(gong)隨(sui)著(zhu)煙(yan)氣(qi)(qi)排放。煙(yan)氣(qi)(qi)進入除塵(chen)設備后，部(bu)分(fen)汞(gong)(gong)(gong)(gong)被(bei)灰(hui)(hui)顆(ke)粒(li)吸附隨(sui)同(tong)殘留在灰(hui)(hui)渣中的(de)汞(gong)(gong)(gong)(gong)一(yi)塊被(bei)排入灰(hui)(hui)場(chang)(chang)。進入大氣(qi)(qi)的(de)汞(gong)(gong)(gong)(gong)通(tong)過干(gan)濕沉(chen)降進入土壤(rang)和水(shui)體。灰(hui)(hui)渣和沖灰(hui)(hui)水(shui)中的(de)汞(gong)(gong)(gong)(gong)進入環境后，其中零價(jia)汞(gong)(gong)(gong)(gong)比(bi)重大，不(bu)易溶(rong)于(yu)(yu)水(shui)，在靠近排放口(kou)處沉(chen)淀下來(lai)。二(er)價(jia)汞(gong)(gong)(gong)(gong)離(li)子(zi)在遷移(yi)過程(cheng)中，被(bei)底泥和懸浮物中顆(ke)粒(li)吸附，漸漸沉(chen)降下來(lai)。其它形態的(de)汞(gong)(gong)(gong)(gong)在水(shui)或沉(chen)降物中也可以轉化成(cheng)二(er)價(jia)汞(gong)(gong)(gong)(gong)。二(er)價(jia)汞(gong)(gong)(gong)(gong)在微生(sheng)物作(zuo)用(yong)下，生(sheng)成(cheng)毒性更(geng)大的(de)甲基(ji)(ji)汞(gong)(gong)(gong)(gong)和二(er)甲基(ji)(ji)汞(gong)(gong)(gong)(gong)。火(huo)電廠灰(hui)(hui)場(chang)(chang)的(de)粉(fen)煤(mei)灰(hui)(hui)也會對土壤(rang)和地下水(shui)造成(cheng)影(ying)響(xiang)。
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