用石灰對電鍍含酸廢水的處理方法
摘要：關鍵詞：
0 引言
許多廠(chang)家處(chu)(chu)理(li)(li)(li)電(dian)鍍(du)含酸(suan)(suan)廢(fei)水(shui)一般采用(yong)(yong)燒(shao)(shao)(shao)堿(jian)中和(he)法和(he)石(shi)灰(hui)中和(he)法，用(yong)(yong)燒(shao)(shao)(shao)堿(jian)操(cao)作(zuo)簡便，但(dan)(dan)成本高(gao)，用(yong)(yong)石(shi)灰(hui)成本低，但(dan)(dan)操(cao)作(zuo)復(fu)雜。目前，許多電(dian)鍍(du)廠(chang)家和(he)專業電(dian)鍍(du)廢(fei)水(shui)處(chu)(chu)理(li)(li)(li)公司使用(yong)(yong)燒(shao)(shao)(shao)堿(jian)處(chu)(chu)理(li)(li)(li)，而一些用(yong)(yong)酸(suan)(suan)量(liang)大的電(dian)鍍(du)廠(chang)則使用(yong)(yong)石(shi)灰(hui)處(chu)(chu)理(li)(li)(li)。
電鍍產(chan)品前(qian)處理(li)(li)脫漆等(deng)工(gong)序用(yong)大(da)量(liang)的(de)硫酸(suan)，每月大(da)約(yue)80t，酸(suan)洗和(he)活化每月使用(yong)鹽酸(suan)大(da)約(yue)20t，廢(fei)水處理(li)(li)車間曾經(jing)(jing)使用(yong)過燒(shao)(shao)堿處理(li)(li)含(han)酸(suan)廢(fei)水，但成(cheng)本太高，不得(de)不改用(yong)石(shi)(shi)灰代(dai)替燒(shao)(shao)堿。在使用(yong)石(shi)(shi)灰處理(li)(li)含(han)酸(suan)廢(fei)水的(de)過程中，通過實驗和(he)長期摸索，成(cheng)功地(di)研究出(chu)一套(tao)用(yong)石(shi)(shi)灰處理(li)(li)電鍍含(han)酸(suan)廢(fei)水的(de)方法，取(qu)得(de)了(le)較(jiao)好(hao)的(de)經(jing)(jing)濟效益和(he)社(she)會效益。
1 設備及工藝流程
1.1 設備 廢水處理車間含酸廢水的處理設備主(zhu)要有(you)：含酸廢水調節池，一級(ji)中(zhong)(zhong)和反應池，二級(ji)中(zhong)(zhong)和反應池，絮凝池，沉(chen)淀(dian)池，清水池，污(wu)泥濃(nong)縮池，板框壓(ya)濾(lv)機和石(shi)灰乳液(ye)配制(zhi)池等。
1.2 工藝流(liu)程 含(han)(han)酸(suan)(suan)廢(fei)(fei)(fei)水(shui)(shui)從(cong)(cong)電(dian)鍍車間流(liu)入(ru)(ru)含(han)(han)酸(suan)(suan)廢(fei)(fei)(fei)水(shui)(shui)調(diao)節池(chi)，用(yong)泵(beng)將含(han)(han)酸(suan)(suan)廢(fei)(fei)(fei)水(shui)(shui)從(cong)(cong)調(diao)節池(chi)泵(beng)入(ru)(ru)一(yi)級(ji)中(zhong)(zhong)(zhong)(zhong)和(he)反應池(chi)，在(zai)一(yi)級(ji)中(zhong)(zhong)(zhong)(zhong)和(he)池(chi)中(zhong)(zhong)(zhong)(zhong)加(jia)(jia)入(ru)(ru)石(shi)灰乳液(ye)中(zhong)(zhong)(zhong)(zhong)和(he)廢(fei)(fei)(fei)酸(suan)(suan)和(he)沉(chen)淀(dian)(dian)(dian)(dian)重金(jin)屬離子。廢(fei)(fei)(fei)水(shui)(shui)從(cong)(cong)一(yi)級(ji)中(zhong)(zhong)(zhong)(zhong)和(he)池(chi)流(liu)入(ru)(ru)二級(ji)中(zhong)(zhong)(zhong)(zhong)和(he)反應池(chi)，在(zai)二級(ji)中(zhong)(zhong)(zhong)(zhong)和(he)池(chi)中(zhong)(zhong)(zhong)(zhong)繼續(xu)加(jia)(jia)石(shi)灰乳液(ye)中(zhong)(zhong)(zhong)(zhong)和(he)廢(fei)(fei)(fei)酸(suan)(suan)，并調(diao)節廢(fei)(fei)(fei)水(shui)(shui)的(de)pH至合適的(de)范圍。廢(fei)(fei)(fei)水(shui)(shui)從(cong)(cong)二級(ji)中(zhong)(zhong)(zhong)(zhong)和(he)池(chi)流(liu)入(ru)(ru)絮凝(ning)(ning)(ning)池(chi)，在(zai)絮凝(ning)(ning)(ning)池(chi)中(zhong)(zhong)(zhong)(zhong)加(jia)(jia)絮凝(ning)(ning)(ning)劑使沉(chen)淀(dian)(dian)(dian)(dian)物絮凝(ning)(ning)(ning)成較大的(de)顆粒，然后(hou)流(liu)入(ru)(ru)沉(chen)淀(dian)(dian)(dian)(dian)池(chi)，在(zai)沉(chen)淀(dian)(dian)(dian)(dian)池(chi)中(zhong)(zhong)(zhong)(zhong)水(shui)(shui)和(he)沉(chen)淀(dian)(dian)(dian)(dian)物分離，上清液(ye)流(liu)入(ru)(ru)清水(shui)(shui)池(chi)，最后(hou)從(cong)(cong)出(chu)(chu)水(shui)(shui)口排(pai)出(chu)(chu)，沉(chen)淀(dian)(dian)(dian)(dian)池(chi)中(zhong)(zhong)(zhong)(zhong)的(de)泥渣(zha)用(yong)泵(beng)泵(beng)入(ru)(ru)污(wu)泥濃(nong)縮池(chi)，然后(hou)用(yong)板框壓(ya)(ya)濾機壓(ya)(ya)濾，濾液(ye)流(liu)回到含(han)(han)酸(suan)(suan)廢(fei)(fei)(fei)水(shui)(shui)調(diao)節池(chi)，濾餅送至相關部門處理(li)。
2 方法研究
2.1 存在的(de)問(wen)題(ti) 用石灰(hui)處理(li)含酸廢(fei)水，首(shou)先在石灰(hui)乳液配(pei)制池中將石灰(hui)配(pei)成乳液，氧(yang)化鈣(gai)與水反(fan)(fan)應生(sheng)成氫氧(yang)化鈣(gai)。氫氧(yang)化鈣(gai)比氧(yang)化鈣(gai)具有更細小的(de)顆粒，與酸反(fan)(fan)應速度較快，且反(fan)(fan)應充分，反(fan)(fan)應中生(sheng)成硫酸鈣(gai)和氯化鈣(gai)。硫酸鈣(gai)是(shi)微(wei)溶(rong)物(wu)質，在水中的(de)溶(rong)度積為：
[SO42-][Ca2+]=k
k為硫酸鈣的溶度(du)積常數(shu)。
為了研(yan)究用石灰(hui)處理(li)含酸(suan)廢水(shui)水(shui)質渾濁的問題，現在(zai)假設有(you)1L硫酸(suan)鈣飽(bao)和溶液，其(qi)中[SO42-]=a，[Ca2+]=b，那么ab=k。再假設另有(you)1L硫酸(suan)鈣飽(bao)和溶液，[SO42-]=2a，那么[Ca2+]=0.5b。如果將這(zhe)兩種硫酸(suan)鈣飽(bao)和溶液混(hun)合到(dao)一起，通(tong)過計(ji)算可知(zhi)，混(hun)合后的溶液中[SO42-]=1.5a，[Ca2+]=0.75b，此(ci)時，[SO42-][Ca2+]=1.5a×0.75b=1.125ab>k
此式(shi)表明，兩(liang)種(zhong)飽和硫(liu)(liu)酸鈣(gai)溶液混(hun)合(he)后，硫(liu)(liu)酸根(gen)和鈣(gai)離子濃度的(de)乘積大(da)于(yu)硫(liu)(liu)酸鈣(gai)的(de)溶度積常數，因此這兩(liang)種(zhong)溶液混(hun)合(he)后，溶液中將(jiang)生成(cheng)硫(liu)(liu)酸鈣(gai)沉淀。
過(guo)去(qu)，在用(yong)石(shi)灰處理含酸廢水的(de)過(guo)程中(zhong)(zhong)(zhong)，沉淀池中(zhong)(zhong)(zhong)的(de)上清液經(jing)常變渾，這個問(wen)題(ti)好長時(shi)間沒有得到很好的(de)解決(jue)(jue)。解決(jue)(jue)這個問(wen)題(ti)的(de)辦法是(shi)，嚴格控制中(zhong)(zhong)(zhong)和(he)(he)反(fan)應池中(zhong)(zhong)(zhong)廢水pH的(de)變化范(fan)圍，確保石(shi)灰用(yong)量的(de)準(zhun)確，使廢水中(zhong)(zhong)(zhong)硫(liu)酸根(gen)和(he)(he)鈣離子濃(nong)度在較小的(de)范(fan)圍內波動。
采用石(shi)(shi)(shi)灰處(chu)(chu)理(li)含(han)酸(suan)(suan)(suan)廢(fei)水(shui)的另一個問題是，石(shi)(shi)(shi)灰加(jia)入(ru)量(liang)(liang)不(bu)易(yi)實現自動控制，使操作復雜，水(shui)處(chu)(chu)理(li)質(zhi)量(liang)(liang)波動較大。采用人(ren)工(gong)控制石(shi)(shi)(shi)灰的加(jia)入(ru)量(liang)(liang)，由于(yu)廢(fei)水(shui)酸(suan)(suan)(suan)度(du)高，變化(hua)大，人(ren)工(gong)控制比(bi)較困難，廢(fei)水(shui)處(chu)(chu)理(li)的質(zhi)量(liang)(liang)得不(bu)到保證。 2.2 解決方法(fa) 含(han)酸(suan)(suan)(suan)廢(fei)水(shui)中含(han)有銅(tong)、鋅和(he)少量(liang)(liang)的鎳等(deng)重(zhong)金屬污染物質(zhi)，在處(chu)(chu)理(li)含(han)酸(suan)(suan)(suan)廢(fei)水(shui)過程中，除了(le)中和(he)廢(fei)酸(suan)(suan)(suan)外，還要(yao)用石(shi)(shi)(shi)灰沉淀這些(xie)重(zhong)金屬離子，根(gen)據有關資料，這些(xie)重(zhong)金屬離子沉淀的條件(jian)為接(jie)近中性和(he)偏堿性。
用(yong)分析純硫(liu)酸鎳(nie)和去離(li)子(zi)水配(pei)制(zhi)硫(liu)酸鎳(nie)溶液(ye)(ye)，用(yong)氫氧化鈉將硫(liu)酸鎳(nie)溶液(ye)(ye)調至pH=8.53，生成(cheng)氫氧化鎳(nie)沉淀，由(you)于(yu)堿性較弱，溶液(ye)(ye)中(zhong)(zhong)還含有(you)少量的(de)(de)鎳(nie)離(li)子(zi)，將溶液(ye)(ye)過濾(lv)后經(jing)過分析得知，濾(lv)液(ye)(ye)中(zhong)(zhong)鎳(nie)離(li)子(zi)的(de)(de)質量濃(nong)度(du)為10.6mg/L。向該(gai)濾(lv)液(ye)(ye)中(zhong)(zhong)加入少許次(ci)(ci)氯酸鈉溶液(ye)(ye)，濾(lv)液(ye)(ye)中(zhong)(zhong)有(you)黑色沉淀生成(cheng)，濾(lv)液(ye)(ye)的(de)(de)pH由(you)8.53降至7.89。這個反應的(de)(de)過程為，次(ci)(ci)氯酸鈉將二(er)價鎳(nie)氧化為三價鎳(nie)，在堿性條(tiao)件下三價鎳(nie)離(li)子(zi)生成(cheng)Ni(OH)3黑色沉淀。分析結(jie)果表(biao)明，pH在8～9的(de)(de)范圍內(nei)，Ni(OH)3溶液(ye)(ye)中(zhong)(zhong)鎳(nie)離(li)子(zi)的(de)(de)質量濃(nong)度(du)符(fu)合國家排放標準的(de)(de)要求(qiu)。
3 結果與討論
3.1 pH的控制
在二(er)級中(zhong)(zhong)(zhong)(zhong)(zhong)和反應池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)用pH控(kong)(kong)制系統自動(dong)(dong)控(kong)(kong)制一(yi)(yi)級中(zhong)(zhong)(zhong)(zhong)(zhong)和池(chi)(chi)和二(er)級中(zhong)(zhong)(zhong)(zhong)(zhong)和池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)石灰的(de)加入量，pH控(kong)(kong)制系統的(de)控(kong)(kong)制值一(yi)(yi)般(ban)設定在7.8～8.4的(de)范(fan)(fan)圍內(nei)，這(zhe)個數值一(yi)(yi)般(ban)依據廢(fei)水在絮凝(ning)池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)pH來調整。絮凝(ning)池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)pH一(yi)(yi)般(ban)控(kong)(kong)制在8.3～8.8的(de)范(fan)(fan)圍內(nei)，當(dang)(dang)絮凝(ning)池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)廢(fei)水pH偏(pian)高時(shi)(shi)，可降(jiang)低二(er)級中(zhong)(zhong)(zhong)(zhong)(zhong)和池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)pH的(de)控(kong)(kong)制值，當(dang)(dang)絮凝(ning)池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)pH偏(pian)低時(shi)(shi)，可提高二(er)級中(zhong)(zhong)(zhong)(zhong)(zhong)和池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)pH的(de)控(kong)(kong)制值。用石灰處理含酸廢(fei)水的(de)過程中(zhong)(zhong)(zhong)(zhong)(zhong)，二(er)級中(zhong)(zhong)(zhong)(zhong)(zhong)和池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)pH有一(yi)(yi)定的(de)波(bo)動(dong)(dong)，當(dang)(dang)流入絮凝(ning)池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)廢(fei)水pH高于(yu)(yu)工(gong)(gong)藝(yi)(yi)(yi)上限(xian)或(huo)低于(yu)(yu)工(gong)(gong)藝(yi)(yi)(yi)下(xia)限(xian)時(shi)(shi)，絮凝(ning)池(chi)(chi)中(zhong)(zhong)(zhong)(zhong)(zhong)的(de)pH控(kong)(kong)制系統自動(dong)(dong)啟(qi)動(dong)(dong)加酸泵(beng)或(huo)加堿泵(beng)，將pH控(kong)(kong)制在工(gong)(gong)藝(yi)(yi)(yi)范(fan)(fan)圍內(nei)。
3.2 廢(fei)水(shui)處(chu)理狀況
自安裝了(le)這套(tao)(tao)自動控制系(xi)(xi)統后，廢水(shui)處(chu)(chu)理(li)(li)狀況有了(le)明顯的(de)改(gai)善，pH控制準確，水(shui)質清澈透明，懸浮物達標。為了(le)驗(yan)證這套(tao)(tao)含酸廢水(shui)處(chu)(chu)理(li)(li)系(xi)(xi)統的(de)可行性，連(lian)續一(yi)(yi)個星期從廢水(shui)出水(shui)口取樣(yang)測(ce)定，測(ce)定項目為pH、銅、鋅、鎳和(he)氰(qing)的(de)質量濃度，結果(guo)列(lie)于表1。在這套(tao)(tao)廢水(shui)處(chu)(chu)理(li)(li)系(xi)(xi)統中，含氰(qing)廢水(shui)經過(guo)處(chu)(chu)理(li)(li)后流入(ru)二(er)級中和(he)池(chi)，與含酸廢水(shui)一(yi)(yi)同進入(ru)下一(yi)(yi)道處(chu)(chu)理(li)(li)工序，因(yin)此，在表1中也給出了(le)氰(qing)化物的(de)測(ce)定數據。分析結果(guo)表明，這套(tao)(tao)系(xi)(xi)統處(chu)(chu)理(li)(li)過(guo)的(de)含酸廢水(shui)pH和(he)重金屬離子(zi)符合國家二(er)級排放標準。
效益
某公司每月約使(shi)用(yong)(yong)(yong)80t硫酸和20t鹽酸，廢(fei)水(shui)處理車間每月約投入55t石(shi)灰(hui)(hui)處理含酸廢(fei)水(shui)，每噸(dun)石(shi)灰(hui)(hui)按440元計(ji)算，合計(ji)人(ren)民(min)幣24200元。如果(guo)使(shi)用(yong)(yong)(yong)燒(shao)堿(jian)處理這些含酸廢(fei)水(shui)，每月需要(yao)質(zhi)量分數為96%的(de)(de)燒(shao)堿(jian)約55t，每噸(dun)燒(shao)堿(jian)以2600元計(ji)算，合計(ji)人(ren)民(min)幣143000元，使(shi)用(yong)(yong)(yong)燒(shao)堿(jian)的(de)(de)成(cheng)本是(shi)(shi)使(shi)用(yong)(yong)(yong)石(shi)灰(hui)(hui)成(cheng)本的(de)(de)5.9倍(bei)。由此可見，使(shi)用(yong)(yong)(yong)石(shi)灰(hui)(hui)處理含酸廢(fei)水(shui)的(de)(de)經濟(ji)效益是(shi)(shi)可觀的(de)(de)。
使用燒堿(jian)處(chu)理(li)(li)含酸廢(fei)水(shui)比使用石灰成(cheng)(cheng)本高(gao)得多(duo)，那(nei)么為什(shen)么還有那(nei)么多(duo)廠(chang)家使用燒堿(jian)處(chu)理(li)(li)含酸廢(fei)水(shui)呢?原(yuan)因(yin)是使用石灰處(chu)理(li)(li)含酸廢(fei)水(shui)存在過程復(fu)雜，操(cao)作難(nan)度大，懸浮物不易達(da)標等(deng)問題。我(wo)們研制(zhi)的(de)這套用石灰處(chu)理(li)(li)電鍍(du)含酸廢(fei)水(shui)系統(tong)，成(cheng)(cheng)功地克服了(le)這些困難(nan)，提高(gao)了(le)廢(fei)水(shui)處(chu)理(li)(li)質量，并降低(di)了(le)運行成(cheng)(cheng)本，取得了(le)較好效益(yi)。
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