電滲析選擇性分離電解錳廢水中的陽離子

何飛陽,向文毓,陳舒琦,胡曉宇,韓 樂

電滲析選擇性分離電解錳廢水中的陽離子

何飛陽,向文毓,陳舒琦,胡曉宇,韓 樂*

(重慶大學(xué)環(huán)境與生態(tài)學(xué)院,三峽庫區(qū)生態(tài)環(huán)境教育部重點(diǎn)實(shí)驗(yàn)室,重慶 400045)

電解錳廢水；錳；電滲析；選擇性分離；選擇透過性

電解錳產(chǎn)生的廢水或廢渣以及滲濾液中含有過量重金屬錳(高達(dá)4000mg/L)與氨氮(高達(dá)6000mg/L)[1-3].針對電解錳廢水、錳渣滲濾液及受其污染的地表、地下水,主要的控制目標(biāo)均為陽離子(錳離子Mn2+、銨離子NH4+以及其他組分如鎂離子Mg2+),現(xiàn)有處置策略主要以堿性藥劑沉淀法除重金屬(如Mn2+、Mg2+),同時(shí)削減一部分NH4+,再以電化學(xué)氧化、折點(diǎn)氯化法等手段進(jìn)一步控制剩余氨氮濃度[4],但存在成本高、藥劑投加量大、難以達(dá)標(biāo)、二次污染風(fēng)險(xiǎn)等缺陷[2,6-7].

電滲析作為具有離子選擇性分離功能的新型膜法脫鹽技術(shù),市場成熟度高,抗污染結(jié)垢能力優(yōu)異[8-9]、可高效篩分具有同種電荷屬性的不同離子[10].電滲析組件中陰陽離子交換膜依次排列,電驅(qū)動下離子發(fā)生定向遷移,最終形成鹽離子濃度不同的濃水與淡水.陽離子交換膜材料類型[11]、目標(biāo)離子與雜質(zhì)離子的價(jià)態(tài)、水合能等固有屬性差異[12]、實(shí)際溶液特征(離子濃度、目標(biāo)離子與雜質(zhì)離子的比例)[10,13]以及電滲析操作條件(電流密度和流量等)都會影響工藝選擇性分離的效果[13-15].

電滲析的離子分離功能在地下水軟化、鹽湖水提鋰、食品有機(jī)酸調(diào)控等案例中已成功應(yīng)用,但在電解錳行業(yè)尚未見報(bào)道.本研究采用電滲析對電解錳行業(yè)污水中價(jià)態(tài)不同的Mn2+和NH4+,價(jià)態(tài)相同的Mg2+和Mn2+進(jìn)行分離,研究不同條件下電滲析對關(guān)鍵陽離子的分離行為與效果,旨在為電解錳行業(yè)的廢水資源化處置和行業(yè)可持續(xù)發(fā)展提供參考.

1 材料與方法

1.1 材料

試劑包括氯化錳(MnCl2·4H2O,分析純)、氯化銨(NH4Cl,分析純)、氯化鎂(MgCl2·6H2O,分析純),硫酸鈉(Na2SO4,分析純),鹽酸(HCl,1.18g/mL,分析純),去離子水(>18.25MΩ cm).實(shí)際廢水取自重慶秀山地區(qū)某錳礦尾礦修復(fù)場地的地表水,電導(dǎo)率為12.82mS/ cm,pH值為5.0,主要含有Mn2+(744mg/L)、NH4+(673mg/L)、Mg2+(1188mg/L)、SO42-(7439mg/L)、NO3-(381mg/L)、Cl-(184mg/L)等離子成分.采用的離子交換膜分別為具有單價(jià)選擇性的陽膜(CSO, Selemion)和標(biāo)準(zhǔn)型陰膜(AMX, Neosepta).

1.2 電滲析實(shí)驗(yàn)

電滲析核心組件(CJED-080,合肥科佳高分子材料科技有限公司)包含10個(gè)陰-陽離子交換膜單元, 單張膜的有效面積為0.008m2.電滲析裝置包括直流穩(wěn)壓電源(漢晟普源)、電導(dǎo)率儀(梅特勒-托利多)、3個(gè)有機(jī)玻璃容器(濃室、淡室和極室)及4臺蠕動泵和管路配套的轉(zhuǎn)子流量計(jì)(圖1)[16].實(shí)驗(yàn)初期在淡室和濃室中加入相同濃度的多陽離子混合溶液,濃、淡室的流量設(shè)置見下文;在極室加入0.3mol/L硫酸鈉溶液作為極液,極液采用恒定160L/h的流量.針對每種實(shí)驗(yàn)水體測定系統(tǒng)的極限電流,由系統(tǒng)電阻-電流倒數(shù)數(shù)據(jù)曲線獲得[17].系統(tǒng)在恒流模式下運(yùn)行(電流均遠(yuǎn)小于對應(yīng)的極限電流值),每隔一定時(shí)間,對濃淡室中溶液取樣、同時(shí)記錄溶液的電導(dǎo)率和體積;為防止過度脫鹽(避免水解及膜損傷),實(shí)驗(yàn)在淡室電導(dǎo)率降至5mS/cm時(shí)停止;通過各離子的濃度與體積變化計(jì)算離子過膜遷移情況.

圖1 實(shí)驗(yàn)用電滲析裝置示意

實(shí)驗(yàn)設(shè)計(jì)采用L9(34)正交試驗(yàn)(表1),針對錳-銨陽離子混合體系開展自配水樣實(shí)驗(yàn):以操作電流密度(其相對極限電流密度的比例為/lim=0.25, 0.375,0.5)、離子總濃度(0.1, 0.2, 0.3eq/L)、離子(當(dāng)量)比例(Mn2+:NH4+=1/2,1/4, 1/6)和淡室濃室流量(40, 60,80L/H)作為4個(gè)因素,每個(gè)因素設(shè)置3個(gè)水平;其中,根據(jù)預(yù)先測定的各條件下電滲析系統(tǒng)的極限電流密度,S1～S9實(shí)驗(yàn)組操作電流分別控制為29.4,68.8,44.4,41.3,94.0,79.1,51.5,165.0,98.1A/m2.

在引入另一常見陽離子(Mg2+)的錳-銨-鎂3離子實(shí)驗(yàn)中,考察電流單因素對分離效果的影響即/lim=0.25,0.375,0.5(對應(yīng)的操作電流分別為50,75, 100A/m2),采用固定的離子復(fù)配體系,包括總離子濃度為0.2eq/L,離子比例為Mn2+:NH4+:Mg2+=1:2:3,淡室濃室流量為80L/H.此外,實(shí)際廢水選用同3離子自配水實(shí)驗(yàn)一致的流量條件,電流為極限電流強(qiáng)度的0.375(對應(yīng)的操作電流為54A/m2).

表1 L9(34)正交實(shí)驗(yàn)設(shè)計(jì)與結(jié)果

注:1,2,3代表某一因素1,2,3水平對應(yīng)實(shí)驗(yàn)組的指標(biāo)平均值,可反映這一水平對指標(biāo)的作用結(jié)果,極差=max-min,用于反映因素的影響權(quán)重.

1.3 方法分析

NH4+與Mn2+的定量分析分別基于納氏試劑分光光度法和高碘酸鉀分光光度法,使用分光光度計(jì)(北京普析T6新世紀(jì))完成的濃度測定;對其他離子成分(如Mg2+)的定量分析采用離子色譜法(賽默飛ICS-90)完成.根據(jù)溶液中離子濃度與溶液體積關(guān)系確定離子遷移情況,評價(jià)指標(biāo)包括離子遷移量、遷移數(shù)、選擇透過系數(shù).

遷移量計(jì)算如下:

式中:Dn為離子遷移量(eq),Ddi和Dci分別為離子在淡室和濃室中遷移量.

Ddi=dd-00(2)

Dci=cc-00(3)

式中:c、d分別為某一時(shí)刻濃室與淡室中離子濃度(eq/L),c、d分別為某一時(shí)刻濃室與淡室中溶液體積(L),0、0分別為初始時(shí)刻的離子濃度、體積(淡室濃室一致).

遷移數(shù),表示遷移的總離子當(dāng)量中,某一離子所占的當(dāng)量百分比(%),定義如下:

選擇透過系數(shù)是最為重要的衡量離子選擇脫過性的指標(biāo),其定義如下:

2 結(jié)果與討論

2.1 錳、銨離子遷移規(guī)律

2.2 自配水及實(shí)際廢水中錳、銨、鎂3離子的分離實(shí)驗(yàn)

表2 25℃時(shí)水溶液中陽離子特征[22]

優(yōu)化電滲析操作條件和強(qiáng)化離子交換膜選擇透過能力可實(shí)現(xiàn)電解錳行業(yè)中Mn2+-NH4+-Mg2+的精準(zhǔn)分離、保障清潔生產(chǎn)和生態(tài)環(huán)境的修復(fù)與保護(hù).

圖4 實(shí)際廢水中3種離子遷移量、遷移數(shù),選擇性透過系數(shù)和,系統(tǒng)電壓U隨時(shí)間變化

3 結(jié)論

3.1 Mn2+-NH4+兩離子體系的正交實(shí)驗(yàn)結(jié)果表明,電流密度對其選擇透過性的影響最為顯著,增大電流密度利于優(yōu)先分離出NH4+.

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Selective separation of cations of different valence during electrodialysis of electrolytic manganese wastewater.

HE Fei-yang, XIANG Wen-yu, CHEN Shu-qi, HU Xiao-yu, HAN Le*

(Key Laboratory of Eco-environment of Three Gorges Reservoir Area, Ministry of Education, College of Environment and Ecology, Chongqing University, 400045, China)., 2022,42(3)：1202～1208

electrolytic manganese wastewater；manganese；electrodialysis；separation；permselectivity

X703.1

A

1000-6923(2022)03-1202-07

何飛陽(1999-),男,浙江義烏人,重慶大學(xué)碩士研究生,研究方向?yàn)榛陔姖B析的水處理技術(shù).

2021-08-13

留學(xué)人員回國創(chuàng)業(yè)創(chuàng)新支持計(jì)劃重點(diǎn)項(xiàng)目;(CX2018004)中央高?？蒲许?xiàng)目(2020CDJQY-A015);重慶大學(xué)本研聯(lián)合項(xiàng)目(20190007)

*責(zé)任作者, 教授, lehan@cqu.edu.cn