改性凹凸棒土/納米鐵復合材料去除地下水的研究

董 磊,龔 磊,林 莉,馮 雪,李青云

(1.長江水利委員會長江科學院流域水環境研究所,湖北 武漢 430010; 2.長江水利委員會長江科學院流域水資源與生態環境科學湖北省重點實驗室,湖北 武漢 430010;3.長江水利委員會長江科學院黨群辦公室,湖北 武漢 430010)

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董 磊1,2,龔 磊3,林 莉1,2,馮 雪1,2,李青云1,2

(1.長江水利委員會長江科學院流域水環境研究所,湖北 武漢 430010; 2.長江水利委員會長江科學院流域水資源與生態環境科學湖北省重點實驗室,湖北 武漢 430010;3.長江水利委員會長江科學院黨群辦公室,湖北 武漢 430010)

凹凸棒土理想結構式是[Mg5][Si8O20](OH)2(OH2)4·4H2O,屬于含水富鎂鋁硅酸鹽纖維狀黏土礦物[13],直徑一般為20～50 nm,長幾百納米至幾微米,是天然的納米材料。凹凸棒土內部具有發育的微孔孔道,其成分、形態、結構、物理化學性質都比較特殊。凹凸棒土的吸附性與比表面積成正相關,將其進行酸改性或熱活化均可增大比表面積。酸改性可使凹凸棒土的八面體層不斷溶解,進而提高礦物的微孔隙及微孔比表面積,增強凹凸棒土的吸附性能[14]。熱改性可使凹凸棒土內部的有機質及其部分礦物質分解,孔道變得疏松,孔隙容積和比表面積增加,其吸附性隨之增強[15]。

基于對凹凸棒土的獨特結構和吸附性能的認識,許多學者將凹凸棒土作為吸附劑進行了深入的研究[16-19]。王金明等[16-17]分別用酸、微波加熱等方法對凹凸棒土進行改性,用于吸附核素Sr2+、苯酚。Sanchez等[18-19]對凹凸棒土進行改性,并對改性后的吸附性能進行研究。總體而言,凹凸棒土具有結構獨特和吸附性能良好的優點,已經取得的成果表明凹凸棒土是一種優良的水處理吸附劑,特別是經過改性后的凹凸棒土吸附性能更佳。

1 試驗材料與儀器

1.1 試驗材料

實驗所用凹凸棒土由江蘇玖川納米材料科技發展有限公司提供。硝酸鉀、亞硝酸鈉、氫氧化鈉、硫酸鋅、碘化鉀、碘化汞、酒石酸鉀鈉、硼氫化鈉、無水乙醇、氨基磺酸、4-氨基苯磺酸胺、N-(1-萘基)-乙二胺二鹽酸鹽、六水合氯化鐵、六偏磷酸鈉等均為分析純,實驗用水為脫氧去離子水。

1.2 試驗儀器

萬分之一電子天平(美國DENVER,TP-21);低速臺式離心機(上海安亭科學,TDL-40B);紫外可見分光光度計(日本島津,UV2600);電熱鼓風干燥箱(上海博迅實業,BGZ-240);多參數分析儀(上海雷磁,DZB-718);水浴恒溫振蕩器(江蘇金壇普天,SHY-2A);冷凍干燥機(美國 GOLD SIM,FD5-3B)。

1.3 改性凹凸棒土、納米鐵和復合材料的制備方法

1.3.1 凹凸棒土的提純

凹凸棒土研磨過200目篩后,將凹凸棒土配成懸浮液,在懸浮液中加入六偏磷酸鈉作為分散劑[20-21],磁力攪拌,50℃下超聲波處理后靜置,取上層乳白色懸浮液離心處理,將離心后的沉淀物在105℃條件下干燥6 h后研磨過200目篩,得到提純后凹凸棒土。

1.3.2 凹凸棒土的酸改性

相關研究采用不同濃度的鹽酸對凹凸棒土進行酸處理[22-23]。本試驗優化后采用濃度為1 mol/L的鹽酸對提純后凹凸棒土酸改性,凹凸棒土與鹽酸的固液比為1∶10。磁力攪拌,50℃超聲波處理,離心過濾,離心后的沉淀物采用去離子水洗滌,洗滌至中性,然后將所得沉淀物在105℃條件下干燥并過200目篩,得到粒徑不大于200目的酸改性凹凸棒土。

1.3.3 凹凸棒土的熱改性

相關研究表明對凹凸棒土進行熱活化改性時不宜超過500℃,且活化時間3 h較為合適[24-25]。因此,本試驗對提純后的凹凸棒土進行熱改性時,焙燒溫度設置為100～500℃,焙燒時間3 h,冷卻后,過200目篩,得到粒徑不大于200目的熱改性凹凸棒土。

1.3.4 復合材料和納米鐵的制備

復合材料和納米鐵均采用液相還原法制備,參考相關文獻[26-27],稱取2 g純化改性凹凸棒土,用50 mL的去離子水和乙醇混合溶液(體積比4∶1)溶解,按質量比為1∶10、1∶5、1∶3、1∶2、1∶1加入六水合氯化鐵,攪拌2 h;并向其中滴加100 mL一定濃度的KBH4溶液,滴加速度控制在0.2 mL/s左右,反應完畢后繼續攪拌1 h,保證KBH4與Fe3+充分反應,反應見式(1),整個試驗過程均在氬氣保護下進行。

12H++6H2

(1)

反應結束后,離心過濾,所得沉淀物用乙醇洗滌3～4次,再真空過濾干燥。納米鐵在相同條件下制備,但不加純化改性的凹凸棒土。復合材料和納米鐵均儲存于密封棕色玻璃瓶(通氬氣除氧)。

1.4 試驗方法

試驗中用錫紙包覆反應離心管,避免光照,以模擬地下水的黑暗環境;向反應溶液中通氬氣,去除反應溶液中的DO以模擬地下水DO環境。

1.4.1 改性凹凸棒土選擇試驗

1.4.2 復合材料制備試驗

2 結果與討論

2.1 復合材料的制備及性能

2.1.1 凹凸棒土改性條件的確定

圖1 3種改性條件下凹凸棒土對去除率

圖2 不同焙燒溫度下凹凸棒土對的吸附性能

圖3 4種改性條件下凹凸棒土對去除率

綜上,本研究選用的凹凸棒土采用先提純,后熱活化的方式進行改性,熱活化條件:焙燒溫度270℃,焙燒時間3 h。

2.1.2 復合材料制備方案的確定

圖4 不同質量比下復合材料對去除率

圖5 不同材料下“三氮”變化情況

圖6 反應過程中溶液pH值變化

圖7 DO對去除率及其還原產物生成率的影響

圖8 光照對去除率及其還原產物生成率的影響

(2)

(3)

(4)

2 Fe0+2H2O+O2→2Fe(OH)2

(5)

4Fe(OH)2+O2+2H2O→4Fe(OH)3

(6)

圖9 溫度對去除率及其還原產物生成率的影響

Fe0+2H2O→Fe2++H2+2OH-

(7)

(8)

(9)

3 結 論

a. 確立凹凸棒土改性條件、凹凸棒土與六水合氯化鐵最佳質量比等關鍵試驗參數,優化了復合材料制備方案;復合材料較單獨納米鐵穩定性好,不易凝聚成團,不容易被氧化。

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Study of removal of nitrate nitrogen from groundwater using modified attapulgite-Fe nano composite material

DONG Lei1,2, GONG Lei3, LIN Li1,2, FENG Xue1,2, LI Qingyun1,2

(1.BasinWaterEnvironmentalResearchDepartment,ChangjiangRiverScientificResearchInstitute,ChangjiangWaterResourcesCommission,Wuhan430010,China; 2.KeyLabofBasinWaterResourceandEco-EnvironmentalScienceinHubeiProvince,ChangjiangRiverScientificResearchInstitute,ChangjiangWaterResourcesCommission,Wuhan430010,China; 3.PartyandMassLineOffice,ChangjiangRiverScientificResearchInstitute,ChangjiangWaterResourcesCommission,Wuhan430010,China)

In this study, we synthesized modified attapulgite-Fe nano composite material (A-NZVI) using the liquid-phase reduction method, and investigated the stability of A-NZVI and changes of three kinds of nitrogen (NO3--N, NH4+-N, and NO2--N) in the reaction process. We also analyzed the effects of groundwater environmental factors (dissolved oxygen, temperature, and light) on the removal of NO3--N with A-NZVI. In the simulation of groundwater environment, the three kinds of materials were ranked in the following descending order according to their reactivity in removing NO3--N: A-NZVI, nanoscale zero-valent iron, and modified attapulgite. The conversion rate of NH4+-N was low, with nearly no NO2--N generated, when using A-NZVI. Dissolved oxygen and temperature had significant influence on the removal of NO3--N from groundwater with A-NZVI. When in the light and dark environment, the removal rate of NO3--N and the amounts of generated NH4+-N and NO2--N had no significant difference. The findings of the study provided a theoretical basis and technical support for restoration projects for groundwater with NO3--N pollution.

groundwater; nitrate nitrogen; modified attapulgite-Fe nano composite material; environmental factor

10.3880/j.issn.1004-6933.2017.01.014

國家自然科學基金(41302204);中央級公益性科研院所基本科研業務費項目(CKSF2014029/SH)

董磊(1987—),男，工程師，碩士,主要從事水環境治理。E-mail: dongleigushi@163.com

X523

A

1004-6933(2017)01-0067-08

2016-04-23 編輯：王 芳)