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硫化亚铁(FeS)常被用于六价铬(Cr(Ⅵ))污染水体的治理修复,主要通过吸附、还原、和共沉淀作用等去除水体中的Cr(Ⅵ). FeS材料的颗粒尺寸、比表面积、形状、存在形态、稳定性等因素对其Cr(Ⅵ)的去除性能有显著影响[1-4]. 与天然FeS矿物相比,人工合成的FeS颗粒具有更大的比表面积和更高的反应活性;采用羧甲基纤维素、海藻酸钠等稳定剂对其进行表面修饰后,可以有效防止颗粒的聚集,使得FeS活性更稳定,对Cr(Ⅵ)的去除性能可得到显著提升[5-7].
FeS的形貌对Cr(Ⅵ)的去除性能可能产生较大影响. Li等[8]使用合成的梭形FeS颗粒修复铬污染土壤,当FeS/Cr(Ⅵ)物质的量比=1.5:1时,在3 d内可以去除98%的Cr(Ⅵ),Cr(Ⅵ)浓度由1407 mg·kg−1降低至16 mg·kg−1. Liu等[7]采用椭球型纳米FeS处理水溶液Cr(Ⅵ),在pH=5.6时去除性能为683 mg Cr(Ⅵ)/g FeS,去除率高达92.48%;Wang等[9]使用棒状FeS去除水溶液中Cr(Ⅵ),当FeS/Cr(Ⅵ)物质的量比=4时,可在30 min内完全去除水溶液中Cr(Ⅵ).
利用溶剂热法、均相沉淀法、NaBH4还原法、生物法等方法[8, 10-12]制备的FeS颗粒形貌差异较大. Sines等[13]采用溶剂热法在Fe2+/S2-物质的量比为5:3.12、200 ℃下反应4 h后,合成了FeS纳米片,平均厚度约为30 nm. Li等[8]在氮气保护下将等量的S2-溶液逐滴加入至Fe2+-CMC溶液中制备了梭形的FeS,平均长度为400 nm,中间直径约为100 nm. Kim等[10]采用改性的NaBH4还原法将S2O42-溶液以3:1的体积比加入至Fe3+溶液中合成了球形FeS. Xiong等[14]制备了微球状FeS纳米颗粒,并通过批处理试验表明FeS纳米颗粒可以有效地固定沉积物中的Hg,当FeS/Hg物质的量比为26.5时,Hg浸出浓度降低97%,毒性浸出率降低99%. 程千文[12]利用希瓦氏菌在代谢过程中将Fe3+和S2O32-还原为Fe2+和S2- 后,合成了球状FeS,粒径范围在20—100 nm.
目前,水热法已被应用于合成形貌多样的硫化物材料,反应时间、反应温度、溶剂、反应物的物质的量比等合成条件会对产物形貌产生显著影响[15]. Gorai等[16]研究表明在乙二胺和水比例在100:0—0:100范围内,随着乙二胺和水的比例减小,趋于球形的铜离子与硫脲的配合物逐渐形成,使Cu1-xSx形貌从树枝状转变为棒状最后成为球状. 用水热法合成Bi2S3微/纳米材料时,当反应时间从10 min延长到6 h时,合成的Bi2S3形貌从纳米带束转变为完整的、均匀的花状结构[17]. Kar和Chaudhuri[17]证实了在反应温度为150—230 ℃范围内,升高温度可使FeS2由纳米线转变为纳米片; Wu等[18]发现,当S/Zn物质的量比分别为1:1、2:1时,ZnS形貌从片状转变为球形. 但是,当前对影响水热法合成FeS颗粒形貌的主要影响因素仍不清楚[19].
本研究旨在观测识别水热法控制FeS形貌的影响因素,并以水溶液中六价铬Cr(Ⅵ)作为目标污染物,探究不同形貌的FeS对Cr(Ⅵ)的去除性能. 具体包括:(1)分析溶剂比、反应温度、反应时间和铁硫物质的量比等因素对人工合成FeS颗粒形貌的影响;(2)探究具有棒状和片状等形貌的人工合成FeS颗粒对Cr(Ⅵ)的去除性能.
硫化亚铁微粒的水热法合成及其对水溶液中Cr(Ⅵ)的去除性能
Hydrothermal synthesis of ferrous sulfide particles and their performance for the removal of Cr(Ⅵ) from aqueous solution
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摘要: 借助扫描电镜(SEM)、X射线衍射(XRD)等手段,对水热合成的硫化亚铁(FeS)微粒进行特性表征,探究了水/乙二胺体积比、反应时间、反应温度、S/Fe物质的量比等因素对FeS微粒微观形貌的影响;通过批实验观测了具有不同形貌的FeS微粒对水溶液中Cr(Ⅵ)的去除性能. 结果表明,在S/Fe物质的量比=1—4时,随着S/Fe物质的量比的增大,FeS形貌由片状逐渐转变为棒状;水/乙二胺体积比、反应温度和反应时间对FeS的形貌的影响不显著,均呈片状. FeS微粒可有效去除水溶液中的Cr(Ⅵ),当溶液pH=5.5时,0.5 g·L-1的片状和棒状FeS对初始浓度为170 mg·L-1的水溶液中Cr(Ⅵ)的去除率分别为79.4%和99.9%.Abstract: Ferrous sulfide (FeS) particles were prepared via a hydrothermal synthesis method, and then characterized by scanning electron microscopy and X-ray diffraction. The effects of water-to-ethylenediamine volume ratio, reaction time, reaction temperature and S: Fe molar ratio on the micromorphology of FeS particles were investigated. The removal of aqueous Cr(Ⅵ) using FeS particles with various morphologies was determined through batch tests. The results showed that the morphology of FeS particles gradually changed from flake-shaped to rod-shaped, as the S: Fe molar ratio increased from 1 to 4. The water-to-ethylenediamine volume ratio, reaction temperature, and reaction time had insignificant effects on the morphology of FeS particles, which remained flake-shaped. The removal efficiencies of aqueous Cr(Ⅵ) using 0.5 g·L-1 flake-shaped and rod-shaped FeS at a pH of 5.5 and initial Cr(Ⅵ) concentration of 170 mg·L-1 were 79.4% and 99.9%, respectively.
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Key words:
- hydrothermal synthesis /
- FeS particles /
- hexavalent chromium /
- influencing factors.
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表 1 人工合成FeS对水溶液中Cr(Ⅵ)的去除性能
Table 1. The removal performances of Cr(Ⅵ) in aqueous solution by hydrothermal synthesized FeS particles(pH = 5.5, Cr(Ⅵ)0 = 170 mg·L−1 , FeS投加量 = 0.5 g·L−1, 200 r·min−1)
实验条件
Experimental conditions拟合级数
Fitting series动力学方程
Kinetic equation速率常数k
Rate constant kR2 Cr(Ⅵ)去除率/%
Cr(Ⅵ) removal efficiency零级 $ \mathrm{C}-{C}_{0}=-kt $ 3.022 mg·(L· h)−1 0.5253 S/Fe=1 一级 $ \mathrm{l}\mathrm{n}(C/{C}_{0})=-kt $ 0.0286 h−1 0.6589 79.4 二级 $ 1/C-1/{C}_{0}=kt $ 0.0002 L(mg· h)-1· 0.7508 零级 $ C-{C}_{0}=-kt $ 13.436 mg·(L· h)−1 0.8007 S/Fe=3 一级 $ \mathrm{l}\mathrm{n}(C/{C}_{0})=-kt $ 0.1765 h−1 0.9358 99.9 二级 $ 1/C-1/{C}_{0}=kt $ 0.0012 L(mg· h)-1· 0.9459 -
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