铬在蒙脱石及改性蒙脱石中的吸附和解吸附产物及机制对比研究

发布时间：2018-01-14 12:13

本文关键词：铬在蒙脱石及改性蒙脱石中的吸附和解吸附产物及机制对比研究　出处：《南京大学》2017年硕士论文　论文类型：学位论文

【摘要】：蒙脱石由于具有一定层间阳离子交换能力、大表面积、化学稳定性以及对环境作用较温和等而被广泛应用。前人主要针对一价、二价金属阳离子,如:Li+、Cd2+、Cu2+等在蒙脱石中吸附和迁移变化进行研究,较少针对Cr3+等三价阳离子进行研究。另外Cr3+被广泛运用于在制革、电镀和颜料等工业生产,过量的铬能破坏生物体内的新陈代谢,对人体健康产生有害影响,被认为是16种污染最严重的重金属元素之一,也是非常强的致癌物质,理解其吸附迁移机制对生产和环境来说有巨大意义。本文一方面研究了钙基蒙脱石吸附Cr3+前后变化,并对产物进行了不同温度热处理(200℃、300℃、500℃、600℃、700℃)及复水条件研究。另一方面利用不同浓度的十六烷基三甲基溴化铵(CTAB)交换层间原Ca2+得到改性蒙脱石,吸附Cr3+。在加热250℃的条件下,探讨其结构变化和离子迁移状况。最后研究了含铬蒙脱石和含铬改性蒙脱石在酸碱性条件下的解吸附情况。结果表明:钙基蒙脱石吸附Cr3+后,Cr3+主要以[Cr(H2O)6]3+的形式替代TOT结构片层间Ca2+。当热处理温度小于500℃时,d001降低,OH伸缩振动和中波数段向高波数偏移,ESR信号峰也有所增加。与加热的样品相比较,复水后d001值有部分的增加,OH伸缩振动峰也向低波数偏移,ESR信号峰也有变化,表明Cr3+在六方孔较浅部位。当温度大于500℃时,根据XRD图谱以及ESR的g=1.97强度变化,出现绿铬矿(Cr2O3),d060由尖锐的窄峰减弱变宽,表明可能有类似于叶腊石的相出现,由于复水后OH伸缩振动区域稍微地向低波数偏移,此时Cr3+处在六方孔的深部。而在CTAB改性蒙脱石中,CTAB以不同的形式排列在层间使其高度d001大大增加,其吸附Cr3+能力下降,根据ICP-AES得到的反应后溶液中Al3+离子浓度以及红外结果显示出现3564 cm-1属于Cr3+Cr3+OH的振动峰,表明此时Cr3+进入八面体甚至取代了部分八面体中的Al3+;而在加热250℃时,CTAB封闭层间之后,Cr3+Cr3+OH的振动峰仍然存在,同时结合ESR中g因子的变化情况,表明改性后的蒙脱石吸附Cr3+后,部分Cr3+因受分子间的吸引力以及热动力而逐渐向蒙脱石结构中迁移,迁移到六方孔中及部分八面体中。酸性条件下,含铬蒙脱石的解吸附明显多于碱性条件下的解吸附,这与H+和表面Cr3+发生交换、H+和蒙脱石的结构羟基使得结构部分发生解体、崩塌有关,而碱性条件下即便发生解吸附,也能因为脱水等转变为氢氧化铬而稳定在蒙脱石的颗粒之间,但相对来说CTAB改性后更易保存。
[Abstract]:With montmorillonite interlayer cation exchange capacity, large surface area, chemical stability and environmental effect is mild and is widely used. The former mainly for two monovalent, divalent metallic cations, such as Li+, Cd2+, adsorption and in migration of Cu2+ changes in montmorillonite, less for trivalent cations were Cr3+ study. In addition Cr3+ is widely used in the tanning, electroplating and paint and other industrial production, excessive chromium can damage the organism The new supersedes the old., have harmful effects on human health, is considered one of the most serious pollution of heavy metals in 16, is also very strong carcinogen, understanding the adsorption mechanism is of great significance to migration the production and the environment. This paper researches the changes of calcium montmorillonite before and after adsorption of Cr3+, and the products were heat treated at different temperatures (200 c, 300 C, 500 C, 600 C, 700 C) and Study on the rehydration conditions. On the other hand the use of sixteen alkyl three methyl bromide (CTAB) with different concentrations of interlayer exchange Ca2+ modified montmorillonite, heating at 250 DEG C under the condition of adsorption of Cr3+., discusses its structure changes and ion mobility conditions. Finally the chromium chromium containing montmorillonite and modified montmorillonite in acid under the condition of desorption. The results showed that calcium montmorillonite after the adsorption of Cr3+, Cr3+ mainly [Cr (H2O) 6]3+ in the form of alternative TOT structure layers Ca2+. when the heat treatment temperature is less than 500 DEG C, D001 decreased, OH stretching vibration and wave number in Duan Xianggao wavenumber offset, ESR signal peak is also increased. Compared with the heating of the sample, after water D001 value is part of the increase of OH stretching vibration peak is shifted to lower wavenumbers, ESR signal peak changes also showed that Cr3+ in the six square hole in the shallow part. When the temperature is greater than 500 degrees, according to the XRD pattern and ESR g=1. 97 strength changes appear eskolaite (Cr2O3), D060 by the narrow peak weakened wider, suggesting that there may be similar to the phase of pyrophyllite, because after water OH stretching region slightly shifted to lower wavenumbers, at Cr3+ in the deep hole. In six CTAB modified montmorillonite in CTAB, in a different arrangement so that its height D001 in between layers is greatly increased, decreased the adsorption ability of Cr3+, according to Al3+ ICP-AES the ion concentration in solution after reaction and the IR results show that vibration peak 3564 cm-1 belongs to Cr3+Cr3+OH, indicating that Cr3+ entered the eight face even replace part of the surface of the body eight Al3+; and heating at 250 DEG C, CTAB closed layer after the vibration peak of Cr3+Cr3+OH still exist, combined with the changes of ESR g factor, that the modified montmorillonite adsorption of Cr3+ after Cr3+ due to thermal power and attraction between molecules And gradually migrated to the structure of montmorillonite, migrated to six square hole and part of the eight surface body. Under acidic conditions, desorption of chromium containing montmorillonite was more than the adsorption solution under alkaline conditions, and the H+ and Cr3+ on the surface of the exchange structure, hydroxyl H+ and montmorillonite makes structure disintegrated, the collapse. But under alkaline conditions even solution adsorption, but also because of dehydration into chromium hydroxide and stable between montmorillonite particles, but relatively CTAB modified and easy storage.

【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P579;X703

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