Spectroscopic study for a chromium-adsorbed montmorillonite.
Samples of purified montmorillonite with trace amounts of quartz were subjected to different concentrations of chromium sulphate solutions for one week to allow cation exchange. The chromium-bearing montmorillonites were verified and tested using powder X-ray diffractometry (XRD), X-ray fluorescence spectrometry, electron spin resonance (ESR) spectrometry and Fourier transformation infrared (FTIR) spectroscopy to explore the occupation sites of the chromium. The ESR spectra recorded before and after the chromium exchange show clear differences: a strong and broad resonance with two shoulders at the lower magnetic field side was present to start, and its intensity as well as that of the ferric iron resonance, increased with the concentration of added chromium. The signals introduced by the chromium, for example at g=1.975 and 2.510 etc., suggested that the chromium had several occupational sites. The ESR peak with g=2.510 in the second derivative spectrum suggested that Cr3+was weakly bounded to TOT with the form of [Cr(H2O)3]3+in hexagonal cavities. This was verified by comparing the FTIR spectra of the pure and modified montmorillonite. The main resonance centred at g=1.975 indicated that the majority of Cr3+occupied the interlayer region as [Cr(H2O)6]3+. The substitution of Ca2+by Cr3+also greatly affected the vibration of the hydrogens associate to water, ranged from 3500 to 2600cm-1in FTIR. Furthermore, the presence of two diffraction lines in the XRD results (specifically those with d-values of 1.5171 and 1.2673nm) and the calculations of the size of the interlayer space suggested the presence of two types of montmorillonite with different hydration cations in the sample exposed to 0.2M chromium sulphate. The two diffraction lines were assigned to [Cr(H2O)6]3+and [Cr(H2O)3O3]3+, respectively. This also suggested that the species of hydration cation was constrained by the concentration of the chromium solution.
State Key Laboratory of Metal Ore Deposits, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China.
Maidina
M
Nurtay
State Key Laboratory of Metal Ore Deposits, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China.
Maierdan
M
Tuersun
State Key Laboratory of Metal Ore Deposits, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China. Electronic address: caiyf@nju.edu.cn.
Yuanfeng
Y
Cai
Faculty of Engineering and Natural Sciences, Bahcesehir University, Beşiktaş, 34353 Istanbul, Turkey.
Muhammed
M
Açıkgöz
Key Laboratory of Surficial Geochemistry, Ministry of Education, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China. Electronic address: wanght@nju.edu.cn.
Hongtao
H
Wang
State Key Laboratory of Metal Ore Deposits, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China.
Yuguan
Y
Pan
State Key Laboratory of Metal Ore Deposits, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China.
Xiaoke
X
Zhang
State Key Laboratory of Metal Ore Deposits, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China.
Xiaomei
X
Ma
Cation occupation; Chromium; Cr-montmorillonite; ESR; FTIR