Quantification of Mixed-Layer Illite-Smectite in Glass Matrices by Fourier-Transform Infrared Spectroscopy

Abstract

The Fourier-transform infrared (FTIR) technique has been used for both qualitative and quantitative determination in mineral species (McMillan et al., 1988; Pandya et al., 1992; Schroeder, 1992; Yanagisawa et al., 1997; Zhang et al., 1997). The method presents a number of important advantages: simple preparation, high sensitivity, and rapid analysis. The quantitative determination of minerals in the presence of glass is an interesting problem in mineralogy because X-ray diffraction (XRD) methods do not provide accurate results, especially for small mineral components. In this paper, we present a method for quantitative analysis of Al-rich smectite, mixed-layer illite-smectite (I-S), or illite in the presence of volcanic glass using FTIR. A series of hydrothermal-alteration reactions were made on volcanic tuff from the Cabo de Gata region, southeast Spain. The glass was crushed, ground, and calcined at 900°C for 2 h. After calcination, the fraction of 10–200 μm in size was selected. XRD and differential thermal and thermogravimetric analysis did not detect any phase other than glass. The glass chemical composition is: 72.89% SiO2, 14.47% Al2O3, 1.25% Fe2O3, 1.44% MgO, 0.86% CaO, 3.34% Na2O, 4.97% K2O. The hydrothermal reactions were made at 80, 120, and 160°C, for 60, 90, 180, and 360 d, in both deionized water and in solutions with K/Na ratios of 0.01, 0.1, 1, 10, and 100. The total ion concentrations were 1.01, 0.33, 0.20, 0.33, and 1.01 M. Five grams of glass were placed in 25 mL of solution for each reaction. The products of reaction were separated from the solutions and washed repeatedly with deionized water by centrifugation. The fraction of <2 μm in size was separated also by centrifugation (further analysis refers to this fraction). The samples were Ca-exchanged with …