CHARACTRIZATION OF SOIL CLAY MINERALS USING MID-INFRARED SPECTROSCOPY AND ITS APPLICATION IN SOIL IDENTIFICATION

摘要

Soil identification depends on the determination of a series of soil agro-chemical properties, and is expensive and time consuming. Soil clay mineral is one of the most important components in soil, and the qualification of soil clay plays main role in soil identification. Chemical analysis of soil clay is time-consuming, while infrared spectroscopic method seems promising. In this research, characterization of three source clay minerals, i. e. illite, kaolin and montmorillonite, were made using three mid-infrared spectroscopic techniques (attenuated total reflectance (FTIR-ATR), transmittance spectroscopy, and photoacoustic spectroscopy (FTIR-PAS). For the FTIR transmittance spectra of the three source clays, there are three main absorption regions: 3000-3800 cm-1, 1300-1800 cm-1, and 500-1200 cm-1, and sharp differences can be found in each region; for the FTIR-ATR spectra of the three source clays, there are absorptions with minor difference in the region of 800-1200 cm-1; for the FTIR-PAS spectra of the three source clays, there are also three similar absorption regions as FTIR transmittance spectra, but more absorptions are found in the FTIR-PAS spectra comparing with FTIR transmittance absorptions. Comprehensively, FTIR-PAS spectroscopy shows more merits in the characterization of soil clays among the three infrared techniques. The FTIR-PAS was applied to charactrize three soil types, i. e, black soil from Hailun (north of China), yellow soil Changwu (west of China) and red soil from Qiyang (south of China); Hailun soil was characterized as montmorillonite type soil with medium calcium carbonate content, Changhu soil was characterized as montmorillonite/illite type soil with high calcium carbonate content, and Qiyang soil was characterized as kaolin type soil with low calcium carbonate content.