Toward an on-line characterization of kaolin calcination process using short-wave infrared spectroscopy

Abstract

In the production of calcined kaolin, the on-line monitoring of the calcination reaction is becoming more relevant for the generation of optimal products. In this context, this study aimed to assess the suitability of using infrared (IR) spectroscopy as a potential technique for the on-line characterization of the calcination of kaolin. The transformation of kaolin samples calcined at different temperatures were characterized in the short-wave (SWIR) spectra using the kaolinite crystallinity (Kx) index and the depth of the water spectral feature (1900D). A high correlation between the standard operational procedure for the quality control of calcined kaolin and the Kx index was observed (r = -0.89), as well as with the 1900D parameter (r = -0.96). This study offers a new conceptual approach to the use of SWIR spectroscopy for the characterization the calcination of kaolin, withdrawing the need of using extensive laboratory techniques.

Spatial Patterns of Chemical Weathering at the Basal Tertiary Nonconformity in California from Multispectral and Hyperspectral Optical Remote Sensing

“…Spectral endmembers chosen from AVIRIS pixels within each the weathered and unweathered units ( Figure 4A) show clear differences, most prominently in the form of: 1) the presence of a strong SWIR absorption feature centered near 2200 nm in outcrops of weathered material located in both the basal Maniobra Formation and uppermost weathered basement near the nonconformity, 2) the absence of this absorption feature in outcrops of unweathered material, best expressed in the hillslope of Maniobra formation above the unconformity which is locally covered in a veneer of Quaternary alluvium ( Figure 3C); and 3) differences in overall amplitude and curvature of the reflectance continuum, particularly the spectral slope at NIR wavelengths near 850 nm. Based on numerous previous studies, we interpret the ~2200 nm absorption to indicate the presence of Al-rich clays (e.g., kaolinite), an expected weathering product reported at multiple BTN outcrops and known to produce absorptions centered in this portion of the spectrum due to the structure of the Al-OH bond e.g., [17,24,25,52,53].…”

Prediction of Soluble Al2O3 in Calcined Kaolin Using Infrared Spectroscopy and Multivariate Calibration

“…Five spectral measurements per sample were taken at different spots of the surface. For consistency with previous studies [13], the units were converted from wavenumbers (cm −1 ) to wavelengths (µm) during the data import. For every sample, the respective five spectral measurements were averaged as means of noise reduction, generating one spectrum per sample.…”

“…The CR spectra appear to be symmetric, whereas the SNV one is biased towards longer wavelengths, also having a difference in the shoulder position to the deeper spectra at 6.24 µm, and that in the shallower one at 6.27 µm. Following the approach proposed in a previous study [13], the depth of the water feature was used to investigate the general behaviour of the spectra of the calcined kaolin samples in relation to the soluble Al 2 O 3 content. Figure 6 shows these parameters using the depth of the δH 2 O feature at 6.15 µm extracted from CR spectra.…”

“…The spectral features describe changes in the mineral structure related to the kaolinite dehydroxylation (Equation 1) and recrystallisation of the spinel and mullite phases (Equations (2) and 3) [14][15][16]. Besides these transformations, the results reported by [13] showed an inverse correlation between the adsorption of water by the calcined clay as detected by the water-related spectral features, and the soluble Al 2 O 3 content. Since the spectral ranges that exhibit the spectrum of water can be measured by using portable and hand-held spectrometers, infrared spectroscopy could be used as an on-site and (near) real-time proxy for the SOP.…”

“…However, these studies did not address a mechanism for quality control of the calcined product directly. Recently, Guatame-Garcia et al [13] investigated the relationship between the infrared spectra of the kaolin calcination reaction and the changes in the calcined clay's reactivity, measured as soluble Al 2 O 3 . Infrared spectroscopy is particularly useful in the characterisation of the kaolin calcination reactions.…”