Identification of clay minerals in mixtures subjected to differential thermal and thermogravimetry analyses and methylene blue adsorption tests

• We study methylene blue adsorption and thermal analysis of clay mixtures.
• Methylene blue adsorption test allowed the identification of types and percentages of clays.
• Results from differential thermal analysis and methylene blue adsorption tests are highly correlated.
• Curve fitting from methylene blue adsorption test results may allow an estimative of heat of reaction of clays.

The study of identification methods for clay minerals is very important because of the very fine particle size (less than 2 μm) of these materials, which makes it difficult to recognize them with the naked eye. Because they consist of electrically charged particles, clay minerals exhibit distinct and dynamic behavior. From geotechnical standpoint, clay minerals are present in a wide variety of rocks and soils. Because their behavior is difficult to predict, careful consideration is necessary because they exert great influence on the design and construction of roads, tunnels, foundations, slopes, and many other types of infrastructure. Their characteristics may have a positive effect, e.g., when acting as clay liners, or a negative one, e.g., when their swelling characteristic causes buildings to lose their stability. In this context, the purpose of this work was to compare the reliability of two clay mineral identification methods: combined differential thermal analysis and thermogravimetry (DTA-TG) and the methylene blue adsorption test (MBAT). Proportional mixtures of kaolinite and bentonite were prepared in order to investigate the two methods. These two types of clay were chosen due to their distinct behaviors: kaolinite is a 1:1 clay mineral, and bentonite is composed mostly of montmorillonite, a 2:1 clay mineral. The two methods showed a positive and highly significant correlation. Moreover, the MBAT is a lower cost test that requires only ordinary chemistry laboratory equipment. Correlations revealed that the MBAT can provide thermal information related to DTA-TG tests.