Mineralogy and geochemistry of clays from Malaysia and its industrial application

Abstract

In Malaysia, kaolinitic clays are still viable as an important industrial minerals. Tepoh, Nitar and Lenggor clays represent the deposit found within Johor and Trengganu, considered to be one of the major deposit for local demand. This paper outlines an assessment of the basic characterisation and calcination behaviour of thus clays. Tepoh clay is of kaolinitic clay, Nitar clay is mica rich kaolinitic clay while Lenggor clay is kaolin. To the naked eyes, Tempoh clays seem to be darker with 72% brightness value, high plasticity, LOI (10.56-12.87), CEC (6.73-8.41 me/100g), BET surface area (16.6 m2/g), zeta potential (-24.1 mV), poor rheological properties, very slow sedimentation rate and composed mainly kaolinite, illite and muscovite. The chemical composition of Tepoh clay was dominantly consists of SiO2 and Al2O3, yet insignificantly contains carbonate. The calcinations from 5000C to 11000C remarkably transformed Tepoh clays into brighter meta-clays. Nitar clay consists of kaolinite (22.01%), illite/mica (38.95%) and quartz (33.77%). High brightness value (94.36%-98.39%) due to low contaminants such as TiO2 (0.75% to 0.99%) and Fe2O3 (0.77% to 1.35%). The plasticity of Nitar clay is equal to kaolinite and contain low proportion of particle < 2 µm fraction (10.2%). Cation exchange capacity (CEC) ranging from 4.37 meq/100g to 5.13 meq/100g which comply to the CEC value of kaolin. Low specific surface area (5.2 m2/g) corresponds to the amount of coarse particles, and zeta potential (-50.9 mV to -54.7 mV) show the colloidal stability. Transformation to metakaolin happened at 510°C and formation of mullite at 900°C. Calcination (up to 1100°C) seems decreased the brightness value of the metakaolin at 0.72%. Lenggor clay is identified as kaolin which essentially comprised of kaolinite (53.60%), mica (10.87%) and quartz (28.66%). Low contaminants such as TiO2 (0.79% to 0.82%) and Fe2O3 (0.61% to 0.62%) increased the brightness value which ranging from 94.50% to 95.5%. Plasticity is low due to low proportion of < 2 µm fraction (30.9%). CEC value (5.24 meq/100g to 6.89 meq/100g) falls between kaolin range. Low specific surface area (23.7 m2/g dan 7.3 m2/g) due to lower amounts of finer particles. Zeta potential (-0.89 mV to -3.76 mV) reflects the unstability of the colloid. Formation of metakaolin is interpreted at 520°C. Calcination increased the brightness at 0.25%. Nitar clay is less viscous but higher sedimentation rate than Lenggor clay. Both clays show good crystalization of pseudohexagonal to hexagonal kaolinite particles. Beneficiations such as sizing and classification are essential to increase the clays quality and therefore comply to the industrial requirement.