Physico-chemical characteristics of some Lesotho's clays and their assessment for suitability in ceramics production

The physico-chemical properties of three clays (reddish, yellow and gray) collected at Ha Motloheloa quarry in Lesotho were determined. The main components in all the clays were SiO2, Al2O3, Fe2O3 and K2O in the form of mica, CaO, MgO, Na2O, TiO2 and P2O5 with less than 6% loss of ignition (LOI). The clays showed a wide variation in particle sizes with clay fractions from 15.81% to 27.38%, silt fractions from 41.95% to 52.32% and sand fractions from 30.6% to 31.9%. The surface area of the clays increased with a decrease in particle size. All the clays showed water content below 9% and shrinkage value below 6%. The clays had moderate plasticity indexes between 20 and 25 and less than 9% water content with 17.32%-20.72% water required to produce sufficient workability. Their densities were less than 3 g/cm(-3) and had low green to dry shrinkage (4.19%-5.35%). For all firing temperatures used (950 degrees C-1100 degrees C), the flexural strength varied from 2.3 to 17.6 MPa, while the water content varied from 6.1% to 12.2%. The reddish clay can be used for making perforated/solid bricks and roofing tiles, while yellow and gray clays can be used only for solid bricks.