Composition and Technological Properties of Clays for Structural Ceramics in Limpopo (South Africa)

• Main Authors: Lawrence Diko-Makia, Rofhiwa Ligege
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Minerals
• Subjects: structural ceramics; pottery; low firing temperature; fluxing agents; South Africa
• Online Access: https://www.mdpi.com/2075-163X/10/8/700

This study evaluated the potential of raw clays from the Mukondeni region for structural ceramics and pottery based on traditional firing techniques. Physical properties were identified by particle size distribution, consistency limits, and clay activity. Mineralogical and chemical properties were investigated by X-ray diffraction (XRD) and X-ray fluorescence (XRF). Extruded clay bodies were fired at 900 °C. Technological characteristics were measured by weight loss (WL), bulk density (BD), dry linear shrinkage (DLS), fired linear shrinkage (FLS), water absorption (WA), and flexural strength (FS). The clays were low in <2 µm fractions (≤19%) and of medium to high plasticity with a clayey silt texture. Smectite was the dominant clay mineral while quartz and feldspar were major non clay minerals. The most abundant oxides were SiO₂ (63.57–68.73%), Al₂O₃ (13.9–15.61%), and Fe₂O₃ (4.86–6.18%), whereas K₂O, CaO, MgO, Na₂O, TiO₂, and P₂O₅ were depleted. Characterization based on the clay workability chart, Winkler’s diagram, and compositional ternary diagrams revealed acceptable extrusion properties and suitability for structural ceramics and earthenware. The clays showed acceptable WL, BD, LS, and WA, but unsatisfactory FS (≤1.08 MPa). Low mechanical strength was attributed to presence of smectites and inert nature of feldspar at 900 °C. Beneficiation through mixing with carbonate-rich raw materials is recommended.