Examining the properties, behaviour in firing and potential application of coal mine overburden for stoneware ceramics

Abstract

Purpose. A binary mixture of a ceramic body was studied, incorporating overburden from a coal mine site in Bontang, East Kalimantan, Indonesia. This overburden material has been tested for the manufacture of stone-ceramic body. Methods. The initial characterization of overburden materials includes testing the chemical composition by XRF analysis and mineral content by XRD analysis on raw materials and overburden exposed to high temperature. The composition of ceramic specimens is a mixture of 85% overburden material and 15% fine sand. Firing temperatures in the range of 900-1100°C were applied to the ceramic body specimen. Then, ceramic properties, such as physical color, plasticity, shrinkage, water absorption and density were analyzed. Findings. The results show that the ceramic specimen experiences densification when exposed to high temperature in this range, which in turn contributes to low water absorption and high flexural strength. This ultimately results in low water absorption below 1.0% at 1100°C, which is favorable for stoneware type of ceramics. The mechanical properties of specimen at 1000°C is in accordance with stoneware body standard. In addition to this, it is believed to be more energy efficient, since the low firing temperature is sufficient to achieve the stoneware specification. Originality. The binary clay-based ceramic have been tested using coal mine overburden and river sand with a high Fe2O3 content. Together with the presence of alkali oxides and calcium in the raw materials, this can potentially reduce the use of fluxing agent. A comprehensive study has been conducted on the characteristics, firing effect and application of stoneware. Practical implications. Some ceramic prototypes from this result were also made using a rotary technique and heated in this temperature range. Since overburden is generally considered to be backfill material, the selective clay material application for ceramics can provide the potential to stimulate local product innovation by utilizing easily available overburden materials.