Insights into the carbon structure, thermal properties and environmental friendliness of composites produced using coal tar pitch and dimethylpolysiloxane as binders for coal waste

Abstract

This study introduces modified coal tar pitch (CTP) and dimethylpolysiloxane (DMPS) polymer as resins for the fixation of carbon-containing wastes into value-added composites. Secondary heat treatment of coal tar at 400 °C with a residence time of 9 h using the air-blowing pretreatment method yielded CTP with a hydrogen-to-carbon ratio of 0.4 and total carbon content (77 %–95 %). The effects of blending coal tar pitch to coal waste regarding the carbon structure, thermal stability, flame ablation rates, corrosion resistance, and leaching potential of coal composites were systematically investigated. The CTP-based composites have more ordered carbon structures compared to the DMPS-based composites. The composites are thermally stable up to 600 °C, beyond which they degrade rapidly. Composites containing 10 % CTP recorded the lowest linear and mass ablation rates. Interestingly, DMPS-based composites recorded higher corrosion rates compared to CTP-based composites. Finally, metal ion contaminants in the composites were below the low-risk threshold, suggesting these wastes can be bound in the composites in that they pose minimal environmental risks. Overall, the CTP binder is better than DMPS for producing composite materials that may serve as carbon sinks for coal waste. The combination of high thermal stability, low resistance to corrosion, low ablation rates, and low susceptibility to leaching suggests that the composites could be shaped into building materials such as tiles or pavers.