Influence of the binder type and quantity on physical, mechanical and thermal properties of shale waste briquettes

Abstract

This study investigates the influence of different binding agents—petroleum pitch, coal tar pitch, and bitumen BND 50/70—on the physicomechanical and thermotechnical properties of shale briquettes produced from fine shale fractions. The results demonstrate that the nature and amount of the binder play a decisive role in the formation of the structural framework, mechanical strength, thermal stability, and energy efficiency of the briquetted fuel. The increase in binder content from 5 to 15 wt.% leads to a consistent rise in density, compressive strength, and calorific value, alongside a decrease in porosity, water absorption, and ash content. Coal tar pitch was found to be the most effective binder, providing the highest mechanical strength (3.0–5.5 MPa), lowest water absorption (8–16%), reduced abrasiveness, and the maximum lower heating value (11.2–13.4 MJ/kg). Its high aromaticity and tendency toward carbonization contribute to the formation of a dense coke residue, ensuring long-lasting and stable combustion. Petroleum pitch exhibited moderate performance in both mechanical and thermotechnical parameters and can serve as a balanced and economically feasible binding agent. Bitumen BND 50/70 resulted in briquettes with the lowest strength, highest porosity and water absorption, and the least stable combustion behavior due to its high volatile content and limited carbonization capability. The obtained results confirm a strong correlation between the chemical nature of the binder, its thermal decomposition behavior, and the resulting performance characteristics of shale briquettes. These findings allow for the targeted optimization of briquette formulations depending on their intended application—ranging from high-strength, thermally stable industrial fuel to low-cost, rapidly igniting briquettes for domestic use. Keywords. shale briquettes; binder; petroleum pitch; coal tar pitch; bitumen BND 50/70; physicomechanical properties; thermotechnical characteristics; thermal stability; energy efficiency; briquette structure.