Carbonized waste bone briquettes for sustainable coal substitution in cement kilns within a circular economy framework

The growing demand for sustainable energy and effective waste management has intensified interest in converting biomass residues into alternative fuels. This study explores the valorization of waste animal bone into carbonized briquettes as a partial substitute for coal in cement kiln applications. Briquettes were produced using particle sizes ranging from 0.75 to 4.8 mm, blending ratios of 5–15%, and binder systems comprising cow dung, waste paper, and their admixture. Their physical, mechanical, and combustion properties were evaluated in accordance with ASTM standards, and statistical significance was assessed using ANOVA (p < 0.05). Results revealed low moisture content (2.1–4.33%), moderate ash content (9.06–12.75%), and relatively high fixed carbon (15.62–29.45%), indicating favorable fuel characteristics. Among the tested formulations, briquettes containing 5% cow dung binder exhibited the highest calorific value (4605.64 kcal/kg). Ultimate analysis of the optimal sample showed a carbon content of 48.51% and a hydrogen content of 5.31%, with nitrogen and sulfur levels below 1%, suggesting reduced potential for NOₓ and SOₓ emissions. ANOVA results confirmed that particle size, blending ratio, and binder type significantly influenced briquette density and shatter resistance. Process optimization identified optimal production conditions at 14.13% admixture binder and 0.786 mm particle size, achieving a briquette density of 0.901 g/cm³ and shatter resistance of 89.01%, with deviations between predicted and experimental values below 5%. Overall, the findings demonstrate that waste bone briquettes possess strong mechanical integrity and promising energy performance, highlighting their potential as a sustainable and environmentally friendly alternative fuel for cement production.