Study on the Pyrolysis Kinetics and Product Characteristics of Flame-Retardant Mining Conveyor Belt

Pyrolysis is considered the most effective method for the disposal of waste flame-retardant mining conveyor belts. As the primary active component of flame-retardant mining conveyor belts, the flame-retardant rubber layer (FRR) poses significant environmental pollution risks through its pyrolysis products. This study systematically elucidates the pyrolysis kinetics and product evolution behavior of FRR and proposes a unified stage-classification framework for the pyrolysis of FRMB. The results indicate that the pyrolysis of FRR can be divided into three stages occurring within the temperature ranges of 483∼593 K, 593∼693 K, and 693∼973 K. The apparent activation energies of the three stages, determined using model-free methods, model-fitting approaches, and the trend-constrained kinetic differential evolution method, are 118.12, 299.48, and 142.38 kJ/mol, respectively. These stages correspond to dehydrochlorination of the PVC backbone coupled with plasticizer bond cleavage, rearrangement of conjugated polyene structures into aromatic frameworks accompanied by decarboxylation, and oxidation/combustion of residual carbonaceous structures, respectively. The major gaseous products in Stage I include HCl, C₂H₄Cl₂, and Dioctyl phthalate (DOP) along with its decomposition fragments; Stage II is dominated by DOP, CO₂, and aromatic hydrocarbons; while Stage III is characterized by the substantial release of DOP and CO₂. During pyrolysis, FRR evolves from a dense structure into a highly porous residue, with chlorine almost completely released into the gas phase, whereas P, Ca, and Mg are significantly enriched in the solid residues. The pore structure evolves from ultramicropore-dominated peaks at 0.55 and 0.75 nm to a mesopore-enhanced system (2∼10 nm). These findings provide theoretical support and a technical basis for the resource utilization and environmental risk assessment of chlorine-containing polymer composites.