Multifunctional Si-C-P flame-retardant coatings blended by chitosan hydrochloride/melamine polyphosphate/ammonium phosphomolybdate in spodumene tailings geopolymer

Spodumene tailings (STs) are the silicon-rich solid waste from the extraction of spodumene concentrate, recycling approaches of STs remain challenging and are worth exploring. Therefore, the STs-based geopolymer coatings blended with chitosan hydrochloride (CHC)/melamine polyphosphate (MPP)/ammonium phosphomolybdate (APM) is prepared by the sol–gel method for flame-retarding plywood. The results show that 0.8 wt% CHC enhances the flame retardancy of the coating, evidenced by a decrease in total smoke production (TSP) and an increase in the flame retardancy index (FRI). The TSP decreases from 3347.16 m2 to 1688.66 m2, and the FRI increases from 1.00 to 3.52, as well as exhibiting 56% formaldehyde adsorption and good water resistance. Because the as-formed Si-C-P residues exert resilient and robust microstructure with embedded acicular carbon. Meanwhile, according to the modified Coats-Redfern pyrolysis kinetic, the as-determined Zhuralev-Lesokin-Tempelman (Z.-L.-T.) 3D diffusion model verifies an increase in Eα from 59.63 kJ·mol−1 to 73.68 kJ·mol−1 (252 ∼ 295℃). Generally, it explores a practical approach for preparing low-carbon, sustainable, and multifunctional Si-C-P synergistic flame-retardant coatings, expanding a cleaner and high-value strategy for recycling STs.