Formation and in-situ identification of unique microplastic-rock blends under anthropogenic thermal conditions

Microplastic (MP) pollution poses a significant challenge for municipal solid waste (MSW) management, while landfills have been recognized as a primary source of secondary MPs, waste incineration offers a potential solution for MP elimination. This study discovered a kind of specifically MP-rock blends, which are generated through the melt-recrystallization of different plastics during incineration. MP-rock blend of polypropylene (PP) and polyethylene (PE) was confirmed using in-situ FTIR microscopy (LUMOS II), and three distinct morphologies, i.e., the type of overlapping intertwined, surface welded, and secondary molten recrystallization, were observed based on bonding intensity. Inorganic materials, such as calcium oxide (CaO) and silica (SiO₂), were observed embedded within MP surfaces. MP blends, including PP+PE, PP + polystyrene (PS), and PS + polyvinyl chloride (PVC), were found in bottom ash from ten incineration plants, with MP concentrations ranging from 0.6 to 3.9 mg/kg of ash and Loss on ignition percentages of 5.55-15.57%. The formation process exhibited strong temperature dependence, as plastic-inorganic sintering occurred above 900°C, corresponding to typical operational temperatures in these incineration facilities. The formation of plastic-inorganic hybrids revealed three plastic blend systems demonstrating distinct structural evolution pathways and hybridization behaviors under high-temperature incineration conditions, as characterized by two-dimensional correlation spectroscopy analysis of simulated byproducts. This work provides empirical evidence for anthropogenic plastic-inorganic hybrids, which should be considered seriously for the potential resource process.