Synergistic co-pyrolysis of fly ash and biomass for sustainable soil amendment: Enhanced nutrient release and toxicity mitigation

As a predominant industrial by-product of coal combustion, fly ash (FA) has been conventionally valorized in construction field due to its cementitious characteristics and adsorption potential. However, diminishing utilization rates driven by market saturation in building materials necessitate innovative approaches for sustainable FA management. This investigation proposes a paradigm shift toward agricultural applications through the synergistic co-pyrolysis of coal-derived FA with corn stalk biomass, developing an eco-friendly soil amendment that concurrently addresses FA remediation and agricultural waste recycling. Through systematic optimization of pyrolysis parameters (500°C, 50 % biomass ratio, 4 h retention), the engineered biochar-FA composite exhibited dual environmental benefits: (1) Effective heavy metals immobilization with leaching concentrations below regulatory thresholds (Cr: <0.1 mg/L, Pb: <0.02 mg/L) through lattice entrapment and surface complexation mechanisms. (2) Enhanced bioavailability of essential nutrients (N: 15 mg/L, P: 50 mg/L, K: 20 mg/L) facilitated by hierarchical pore structures. The carbonaceous matrix demonstrated superior cation exchange capacity and specific surface area, enabling simultaneous nutrient retention and contaminant sequestration. This integrated strategy establishes a circular economy model that transforms dual waste streams into value-added soil amendments, presenting scalable solutions for both energy field by-product management and degraded land rehabilitation. • A method for preparing organic nutrient soil by co pyrolysis of fly ash and agricultural biomass was proposed. • The melting lattice solidification of toxic and harmful substances in fly ash has been achieved. • It was found that high-temperature pyrolysis can promote the release of available elements in plants.