Phosphorus-induced polymerization-depolymerization mechanism of high silica-alumina and high calcium-iron coal gasification slag network structure

Abstract

The flow behavior of slag during the co-gasification of phosphorus-containing wastes and coal is crucial for developing the co-treatment technology of phosphorus-containing wastes in the entrained flow gasification. In this work, high silica-alumina (Si-Al) and high calcium-iron (Ca-Fe) coal were used as reference materials, simplified to SiO₂-Al₂O₃-CaO-Fe₂O₃. Synthetic ash was prepared with oxidizing reagents, and P₂O₅ was added to study its impact on coal ash flow behavior and the phosphorus-induced polymerization-depolymerization mechanisms in the slag network structure. Results showed that P⁵⁺ competed with Si⁴⁺ for Al³⁺ and O^2– in high Si-Al slag, causing depolymerization of silica-alumina tetrahedra and forming berlinite. The AFTs of the mixed ash decreased to 1413 °C at 10 % P₂O₅. In high Ca-Fe slag, P formed the [PO₄]^3- tetrahedral structure and induced the repolymerization. The formation of calcium phosphate and anorthite increased the AFTs of the mixed ashes from 1206 °C to 1315 °C at 15 % P₂O₅.