The effect of magnesium–aluminum hydrotalcite intercalated with PO43− on the ash melting behaviours of Naomaohu coal

Abstract

The utilization of coal combustion supports the long-term stable development of the socio-economy, but slagging and ash deposition phenomena constrain its efficient utilization. This study employed a co-precipitation method to prepare a layered PO₄³⁻-intercalated magnesium–aluminum hydrotalcite (MAP) additive to improve coal ash fusion characteristics. Combustion experiments demonstrated that the MAP additive significantly increased the ash fusion temperature of Naomaohu coal (NC) (the softening temperature rose from 1161 °C to 1393 °C) while reducing fine particulate matter generation. The mechanisms include: (1) solid-phase reconstruction: promoting the phase transformation of low-melting-point alkaline minerals (e.g., anorthite, nepheline, anhydrite) into high-melting-point crystals (e.g., akermanite, forsterite, magnesium calcium phosphate); (2) ion immobilization: layered phosphates capturing alkali metal ions (Na⁺, K⁺) through ion exchange. The dual mechanisms synergistically altered ash particle distribution: the peak particle size of fine particles (PM₁) shifted from 0.03 μm to 1.05 μm, the proportion of coarse particles (PM_2.5) increased by 48 %, and the peak distribution expanded from 2.46 μm to 3.64 μm. Concurrently, the surface adhesion of ash was reduced, enhancing dispersion efficiency and effectively inhibiting slagging and ash deposition. The MAP additive exhibits excellent potential for regulating ash fusion behaviour, providing a novel strategy for the clean and efficient utilization of coal.