Thermo-chemical coupled activation of multisource solid waste for silicon fertilizer preparation

The utilization of solid waste resources is currently hampered by the low activation efficiency and high production cost of silicon fertilizer. Herein, the synergistic processing of coal gangue (CG), magnesium slag (MS), and plant ash (PA) through thermo-chemical coupled activation was proposed for developing a cost-effective silicon fertilizer, and the migration and transformation of typical pollutants during the solid-phase reaction process was systematically evaluated. The calcination temperature, proportion of the components, and calcination time are the key factors influencing the activation effect during the co-disposal reaction. Notably, with the optimal parameters (850 °C, 2 h, CG:MS:PA mass ratio = 60:30:10), a multisource solid waste-based silicon fertilizer was successfully prepared, having an effective silica content of 23.92 % and activation efficiency of 55.19 %, with improved physicochemical properties that support sustainable waste valorization. Combined experimental and modeling approaches revealed synergistic reactions between alkaline oxides (CaO, MgO, K₂O) and siliceous minerals to generate key plant-available silicate phases. The process effectively removed and immobilized typical pollutants (e.g., S, Cl, Cd) while stabilizing heavy metals in the F3 and F4 fractions to mitigate environmental risks. The silicon fertilizer complied with the Agricultural Industry Standard of the People's Republic of China for silicon fertilizer (NY/T 797-2004) in terms of the critical parameters (effective silica content and heavy metal limits). This integrated strategy synergizes waste valorization and pollution control to provide a scalable solution for producing a multisource solid waste-based silicon fertilizer.