Rapid conversion of fly ash into synthetic soil via polymer-assist granulation

Abstract

Accumulating stockpiles of unutilized coal fly ash (FA) presents a major challenge due to its vast production and limited reuse. Converting FA into soil-like media offers a promising valorization pathway, yet its non-cohesive nature impedes direct utilization. Conventional strategies often rely on the incorporation of organic matter to promote aggregation, but such indirect approaches are inefficient and difficult to control. This work introduces a rapid and controllable approach using a synthetic polymer adhesive to directly form water-stable FA aggregates, overcoming the inefficiencies of traditional organic matter-based aggregation methods. First, an FA-PVA composite is prepared through mixing and drying, after which strong hydrogen bonding between PVA and FA ensures the composite's high water stability. The bulk composite is then granulated into aggregates with controllable size and assembled into soil. This process converts non-cohesive FA - which otherwise forms dense, waterlogged structures with critically low aeration porosity (<3%) - into a well-structured soil with balanced hydration and aeration properties (66% water-holding capacity and 21% air-filled porosity) with one week. Agricultural validation confirmed successful seed germination and 70% of the eggplant yield relative to that in natural soil. This work demonstrates a rapid and scalable pathway to convert industrial solid waste into well-structured soil, offering new opportunities for landfill reclamation and the reuse of FA.