Phytoextraction of Heavy Metals from Fly-Ash-Contaminated Soils: A Review

Fly ash (FA) is a coal combustion product with variable mineral composition, high alkalinity, and elevated enrichment of heavy metals (HMs) such as As, Se, Mo, Cd, and Pb. Fly ash greatly influences soil dynamics by altering soil pH, nutrient mobility, microbial activity, soil structure, and texture. This review evaluates phytoextraction as a sustainable and eco-friendly strategy for remediating FA-contaminated soils. It explores the physicochemical properties of FA, the impact of FA and associated heavy metals (HMs) on soil, the mechanisms of HM hyperaccumulation in plants, and the effectiveness of phytoextraction based on the bioaccumulation factor (BAF) and translocation factor (TF). Case studies from various regions demonstrate the great potential of hyperaccumulator species to extract toxic HMs from FA-impacted soils. However, challenges such as low metal bioavailability, limited field validation, and inadequate management of contaminated biomass hinder large-scale application. Future research should focus on optimizing biomass utilization, developing comprehensive hyperaccumulator databases, and advancing genetic and policy frameworks to enhance the scalability and effectiveness of phytoextraction.