Thermochemical valorization of metal-enriched hyperaccumulator biomass

Heavy metals (HMs) pollution of soils is a continuous environmental and health issue globally. Phytoremediation with hyperaccumulator plants is a green and cost-effective strategy for soil restoration, but the HMs-enriched biomass obtained can become a secondary pollution source if not properly managed. Thermochemical conversion technologies, particularly pyrolysis and hydrothermal conversion, provide sustainable pathways to stabilize HMs and valorize biomass into functional carbonaceous materials simultaneously. Departing from the conventional view of accumulated HMs as mere contaminants, this review proposes a novel paradigm that treats them as biologically preorganized metal precursors. We comprehensively summarize how endogenous subcellular coordination influences metal dispersion, phase transformation, and metal-carbon interactions during thermal conversion. Rather than claiming universal superiority, we comparatively evaluate the distinct structural regulatory roles of endogenous pre-organization versus exogenous modifications, highlighting their complementary advantages in tailoring pore topologies and catalytic active sites (e.g., highly dispersed single atoms). Furthermore, we evaluate the structure-activity relationships of these derived materials in targeted applications, including pollutant adsorption, non-radical persulfate activation, and photo-/electrocatalysis. Finally, to advance this field from laboratory-scale concepts to circular economy implementation, this review emphasizes the necessity of speciation-resolved environmental risk assessments coupled with Life Cycle Assessment (LCA) and Techno-Economic Analysis (TEA).