Ground-Breaking and Safe Recycling of Hazardous Hyperaccumulators

Hyperaccumulators are annually mass-produced, which may ultimately endanger the environment and human health without an appropriate treatment. However, the current pyrolysis technique cannot achieve efficient metal removal and produces low-value materials due to its limited heating temperature and unitary operational principle. Herein, a ground-breaking flash Joule heating (FJH) was proposed to recycle a typical zinc-enriched hyperaccumulator to a profitable material (flash graphene) with a superior metal removal efficiency. The results indicate that the FJH-induced instantaneous ultrahigh temperature (similar to 3000 K, 20 s) promotes metal removal efficiency and graphitization of hyperaccumulators and simultaneously current exfoliates to form 3-7 layer graphene. Moreover, light spot moving and luminance fluctuation visualized by a high-speed camera confirm that metals are adequately evaporated to squirt out from the parental hyperaccumulator. Furthermore, the crystal phase inducer evokes the chlorination reaction to improve metal removal efficiency (98.6%) under less impacts on forming a graphene structure. Accordingly, flash graphene is examined by seed germination, indicating that it is environmentally safe with a few remaining metals or environmentally persistent radicals. Then, the tested graphene with a thin layer enables a more efficient photothermal conversion for solar-driven water evaporation than pyrochar. Moreover, the economic assessment indicates that profits from the FJH treatment are similar to 850-fold higher than that from pyrolysis. Thus, FJH is an avant-garde recycling technique to renovate hazardous hyperaccumulators.