![]() In addition to the functional materials synthesis capability 34, 35, 36, the FJH process has been demonstrated to be an efficient method for sustainable management of carbon-rich wastes, such as consumer plastic 37, 38, rubber 39, end-of-life vehicle waste 40, and asphaltenes 41. The FJH process has been used to convert carbon-containing sources into flash graphene 33. The carbothermic shock was then widely applied for various nanomaterial syntheses 30, including silicon nanoparticles 31, high-entropy alloy nanoparticles 28, and single-atom catalysts 32. first reported the rapid Joule heating for the ultrafast synthesis of nanoparticles in reduced graphene oxide films 27. Recently, highly efficient, short-burst electric heating is emerging as a high-temperature technology for materials production 22, 23, 24, 25, 26, 27, 28 and solid waste management 29. The present methods for heavy metal removal mostly rely on the acid washing process, including the use of inorganic 20 or organic acids 21, both of which suffer from the consumption of chemicals and generation of large wastewater streams that reduce the value of economic incentives and result in secondary pollution 17, 20. Therefore, the removal of toxic elements from CFA is necessary prior to landfilling or secondary use. However, the leachability of heavy metals from CFA 16, 17, when it is in contact with aqueous environments such as rainwater, has impeded its applications in cement 18, 19. ![]() CFA with high calcium content has considerable cementitious properties 13, making it useful for OPC dilution 14, 15. As a result, reuse, rather than disposal or landfilling, of CFA is sought for both economic and environmental reasons 2, 7. The improper disposal of CFA has become an environmental concern because of potential water, soil, and air pollution 6, 12. Hence, CFA is classified as hazardous waste in some countries if the toxic substances exceed limits other countries regulate it as non-hazardous with special regulations 11. CFA is primarily silicon (Si), aluminum (Al), iron (Fe), and calcium (Ca) oxides while containing smaller amounts of heavy metals, such as cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), and mercury (Hg) 9, 10. CFA is the predominantly inorganic residue of coal combustion in power plant furnaces, with an annual worldwide production of ~750 million tons 7, 8. Hence, the cement industry is an important sector for GHG emission mitigation strategies 4, and there is renewed interest in alternative raw materials 5 with lower production emissions to replace or partially substitute the highest volume building material, ordinary Portland cement (OPC).Īmong the alternative cementitious materials 5, coal fly ash (CFA) has been extensively investigated and utilized worldwide 6. For example, global CO 2 emissions of cement production are ~1.5 Gt annually, representing ~8% of the total global GHG emissions 2, 3. Building materials are the third-largest source of anthropogenic carbon dioxide (CO 2) emission 2. The growing global demand for materials continuously increases greenhouse gas (GHG) emissions 1. The FJH strategy also works for decontamination of other industrial wastes such as bauxite residue. Life cycle analysis reveals the reuse of CFA in cement reduces greenhouse gas emissions by ~30% and heavy metal emissions by ~41%, while the energy consumption is balanced, when compared to landfilling. Techno-economic analysis shows that the process is energy-efficient with the cost of ~$21 ton −1 in electrical energy. The purified CFA is partially substituted in Portland cement, showing enhanced strength and less heavy metal leakage under acid leaching. The FJH process ramps the temperature to ~3000 ☌ within one second by an electric pulse, enabling the evaporative removal of heavy metals with efficiencies of 70–90% for arsenic, cadmium, cobalt, nickel, and lead. Here, we report a rapid and water-free process based on flash Joule heating (FJH) for heavy metals removal from CFA. ![]() ![]() Traditional acid washing processes for heavy metal removal suffer from high chemical consumption and high-volume wastewater streams. ![]() Coal fly ash (CFA) is an attractive diluent additive in cement due to its widespread availability and ultralow cost, but the heavy metals in CFA could leach out over time. Development of cementitious materials with low carbon footprint is critical for greenhouse gas mitigation. ![]()
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