Heavy metal removal from coal fly ash for low carbon footprint cement

Abstract

Development of cementitious materials with low carbon footprint is critical for greenhouse gas mitigation. 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. Traditional acid washing processes for heavy metal removal suffer from high chemical consumption and high-volume wastewater streams. Here, we report a rapid and water-free process based on flash Joule heating (FJH) for heavy metals removal from CFA. The FJH process ramps the temperature to ~3000 °C 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. The purified CFA is partially substituted in Portland cement, showing enhanced strength and less heavy metal leakage under acid leaching. Techno-economic analysis shows that the process is energy-efficient with the cost of ~$21 ton−1 in electrical energy. 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. The FJH strategy also works for decontamination of other industrial wastes such as bauxite residue.

Editors’ Choice 2023

“…To address this problem, Deng et al reported in Communications Engineering 9 a rapid and water-free process for heavy metal removal from CFAs for low-carbon footprint cement. Flash Joule Heating (FJH), an efficient high-temperature technology 10 , was used.…”

Electric Field Effects in Flash Joule Heating Synthesis

“…Flash Joule heating (FJH), as a method exhibiting high-energy efficiency and an ultrafast heating rate, has recently been used in the synthesis of many materials including graphene, − transition metal chalcogenides, inorganic nanoparticles, , and various other carbide and inorganic compounds. − It has also been widely explored as a method for effective remediation of soil and battery electrodes as well as a method for recycling and upscaling materials. − In contrast to conventional chemical heating methods, which use conductive or radiative heating, Joule heating requires an electric current to flow through the sample itself, which, in turn, directly heats the feedstock. Passing this electric current through the reactants involves imposing an electrical potential difference, typically up to several hundred volts, across a reaction vessel that is several centimeters across, leading to average electric fields on the order of 10 3 –10 4 V/m and a current density of 10 5 –10 7 A/m 2 .…”

Recovery of rare earth elements from low-grade coal fly ash using a recyclable protein biosorbent

“…Coal power plants worldwide release millions of tons of coal ash annually and are landfilled. The leaching of toxic trace elements and ash spill events make landfills a significant environmental challenge ( Deng et al, 2023 ). The recovery of REEs from FA has several advantages, which include readily available waste products, not requiring extensive excavation, and having a fine powder nature that makes it ideal for chemical processing ( Taggart et al, 2016 ).…”