Efficient leaching of Li from coal fly ash and application of leaching residue for removal of Cu(ii) from wastewater: New waste-to-value approach

Coal fly ash (CFA), a significant industrial solid waste, presents environmental challenges, while the management of heavy metal contaminated water remains a global concern, and lithium (Li) plays an irreplaceable role in supporting global economic and technological progress. Consequently, to overcome the double challenge of limited supply of strategic metals and environmental threats, a sustainable process for the efficient leaching of lithium from CFA (LRCFA) and removal of Cu(ii) from electroplating wastewater using leaching residue was developed in this study. Roasting leaching experiments demonstrated that the leaching efficiency of elemental Li was as high as 95.33 % under the most favorable experimental conditions. Environmental risk assessment confirmed that the leachability of heavy metals from all solid residues met relevant environmental standards, ensuring their environmental safety. The adsorption and removal of Cu(ii) from LRCFA were significantly better than that from CFA and roasting residue (RCFA) at pH 6–7. The adsorption of Cu(ii) on LRCFA was in accordance with the proposed pseudo-second-order kinetics and Langmuir model, and the maximum adsorption of Cu(ii) was 41.76 mg/g. The results of the mechanistic analyses exhibited that the roasting of NaCl disrupted the CFA structure and enhanced the leachability of Li, while the Si-O-Al framework of the generated LRCFA promoted the binding of Cu(ii) through ion exchange and complexation with surface functional groups. This work demonstrates the valuable utilization of solid waste for critical metal recovery and wastewater remediation.