Self-catalytic decomplexation of Cu-TEPA and simultaneous recovery of Cu by an electrochemical ozone production system using heterojunction Ni-Sb-SnO2 anode

Recovery of heavy metal complexes from wastewaters: A critical review of mechanisms and technologies

Heavy metal complexes (HMCs) pose significant ecological challenges while also holding attractive economic value. This review comprehensively summarizes advanced techniques for recovering HMCs from wastewater, including reductive recovery, oxidative decomplexation-recovery, and non-redox separation. Physical and chemical separation approaches utilize specific properties of metal complexes for efficient segregation. Specifically, we explore oxidative decomposition techniques, emphasizing the underlying mechanisms and practical application for selective and non-selective decomplexation techniques. The crucial role of cathodic potential on the efficiency and selectivity of electrochemical reduction processes is also examined. In addition, a comprehensive cost assessment, including energy consumption, associated with these recovering processes is investigated, and opinions on the inadequacy of current studies are provided. Overall, this review uniquely integrates findings on selective physical separation, oxidation, and reduction processes as well as the cost assessments for these techniques, providing a novel and comprehensive perspective on heavy metal recovery. It aims to bridge existing gaps in literature and advance the development of effective recovery methodologies for HMCs.

Removal of Nickel-Citrate by KOH-Modified Arundo donax L. Biochar: Critical Role of Persistent Free Radicals

Removal of heavy metal complexes (HMCs) from wastewater poses significant challenges to waste water treatment due to the inherent stability of these compounds. In this study, KOH modified Arundo donax L. leaves biochar was developed, which demonstrated a remarkable capacity for nickel-citrate (Ni-Cit) removal. The results found that the modified biochar with a KOH-to-biomass ratio of 1:1 (1KBC) showed over 500-fold increase in specific surface area compared to the original biochar, along with enhanced surface functional groups and persistent free radicals (PFRs). 99.2 % of nickel was removed from 50 mg/L Ni-Cit with 1 g/L of 1KBC in 4 h. It also demonstrated exceptional potential in continuous treatment. LC-MS, EPR analysis, and DFT calculations revealed that the PFRs on the biochar surface played critical role for the Ni-Cit removal. Reactive oxygen species (ROS) initiated by PFRs, especially O₂•⁻, targeted the Ni-O coordination bonds, resulting in the decomplexation of Ni-Cit, while •OH and ¹O₂ facilitate the decarboxylation of the citrate ligand. The released Ni was then adsorbed onto the biochar. It indicated that the 1KBC removed Ni-Cit in one-step process with combined oxidation and adsorption. This research offers a promising technique for the efficient decomplexation and recovery of HMCs.

Cu/Mn-mediated electron shuttle and high-valent metals enhance hydroxyl radicals production during the electrochemical oxidation on the CuMn-Sb-SnO2 electrode

In this work, a novel CuMn-Sb-SnO2 anode is developed by a simple, low-cost preparation process. The doping of Cu and Mn causes surface reconstruction, which optimizes its electronic structure, compared to the Sb-SnO2 anode. Experimental results demonstrate that the levofloxacin degradation kinetics constant in the CuMn-Sb-SnO2 system (0.188 min-1) was 8.5 times higher than that in the Sb-SnO2 system, which is surpassing most reported anodes. Moreover, electrochemical characterization also revealed that the CuMn-Sb-SnO2 anode possessed more active sites, higher OEP potential, and lower charge transfer resistance. Notably, electrochemical characterization and EPR experiments confirmed the formation of Cu (III), highlighting their crucial role in promoting the generation of •OH during the catalytic process. Additionally, theoretical calculations and XPS analysis revealed that Cu and Mn rely on self-mediated redox shuttles to act as "electron porters", significantly accelerating internal electron transfer between Sn and Sb to enhance the production of •OH. Furthermore, the CuMn-Sb-SnO2 anode exhibits great practicability due to its efficient degradation of various antibiotics. This study offers valuable new insights into developing novel electrodes for the efficient degradation of antibiotic wastewater.