Remediation of heavy metal complexes from water and wastewater: a comprehensive review of commonly used methods

Heavy metals are emerging pollutants that originate largely from anthropogenic activities. Their remediation in the free ion state was successfully achieved by simple alkali precipitation. However, the presence of organic compounds in aqueous media from diverse sources coexisting with heavy metals leads to the formation of stable, soluble, and recalcitrant complexes that challenge conventional treatment methods. Therefore, the remediation of heavy metal complexes (HMCs) has been extensively studied by researchers, resulting in the development of methods and techniques such as the use of chelating agents, bioadsorbents, and advanced oxidation processes for their treatment. In this review, the route to the environment, concentration level, and associated potential harm or damage caused by HMCs were covered. A detailed and comprehensive bibliometric analysis of publications dealing with the methods and mechanisms for the removal of various metal complexes was conducted. This review introduces the chemical interaction within the heavy metal complex (metal + organic ligands), summarises and discusses the newly developed methods, as well as their treatment performance and limitations for such newly formed pollutant compounds. To the best of our knowledge, this is the first article to provide a systematic summary of common and attractive methods employed for the remediation of HMCs.