Extraction of heavy metals from water using chelating agents: a comprehensive review

Concern over heavy metal pollution has rapidly grown over the past few years due to rapid industrialization and population growth. These metal cations are known to have various detrimental effects on the environment, more so on humans and plants. To date, several technologies such as photocatalysis, adsorption and ion exchange have been employed to remove these heavy metal pollutants from the environment and specifically water. However, most of these methods suffer from several disadvantages that limit their application for the speciation of heavy metals, particularly at trace levels. Chelation extraction technique is thus emerging as a promising alternative for the removal of heavy metal cations as it is effective even at trace levels of the cations. In addition, chelation extraction has high selectivity as the nature of the chelating agent/ligand can be fine-tuned towards specific metal cations. This review article captures research findings reported over the past decade on the design and applications of chelating ligands in the removal of heavy metal cations from water. The main focus is on the ligand design, mode of administration, and optimum extraction conditions while also comparing these ligand moieties with other chelating compounds utilized in heavy metal extraction. A summary of the sources and effects of heavy metals in the environment as well as the existing technologies for heavy metal remediation are also highlighted.