Abstract:
With the rapid development of the economy and society and the continuous emission of cadmium (Cd), Cd pollution has become a major environmental problem faced by China and even the world. As the most active component in organic matter, molecular weight of DOM is usually between several Da and several hundred kDa.The various active functional groups contained in DOM, such as carboxyl, hydroxyl, and phenolic groups, are ligands and migration carriers for many heavy metals in the environment. The interaction between DOM and Cd significantly affects the morphology, bioavailability, toxicity, and migration transformation of Cd in the environment through physical adsorption, ligand exchange, and surface complexation. However, from the perspective of cadmium pollution remediation, the complexation between Cd and DOM is a key factor controlling the effectiveness of Cd remediation. DOM can directly form DOM Cd binary complexes through ligand exchange. According to the different bridging positions of DOM, Cd(Ⅱ), and mineral/metal surface cations (Mi/Me), two types of ternary complexes can also be formed: A or B.DOM has complex and diverse sources, components, and structures, under different conditions, DOM exhibits two effects on Cd: passivation or activation, which has been widely used in in-situ passivation remediation, leaching remediation, or phytoremediation of Cd pollution. Based on the review of relevant research results in recent years, this article evaluates the types of complexation between Cd and DOM, and analyzes the effects of factors such as DOM molecular weight, pH, ion strength, and temperature on Cd-DOM complexation and the mechanism of Cd adsorption and desorption. On this basis, Summarize the application research of DOM in in-situ passivation remediation and ex-situ remediation of soil/sediment Cd pollution. These methods help to reduce environmental risks and remediation costs of Cd pollution remediation. Under normal circumstances, small molecular weight DOM contains richer functional groups and more complex coordination sites, making it easy to form soluble DOM-Cd complexes. Especially for DOM components with molecular weight<30kDa, which can release more Cd into the environment; Under higher pH environmental conditions, it is beneficial to enhance the stability of DOM-Cd complexes and soil adsorption of Cd, while high ionic strength has a strong inhibitory effect on Cd adsorption; In the remediation of Cd pollution, selecting larger molecular weight DOM (>30kDa) with higher humification degree and applying inorganic passivators such as iron oxides can significantly improve the in-situ passivation and remediation effect of Cd pollution; In the chemical leaching or phytoremediation of Cd, small molecular weight DOM (<5kDa) is selected to improve the effectiveness of pollution remediation. it is recommended to conduct research in the following three areas in the future: firstly, study the complexation between different molecular weights of DOM and Cd, and accurately analyze the complexation between functional groups of different components inside DOM and Cd. Secondly, strengthen the research on the adsorption, desorption, migration, transformation, and bioavailability of Cd by DOM under the influence and control of multiple factors. Finally, Strengthen the research on DOM in Cd pollution remediation technology, improve the numerical simulation model of the interaction between DOM and Cd, provide path guidance and data support for long-term observation of Cd pollution, and more accurately reveal the migration and transformation process of Cd in the environment.