关键词: 煤基腐植酸, 结构特征, Cd2+, 解吸, ζ电位

Abstract: HA-Cd stability is the key to the effectiveness of humic acid adsorbents in treating cadmium-contaminated wastewater or soil. There is a risk of release of Cd2+ from HA-Cd in different pH environments. In this paper, pure water, pH=3 acetic acid, pH=5 or 7 acetic acid-sodium acetate buffer solutions were used as desorption agents to study the adsorption stability of coal-based HA-Cd. The results show that the functional group, humification and aromatization degree of coal humic acid are the main structural features that affect the stability of HA-Cd. HA1 has more active oxygen-containing functional groups than HA2, so adsorption capacity of Cd2+ is higher than HA2. At the initial concentration of Cd2+ is 100mg/L, Cd2+ adsorption capacity of HA1 and HA2 could reach 905mg/g and 582mg/g. Both HA1-Cd and HA2-Cd show excellent stability in pure water desorption. As the initial concentration of Cd2+ increases, the retention rate of Cd2+ decreases slightly, but overall more than 80%. After desorption of acetic acid solution with pH=3, the retention rate of Cd2+ decreases significantly. Due to the higher degree of humification and aromatization, HA2 has a larger degree of agglomeration in the adsorption process of high concentration Cd2+ solution, and the retention of Cd2+ is stronger. The desorption regularity of HA1-Cd and HA2-Cd is consistent with the increase of initial concentration of Cd2+ in desorption solution with pH=5 and 7. When the concentration of Cd2+ is higher, the retention rate after three desorption is higher, which is about 60%. Zeta potential analysis shows that there are two pathways of Cd2+ dissociation including spontaneous dissociation and ion exchange. The co-action of H+, Na+ and acetate ligand would lead to the re-release of the unstable Cd2+. This study clarified the desorption law of HA-Cd in different acidity environments and the influence of HA composition and properties on the retention characteristics of Cd2+, which provided a scientific basis for the effective treatment of cadmium pollution in wastewater or soil by coal humic acid and the prevention of secondary pollution caused by unstable adsorption.