Coagulation behavior of humic acid in aqueous solutions containing Cs+, Sr2+ and Eu3+: DLS, EEM and MD simulations. (May 2018)

• Record Type: Journal Article
• Authors: Tan, Liqiang; Tan, Xiaoli; Mei, Huiyang; Ai, Yuejie; Sun, Lu; Zhao, Guixia; Hayat, Tasawar; Alsaedi, Ahmed; Chen, Changlun; Wang, Xiangke
• Is Part Of: Environmental pollution. Volume 236(2018)
• Page Start: 835
• Page End: 843
• Publication Date: 2018-05
• Subjects: Humic acid -- Coagulation -- Nuclides -- Fluorescence -- Molecular dynamic simulation; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2018.02.019
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: The coagulation behaviors of humic acid (HA) with Cs + (10–500 mM), Sr 2+ (0.8–10.0 mM) and Eu 3+ (0.01–1.0 mM) at different pH values (2.8, 7.1 and 10.0) were acquired through a dynamic light scattering (DLS) technique combined with spectroscopic analysis and molecular dynamic (MD) simulations. The coagulation rate and the average hydrodynamic diameter (< D h >) increased significantly as the concentration of nuclides increased. < D h > could be scaled to time t as < D h > ∝ t a at higher Sr 2+ concentrations, which shows that HA coagulation is consistent with the diffusion-limited colloid aggregation (DLCA) model. Trivalent Eu 3+ induced HA coagulation at a much lower concentration than bivalent Sr 2+ and monovalent Cs + . The coagulation value ratio of Sr 2+ and Eu 3+ to Cs + is almost proportional to Z −6, indicating that the HA coagulation process is generally consistent with the Schulze-Hardy rule. Spectroscopic analysis indicated that the complexation between nuclides and carboxylic/phenolic groups of HA molecules played important roles in the coagulation of HA. MD modelling suggested that Sr 2+ and Eu 3+ ions increased the coagulation process through the formation of intra- or inter-molecular bridges between negatively charged HA molecules, whereas for Cs +, no inter-molecular bridges were formed. This work offers new insight into the interactions between HA and radionuclides and provides a prediction for the roles of HA in the transportation and elimination of radionuclides in severely polluted environments. Graphical abstract: Image 1 Highlights: Carboxylic/phenolic groups play important roles in the coagulation of HA. Nuclides affect the HA coagulation by forming intra- or inter-molecular bridges between different HA molecules. Decrease in pH, increases in nuclides' concentration and valence promote the coagulation of HA in the environment. Abstract : The coagulation of HA in the presence of different metal ions was studied by batch, DLS, EEM and MD simulations, and the complexation between HA and metal ions strongly influenced the physicochemical behavior of HA in the natural environment.