Yanting Wang,Youmin Sun,Shengying Gong,Zhengqing Cai,Jie Fu
Silver nanoparticles (AgNPs) are one of the main nano-contaminants and their entry into the environment may pose a threat to the aquatic ecosystems . Meanwhile, AgNPs have an important impact on geological processes . In this paper, we studied the influence of AgNPs on the sedimentation of suspended sediments . Results showed the settling rate of sediments increased from 13.06 to 20.08 h −1 in the presence of 0.2 mg/L AgNPs. The morphology characterization indicated the average particle size of sediments increased from 34.74 to 42.87 μm after interacting with AgNPs, resulting in the acceleration of settlement on the basis of Stokes' law. The chemical analysis detected 43–57% of AgNPs were incorporated onto sediments, which was the dominant reason for the increased sediments size and settling rate. The influences of various water quality parameters, e.g., pH, ionic strength , temperature, humic acid and surfactant , on the sediments settlement and interaction with AgNPs were comprehensively studied. Elevating the solution pH, ionic strength, temperature, contents of humic acid and anionic/nonionic surfactants would suppress the settling of suspended sediments , whereas cationic surfactant showed a promoting effect on sediments settlement. In addition, the settling experiments were conducted in collected lake water and seawater , and results showed the real water matrices hindered the sediments settlement and interaction with AgNPs.
Green and efficient flocculants are crucial for the effective treatment and recycling of mine wastewater. Herein, the flocculation performance and mechanism of a novel amphoteric chitosan-based flocculant CMC-g-CPAM on kaolinite suspensions were investigated through settling tests, zeta potential measurements, floc size distribution, quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) measurements. Settling tests results revealed that CMC-g-CPAM displayed exceptional flocculation performance, achieving a settling rate of 18.21 m/h for kaolinite at natural pH, higher than that of chitosan-grafted-cationic acrylamide Chi-g-CPAM (11.19 m/h). The in-situ adsorption layer of CMC-g-CPAM on silica and alumina surfaces was more rigid than that of Chi-g-CPAM. Subsequently, more kaolinite particles were flocculated by CMC-g-CPAM, and formed a denser floc layer. The adsorption amounts of CMC-g-CPAM and Chi-g-CPAM on silica surfaces were found to be greater than those observed on alumina surfaces at natural pH. This phenomenon was related to the different surface charges of silica and alumina, electrostatic interactions between the polymers and surfaces. From AFM measurements, an attraction between the CMC-g-CPAM functionalized probe and the functional substrate as they approached each other and a weak adhesion force among CMC-g-CPAM (0.31 nN over 50 nm) were observed. These indicated the presence of intermolecular interactions among CMC-g-CPAM, which contributed to the formation of compact flocs. In contrast, an obvious repulsion was detected when the Chi-g-CPAM functionalized probe approached the functional substrate, inhibited the entanglement of polymer chains. Meanwhile, the interactions between multiple molecules and the substrate displayed a large adhesion force (2.10 nN over 150 nm), attributed to the less rigid adsorption layer of Chi-g-CPAM. Our findings would provide new insights into the design of flocculants and effective wastewater treatment.
危险品化学品经营许可证（带存储）