Experiments on Zn^2＋ and Cd^2＋ adsorptions on vermiculite in aqueous solutions were conducted to investigate the widely observed adsorbent concentration effect on the traditionally defined adsorption isotherm in the...Experiments on Zn^2＋ and Cd^2＋ adsorptions on vermiculite in aqueous solutions were conducted to investigate the widely observed adsorbent concentration effect on the traditionally defined adsorption isotherm in the adsorbate range 25--500 mg/L and adsorbent range 10--150 g/L. The results showed that the equilibrium ion adsorption density did not correspond to a unique equilibrium ion concentration in liquid phase. Three adsorbate/adsorbent ratios, the equilibrium adsorption density, the ratio of equilibrium adsorbate concentration in liquid phase to adsorbent concentration, and the ratio of initial adsorbate concentration to adsorbent concentration, were found to be related with unique values in the tested range. Based on the assumption that the equilibrium state of a liquid/solid adsorption system is determined by four mutually related components： adsorbate in liquid phase, adsorbate in solid phase, uncovered adsorption site and covered adsorption site, and that the equilibrium chemical potentials of these components should be equalized, a new model was presented for describing ion adsorption isotherm in liquid/solid systems. The proposed model fit well the experimental data obtained from the examined samples.展开更多
Metal contaminants from surface water pollution events often enter hyporheic zones,under certain conditions,they may be released back into streams,causing secondary pollution to the water quality.The present study inv...Metal contaminants from surface water pollution events often enter hyporheic zones,under certain conditions,they may be released back into streams,causing secondary pollution to the water quality.The present study investigated the effects of adsorption,permeability,and anisotropy of sediment beds on the release of zinc ions(Zn^(2+))from the hyporheic zone into overlying turbulent flows using large-eddy simulations(LES).The volume-averaged Navier-Stokes equations and advection-diffusion equation with adsorption term were used to describe the sediment in-flow,adsorption,and convective diffusion of Zn^(2+) within the sediment layer.The effects of sediment permeability on the Zn^(2+)concentration distribution and mass transfer processes were investigated by time-averaged statistics of flow and concentration fields.The results show that adsorption becomes stronger as the pH value increases,leading to a slow increase in Zn^(2+)concentration in the overlying water layer and reaching a lower steady-state concentration.Higher overall permeability of the sediment layer can enhance mass and momentum exchange near the sediment-water interface(SWI),and intensify the release of Zn^(2+)from the sediment layer into the overlying water.As the wall-normal permeability of the sediment layer increases,the normal turbulent intensity strengthens,momentum transport enhances,the wall-normal Zn^(2+)concentration flux increases,the effective diffusion coefficient increases,and the concentration in the overlying water increases.展开更多
文摘Experiments on Zn^2＋ and Cd^2＋ adsorptions on vermiculite in aqueous solutions were conducted to investigate the widely observed adsorbent concentration effect on the traditionally defined adsorption isotherm in the adsorbate range 25--500 mg/L and adsorbent range 10--150 g/L. The results showed that the equilibrium ion adsorption density did not correspond to a unique equilibrium ion concentration in liquid phase. Three adsorbate/adsorbent ratios, the equilibrium adsorption density, the ratio of equilibrium adsorbate concentration in liquid phase to adsorbent concentration, and the ratio of initial adsorbate concentration to adsorbent concentration, were found to be related with unique values in the tested range. Based on the assumption that the equilibrium state of a liquid/solid adsorption system is determined by four mutually related components： adsorbate in liquid phase, adsorbate in solid phase, uncovered adsorption site and covered adsorption site, and that the equilibrium chemical potentials of these components should be equalized, a new model was presented for describing ion adsorption isotherm in liquid/solid systems. The proposed model fit well the experimental data obtained from the examined samples.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12172207,92052201).
文摘Metal contaminants from surface water pollution events often enter hyporheic zones,under certain conditions,they may be released back into streams,causing secondary pollution to the water quality.The present study investigated the effects of adsorption,permeability,and anisotropy of sediment beds on the release of zinc ions(Zn^(2+))from the hyporheic zone into overlying turbulent flows using large-eddy simulations(LES).The volume-averaged Navier-Stokes equations and advection-diffusion equation with adsorption term were used to describe the sediment in-flow,adsorption,and convective diffusion of Zn^(2+) within the sediment layer.The effects of sediment permeability on the Zn^(2+)concentration distribution and mass transfer processes were investigated by time-averaged statistics of flow and concentration fields.The results show that adsorption becomes stronger as the pH value increases,leading to a slow increase in Zn^(2+)concentration in the overlying water layer and reaching a lower steady-state concentration.Higher overall permeability of the sediment layer can enhance mass and momentum exchange near the sediment-water interface(SWI),and intensify the release of Zn^(2+)from the sediment layer into the overlying water.As the wall-normal permeability of the sediment layer increases,the normal turbulent intensity strengthens,momentum transport enhances,the wall-normal Zn^(2+)concentration flux increases,the effective diffusion coefficient increases,and the concentration in the overlying water increases.
