| Metal-based nanoparticles(MNPs)have the potential to be released into the environment during the process of manufacturing,transportation,usage and eventual disposal which may pose potential risks to ecological environment and human health.The potential risks of MNPs directly depend on their transport and distribution in porous media represented by soil and groundwater,investigation of the transport and retention behaviors of MNPs in porous media is important to accurately predict the exposure risks.Therefore,This study selected CuO NPs as typical MNPs to investigate the impact of solution properties(pH,ionic strength,dissolved organic matter(NOM)and flow rate)on the transport and retention behaviors of typical MNPs in porous media filled with clean quartz sand,the transport and retention characteristics and related mechanism of CuO NPs were discussed by DLVO and colloid filtration theory.The main conclusions are as follows:(1)The effects of solutions properties on the aggregation behaviors of CuO NPs were revealed:The aggregation degree of CuO NPs increased with the increase of ionic strength.In the case of low concentration of NOM(0.1 mg-C/L HA and 0.01 mg-C/L Cit),CuO NPs aggregation degree increased with the nonpolar reaction between NOM long chain fraction;In the case of high concentration NOM(0.25-10 mg-C/L HA and 0.025-1 mg-C/L Cit),NOM inhibited the aggregation degree of CuO NPs by increasing the electrostatic repulsion and steric repulsion between CuO NPs,and the degree of inhibition increased with the increase of NOM concentration.(2)The influence mechanisms of pH,ionic strength on the transport and retention of CuO NPs in different flow rate were clarified:the influence of pH and ionic strengtih on the tranport behavior of CuO NPs was related to the flow rate.At low flow velocity 0.375 cm/min,the influence of pH and ionic strength on the transport and retention behavior of CuO NPs was not obvious,the deposition of CuO NPs on the surface of quartz sand due to that the drag force of hydrodynamic was smaller than its own gravity,which was the NOMinant mechanism to control the transport and retention behavior of CuO NPs;At 0.750 cm/min,for pH 6,the CuO NPs-Collector DLVO interaction was NOMinated by attraction,the influence of ionic strength on the transport and retention behavior of CuO NPs was not obvious;for pH 8 and pH 9,CuO NPs-CuO NPs DLVO potential energy barrier was less than the CuO NPs-Collector,new inputs CuO NPs were easy to aggregate on the surface of CuO NPs deposited on the surface quartz sand,resulting that Straining phenomenon bacame the NOMinant mechanism to control the transport and retention behavior of CuO NPs.At 3 cm/min,the effects of pH and ionic strength on the transport and retention behavior of CuO NPs was also not obvious,the deposition of CuO NPs on the surface of quartz sand due to that the drag force of hydrodynamic was bigger than CuO NPs-Collector DLVO potential energy barrier.which was the NOMinant mechanism to control the transport and retention behavior of CuO NPs.(3)The influence mechanisms of initial NOM concentration on transport and retention of CuO NPs were clarified:In the case of low concentration of HA(0.1 mg-C/L),CuO NPs deposited on the surface of quartz sand due to Straining phenomenon and the increase of coefficient of deposition rate,and with the increase of HA concentration,the transport ability of CuO NPs increased first and then decreased,the transport ability was strongest at 0.5 mg-C/L HA,which was consistent with the variation trend of CuO NPs-Collector XDLVO potential energy barrier.In the case of low concentration of Cit(0.01 mg-C/L),CuO NP deposited on the surface of quartz sand due to ripening phenomenon and the increase of coefficient of deposition rate,and with the increase of Cit concentration,there was no significant changes in the transport ability of CuO NPs after the first increase,which was consistent with the variation trend of CuO NPs-Collector XDLVO potential energy barrier. |
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