Study On Adsorption Behavior And Mechanism Of U(Ⅵ) By Polystyrene Microplastics

Microplastics,as a kind of emerging environmental pollutants,are regarded as an ideal carrier of heavy metal pollutants due to their small size and large specific surface area.After ultraviolet irradiation,the surface properties and microstructure of microplastics will change,and then affect the adsorption behavior of heavy metals on microplastics.Besides,other complex external environmental factors and the properties of microplastics will also affect the adsorption behavior of heavy metals on microplastics.Furthermore,microplastics can form compound pollution with heavy metals,and thus change their original environmental behaviors and harms.However,as a heavy metal with both radiological and chemical toxicity,the interaction characteristic and mechanism between radionuclides and microplastics remain very limted.In the present work,the typical polystyrene（PS）microplastics was selected.The aging characteristics of PS were investigated under UV irradiation,and the adsorption behavior of typical radionuclide uranium（U（Ⅵ））on virgin and aged PS microplastics was studied.The effects of solution p H,the dosage of microplastics,the particle size of microplastics,solution salinity and coexisting ion on the adsorption of U（Ⅵ）by virgin and aged PS microplastics were explored.The interaction of virgin and aged PS microplastics for U（Ⅵ）was studied by adsorption kinetics,adsorption isotherm and adsorption thermodynamics.Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to analyze the properties of virgin and aged PS microplastics and the adsorption mechanism of U（Ⅵ）.These results may provide a theoretical basis for evaluating the combined pollution migration of microplastics and heavy metals.The main conclusions of this paper are as follows.（1）After aging,there were cracks and pits on the surface of PS microplastics,and the color of PS microplastics was yellow.The characteristic absorption peaks of OH,C=O,C-OH and other functional groups were observed on the fourier transform infrared spectroscopy spectrum of aged PS microplastics,indicating that oxygen-containing groups were formed on the surface of aged PS microplastics.（2）The adsorption capacity of PS microplastics for U（Ⅵ）first increased and then decreased with the increase of solution p H value.The adsorption capacity of virgin PS and aged PS microplastics for U（Ⅵ）reached the peak at p H5 and p H7,respectively.The phenomenon differences are related to the potential change of PS microplastics and the different morphological distribution of U（Ⅵ）under different p H conditions.（3）Cd²⁺,Cu²⁺,Fe³⁺,Zn²⁺,Mn²⁺and Pb²⁺ions significantly reduced the adsorption capacity of virgin and aged PS microplastics for U（Ⅵ）.Cs²⁺and Ca²⁺ions promoted the adsorption capacity of virgin PS microplastics for U（Ⅵ）,while K⁺and Sr²⁺ions increased the adsorption capacity of aged PS microplastics for U（Ⅵ）.（4）The adsorption of U（Ⅵ）by virgin and aged PS microplastics conformed to the pseudo-second order kinetic model and Freundlich model,indicating that the adsorption of virgin and aged PS microplastics for U（Ⅵ）can be controlled by chemical adsorption,which was a multi-layer adsorption process.（5）Based on the analysis of characterization,adsorption experiment,adsorption isotherm,adsorption kinetics and thermodynamics of PS microplastics,the adsorption mechanisms of U（Ⅵ）onto PS microplastics mainly included electrostatic interaction,hydrogen bonding and complexation（aged PS）...