The Study On Adsorption Of Heavy Metal Ion Onto Surfaces Of PE And PP In Freshwater

As a new environmental pollutant,microplastics have been attracted worldwide attention in recent years.Some other additives will be added in plastic products during the production process,since microplastics formed by plastics under natural conditions have strong adsorption properties,microplastics are easy to absorb other pollutants in environmental media.When microplastics are excessively intaked into the body of aquatic organism in water,they will do harm to the normal function of organisms.Because of the difficult degradation of microplastics,the pollutants carried by microplastics can be transmitted along the food chain,which will eventually threaten the stability of the ecosystem and human health.In addition,heavy metal pollution has been given much emphasis.for a long time.The microplastics in water environment can enrich heavy metals from industiral sewage,and cause further environmental pollution through migration and diffusion in water.In this study,freshwater midia was taken as the experimental background,abundant microplastics in the environment such as polyethylene(PE)and polypropylene(PP)were selected as study objects.The adsorption of Cu(?),Cr(?)and Cr(?)onto PE or PP in ultrapure water or tap water was discussed.The adsorption fitting was done by kinetic model and adsorption isotherm:model.The kinetic model included quasi-first-order,adsorption kinetic model and quasi-second-order adsorption kinetic model.The adsorption isotherm model included Langmuir adsorption model,Freundlich adsorption model and Linear adsorption model.According to the fitting results,the adsorption mechanism was discussed.The study results were obtained as follows:(1)The adsorption behavior of Cu(?)?Cr(?)and Cr(?)onto surfaces of PE and PP had the highest fitting degree with quasi-second-order adsorption kinetic model and Langmuir adsorption isotherm model,this showed that the adsorption process had multiple adsorption phases,physical and chemical adsorption behavior existed at the same time,and adsorption behavior was a typical nonlinear adsorption process.Physical adsorption was mainly affected by Van Der Waals force,electrostatic force and micropore filling mechanism.Chemical adsorption mainly involved ion coordination of adsorbate with active groups of adsorbent molecule.Chemical adsorption is mainly based on the ion coordination between the adsorbate and the active group of the adsorbent molecular.(2)T he adsorption capacity of Cu(?)and Cr(?)onto surfaces of PE and PP was different.The adsorption capacity of the same heavy metal ions onto microplastics was ranked as PP in ultrapure water>PE in ultrapure water>PP in tap water>PE in tap water.The adsorption was not only affected by microplastics characteristics such as type or amount of active groups,degree of crystallinity,and surface free energy,but also affected by environmental media such as pH and ionic strength of solution.Under the same solution condition,the adsorption rate of Cr(?)was higher than Cu(?),It depends on heavy metals properties such as crystal structure,solubility product and partical charge.(3)The adsorption was also affected by different valence state of metal ions.The adsorption capacity of Cr(?)and Cr(?)onto surfaces of PE and PP was different.Under acidic conditions,the adsorption rate of Cr(?)was higher than Cr(?).Their adsorption mechanism was same,such as ion coordination and combination with methyl or methylene on adsorbent molecule.Cr(?)formed complexes with water molecules under acidic conditions,further weakened the coordination ability of Cr(?)with methyl or methylene,but Cr(?)had little effect on coordination ability because it formed acid radical anion.