Effect of microplastics on the adsorption and desorption characteristics of heavy metal Ni(II) under different aging modes

Abstract Plastic products have brought great convenience to people's lives, but microplastics are formed when waste plastic products are discharged and undergo weathering and degradation processes. Microplastics can act as carriers of pollutants such as heavy metals through adsorption and desorption, thus threatening the health of living organisms. In this study, typical microplastics Polystyrene (PS) and Polylactic acid (PLA) were targeted to investigate the adsorption and desorption characteristics of heavy metal nickel before and after freeze-thaw cyclic aging, alternating dry and wet aging, and alkali aging. After three kinds of aging, the specific surface area, pore size, and crystallinity of the two microplastics increased, and oxygen-containing functional groups appeared on the surface of the microplastics. Adsorption experiments demonstrated that the kinetics of nickel adsorption by microplastics was more compatible with the proposed second-order model and the adsorption isotherms were more consistent with the Langmuir model. The adsorption capacity after aging was greater than that of the original microplastics, and the adsorption capacity was alkali aging > alternating wet and dry aging > freeze-thaw cycle aging. The adsorption capacity of PLA was greater than that of PS. Alkali aging resulted in the highest amount and rate of nickel desorption from the microplastics. The results of freeze-thaw cycle aging and alternating wet and dry aging did not differ much. It provides a basis for studying the aging process of microplastics and its potential impact on the adsorption and desorption of heavy metals in the environment.