Adsorption of Pb, Ni and Zn by coastal soils: Isothermal models and kinetics analysis

Coastal areas are facing increasing heavy metal pollution as a result of various anthropogenic activities, posing a serious threat to ecosystems. Modeling and understanding the sorption behavior of heavy metals in soils are essential for assessing their mobility and risk in the coastal landscapes. The aim of this study was to examine the adsorption behavior of Pb²⁺, Ni²⁺, and Zn²⁺ by common soil types of the Lower Don and the Taganrog Bay coast in Russia to better understand their potential environmental implications. The soil capacities for heavy metal adsorption and retention were determined using isothermal models. The maximum adsorption capacity and the binding strength parameter for the heavy metals were calculated, revealing significant differences among the soils. Haplic Chernozem emerged with superior values, while Gleyic Solonchak Sulfidic and Umbric Fluvisol trailed the lowest. All soils exhibited a greater adsorption capacity and binding strength for Pb compared to the other metals. The influence of soil characteristics on sorption and retention was also examined. The Pseudo-second-order model provided a more accurate description of the adsorption kinetics of heavy metals by the studied soils. The co-presence of metals in the system affected their sorption by the soils due to competition: soils adsorbed fewer metals but retained them more strongly. These findings are important for developing effective strategies to reduce heavy metal pollution in coastal ecosystems.