Investigating adsorption of various heavy metal ions by the reaction products of chrysotile and lizardite-acid interface

Abstract

With the intensification of mineral resource exploitation, processing activities, and industrial operations worldwide, local soil and water bodies are becoming more and more acidified. Under acidic conditions, the chemical reaction at the interface between serpentine minerals, which are abundant on Earth, and water becomes more complex. Particularly, in slightly acidic wastewater, multiple heavy metal ions often coexist. Therefore, it is of great significance to study the interface ion-specific adsorption behavior of different heavy metal ions by the reaction products at the serpentine-water interface. This study, selected chrysotile and lizardite with distinct structures as raw materials to investigate the variations in their structure, morphology, and associated properties in a 1 mol/L sulfuric acid solution, along with the adsorption characteristics of the reaction products for typical heavy metal ions such as Cr³⁺, Mn²⁺ and Ni²⁺. The results indicate that during the acid treatment process, serpentine minerals with different structures are subjected to varying degrees of structural damage, particularly lizardite, which suffers more severe structural damage. Additionally, the specific surface area and pore volume of the reaction products increased, especially the increase in the edge structure, which enhanced the saturated adsorption capacity for Cr³⁺, Mn²⁺ and Ni²⁺. Kinetics studies revealed that the adsorption effect of the reaction products of serpentine on Cr³⁺ was the most pronounced, indicating an obvious preferential competitive adsorption behavior. The adsorption of these heavy metal ions onto the reaction products followed pseudo-second-order kinetic models as well as Langmuir isothermal adsorption models. This suggests that their adsorption mechanism is mainly a chemical process of monolayer adsorption. Thermodynamic analysis showed that temperature had the most significant influence on the adsorption process of Cr³⁺ among the studied heavy metal ions. These findings contribute to a deeper understanding the serpentine-water interface reaction process, the self-purification effect, and its impact on Earth's surface ecosystems.