Adsorption characteristics and mechanism analysis of heavy metal Cu(II) by cement soil

Cemented soil (CS), a specialised construction material, holds application value in controlling heavy metal ion migration and preventing environmental contamination. This study systematically investigated the adsorption behaviour and mechanisms of copper ion (Cu(II)) on CS under varying particle sizes and curing times through adsorption kinetics and isothermal adsorption experiments. The results demonstrated that the Elovich model (R2 > 0.94) exhibited lower error functions and more accurately described the heterogeneous surface diffusion reaction processes of CS. Chemisorption was the dominant mechanism. The isothermal adsorption behaviour evolved from the Freundlich model at the curing time of 14 days to the Sips model at the curing time of 28 days (approximating the Langmuir model), indicating a gradual transition from multilayer adsorption on heterogeneous surfaces to saturated monolayer adsorption. Notably, the equilibrium adsorption capacity of fine-grained CS (<0.075 mm) increased by 57.81% during the 7–28-day curing period, whereas coarse-grained CS [0.1–0.25 mm) exhibited only an 8.58% increase. This study identified a critical copper ion concentration threshold of 200–400 mg/l, marking the transition of CS from adsorption-dominated removal to a synergistic adsorption–precipitation mechanism. These quantitative findings provide a foundation for optimising CS-engineered barrier design and demonstrate value in heavy metal contamination remediation.