<p>Mercury and its compounds, particularly mercury chloride (HgCl₂), are highly toxic and persistent environmental pollutants. Understanding the adsorption behavior of HgCl₂ in clay-water systems is essential for developing effective mercury remediation strategies. This study investigates the effects of pH and background cations on the adsorption kinetics, adsorption energy, and dipole moment of HgCl₂ in montmorillonite clay systems. Adsorption experiments, along with infrared spectroscopy, were employed to measure the equilibrium adsorption capacity and kinetic behavior of HgCl₂. The results showed that the adsorption capacity of non-polar symmetric HgCl₂ is strongly dependent on pH and the type of background cation. Specifically, the adsorption energy increased with the surface electric field strength, which is modulated by pH and cation type. The dipole moment of HgCl₂, induced by the polarization in the montmorillonite electric field, also increased with pH values. Infrared spectroscopy analysis revealed that the covalent interaction between HgCl₂ and surface oxygen atoms (denoted as “O”) was more pronounced at a higher pH value. These findings not only provide new insights into the environmental behavior of HgCl₂ but also suggest improved approaches for mercury pollution control and soil remediation, with implications for enhancing the effectiveness of soil-water systems in mercury removal.</p>