Adsorption of Mercury on Coarse Loamy Mixed Hyperthermic Ustic Haplocambids of Punjab

A coarse loamy mixed hyperthermic Ustic Haplocambid of Punjab was used in a laboratory study to test it for remediation of mercury (Hg) contaminated water using adsorption mechanism. In this study, the Langmuir adsorption model proved to be reasonable approximation of mercury adsorption onto the soil. With the increase in equilibrated soil solution temperature from 278 to 318 μK, the bonding energy of Hg adsorption by the soil enhanced from 0.0526 cm³ μg⁻¹ to 0.0869 cm³ μg⁻¹. However, the mercury adsorption maxima of the soil remained the same. The differential isosteric heat of Hg adsorption (∆H) was derived by applying Clausius-Clapeyron equation. As the amount of mercury adsorbed increased from 1100 to 1200 ìg Hg g⁻¹ soil, ∆H of soil markedly declined from 26.19 to 6.02 kJ mol⁻¹. However, at further higher levels of Hg adsorption (1200 to 2500 μg g⁻¹ soil), relatively slight change in ∆H (6.02–1.50 kJ mol⁻¹) was observed. Pourbaix diagrams drawn to understand the aqueous species and solid phases of Hg as a function of pe-pH in soil solution indicated that at highly reduced conditions between pH 4 to 8, HgS(c) was the dominant solid phase. The predominant aqueous forms of mercury found in soil solution, computed using Visual MINTEQ 2A, were Hg(OH)₂⁰ and HgS(SH)⁻¹.