Efficacy of Lime Treatment on the Mercury Retention Characteristics of Semi Arid Soils

Effective treatment of mercury contaminated soil is highly challenging due to high toxicity, volatility and environmental mobility and the varied nature and composition of industrial waste products. Conventional stabilization /solidification methods include fixation of metals using Portland cement and fly ash. However it is difficult to stabilize mercury with cement based processes because it does not form a low solubility hydroxide surface. Hence the use of lime as a prospective soil amendment to retain mercury is studied. In this study, locally available semi-arid soils (Al-Ghat and Al-Qatif) having different chemical and mineralogical characteristics are considered and their response to mercury adsorption at varying initial concentrations, pH conditions, temperature and dilution ratios are studied. Empirical models (Langmuir and Freundlich) are applied to ascertain monolayer or heterogeneous adsorption. The adsorption studies are even carried out after amending the soils with lime. Kinetic models are employed to validate the type and nature of sorption taking place (whether pseudo first-order or second-order). It was found that both Al-Ghat and Al-Qatif soils when amended with lime attenuate mercury and the experimental results correlate well with selected empirical models.