Sorptive Response of Chromium (Cr+6) and Mercury (Hg+2) From Aqueous Solutions Using Chemically Modified Soils

Abstract The presence of xenobiotic (human induced) chemicals from mining, refining and electroplating industries causes significant damage to the natural soil system, altering its physico-chemical geochemistry. Most of these chemicals contain metal pollutants that are non-biodegradable and the only way to contain or limit their movement is through sorption. In this study, the sorptive response of two most commonly found metal contaminants, hexavalent chromium (Cr+6) and mercury (Hg+2), were studied using two semi-arid soils from Saudi Arabia. To enhance their retention capacity, these soils were amended with lime. The response to sorption at varying initial contaminant concentrations, pH conditions, temperature levels, and dilution ratios was investigated. Relying on empirical models (Langmuir and Freundlich), the nature of sorption (monolayer or heterogeneous) was ascertained. Furthermore, kinetic models were employed to validate the type and nature of sorption occurring (whether pseudo first-order or second-order). It was found that the experimental results correlated well with the selected empirical models for both the Al-Ghat and Al-Qatif soils when amended with lime and attenuate Cr and Hg to satisfactory levels. The R2 values were close to 1 for all the tested models. The order of sorption was Cr > Hg for heavy metals considered, and also for soils and soil mixtures considered Al-Qatif soil amended with 6 % lime > Al-Ghat soil with 6 % lime > Al-Qatif > Al-Ghat. Lime treated soils sorbed 69 % and 63 % more than the untreated soils for Cr and Hg, respectively.