Remediation of soil contaminated by lindane wastes using alkaline activated persulfate: Kinetic model

In this work, remediation of a soil highly polluted with chlorinated organic compounds (COCs), including chlorobenzenes, hexachlorocyclohexane (HCH) and heptachlorocyclohexane (HeptaCH), has been carried out using persulfate (PS) activated by alkali (NaOH). The contamination was caused by wastes from lindane production. Soil samples were sieved in two fractions: F (dp < 0.25 mm) and G (2 mm < dp < 0.25 mm), and both were used to study the influence of the oxidant and activator concentrations (CPS = 100–400 mmolL-1, CNaOH =100–200molL-1) on COC abatement. The alkali causes rapid dehydrochlorination of HCHs and HeptaCHs to Trichlorobenzenes (TCBs) and Tetrachlorobenzenes (TetraCBs), respectively. A COC conversion of about 96% and 70% was obtained at 21 days in fractions G and F, respectively, when using PS and NaOH concentrations of 400 mmolL-1. The discriminated kinetic model reveals that the oxidation reaction takes place in both the soil and aqueous phases. This explains in detail the TCB and TetraCB concentration change seen in both phases with the reaction time, at the oxidant and activator concentration range studied, for the two soil particle sizes and contamination levels used. Reaction order for NaOH concentration was zero if pH was above 12. The reaction order for PS was 1.0 for the oxidation rate in the aqueous phase and lower than 1.0 for the oxidation rate in the soil phase, which is lower in the soil fraction with smaller particles. Moreover, while equilibrium between phases was not achieved, the model takes into account the mass transfer of COCs from the soil to the aqueous phase.