Remediation of real soil polluted with hexachlorocyclohexanes (α-HCH and β-HCH) using combined thermal and alkaline activation of persulfate: Optimization of the operating conditions

Abstract

Contamination of organic pollutants such as hexachlorocyclohexane (HCH) isomers poses a significant threat to human health and the environment. The alkaline activation of persulfate (PS) intensified by temperature to remediate surface sediments contaminated with HCH-wastes dumped by a lindane producing company (mainly α-HCH = 254 mg kg−1 and β-HCH = 99 mg kg−1) has been optimized. The treatment leads to promising results at 40 °C. Batch experiments were carried out to evaluate the influence of reagent addition order (simultaneous or sequential), reaction temperature (40–60 °C), liquid/soil ratio (VL/WS = 1 and 2), PS concentration (20–60 g L−1) and stirring rate (10–100 rpm) on chlorinated compound abatement. The reagent addition order did not affect the efficiency of the process. Raising either temperature or PS concentration significantly accelerates the hydrolysis rate of β-HCH and the generated trichlorobenzenes (TCBs) oxidation rate. Increasing the VL/WS ratio also accelerated the pollutant oxidation rate. At the selected operating conditions (pH > 12, simultaneous addition of PS and NaOH, 50 °C, PS = 40 g L−1, VL/WS = 2, NaOH/PS = 2 and 100 rpm), a conversion of α-HCH and β-HCH of 100% and 81%, and a dechlorination degree of 94% were achieved in 3 days. PS consumption was 29%; thus, the aqueous solution could be reused in a new batch of soil remediation, the separation of the aqueous and the soil phases being a rapid sedimentation step.