Horizontal Planetary Mechanochemical Method for Rapid and Efficient Remediation of High-Concentration Lindane-Contaminated Soils in an Alkaline Environment

Abstract

Lindane is a persistent organic pollutant that has attracted worldwide attention because of its threat to human health and environmental security. A horizontal planetary mechanochemical method was developed for rapid and efficient degradation of lindane from soil in an alkaline environment. Under the condition of a very low reagent-to-soil ratio (R=2%), ball-to-powder ratio (CR=6:1), rotation speed (r=300 rpm) and high single treatment capacity (SC=60 g), the lindane in four typical soils (~100 mg/kg) can be degraded up to 96.30% in 10 min. This method also can repair high-concentration lindane-contaminated soils (833 mg/kg). The experimental results and theoretical calculations proved that the stepwise dechlorination and final carbonization of lindane in soil are mainly attributed to the combined action of mechanical energy and alkalinity. The E2 elimination reaction was the first step of lindane destruction; Subsequently, the E1 elimination reaction tended to occur with the weakening of alkalinity; Then, benzene was obtained through stepwise nucleophilic substitution reaction; The last was the generation of carbon substances by splicing and condensation of benzene rings. This work proposes a practical remediation technology for organic contaminated soils and improves the understanding of the specific degradation pathways of lindane in soil in alkaline-assisted mechanochemical system.

Keywords: Horizontal planetary ball mill, NaOH, Four soils, Mechanochemical degradation, dechlorination