Thermal reduction-desorption of cadmium from contaminated soil by a biomass co-pyrolysis process

Abstract

Thermal desorption is one of the methods commonly used for the remediation of contaminated soil. However, its suitability for the treatment of widespread Cd-contaminated soil was seldom investigated, because the desorption of Cd was found to be difficult, even at a high heating temperature. In the present study, a biomass co-pyrolysis (BCP) method is proposed for the thermal treatment of Cd-contaminated soil. The results showed that, when the mixture of biomass and contaminated soil was pyrolyzed at ~550 ^oC, the gaseous pyrolytic products (such as CO and hydrocarbon gases) from the biomass could chemically reduce the Cd(II) into volatile Cd⁰, thereby allowing the evaporation of vaporized Cd⁰ from the soil within a short operating time. The BCP method can achieve a highly efficient removal of Cd from the soil samples spiked with a large amount of Cd(II). The remediated soil, containing the remaining biochars, showed a good regreening potential and a significant decrease in Cd bioavailability. It also showed a good performance for the remediation of field soils from four contaminated sites (>92% removal efficiencies), and one of the treated soils could even meet the Cd screening level of agricultural land of China.

Keywords: Biochar; Biomass pyrolysis; Cd-contaminated soil; Soil remediation; Thermal treatment.