Remediation of manufactured gas plant soils contaminated with free and complex cyanide

摘要

Cyanide is one of the main contaminants present in soil from manufactured gas plants (MGP) . Several treatment methods including thermal treatment, chemical treatment, ultraviolet irradiation, and biological treatment were evaluated for their ability to degrade the cyanide present in these soils. In the thermal treatment, raising the temperature of the purified waste to 2000--3000C resulted in complete removal of complex cyanide from the soil; however, the cyanide emitted was in a the toxic gaseous HCN form. Chemical treatment, using the oxidant Fenton`s reagent in a 10% soil slurry, resulted in the destruction of 80% of the free cyanide but little, if any, complex cyanide. Ultraviolet irradiation of the basic leachate from MGP wastes in the presence of the chelating agent EDTA yielded 90% degradation of the complex cyanide. For biological treatment, using an aerobic mixed culture, almost 60% of the free cyanide disappeared from the system with minimal degradation of the complex cyanide. Each treatment has its limitations. Thus, a combined physical-chemical-biological treatment in which the complex cyanide is degraded to free cyanide by photodegradation under alkaline conditions, the free cyanide then chemically (by Fenton`s reagent) or biologically converted to NH{sub 3} and CO{sub 2}, is proposed for the removal of cyanide from MGP sites.