Cyanide Destruction in Molten Carbonate Bath: Melt and Gas Analyses

Abstract

Oxidation of combustible wastes in molten salt baths is being considered as an alternative to incineration. This paper examines the oxidation of cyanide ions (present in molten carbonate bath) by molecular oxygen as a function of the total gas mixture (O2−Ar) flow rate, input gas composition (vol % O2 in O2−Ar mixtures), melt composition (initial mol % CN- in CN-−CO32- baths), and melt temperature. The melts were sampled for the presence of CN-, CNO-, NO2-, and NO3- while the gas streams were sampled for N2, N2O, NO, NO2, CO, and CO2. While cyanide destruction proceeds rapidly (>90% loss of CN- at 486 standard cm3 per min, 40 vol % O2, and 1243 K), NO2 and CO emissions remain within the limits of air quality standards. Under all conditions CN- and CNO- were the major components, while NO2- and NO3- were the minor components of the melt. The amount of CNO- present in the melt after any period of reaction was always smaller than the amount of CN- lost from the melt during the same time period. The CO + CO2 content of the gas was always much larger than the NO + NO2 content. The CO/CO2 ratio was always small while the NO/NO2 ratio was always large. While N2 content was larger than the NO + NO2 content, no N2O was ever detected. Material balance indicated that most of the nitrogen input to the system remained unaccounted after the reaction. Significance of the data are discussed.