Thermal remediation of cyanide-contaminated soils : process optimization and mechanistic study

摘要

Site soils with persistent cyanide compounds (primarily iron-cyanide complex) pose potential hazards to the environment and require remediation before redevelopment. This study evaluated the possibility of thermal treatment on remediation of cyanide-contaminated soils via batch heating experiments spanning a wide temperature range (200-500 degrees C). The change with operation variables of total cyanide and some reaction intermediates (e.g. CN-) was analyzed in order to elucidate the optimal variables that guarantee cyanide removal while generating no hazardous byproducts. Temperature, heating time and cyanide species have been found to be important parameters influencing removal/destruction of cyanide in soils. For soils bearing K-3[Fe(CN)(6)] and K-4[Fe(CN)(6)], a removal efficiency of >99.9% can be obtained with temperatures over 350 degrees C at 1 h, while for samples bearing Fe-4[Fe(CN)(6)](3), a higher temperature (>450 degrees C) is needed to obtain an equivalent efficiency. During heating, the iron-cyanide complexes decomposed, releasing highly toxic free cyanides, which will subsequently be oxidized. However, a small percentage of free cyanide can always be detected as a result of incomplete oxidation, thus caution should be taken to minimize the accumulation of free cyanide during thermal treatment. (C) 2019 Elsevier Ltd. All rights reserved.