Cyanide and thiocyanate in coal gasification wastewaters
Procedures for thiocyanate preservation and analysis have been evaluated. A copper-pyridine colorimetric analytical method with preextraction has been tested successfully on a number of coal gasification wastewaters, although difficulties have been encountered with some samples containing very high levels of organic compounds. Improved preservation procedures for cyanide analysis require removal of exceptionally high levels of carbonate to eliminate analytical difficulties during sample distillation. Sulfide removal is also necessary to eliminate the possibility of reaction of cyanide with sulfide oxidation products, especially polysulfide. The extent to which thiocyanate may be present in coal gasification process quench waters as a result of reactions occurring in the gasifier as compared to aqueous-phase reactions is unknown. Aqueous-phase thiocyanate formation pathways were reviewed, and a model is proposed whereby the reaction of cyanide with polysulfide-sulfur and thiosulfate are plausible pathways for aqueous-phase thiocyanate formation. Preliminary kinetic studies on reaction of cyanide and polysulfidesulfur in clean water and wastewater over the pH range 8.2 to 12 showed that the reaction was of mixed order (1.54 +- 0.25) with a rate constant of about 0.24 (M/l)/sup -0.54//min. Thus SCN- formation via poly-S/sup 0/ may be much more significant than formation via S/sub 2/O/sub 3//sup 2 -/; and additional work, which has included an investigation of catalysis/inhibitory effects, suggests that this may be the case. Results of this work may be useful to predict or explain quality changes in coal gasification wastewaters. Attempts to engineer these reactions may largely entail sulfide oxidation kinetic control. 9 figures, 6 tables.
- Research Organization:
- Carnegie-Mellon Univ., Pittsburgh, PA
- OSTI ID:
- 6812939
- Journal Information:
- J. Water Pollut. Control Fed.; (United States), Journal Name: J. Water Pollut. Control Fed.; (United States) Vol. 51:9; ISSN JWPFA
- Country of Publication:
- United States
- Language:
- English
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37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
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54 ENVIRONMENTAL SCIENCES
ABSORPTION SPECTROSCOPY
CARBONIC ACID DERIVATIVES
CHALCOGENIDES
CHEMICAL REACTIONS
COAL GASIFICATION
CYANIDES
ELEMENTS
GASIFICATION
HYDROGEN COMPOUNDS
KINETICS
LIQUID WASTES
NONMETALS
ORGANIC COMPOUNDS
ORGANIC SULFUR COMPOUNDS
OXIDATION
OXYGEN COMPOUNDS
PH VALUE
POLLUTION
REACTION KINETICS
SAMPLING
SPECTROSCOPY
STABILITY
SULFIDES
SULFUR
SULFUR COMPOUNDS
THERMOCHEMICAL PROCESSES
THIOCYANATES
WASTE WATER
WASTES
WATER
WATER POLLUTION