Kinetics of reactions of cyanide and reduced sulfur species to form thiocyanate

Interactions of cyanide and reduced sulfur species in aqueous solution can produce thiocyanate. Kinetics of reaction of cyanide and polysulfide, and cyanide and thiosulfate were investigated. Initial rate kinetic data for reaction of cyanide and polysulfide showed the reaction is mixed order and that the order decreases from 1.91 to 1.18 as pH increases from 8.2 to 12; this was largely accounted for by a decrease in reaction order with respect to cyanide as pH increases above the pK/sub a/ for hydrogen cyanide. Catalysis and inhibition studies showed that high concentrations of ammonia were inhibitory and that coal char fines were catalytic. The rate of reaction of cyanide and polysulfide is approximately three or more orders of magnitude faster than reaction of cyanide and thiosulfate depending on pH value. A neutral or slightly alkaline solution containing on the order 10/sup -3/ M or more total sulfide can form polysulfide on exposure to oxygen, and in the presence of cyanide there should be reaction to yield thiocyanate. 7 figures, 3 tables.