Cydnidation tailings disposed of in a surface impoundment experience a loss
of cyanide due to natural attenuation, which frequently reduces the cyanid
e concentration to very low levels. Quantifying cyanide losses in terms of
impoundment geometry, local weather conditions and feed-solution chemistry
has been largely empirical in spite of the fact that, in many cases, mining
operations rely on surface impoundments to reduce cyanide to below an inte
rnally regulated concentration or below an effluent limitation. To permit a
quantitative evaluation of cyanide losses in an impoundment, a computer si
mulation was developed to estimate the losses of free, weak acid dissociabl
e (WAD) and total cyanide due to dissociation, photolysis and volatilizatio
n. Results of the model are compared with data collected for a North Americ
an tailings impoundment in 1998.