BIOLOGICAL TREATMENT OF CYANIDATION WASTEWATERS
Terry I. Mudder, Environmental Engineer
James L. Whitlock, Chief Chemist
Homestake Mining Company
Lead, South Dakota 57754
INTRODUCTION
Metal complexed cyanides in wastewaters form as a result of interactions of free cyanide with
metals present in the wastewater and exhibit varying degrees of stability, toxicity, and treatability.
Thiocyanate, a pollutant commonly found in cyanide bearing wastewaters, is formed through the
interaction of free cyanide with sulfur containing species (i.e. pyrrhotite) both present in the wastewater.
In certain industrial processes, such as the beneficiation of gold and silver, cyanide is an essential
reagent. Since free cyanide, complexed cyanides, and thiocyanate are potentially toxic to humans and
aquatic organisms, these compounds must be removed from wastewaters prior to their discharge into
surface or ground waters serving as potential potable water sources, marine or fresh water habitats.
Since 1977, personnel at Homestake Mining Company's Homestake Gold Mine in Lead, South
Dakota, have been engaged in research and development of a process to treat a maximum of 5.5 MGD
(3600 gpm) of combined mine and tailings impoundment wastewaters (Table I). The treated wastewater must be of high quality as it is discharged into Whitewood Creek which serves as a cold water
marginal trout fishery, stocked seasonally with catchable-size brown trout.
Various chemical and/or physical treatment processes were pilot plant tested and the effluents
evaluated on both a numerical and toxicological basis in a flow-through bioassay facility to ensure
effluent compatibility with the receiving stream. However, construction of a treatment facility based
upon chemical and/or physical processes never materialized due either to inadequate treatment
performance, residual toxicological effects associated with the effluent, or prohibitive capital and/or
operating costs.
Table I. Wastewater Characteristics
Parameter
Mine Water"
Tailings Impoundment Water*
Thiocyanate
Total Cyanide
Method-c Cyanide
Iron
Copper
Nickel
Zink
Ammonia-N
Phosphorous-P
PH
Temperature (°F)
1.0-16.0
.10-.50
.02-.10
.10-10.00
.07-1.60
.01-.04
.01-.10
5.0-6.0
trace
5.0-6.5
70-85
110.0-240.0
7.00-30.00
4.00-20.00
1.50-6.00
1.40-6.00
.20-.40
.01-1.50
less than 1.0
trace
7.00-9.5
34-70
"AH values in mg/l except temperature and pH.
NOTE: The actual wastewater ratio is varied throughout the year from 70/30 mine/tailings impoundment wastewater ratio in the winter to 50/50 mine/tailings impoundment wastewater ratio in the
summer.
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