Dadkhah A.A and Moradi F, Modeling and comparison of cyanides elimination from wastewater of an industrial unit by chemical treatment and physical absorption, ICHEC 2011, Kish, Iran, 2011

Abstract:
Cyanides are chemical compounds containing the cyano group CN-. These compounds are
strongly toxic for human and other living species. Cyanides are used in many industries specially
the mining of metal ores and hence are found in wastewaters produced by these industries.
Without treatment and reducing the cyanide levels in these wastes, they grossly harm the
environment. Based on experimental results of chemical treatment of ammonium cyanide in
wastewater of coking unit in Isfahan Steel Company (CUISC) in Iran with sodium sulfide which
converts the volatile ammonium cyanide to stabilized form of sodium cyanide a mathematical
model is proposed. As there are many different chemicals in the wastewater of coking unit such as
phenols, ammonia, cyanide compounds etc., in order to estimate the concentration of hydrogen
cyanide in the air, modified Raoult’s law is used. Activity coefficient of hydrocyanic acid was
calculated from liquid-vapor equilibrium data. Based on available data in literature for physical
absorption of cyanide ions on three type of absorbers (activated carbon AC, and activated carbon
impregnated with cupper and silver, AC-Cu and AC-Ag), a mathematical model was proposed for
physical absorption of cyanide on these absorbers, and by using the calculated activity coefficient
from first part, these models were used for predicting the reduction in cyanide content of
wastewater of CUISC for three scenarios of using AC, AC-Cu, and AC-Ag absorbers. Comparing
the results of models for chemical treatment and physical absorptions show that AC-Ag absorber
has the best ability to remove the cyanide from both wastewater and air above it. But in areas with
average ambient temperatures less than 36 °C where cyanide of coking unit is mostly in form of
ammonium cyanide, chemical treatment with sodium sulfide is more practical. Also in case of
chemical treatment capacity of cyanide removal is higher and process can continue for longer
time.