56    CYANIDE DESTRUCTION BY CATALYTIC OXIDATION
Yi-shen Chen, Engineer
Chung-guang You, Engineer
Shanghai Environmental Science Research Institute
Shanghai 200233, China
Wei-chi Ying, Scientist
Occidental Chemical Corporation
Occidental Chemical Technology Center
Grand Island, New York 14072
INTRODUCTION
Cyanide-containing wastewaters are mostly highly toxic industrial effluents from gold refining,
electroplating of metals, chemical manufacturing, iron and steel industry and other sources. Alkaline
chlorination is the most common oxidative treatment technique for destruction of cyanide; however,
it has many disadvantages-high chemical costs, chloride ion contamination of the treated stream, and
potential formation of cyanogen chloride.' A variety of other chemical oxidation methods, employing
electrolysis,2 chlorine dioxide,3 Caro's acid,4 ozone,5 and hydrogen peroxide6 have been reported, but
they all suffer from high chemical cost, incomplete treatment, and/or formation of undesirable
residues. Oxidation of cyanide by molecular oxygen in air is thermodynamically possible;
2 CN" + 02 = 2 CNO"
which may be further oxidized:
2 CNO" + 1.5 02 + H20 = N2 + 2 C02 + 2 OH"
or hydrolyzed:
C02 + NH4+  + H20
Unless catalyzed, however, the reaction rate is very slow. Activated carbon and cupric ions are
known to be effective catalysts for air oxidation of cyanide.7,8 Calgon developed a pressure oxidation
process employing cupric ion-catalyzed oxidation of cyanide in an activated carbon adsorber. In
addition to the requirement of expensive pressure vessels, the process did not achieve destruction of
complexed cyanide.9 The Inco's S02/air cyanide removal process, with both cupric ion and S02 or
sulfite for promoting the oxidation reactions, did achieve destruction of complexed cyanide, but it
would have a high energy cost due to its inefficient aeration method employing air bubbling.10 We
have combined the enhanced oxidation achieved with additions of cupric ion and sulfite with trickling
bed technology in developing a more efficient, lower cost treatment process for destruction of cyanides present in industrial wastewater." Both free and complexed cyanide species are destroyed
quickly in the process which is now being practiced for full-scale treatment of cyanide-containing
wastewaters in China. This paper presents the excellent results of carbon adsorption-cupric ion/sulfite
promoted air oxidation of free and complexed cyanide species, which were present in actual chemical
plant effluents, in laboratory bench-scale and onsite pilot-scale activated carbon adsorbers.
EXPERIMENTAL SECTION
Adsorption Isotherm Experiments
Experimental runs were first conducted to determine the adsorptive capacity of activated carbon
for free cyanide (NaCN) and copper cyanide complex (Na2Cu(CH)4). Cylindrical carbon (Shanghai
Activated Carbon Plant, No. 20, 3 mm diameter x 4 mm) was pulverized, and then a prescribed
46th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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