OZONE-ULTRAVIOLET TREATMENT OF COKE OVEN AND
BLAST FURNACE EFFLUENTS FOR DESTRUCTION OF
FERRICYANIDES
Richard Prober, Associate Professor
Peter B. Melnyk, Assistant Professor
Lee A. Mansfield, Research Associate
Department of Chemical Engineering
Case Western Reserve University
Cleveland, Ohio 44106
INTRODUCTION
Regulations concerning wastewater discharges of cyanides are under consideration in
many areas.   The more stringent proposals would require removal of total cyanides to
residual levels as low as 25 /ig/1.   This lumping of iron-cyanide complexes together with
the other much more toxic forms would have particularly significant implications for
the iron and steel industry.   Effluents from blast furnace gas washing and various coking
wastewaters contain significant amounts of cyanides, both free and complex, and iron.
Formation of the refractory ferricyanide and ferrocyanide species is inherent in iron-
making operations.
A new treatment method, involving both ozonation and ultraviolet (UV) irradiation,
has been proposed for removal of iron-cyanide complexes [ 1 ].   A study conducted by
Houston Research, Inc. showed that cyanide in a photographic bleaching waste could
be reduced to less than 0.2 mg/1 with this treatment.   The major components of this
waste were cyanide and a 9.5% stoichiometric excess of iron.   Recently, Johnston [2]
reported on a demonstration plant which also treated a concentrated cyanide-bearing
waste with ozone and UV irradiation.   The waste was a mixture of free and metal-
complexed cyanides, the latter accounting for less than 6% of total cyanides present.
During this demonstration, less than half of the iron-cyanide complexes were destroyed,
although all other forms of cyanide were completely removed.
EXPERIMENTAL
The reactor consists of a standard 1.8-liter or 3.8-liter glass resin kettle, fitted with
gas diffusers and a specially designed nylon lid.   Supported by the lid are a pH probe,
thermocouple, 304 stainless steel heat exchanger, and a fused quartz tube to house the
UV lamp.  The kettle and lid are sealed together with a quick release clamp.
A solution of ethylene glycol and water is the heat exchange medium.   This fluid
is circulated from a Masterline constant temperature bath, which maintains constant
temperatures in the reactor to within ±0.5 C, over a range of reactor temperatures from
0 C to 70 C.   Three different reactor configurations are used:
Al. A draft tube divides the vessel into irradiated and nonirradiated sections (see Figure 1).
Ozone is introduced in the nonirradiated section.  The rising gas bubbles cause upward
flow of liquid outside the draft tube and downward flow through the irradiated section.
A 2. A draft tube is used here also, but the ozone is introduced directly into the irradiated
section.   The flow pattern is the reverse of that in configuration Al.
B. No draft tube is used, It., the entire volume is irradiated. The heat exchange coils are
at the reactor vessel wall.
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