FIELD OF THE INVENTION
The present invention relates to a safe, simple, economic and efficient process for the
Coke Oven Effluent Treatment in particular of left over cyanide complements in order to
restrict the Cyanide discharge within the norm of 0.2 mg/lit in large integrated steel
plants. More advantageously, the process and the system of the invention is capable to
be easily retrofitted in to the existing effluent treatment plants with less cost involvement
and protecting the environment from the deleterious effect of excess cyanide discharge
beyond acceptable norms. The system and the process for the Ferrate treatment of coke
oven effluent according to the present invention is further directed to removal of the
color, suspended solid particles from the final biologically treated effluent, thus improving
the overall treated effluent quality as compared to conventional prior practices in the
same field and is thus having prospects of wide industrial application in BOD plants of
large integrated Steel Industries.
BACKGROUND ART
It is well known in the existing art of the Coke Oven and Coal Chemicals Plant (CO & CC)
Effluent Treatment Plant (ETP), also commonly known as the Biological Oxidation and De-
phenolisation (BOD) Plant in the Integrated Steel Plants, are configured in general to
eliminate the contaminants comprising Oil & Grease, Ammonia, Phenol, Thiocyanate,
Cyanide etc.
The requirement of treatment of effluent generated from operations in coke ovens and
coal chemicals units is of critical concern because of the presence of highly toxic
constituents like phenol, ammonia, cyanide, etc. The coke ovens and coal chemical plants
in integrated steel plants all over the world essentially involve phenolic effluent treatment
plant which conventionally use biodegradation technique for removal of phenol, ammonia
and cyanide Such BOD plants makes use of where-in bacterias are grown which consume
the pollutants as their food and grow, multiply and die. The dead bacterias in the form of
suspended solids from the biological reactors are removed in the settling tanks and
dewatered, sun dried and disposed off by mixing with coking coal and recharged back in
the coke ovens.

Existing BOD plants or the Effluent Treatment Plants (ETP) in integrated steel plants
consists of waste water collection tank, tar settling unit, dissolved air floatation unit
equalization basin, flash mixer, clarrifloculator, carrying out processes of two stage
activated sludge process with separate clarifiers and trickling filter system followed by
final clarifier and chlorine contact tank. In addition, sludge thickener and sludge drying
beds are also provided for dewatering of sludge generated. The treated effluent is mostly
used in coke quenching and occasionally discharged on to inland surface waters like
Rivers.
Conventional BOD plants in Integrated steel plants, comprise 3 or 2 stages of biological
treatment units in series, like activated sludge process with completely mixed extended
aeration reactors and trickling filters along with associated settling tanks for activated
sludge recycling system.
The existing BOD plants are found to exhibit with stringent operational control on process
parameters, meeting the desired limit of effluent in respect of the ingredients like oil and
grease, phenol, ammonia and thiocyanate and the prevailing technology applied in BOD
plants could bring down the total cyanide at best to a level ranging about 0.9 to 1.2
mg/lit, as against the desired safe cyanide discharge norm of 0.2mg/lit. Cyanide being
very toxic in nature needs to be removed from the waste water prior to discharge or to
be used in coke quenching.
In an attempt to bring down the total cyanide level further to meet the norm of 0.2
mg/lit, some steel plants reported to be using Alkaline Chlorination method as a polishing
method for Cyanide. But there remained substantial difficulties and risks that are
encountered in the use of alkaline chlorination for final polishing treatment for cyanide
reduction in BOD plants as follows:
(i) Risk of emission of cyanogen chloride toxic gas, which will pose a safety risk to the
health of employees working in the BOD plant;
(ii) Chlorination makes organic chloro compounds which are still toxic to environment;
(iii) When the chlorination is done in the BOD plant, treated effluent which contains
phenolic compounds (less than 1 mg/L), lead to formation of chlorinated phenols
which are still harmful to the receiving environment;

(iv) The presence of ammonia also creates a high demand for chlorine.
(v) Alkaline chlorination is effective for oxidation of all cyanides except iron cyanide
complexes. Thus meeting CN norm of 0.2 mg/lit is still a problem even with Alkaline
Chlorination, for which high doses of Chlorination is resorted to, which cause high cost
of treatment and high chloride / chlorine levels in the treated effluent, which itself pose
other associated pollution problems.
Also since the discovery of Chlorinated By-F'roduct (CBP) and their negative health effects,
considerable attempts have been made to minimize the concentration of CBP and removing the
CBP after chlorination to bring the harmful effects within safe limits. But such processes greatly
increase the overall cost of waste water treatment.
The United States Environment Protection Agency's (US - EPA) 'Best Available Technology' (BAT)
model for treatment of coke oven effluent incorporates the chlorination and de-chlorination, multi
media filtration and granular activated carbon to arrest chlorinated organic carbons, before it is
discharged to surface waters like rivers. However, these de-chlorination and activated carbon
filtration steps are very costly procedure.
Other methods in use for combating the problem of controlling the Cyanide contents in the BOD
effluent include electrolytic decomposition, ozonation, electrodyalysis catalytic oxidation
reverse osmosis ion exchange, genetic engineering applications and photo catalytic
oxidation, etc, are evolving and require higher capital and operating costs to meet the
demands of discharge limits.
Cyanide precipitation with ferrous salts is also tried which have achieved partial removel
of cyanide but failed to achieve desired limit safe of 0.2 mg/L CN in the Coke Oven
Effluent Treatment Plant.
Some relevant prior patents are referred to for assessing the effectiveness of the existing
technology in the same field of cyanide based waste treatment with ferrate.
US Patent 5160632 entitled 'Cyanide removal from Coke oven wash waters'
discloses a treating Cyanide waste water from Coke ovens by adding ferric sulfate while
adjusting pH with H2SO4. The ferric ferricyanide formed are agglomerated and settled
and removed in the form of sludge. The Iron cyanide complex formed are separated in
the form of sludge and needs to be disposed off in protected landfill, since it is a

Hazardous waste. This method can only remove some cyanide concentration in coke
oven waste water and does not ensure meeting the cyanide discharge quality norm of
0.2 mg/lit.
US Patent 6,790,429 titled 'Methods of synthesizing an oxidant and application there
of deals with a tretment of cynide based waste wherein Ferrate is synthesized in the
form of potassium ferrate which are costly and not suitable for treatment waste water
used in Coke quenching which will carry residual "Potassium" in coke which will
interfere in Metallurgical quality of Hot metal in Blast Furnaces.
US Patent 5,202,108 is directed to a Process for making stable, high purity ferrate (VI)
using beta ferric oxide which requires obtaining costly beta ferric oxide for making high
purity ferrate. This is not economically attractive for ferrate application in treatment of
Coke oven effluent treatment plant.
As compared to the prior patents cited herein above, the process according to the
present invention directed to final removal of the remaining Cyanide complex,
Thiocyanate, Ammonia, Colour causing chemicals and Suspended Solids, etc, after
Biological removal stage in the existing Coke Oven Effluent Treatment Plants of Coke
Ovens and By-product Plants in Integrated Steel Plants, using ferrate, is cost effective
and meets the respective discharge quality norms. The sodium ferrate production at the
site using easily available commercial grade chemicals and at atmospheric temperature
and pressure and recycling of extra ferric hydroxide produced in ferrate making stage
are more cost effective and avoid sludge handling and disposal problems. This polishing
treatment process can be easily incorporated / retrofitted in the existing BOD Plant at
lesser capital and operating costs in comparison to other known methods.
The present invention is therefore directed to meeting the persistent need for developing
a safe, economic yet efficient process for treatment of the Iron cyanide complexes, which
are refractory cyanide present in the BOD plant for coke oven effluent treatment, which
cannot be removed by treating biologically (bacterial treatment), by adopting the
economic and convenient way of oxidizing using ferrate at the point of use prepared with
commercially available chemicals, Sodium Hypochlorite, Ferric chloride and Sodium
Hydroxide. The Ferrate oxidation treatment process thus would over come the limitations
and disadvantages of the existing effluent treatment in BOD plant and avoid producing

harmful intermediates/final end products such as cyanogens chloride and organochloro
compounds causing injury to health and polluting environment. The process involving
Ferrate oxidation of left over cyanide complements/refractory complex shall be capable
to be retrofitted to the existing coke oven ETP, and would meet the cyanide disposal
norm within 0.2mg/lit.
OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to develop a process and a system for
ferrate treatment of Iron cyanide complexes by providing for selective treatment right at
the point of use in the coke oven ETP, such as to achieve the desired cyanide discharge
norms of 0.2 mg/lit, in a safe, economic, cost effective and environment friendly manner.
A further object of the present invention is to develop a process and a system for
selective treatment of Iron cyanide complexes to avoid producing harmful
intermediates/final end products such as cyanogens chloride and organochloro
compounds causing injury to health and polluting environment as obtained in
conventional BOD plant in coke oven ETP processes.
A still further object of the present invention directed to develop a process for ferrate oxidation
treatment of Iron cyanide complexes wherein the chlorination is avoided in the BOD plant such
that the treated effluent contain phenolic compounds (less than 1 mg/L), leading to formation of
chlorinated phenols which are harmful to the receiving environment.
A still further object of the present invention directed to develop a process for ferrate oxidation
treatment of Iron cyanide complexes in ETP of BOD plant wherein the de-chlorination and
activated carbon filtration steps that are very costly procedure, are replaced with simple and less
costly ferrate oxidation process.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a process
for the cyanide removal in Biological oxidation and De-phenolisation Plant (BOD)
comprising:

subjecting the left over cyanide complexes in the biologically treated coke oven effluents
in BOD plants to treatment with Ferrate such as to selectively carry out Ferrate oxidation
and removal of left over cyanide complexes there from.
In the above process for the cyanide removal in Biological oxidation and De-
phenolisation Plant (BOD) the said Ferrate includes high oxidation potential selectivity
and generates non-toxic by products. Advantageously, the treatment with Ferrate is
directed to simple end products Fe(OH)3, CO2, (HCO3) and NO3 which are environment
friendly.
In particular, in the above process for the cyanide removal in Biological oxidation and
De-phenolisation Plant (BOD) the same advantageously involves the formation of
intermittent products nitrite and cyanate (CNO) and ultimately IMO3 & CO2 (HCO3) of the
end products of oxidation of cyanide by Ferrate (F(VI)), by way of the following
reactions:
a. HFeO4- + CN- + OH- ---→ H2Fe04 + CNO-
b. HFeO4- + 2CNO- + 5/2 O2 + 2H + ---→ Fe(OH)3 + 2NO2 + 2CO2
c. 2HFeO4- + 2HCN + 5/2O2 + H2O + 2OH- ---→ 2Fe(OH)3 + 2HCO3 +2NO2
d. 2HFeO4-+ 3NO2 + 2H2O ---→ 2Fe(OH)3 + 3NO3
Advantageously also, the Ferrate used in the process is obtained by oxidizing a basic
solution of Ferric chloride by Sodium Hypochlorite, said Ferrate being stable in aqueous
solutions at a pH 9.0 and dark purple colour.

Importantly, the Ferrate reaction is carried out at ambient temperature and pressure for
a period of about 1 hr to 6 hrs. Once the prepared ferrate is dosed in effluent stream ,
the cyanide level in the treated effluent is reduced to about 0.2mg/L , in 10 to 30
minutes time.
In accordance with another aspect of the invention there is provided a system for
carrying out cyanide removal in Biological oxidation and De-phenolisation Plant (BOD)
as discussed above adapted for easy retrofitting in to the existing effluent treatment
plants comprising:
Ferrate Storage means;
a trickling filter outlet Tank chamber holding the effluent to be treated;
means for dosing said Ferrate from the storage means into the said Trickling filter outlet
Tank Chamber; and
means for exiting the treated environmentally safe effluent.
In accordance with a preferred aspect of the invention, in the above system the said
Ferrate storage is operatively connected to a Ferrate Sol preparation tank comprising
means for introducing Ferric Chloride, water ,NaoH, NaoCI and Ferric Hydroxide slurry
recycle alongwith a mechanical stirrer and pump means to pump the Ferrate sol into the
Ferrate Sol Storage.

In accordance with yet further aspect of the invention, in the system for carrying out
cyanide removal in Biological oxidation and De-phenolisation Plant (BOD), said Ferrate
treated effluent is exited through the existing final clarifier and CCT.
BRIEF DESCRIPTON OF THE ACCOMPANYING FIGURES
Figure 1: is the schematic illustration of the process of Ferrate oxidation of left over
cyanide complex in the coke oven Effluent Treatment Plant according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
Reference is first invited to the accompanying Figure 1, wherein the schematic diagram
show the basic process steps involved in the Ferrate treatment of left over cyanide
complex of the present invention, and in particular, for the treatment of Iron cyanide in
the ETP of coke oven plant in the steel plants, which is otherwise resistant to being
biologically/bacterially treated, and as such is susceptible to generation of toxic cyanide
and other pollutants damaging the environment on disposal. The present invention is
thus directed to avoid the safety and health risks and achieve a simple and economic
method by way of the novel Ferrate Oxidation of left over cyanide complexes in the
biologically treated coke oven effluent in BOD plants in the Integrated Steel Plants.
Ferrate oxidation of left over cyanide complexes according to the present invention, is
directed to treatment in ETP of BOD plant effluent in a safer, effective and economical
way and limit the Cyanide discharge norms within statuatory level of 0.2 mg/lit. Ferrate
treatment as polishing process after biological treatment in Coke Oven effluent treatment
plant does not generate harmful intermediate/final end products such as cyanogen
chloride and organo chloro compounds which are dangerous and health / safety risk.
Apart from cyanide oxidation, the ferrate treatment also removes color and suspended
solids from the final biologically treated effluent, thus improving the overall treated
effluent quality, from the existing plant.

The treated effluent has been evaluated using Fe(VI) for removing cyanide complexes
which are leftover after 3 stage biological treatment in Coke Oven Effluent Treatment
Plant, in order to meet the norm of 0.2 mg/lit, successfully achieved relatively in low
dosages of Ferrate. This Ferrate treatment process, not only solves the long pending
technological limitations in the Existing BOD Plants in Indian Steel Industry but also can
be applied to other industries facing identical problem as well.
It is clearly apparent from the accompanying Figure 1, that the preparation and use of
Ferrate is done economically and conveniently by way of providing the same at the point
of use at the ETP. Commercially available chemicals such as the Sodium Hypochlorite,
Ferric Chloride and Sodium Hydroxide are mixed in a tank using mechanical mixer with
appropriate quantity of water such as to generate the Ferrate solution sent to storage
tank by means of a pump and also the ferric hydroxide slurry separated is recycled back
to the mixing tank. The Ferrate from the storing tank is carried to the trickling filter
outlet tank wherein the effluent from the trickling filter outlet is carried to the same
outlet tank for treatment of iron cyanide, which is not removed by even three stage
biological reduction/treatment of the effluent obtained at trikling filter outlet of the ETP of
BOD Plant of coke ovens. The treated cyanide containing effluent from trickling filter tank
is sent through a final clarifier. The finally Ferrate treated effluent having the cyanide
limit within the safe norm of 0.2mg/lit is either sent to disposal in to Inland water bodies
like rivers or used in coke quenching.
The basic steps involved in the Ferrate treatment of iron cyanide complex in the
biologically effluent of the coke oven effluent at the out let of BOD plant is further
illustrated and the results obtained in the laboratory scale experimental application of the
process according to the invention is described in the following examples:
EXAMPLE:
The Use of Ferrate in the oxidation process involves iron in +6 valence state. Fe(VI)
species are strong oxidizing agents that can be seen from the reduction potentials
mentioned in the following Table 1 .


It has been observed that the ozone method requires the excess amount of ozone
because of mass transfer limitation on the reaction rate. In addition ozonation involves
high capital & operational costs. The other chemical oxidation methods, employing
electrolysis, chlorine dioxide, and hydrogen peroxide suffer from high chemical costs,
incomplete treatment and formation of undesirable residue / byproducts which are
harmful to environment.
On the other hand, Ferrate is having favorable properties such as high oxidation potential
selectivity and a non-toxic by product, Fe(III), that makes Fe(VI) an environment
friendly oxidant. Ferrate also destroys left over bacterias in the BOD plant effluent
without forming any harmful organochloro compounds.
Thus Fe(VI) has a better potential to serve as a reliable, safe oxidation and cost effective
treatment for removing complex cyanide compounds in the biologically treated effluent.
The Cyanide Removal process using Ferrate:
The removal of cyanide in Fe(VI) is accomplished within a very short reaction time by the
formation of a simple end products CO2 (HCO3) and NO3 that are less harmful to the
environment. The final product of Fe (VI) after reaction is Ferric Hydroxide Fe(III) which
is also acts as coagulant.

Formation of intermittent products nitrite and cyanate (CNO) and ultimately NO3 & CO2
(HCO3) of the end products of oxidation of cyanide by Ferrate (F(VI)), are as detailed in
the following reactions.
e. HFeO4- + CN- + OH- ---→ H2FeO4 + CNO-
f. HFeO4- + 2CNO- + 5/2 O2 + 2H + ---→ Fe(OH)3 + 2NO2 + 2CO2
g. 2HFeO4- + 2HCN + 5/2O2 + H2O + 2OH - ---→ 2Fe(OH)3 + 2HCO3+2NO2
h. 2H FeO4- + 3NO2 + 2H2O---→ 2Fe(OH)3 + 3NO3
It may be observed that Ferrate is conveniently produced by, oxidizing a basic solution of
Ferric chloride by Sodium Hypochlorite as described with reference to the accompanying
Figure 1. Ferrate is stable in aqueous solutions at a pH 9.0. Ferrate (VI) has a dark
purple color.
2Fe(OH)3 + 3 NaOCI + 4 NaOH ---→ 2Na2FeO4 + 3NaCI + 5H2O
The ferrate reaction is carried out at ambient temperature and pressure, for a period of
about 1 hr to 6 hrs, depending upon the concentration and quality of chemicals used in
the process.
RESULTS OBTAINED BY " FERRATE " TREATMENT OF CYANIDE COMPLEX IN
LABORATORY SCALE AND ACTUAL PLANT TRIAL:
The laboratory scale tests and pilot plant trials have been carried out with laboratory
grade reagents and commercial grade chemicals for accomplishing the Ferrate production
and dosing requirements for effective removal of the left over cyanide complexes,
Thiocyanate, Color causing chemicals, Suspended Solids, etc, from the treated effluent
of a running BOD plant in one of the Integrated Steel Plants. The successful test results
are highlighted in Table 2 .


The schematic process flow diagram for retrofitting of the Ferrate generation and use at
BOD plant Site and the dosing arrangements has already been illustrated and described
with reference to the accompanying Figure 1. The reaction vessel and piping
arrangements are simple and can be implemented with locally available resources and
involving available in house technical skills.
The Laboratory test results and field scale pilot test results being successful, the
Ferrate Treatment in the actual field operation of BOD plant is taken up for meeting
the need of cyanide norm of 0.2 mg/lit at the outlet of the BOD plant, eliminating the
harmful chemical by-products from the existing BOD plant effluent. Moreover, the
norms of "Color" and "Turbidity", has also been met in a simple and most cost
effective manner.

It is thus possible by way of this invention to obtain treated effluent free of any harmful
contaminants or cyanide content beyond the safe limit at the outlet of BOD plants of
Coke Ovens in Integrated Steel Plants, after carrying out the Biologically treated
effluent, facilitating removal of the left over Iron Cyanide Complexes, Color and
Turbidity, COD and Suspended Solids, achieved to meet the Norms by dosing a single
chemical Ferrate in a simple and cost effective manner. Thus the Ferrate treatment of
the present invention, as a final polishing step after Biological units of existing BOD
plants could be introduced with in-house efforts and resources available in
Integrated Steel Plants. The process of the present invention not only solves the long
pending technological limitations in the existing BOD Plants in Indian Steel Industry
but also is effectively applicable for similar other industries.

WE CLAIM:
1. A process for the cyanide removal in Biological oxidation and De-phenolisation Plant
(BOD) comprising:
subjecting the left over cyanide complexes in the biologically treated coke oven effluents
in BOD plants to treatment with Ferrate such as to selectively carry out Ferrate oxidation
and removal of left over cyanide complexes there from.
2. A process for the cyanide removal in Biological oxidation and De-phenolisation Plant
(BOD) as claimed in claim 1 wherein said Ferrate includes high oxidation potential
selectivity and generates non-toxic by products.
3. A process for the cyanide removal in Biological oxidation and De-phenolisation Plant
(BOD) as claimed in anyone of claims 1 to 2 wherein the treatment with Ferrate is
directed to simple end products CO2,(HCO3) and NO3 which are environment friendly.
4. A process for the cyanide removal in Biological oxidation and De-phenolisation Plant
(BOD) as claimed in anyone of claims 1 to 3 comprising:
formation of intermittent products nitrite and cyanate (CNO) and ultimately NO3 & CO2
(HCO3) of the end products of oxidation of cyanide by Ferrate (F(VI)), by way of the
following reactions:
HFeO4- + CN- + OH- ---→ H2FeO4 + CNO-
HFeO4- + 2CNO- + 5/2 O2 + 2H + ---→ Fe(OH)3 + 2NO2 + 2CO2
2HFeO4- + 2HCN + 5/2O2 + H2O + 2OH - ---→ 2Fe(OH)3 + 2HCO3 +2NO2
2H FeO4- + 3NO2 + 2H2O---→ 2Fe(OH)3 + 3NO3

5. A process for the cyanide removal in Biological oxidation and De-phenolisation Plant
(BOD) as claimed in anyone of claims 1 to 4 wherein Ferrate used in the process is
obtained by oxidizing a basic solution of Ferric chloride by Sodium Hypochlorite, said
Ferrate being stable in aqueous solutions at a pH 9.0 and dark purple colour.
6. A process for the cyanide removal in Biological oxidation and De-phenolisation Plant
(BOD) as claimed in anyone of claims 1 to 5 wherein Ferrate reaction is carried out at
ambient temperature and pressure for a period of about 1 hr to 6 hr and the cyanide
level in the treated effluent is reduced to about 0.2mg/L
7. A system for carrying out cyanide removal in Biological oxidation and De-
phenolisation Plant (BOD) as claimed in anyone of claims 1 to 6 adapted for easy
retrofitting in to the existing effluent treatment plants comprising:
Ferrate Storage means;
a trickling filter outlet Tank chamber holding the effluent to be treated;
means for dosing said Ferrate from the storage means into the said Trickling filter outlet
Tank Chamber; and
means for exiting the treated environmentally safe effluent.
8. A system for carrying out cyanide removal in Biological oxidation and De-
phenolisation Plant (BOD) as claimed in claim 7 wherein said Ferrate storage is
operatively connected to a Ferrate Sol preparation tank comprising means for introducing

Ferric Chloride, water, NaoH, NaoCI and Ferric Hydroxide slurry recycle alongwith a
mechanical stirrer and pump means to pump the Ferrate sol into the Ferrate Sol Storage.
9. A system for carrying out cyanide removal in Biological oxidation and De-phenolisation
Plant (BOD) as claimed in anyone of claims 7 to 8 wherein said Ferrate treated effluent is
exited through a final clarifier.
10. A process for the cyanide removal in Biological oxidation and De-phenolisation Plant
(BOD) and a system for carrying out cyanide removal in Biological oxidation and De-
phenolisation Plant (BOD) substantially as herein described and illustrated with reference
to the accompanying figures.

The present invention relates to a safe, simple, economic and efficient process for the
Coke Oven Effluent Treatment subjecting the left over cyanide complexes in the biologically treated coke oven effluents in BOD plants to treatment with Ferrate such as to selectively carry out Ferrate oxidation and removal of left over cyanide complexes there from, in order to restrict the Cyanide discharge within the norm of 0.2 mg/lit in large steel plants/other industries. Advantageously, the process and the system of the invention is capable to be easily retrofitted in to the existing effluent treatment plants with less cost involvement for protecting the environment from cyanide discharge beyond statutory norms. The Ferrate treatment of coke oven effluent is further directed to removal of the color, suspended solid particles from the final biologically treated effluent, thus improving the overall treated effluent quality and is having potential for wide industrial application in BOD plants of large integrated Steel Industries.