FORM 2
THE PATENTS ACT, 1970
(Act 39 of 1970)
COMPLETE SPECIFICATION
(See Section 10)
Title: "An improved process for treating Sodium Cyanide containing liquid effluent on Industrial Scale"
Name: M/s. Gujarat Alkalies and Chemicals Limited.
Address: P.O. Petrochemicals - 391 346,
Dist: Vadodara, Gujarat-India.
Nationality: Indian
The following specification particularly describes the invention and the manner in which it is to be performed.

Title of the Present Invention:
An improved process for treating Sodium Cyanide containing liquid effluent on Industrial scale.
Field of the Present Invention
This invention relates to an improved industrial process to achieve a dual objective of both treating the liquid effluent of the Sodium cyanide plant effectively/economically and simultaneously manufacturing high purity Sodium Ferrocyanide Decahydrate on commercial scale.
Background of the Present Invention
There are various chemicals that are present in waste water from industrial operations. These chemicals have adverse effects on the environment as these chemicals or heavy metals may be toxic. Most waste water processing technologies emphasize the removal of the chemicals or heavy metals as cations, whereas anions associated with heavy metal cations can be equally toxic. Among such anions, Cyanide is a singly charged anion containing unimolar amounts of carbon and nitrogen atom. It is capable of complexing at low concentrations with virtually any heavy metal due to its strong ligand properties. The liquid waste generated by the Sodium Cyanide plant primarily contains Sodium Cyanide, Sodium Formate & Sodium Hydroxide. Due to its high toxicity, the waste cannot be released in the effluent channel directly. The present invention deals with a viable process for the treatment of the Sodium Cyanide plant waste and simultaneous production of Sodium Ferrocyanide Decahydrate.
IN 172677 reported that Sodium Cyanide Plant waste can be treated by reacting the waste with Ferrous Chloride thus producing Sodium Ferrocyanide Decahydrate Sodium Ferrocyanide Decahydrate is a valuable product & has many Industrial applications.
There are several methods employed for the treatment of Cyanide containing waste water in the metallic coating industry. The methods are namely Cyanide removal by Ion - exchangers, Cyanide decomposition by alkaline chlorination, Electrolytic Chlorination, Electrolytic oxidation, Ozonation, oxidation by Hydrogen Peroxide using a metallic catalyst, oxidation using permanganates or chromates, decomposition of activated carbon eluate by copper Sulphate & oxygen, Biodegradation, Irradiation, Thermal hydrolysis or addition of Ferrous salts. The other Methods of Cyanide waste treatment known are Volatilization & catalytic oxidation of HCN after the acidification of the highly concentrated Cyanide solution, Oxidation of Cyanide solution by Air in combination with activated carbon, Cyanide destruction by microorganisms, Hydrolysis of Cyanide at high pressure & temperature.

There are several ways reported in the literature to prepare Sodium Ferrocyanide. It has been reported earlier that the high - enriched Cyanogens in Pyrethrin waste water can be treated with Ferrous Sulphate followed by aeration & treatment with Sodium Hydroxide to yield Sodium Ferrocyanide. The Sodium Cyanide containing waste water can also be reacted with Ferrous Sulphate to prepare Sodium Ferrocyanide.
The reported methods for the treatment of Cyanide waste either revolves around the degradation of Cyanide or Cyanide being converted in to the non toxic products. The alkaline chlorination is still the most popular commercial way for the treatment of Cyanide waste but it consumes large quantity of Sodium Hydroxide, Chlorine and Water (for dilution). The methods are known for treating the Cyanide containing waste water by Ion exchange and reverse osmosis but they are not economically viable.
It has been found that as such no process at the industrial scale has been reported in the literature for manipulating the Sodium Cyanide plant waste to achieve the dual objective of both treating the waste effectively / economically and simultaneously manufacturing a value added product on the commercial scale, which is suitable for industrial applications / uses. The commercial Plant manufacturing 2500-2700 MTA Sodium Cyanide generates about 125-150 M3 liquid effluent containing 25-35 % Sodium Cyanide along with 15 - 20 % Sodium Formate & 2 - 2.5 % Sodium Hydroxide per annum. The given process is able to reduce the Sodium Cyanide content in the liquid effluent from 25 - 35% to less than 50 ppm.
Summary of the Present Invention
The present invention discloses an improved and economical industrial process for treating Sodium Cyanide effluent waste liquor. The process comprising the step of reacting the alkaline waste liquor with separately produced 25-35% Ferrous Chloride with efficient stirring under an inert atmosphere, the step of centrifuging for the separation of insolubles collected separately, followed by the step of crystallization of high purity Sodium Ferrocyanide Decahydrate and the step of centrifuging the Sodium Ferrocyanide Decahydrate leaving the liquid effluent with less than 50 ppm Sodium Cyanide content, which in turn is easily treated separately and released in the effluent channel. The Solid Sludge collected separately is incinerated at 900 -1100°C.
The present invention provides an economically viable solution on the industrial scale to treat 0.3 - 0.6 M per day liquid effluent of Sodium Cyanide Plant. The option of using the stored Ferrous Chloride (under Nitrogen) has provided flexibility in the process management. The process operating parameters including the reactant ratios have been modified and improved in such a way that it is able to give a value added Cyanide free product - Sodium Ferrocyanide Decahydrate in 95 - 98 % yield on the commercial scale having Industrial applications / uses. The pH adjustments in the process have been made to ensure that no additional Sodium Hydroxide is required in the process.

The process assumes immense economical significance with respect to the appreciable savings in terms of chemicals, which otherwise would have been required to treat the effluent with such a high content of Sodium Cyanide and the commercial value of the highly pure, cyanide free Sodium Ferrocyanide Decahydrate.
Detailed Description of the Present Invention
The present invention is such a desirable process which has the capacity for manipulating the Sodium Cyanide plant waste to treat the waste effectively, economically and simultaneously manufacture a value added product on the commercial scale which is suitable for industrial application. The present invention has successfully provided an improved / modified economical industrial process for successfully and effectively treating 125 - 150 M liquid effluent (containing 25 - 35 % Sodium Cyanide) generated per annum from a commercial plant manufacturing 2500-2700 MTA Sodium Cyanide and simultaneously producing high purity value added marketable product - Sodium Ferrocyanide Decahydrate (99.99% purity) in 95-98% yield.
The process of the present invention has the following steps:
Stepl:
The 25 - 35% Ferrous Chloride is prepared separately in 1 M3 capacity MS reactor provided with internal glass flake coating by reacting 17 - 20% Hydrochloric Acid with Iron powder under Nitrogen. The Ferrous Chloride solution so prepared is stored in a storage tank under the Nitrogen blanketing & used according to the requirement.
Step2:
The Sodium Cyanide containing liquid effluent is charged in 1.9 M1 capacity SS - 316 L reactor along with the required amount of soft water. The contents are gradually heated to 45 - 60°C under stirring & the Ferrous Chloride solution (prepared & stored separately) is added gradually by maintaining the temperature in between 65 - 85°C. The pH throughout the reaction is maintained in the vicinity of 12.0. The Cyanide content in the reaction mixture is also monitored continuously till it reaches less than 50 ppm.

Step3:
The contents are centrifiiged to remove the insolubles, which are collected separately and the clear liquor is transferred in 1.6 M capacity S S - 316 L crystallizer, where it is gradually cooled up to 10 - 15°C The crystallized slurry is then fed to basket centrifuge for separating the mother liquor & product - Sodium Ferrocyanide Decahydrate.
Step4:
The product is dried in fluidized bed dryer for 1 - 5 hrs. at 45 - 50°C and is completely free from cyanide.
Step5:
The mother liquor obtained is collected separately, which is having less than 50 ppm cyanide content is treated appropriately & drained in the effluent channel.
Sodium Ferrocyanide Decahydrate obtained as a by product is having 99.99% purity . The final product is completely free from cyanide in 95-98% yield having industrial applications/uses.
Step - 6
The insolubles (collected separately in Step - 3) of various batches are combined together and incinerated at 900 - 1100°C.
The present invention will be described in terms of specific examples and examples should be considered as illustrative of the invention and not as limiting the same. The examples described herein will substantiate our claims
Example -1
0.342 M3 liquid effluent of Sodium Cyanide Plant (containing 29.50 % Sodium Cyanide, 2 16 % Sodium Hydroxide and 15 - 20% Sodium Formate) and 0.255 M3 Soft water were charged in the reactor. The reactants were heated to 50-60 C and to this 0.152 M3 30% Ferrous Chloride (prepared earlier and stored under nitrogen atmosphere in a storage tank ) was added in an inert atmosphere keeping the reaction temperature in the vicinity of 85° C. The reaction pH was maintained in between 11.5 - 12.0. The total reaction time including addition of Ferrous Chloride was 3 hrs. The reaction mass was subjected to the centrifuging to remove the insolubles / solid sludge, which is approximately 9-11 kg.. The clear light pale yellow liquor was transferred to the crystallizer where the temperature was gradually brought down to

10 C, The crystallization got completed between 6-7 hrs. The crystals were isolated by centrifuging, washing and finally drying at 45 - 50° C for 4 hrs to yield 210 kg. Sodium Ferrocyanide Decahydrate (having purity 99.99 % and completely free from Cyanide) thereby giving 98 % product yield.
Example - II
0.371 M liquid effluent of Sodium Cyanide Plant (containing 27.68 % Sodium Cyanide, 2.07 % Sodium Hydroxide and 15 - 20% Sodium Formate) and 0.224 M3 Soft water were charged in the reactor. The reactants were heated to 55- 65 °C. and to this 0.165 M3 28.9% Ferrous Chloride (prepared earlier and stored under nitrogen atmosphere in a storage tank) was added in an inert atmosphere keeping the reaction temperature 70 - 85° C. The reaction pH was maintained in the vicinity of 12.0. The total reaction time including addition of Ferrous Chloride was 3-4 hrs. The reaction mass was subjected to the centrifuging to remove the msolubles / solid sludge, which is approximately 9 - 11 kg. The clear light pale yellow liquor was transferred to the crystallizer where the temperature was gradually brought down to 15 °C. The crystallization got completed between 6-7 hrs. The crystals were isolated by centrifuging, washing and finally drying at 45 - 50 °C for 3 hrs to yield 204 kg. Sodium Ferrocyanide Decahydrate (having purity 99.99 % and completely free from Cyanide) thereby giving 95 % product yield.

We Claim:
1. An improved and economical industrial process for treating Sodium Cyanide
containing liquid effluent, the process comprising :
- the step of reacting the alkaline waste liquor with separately produced 25-
35% Ferrous Chloride with efficient stirring under an inert atmosphere;
the step of centrifuging for the separation of insolubles, which in turn is collected separately,
- the step of crystallization of high purity Sodium Ferrocyanide Decahydrate;
- the step of centrifuging the Sodium Ferrocyanide Decahydrate, which in
turn is collected & dried, leaving the mother liquor, which is collected &
further treated separately.
- the step of incinerating the solid sludge generated in the process.
2. A process as per claim 1, wherein high purity Cyanide-free Sodium Ferrocyanide Decahydrate is produced in 95-98% yield having 99.99% purity.
3. A process as per claim 1, wherein liquid effluent having composition of 25-35% Sodium Cyanide, 15-20% Sodium Formate, 2-2.5% Sodium Hydroxide and 40-50% Water can be treated at a time.
4. A process as per claim 1, wherein the reaction temperature is 50-85°C
5. A process as per claim 4, wherein the reaction including the addition of Ferrous Chloride is completed in 3-4 hours.
6. A process as per claim 1, wherein the optimum pH of the reaction is between 11.5-12.0.
7. A process as per claim 1, wherein the range of molar ratio of Sodium Cyanide to Sodium Hydroxide is 6:0.5 to 6.0.9.
8. A process as per claim 1, wherein the range of molar ratio of Sodium Cyanide to Ferrous Chloride is 6:1 to 6:1.2.
9. A process as per claim 1, wherein the crystallization of Sodium Ferrocyanide Decahydrate is completed at 10-15 °C.
10. A process as per claim 9, wherein the crystals of Sodium Ferrocyanide Decahydrate are dried at 45-50 °C for 1-5 hours.

11. A process as per Claim 1, successfully reduces the Sodium cyanide content in the liquid effluent by 99.99% on the industrial scale.
12. A process as per Claim 1, the solid sludge generated in the process is incinerated at 900 -1100°C.