TITLE:
Supramolecular Metallo Cage as Flocculent
FIELD OF INVENTION:
This invention relates to a process for removal of free cyanide (CN) from the industrial waste water.
The process involves heterogeneous mixing of solid non-ferrous metal (3d block) complex [L{M}] (supramolecular metallo cage; L; Organic receptor (Cryptand) , M; non-ferrous metal) and CN" containing waste water (enriched with other interfering anions like; Cl-, SO42-, NO3-, NO2- etc.) through mechanical or magnetic stirring and continuous removal of CN- in high efficiency to permissible limit. Actually the invented compound is coinized metal complex. In the process application, the coinized metal complex has been thoroughly described and explained as a complex [L{M}]. It involves three independent steps; (i) mixing of [L{M}] with waste water, (ii) filtration of processed water and recycling the existing [L{M}] for further use, and (iii) treatment of waste water with certain volume percent of mother solution made of sparingly soluble [L{M}].
BACKGROUND OF THE INVENTION:
Source of cyanide:
The wastewater from the coke plant and blast furnace blow down have been identified as the contributors of aqueous cyanide emissions in the iron and steel industries, however;

the characteristics of cyanide from those sources are significantly different due to presence of lots of interferences. Cyanide present in the coke plant discharge water is in association with other interferences such as ammonia, thiocyanate, sulfides, pyridine, oil, tar, phenol, cresol, benzol, PAH, etc. whereas, the blast furnace blow down water contains various forms of cyanide along with high concentration of chloride and ammonia including other inorganic recalcitrant e.g. Fe, Na, K, SO42-, etc. Formation of cyanide in Coke Plant:
Coke is required for reduction process in blast furnace. In the coking operation, (coal to coke conversion) several by-products such as water, oil, tar, ammonia, phenol, cresol, benzol, cyanides, thiocyanate, sulphides, pyridine, PAH, etc. are generated during cooling of exhaust gas form the coke oven. After separation in decanter, coke oven battery liquor is generated which is eventually sent to ammonia still (for scrubbing) to reduce further ammonia and cyanide concentration up to certain extent. However, the effluent of ammonia still content large amount of cyanide, thio-cyanide, sulphur, etc. Further, it is treated in activated sludge process using aerobic stain bacteria in BOT plant. The treatment process schematically represented in the figure 1 and some results has been given in subsequent table 1.


Cyanide formation in Blast Furnace:
Small amounts of cyanides are formed in the blast furnace. Alkali metals (mainly sodium
and potassium) play a major role in cyanide formation. The oxides, carbonates and
silicates of the alkali metals contained in coke and the acidic flux (silicates such as
feldspar) are reduced and vaporized in the hearth of the blast furnace at temperatures
above 1300°C.
M2SiO3 + 3C= 2M + Si + 3CO (M = Na // K)
Sodium and potassium vapors react with nitrogen from the preheated blast air and with
carbon from the coke to form sodium cyanide and potassium cyanide.
2M + 2C + N2= 2MCN (M = Na // K)
Sodium and potassium cyanides are present in gaseous form in the hearth (boiling points:
(NaCN) = 1530 °C; (KCN) = 1625 °C). They are carried upwards in the rapidly moving
gas stream to the cooler zone (T <1000 °C), where they condense and can decompose by
reacting with CO2 to form carbonates.

2MCN+4CO2=M2CO3+N2+5CO
A part of the alkali cyanide reduces iron Oxide with the formation of alkali oxide. A part
of the alkali cyanide leaves the blast furnace with the top gas.
2MCN+2FeO=M2O+2Fe+2CO+N2
Gas cleaning plant:
Top gas (blast-furnace gas) consists of 40-60% nitrogen, 20-30% carbon monoxide, 20-
25% carbon dioxide, 2-4% hydrogen etc. The scrubbing water of top gas contains
dissolved cyanide (HCN, alkali cyanide) and complex cyanide (unidentified) along with
Fe, SO42-, Cl-, NH4+ (details result given below) complexes (e.g. of iron). The scrubbing
water can be used several times for purifying the top gas.
Blow down water of gas cleaning plant of Blast furnace (BF) releases free and complex
cyanide along with appreciable amount of chloride. Cyanide content of BF water is
associated with alkali and alkali earth metal, iron, chloride and ammonia.
Both blast furnace and coke plant water contain environmentally hazardous contaminants
and on the other hand, these water sources contain high amount of cyanide content above
the permissible limit which causes impact on environment. In light of the above, there is
need of innovative and cost friendly method that can enable reuse of blast furnace and
coke plant water. Further, the method should be feasible from implementation
perspective without making any changes in the ongoing process of heavy industry.

History of Supramolecular bi-metallic cage receptor:
Supramolecular cage receptors have a vast background in literature which started with the pioneering works by Lehn and co-workers in way back in 1970's. 1-7 Further, Lehn had expressed huge expectation from this class of receptor and mentioned in his 1977's communication that cascade complex could be of much help in bi- (or poly-) nuclear catalysts for multicenter-multi-electronic processes and synthetic models of polynuclear metallo-proteins. But till date these targets are far to be achieved and supramolecular cage receptors are only extensively utilized in anion recognition processes. From its initial days, this field of research emerged with a focus towards size and shape of these receptors which should be in accordance with that of the shape of the coordinating metal center and incoming guest anion. Often the geometry around the metal center in such complexes are found to be distorted square pyramidal or trigonal bi-pyramidal where a loosely bound solvent molecule is found to be present. Thus the guest anion has a tendency to displace this solvent molecule to form a complex. In this regards it is noteworthy to mention that the very first crystal structure of bi-metallic cascade complex was reported by Martell et al.8 References are present in the literature that evokes that these cages are capable of coordinating different guest anions like N3-, imidazole, OH-, CO32-, CN-, Cl-, I-, ClO4-, NO3-, TcO4- etc. in its neutral and protonated state.1, 9-52 Interestingly, the recognition processes with metallic cage receptors are found to occur in organic solvent medium. But, our approach is to trap free CN- present in industrial waste

water in aqueous medium with known pre-existing supramolecular metallo cage receptor which is challenging as well as targets towards real life application with environmental concern. This brief discussion evokes the potentiality of supramolecular metallo cage for application on CN- removal from industrial waste water as shown in figure 2.
OBJECTS OF THE INVENTION:
An object of the present invention is to propose a process for removal of free cyanide(CN) from the industrial waste water.
Another object of the present invention is to propose a process of treating waste water, the [L{M}] will be further recycled to process the second phase of waste water treatment.
Further, object of the present invention is to propose a [L{M}] which is a scavenger for CN- for efficient removal of CN-.
Still further object of the invention is to propose an efficient process of cyanide removal.
Yet another object of the present invention is to propose a process of cyanide removal which is cost effective.

BREIF DESCRIPTION OF THE INVENTION:
According to this invention there is provided a process for removal of free cyanide (CN-)
from the industrial waste water comprising:
fixing of the optimal concentration and retention time of the supramolecular metallo cage
[L{M}] as flocculent treating 10 ppm and 100 ppm standard solution of CN- with
supramolecular metallo cage [L{M}] through mechanical stirring, subjecting the sample
to the step of analysis treating waste water with another liquor prepared from flocculent
[L{M}].
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:
Fig. 1: shows the diagram of BOT plant
Fig. 2: shows the schematic representation of different zone of blast furnace
Fig. 3: shows the Optimization of temperature and compound concentration

DETAILED DESCRIPTION OF THE INVENTION:
The present invention provides a process of removing free CN- from the waste water containing high content of CN- up to its permissible limit. This work emphasizes on CN-removal from industrial waste water instead of binary organic solvent mixture and also waste water serves as a source of CN-. [L{M}] complex was never utilized for selective removal of CN- from waste water of any type or water through heterogeneous phase mixing. That's the point of focus in this case. We have utilized the supramolecular metallo cage [L{M}] as a flocculent for heterogeneous phase mixing of solid flocculent [L{M}] and waste water through magnetic or mechanical stirring and 65%-85% removal of the CN- was observed within 10 minutes. Here the solvent used for the process was blast furnace waste water of steel plant which contained other interfering anions (Cl-; 1000-1200 ppm, SO42-; 90 ppm, NO3-; 35 ppm, NO2-; 1 ppm, CN-; 3-6 ppm) too and it was again the source of CN- itself. The process includes mixing of [L{M}] with blast furnace waste water with varying concentration range from 0.5 mmol/liter - 2 mmol/ liter. To the best of our knowledge, such efficient and quick CN- removal process from waste water (blast furnace or any other industrial waste water) through heterogeneous phase mixing of solid [L{M}] and waste water is neither present in literature nor being patented earlier.

The entire operation is mainly comprised of four steps:
1. Fixing of the optimal concentration and retention time of the supramolecular metallo cage [L{M}] as flocculent for CN- treatment in industrial waste water.
2. Treatment of 10 ppm and 100 ppm standard solution of CN- with supramolecular metallo cage [L{M}] through mechanical stirring
3. Use of recycled supramolecular metallo cage [L{M}] for CN- treatment and analysis of the samples.
4. Treatment of waste water with mother liquor prepared from flocculent metallo cage [L{M}] in distilled water.
> Step 1: Fixing of the optimal concentration and retention time of the supramolecular metallo cage [L(M}] as flocculent for CN- treatment in industrial waste water:
In order to fix the optimal concentration and retention time of the supramolecular metallo cage [L{M}] for efficient and quick removal of CN-, we scanned different concentration ranges of it with industrial waste water (e.g. blast furnace waste water). The blast furnace waste water contained different interfering anions like Cl-; 1000-1200 ppm, SO42-; 90 ppm, NO3-; 35 ppm, NO2-; 1 ppm, CN-; 3-6 ppm. This solutions were stirred over a wide range of time intervals with supramolecular metallo cage [L{M}] and the solutions were then filtered. To start with, we first fixed the concentration to 0.5 mmol/ lit and increase it up to 3 mmol/lit. The results are tabulated below. Here, CN- content in the feed sample was 5.65 ppm.


Table 2 justifies that optimal retention time for CN- removal through mechanical stirring is 10 minutes. The removal rate of CN- was found to be up to 48% with [L{M}] concentration 0.5 mmol/lit where as if the concentration was increased up to 2 mmol/lit, the removal efficiency was found to be increased up to 76%. Further increase in [L{M}] concentration up to 3 mmol/lit did not affect the removal efficiency much. Hence the study justified the optimal concentration of [L{M}] for CN- removal was found to be 2 mmol/lit whereas the optimal retention time was found to be 10 minutes and the process involved was heterogeneous phase mixing of flocculent [L{M}] and CN-waste water.

During the treatment process, we observed that portion of the flocculent was found to be dissolved in waste water which turned pale green upon treatment. That means partial solubility of the fiocculent played the pivotal role in CN- removal. We estimated that the percentage loss of fiocculent in each treatment cycle was 4.5 W% (weight percent). Further, in later sections we will show how this fiocculent solution was utilized for CN-removal.
> Step 2: Treatment of 10 ppm and 100 ppm standard solution of CN- with supramolecular metallo cage [L(M11 through mechanical stirring
A standard solution of K2[Zn(CN)4] (1000 mg/lit, i.e. 1000 ppm.) in water was used to prepare a 10 ppm/ 100 ppm standard solutions of CN-. This standard solutions were stirred for half an hour with supramolecular metallo cage [L{M}] and the solutions were then filtered. The concentration of fiocculent maintained during experiment was 2 mmol/ lit. The strength of CN- in the filtrate (10 ppm standard) was found to be 0.49 ppm which meant 95% removal of the CN-. Further, strength of CN- in the filtrate (100 ppm standard) was found to be 2.3 ppm which meant 97% removal of the CN-. Thus these experiments proved that [L{M}] can efficiently remove CN- in form of [L{M}(CN)] from water through hetero generous phase mixing within 10 minutes time.
> Step 3: Use of recycled supramolecular metallo cage [L{M} for CN-treatment and analysis of the samples.

We used the recycled flocculent in solid form as precipitate after treatment form the step 1 and further utilized it for treatment of fresh waste water. After each treatment cycle we filtered the solution and recycled the residue for further treatment. The process was repeated several times and here we include only six treatment cycles. It is noteworthy to mention that during step 3 we used 2 mmol/lit flocculent concentration and 10 minutes retention time for each treatment cycle. The details of the results are tabulated below in table 3. The results reflected that the CN- removal efficiency was found to be >70% through heterogeneous phase mixing.

We have further analyzed the flocculent filtrate after each cycle with ICP-MS in a separate indigenous experiment and the data are tabulated in table 4. Here the CN-content in the feed sample was 3.2 ppm. The only change in the overall process was the stirring. Here we have used mechanical stirring instead of previously used magnetic stirring. The data revealed that this process encountered up to 85% of CN- removal in

each cycle. Even the total dissolved solid (TDS) was not increasing after each cycle. We observed nominal change in pH of the waste water before and after treatment. Thus heterogeneous phase mixing of flocculent [L{M}] with waste water and mechanical stirring showed efficient CN- removal. Here partial solubility of the flocculent played the pivotal role in the treatment process.

> Step 4; Treatment of waste water with mother liquor prepared from flocculent [L{M}] in distilled water:
In the previous three sections we have explained how flocculent [L{M}] or its solution was utilized to trap CN- form waste water. Here we discuss how change in concentration of the flocculent and retention time affects the removal efficiency. In order to do so, we prepared two different aliquots of [L{M}] in 1litre distilled water. One aliquot had concentration 2mM/lit which we term as aliquot A and another aliquot had concentration 0.5mM/lit which we term as aliquot B. During the study, we dissolved the partially soluble flocculent to prepare its corresponding mother liquor and mixed its certain

percentage with the waste water to remove CN-. In this case, we show removal efficiency depending on concentration and retention time. As we have mentioned in the earlier section, that flocculent [L{M}] was partially soluble in water hence we utilized mother solution with and without filtration to have a complete overview on the removal process. Table 5 summarizes all the data which were obtained during these set of experiments.

Table 5 reveals that 80% CN- removal efficiency was obtained with 10%-20% volume of the aliquot A within a time span of 10-30 minutes. Even we used 2-5% of volume of the aliquot A and make up the rest with the waste water, then also the removal efficiency was found to be ~75%. Now we move towards the minimum amount of flocculent required for CN- removal and in that case we went for no filtration method which is more apt for industrial application. Here we also observed ~ 65% removal of CN- from the waste water with use of 1-0.1% volume of aliquot A. Thus it justified that >65% removal of CN- was obtained upon using different volume percent of aliquot A within a certain

interval of time through heterogeneous phase mixing followed by dilution with waste water containing CN-.
Now let's discuss the result obtained from aliquot B. In case of aliquot B also, we obtained 65% CN- removal efficiency within 10-30 minutes retention time interval with just 0.1-0.5% volume of aliquot B. Thus it justifies that there was no change in the percentage removal of CN- with lower volume percent (0.1%-0.5%) irrespective of concentration of the mother liquor (aliquot A or aliquot B). Thus step 4 justifies the efficiency of the flocculent [L{M}] for quick and efficient removal of CN-.
Supramolecular metallo cage [L{M}] behaved as a flocculent to remove CN- from industrial waste water through heterogeneous phase mixing. The waste water contained several other interfering anionic species e.g. Cl- , SO42- , NO3- , NO2- etc. whose presence did not affect the efficiency of CN- removal process as the flocculent has specified pockets for CN- binding as shown in figure 3.


WE CLAIM:
1. A process for removal of free cyanide (CN-) from the industrial waste water
comprising:
fixing of the optimal concentration and retention time of the supramolecular metallo cage
[L{M}] as flocculent;
treating 10 ppm and 100 ppm standard solution of CN" with supramolecular metallo cage
[L{M}] through mechanical stirring,
subjecting the sample to the step of analysis;
treating waste water with another liquor prepared from flocculent [L{M}].
2. The process as claimed in claim 1, wherein the said optimal concentration of [L{M}]
for CN- removal was found to be 2 mmol/lit whereas the optimal retention time was
found to be 10 minutes and the process involved is heterogeneous phase mixing of
flocculent [L{M}] and CN- waste water.
3. The process as claimed in claim 1, wherein the said standard solution comprises of
K2[Zn(CN)4] in water to prepare 10 ppm /100 ppm standard solutions of CN- and the
standard solution was stirred with supramolecular metallo cage [L{M}] and the solutions
were then filtered.

4. The process as claimed in claim 1, where the said flocculent in solid form as
precipitate after step 1 was reutilized for fresh waste water and after each treatment cycle
the solution was filtered and recycled and the residue was used for further treatment and
the said process was repeated several times.
5. The process as claimed in claim 4, wherein the said process was repeated several
times and during step 3 2mmol/lit flocculent concentration and 10 minutes retention time
for each treatment cycle and the removal efficiency was found to be >70% through
heterogeneous phase mixing.