Title of Invention	"A COST EFFECTIVE PROCESS FOR PREPARATION OF IODATE SALT SOLUTION FOR DIRECT IODIZATION OF COMMON SALT"
Abstract	The invention comprises the preparation of 3% pure potassium iodate solution for direct salt iodisation. The procedure involves the use of iodine, sodium hydroxide, potassium hydroxide and chlorine gas. The present method avoids the use of carcinogenic catalysts, costly membranes, several cost implicated process steps. This method is convenient to adopt for the iodised salt manufacturers and stops the possibility of adulteration.

Title of Invention

"A COST EFFECTIVE PROCESS FOR PREPARATION OF IODATE SALT SOLUTION FOR DIRECT IODIZATION OF COMMON SALT"

Abstract

The invention comprises the preparation of 3% pure potassium iodate solution for direct salt iodisation. The procedure involves the use of iodine, sodium hydroxide, potassium hydroxide and chlorine gas. The present method avoids the use of carcinogenic catalysts, costly membranes, several cost implicated process steps. This method is convenient to adopt for the iodised salt manufacturers and stops the possibility of adulteration.

Full Text	FIELD OF THE INVENTION This invention relates to a cost effective process for preparation of iodate salt solution for direct iodization of common salt The present relates to the preparation of potassium iodate solution for direct salt iodization using chlorine gas, sodium hydroxide, potassium hydroxide and iodine. BACKGROUND OF THE INVENTION The daily intake of iodine recommended by the National Research Council of the US National Academy of Sciences in 1989 (Report of a joint FAO/WHO expert consultation Bangkok, Thailand, Chapter 12 in Human Vitamin and Mineral Requirements published by World Health Organization Food and Agriculture Organization of the United Nations Rome, 2002, http://www.fao.Org/DOCREP/004/Y2809E/v2809e0i.htm#bm18.5) was 40 ug/day for young infants (0-6 months), 50 ug/day for older infants (6-12 months), 60-100 ug/day for children (1-10 years), and 150 ug/day for adolescents and adults (US National Research Council, 1989, Recommended dietary allowances, 10th edition, Iodine Food and Nutrition Board, P. 213-217, Washington D.C., National Academy Press Publication), approximating to 7.5 ug/kg/day for age 0-12 months, 5.4 ug/kg/day for age 1-10 years, and 2 ug/kg/day for adolescents and adults. These amounts are proposed to allow normal T4 production without stressing the thyroid iodide trapping mechanism or rising TSH levels. The iodine deficiency for long time, leads to biological disorders like gout, mental retardation, deaf mutism, short stature, cretinism and risk of death during the childhood (Scientific Encyclopedia, Van Nostrand's, 8th ed. D. M. Considine, Ed. Van Nostrand Reinhold, New York, p1751-1755, 1995; Iodised salt for preventing iodine deficiency disorders, T. Wu, G. J. Liu and P. Li, C. Clar Cochrane Review in The Cochrane Library, Issue 3 2002. Oxford, Update Software; Iodine Deficiency Disorders in India Report of Nutrition and IDD Cell, Ministry of Health and Family Planning, October 1997, http://www.people.virginia.edu/~itd/iccidd/mi/ idd 075.htm; P. Pongpaew, S. Saowakontha, R. Tungtrongchitr, U. Mahaweerawat, F. P Schelp Nutrition Research (New York), 2002, 22(1/2), 137-144; K. A.McMonigal, L. E. Braverman, J. T. Dunn, J. B. Stanbury, M.L. Wear, P.B. Hamm, R. L. Sauer, R. D. Billica and S. L Pool in their publication entitled 'Thyroid function changes related to use of iodinated water in the U.S. space program' in Aviation, Space and Environmental Medicine, 2000, 7f(11), 1120-1125; S. Muslimatun, R. Gross, D. H. S. Dillon, W. Schultink Asia Pacific Journal of Clinical Nutrition, 1998, 7(3/4), 211-216). It is supplemented by different ways of iodization of edible materials like salt, oil (capsule and injections), water, bread, soya sauce, iodoform compounds used in dairy and poultry, and certain food additives (World Health Organization. 1994. Iodine and health: A statement by WHO. WHO/NUT/94.4). Iodized salt is normally recommended for edible purposes as most of the people consume it irrespective of religion, caste, creed and sex. Alkali iodides and iodates are known to be useful in the iodization of salt for edible purposes to prevent thyroid gland diseases. Both of these forms of iodine are absorbed as iodide ions and are completely bio-available (ICCIDD/MI/UNICEF/WHO, 1995. Salt iodisation for the elimination of iodine deficiency). Potassium iodate is preferred to other salts of iodine for the iodization of salt in all Asian countries including India because of weather conditions. Presently, the iodization of salt is done either by using potassium iodate or potassium iodide in amounts that ensure a minimum intake of 150 ug iodine/day/person. Reference is made to Indian Patent No. 173, 008 (1994) assigned to S. Balagopalan et. al. has disclosed that a flow reactor with an externally insulated stainless steel tank as cathode and a cylindrical lead oxide coated graphite anode placed at a distance of 1.5 - 3 mm gap can be used for the preparation of potassium iodate from elemental iodine in a potassium hydroxide solution. The product is cooled and isolated. The drawbacks of this process is that the product obtained in solution form is not pure and to be isolated to avoid the impurities. The columbic efficiency of the cell gets reduced as the products, potassium iodate and hypo iodite are unstable at the cathode. Even, the isolated solid contains impurities like lead in ppm level, which affects the health in the long run. J. von Liebig in his paper published in Ogg. Ann. 1832, 24,362 and G. S. Serullas in his paper published in Ann. Chim. Phys. 1830, 43, 125 have independently reported the preparation of sodium iodate and potassium iodate by a multi-stage method. The procedures comprise saturating chlorine gas in water containing a fine suspension of iodine, neutralizing the liquid with the respective carbonate; and again passing chlorine until the iodine is dissolved, and further neutralizing with the carbonate. The solution is to be evaporated to one-tenth of its volume, mixed with half its volume of alcohol, and the sodium/potassium chloride was washed from the precipitate by means of aqueous alcoholic solutions. The sodium carbonate is to be removed by treatment with acetic acid, and the sodium acetate is then washed with alcohol. The drawbacks of this process are that it is a multi-stage process and involves the use of a weak base. Acetic acid is required to neutralize the excess sodium carbonate. Besides, it requires heating to concentrate the solutions and adding alcohol to precipitate the iodate salts which makes the process costlier. J. L. Gay Lussac in his paper published in Ann. Chim. Phys. 1814, 91(1), 5, has reported a procedure for the preparation of potassium iodate from iodine and potassium hydroxide. In this method, iodine is dissolved in a preheated solution of potassium hydroxide to give 16.67% of potassium iodate and 83.33% of potassium iodide. Later on, the solution is concentrated and precipitated the potassium iodate by the addition of alcohol. The main drawback of this method is that only a part of the total iodine taken gets converted to potassium iodate and hence the yield of potassium iodate is equal to one-sixth of total iodine taken or less of it. The method requires an additional chemical step to convert the major portion of iodine left as potassium iodide to its iodate for improving the yields of potassium iodate. 0. Henry in his published paper in Journ. Pharm. 1862, 18, 345, has prepared potassium iodate by melting together an intimate mixture of potassium iodide and potassium chlorate between 450-500 degree Celsius, at which chlorate begins to decompose. The product is separated from the un-reacted potassium chlorate by the fractional crystallization. The drawbacks of this method are that potassium chlorate is an explosive and requires special equipment and intensive care to be taken to handle the reaction at higher temperature greater than 450 degree Celsius. J. S. Stas in his paper published in Mem. Acad. Belgque, 1865, 35, 3, has disclosed a method for the preparation of potassium iodate on a laboratory scale. In this method elemental iodine or potassium iodide was heated with potassium chlorate between 450-500 degree Celsius, at which chlorate begins to decompose. The drawbacks of this method are that potassium chlorate is an explosive and requires special equipment and intensive care to handle the reaction. Chinese patent no. CN 1,121,540 (1996) assigned to N. H. Hugo et al. reveals a method for preparing potassium iodate by electrolytic method. In this method iodine is reacted with 30-40 lit of potassium hydroxide in a cooling reactor and subjected to electrolysis in multistage series-connected electrolytic cells. The voltage of each cell is maintained at 2.0 -3.5 V and the flow rate at 5 - 10 lit/min. The current density was between 0.1 and 0.2 A/m2 while the temperature of the last cell was reported to be 80-100 °C. The potassium iodate is crystallized and separated. About 1 - 3 g/lit potassium dichromate was added to the electrolyte to prevent the reduction of iodates and/or hypo iodite at the cathode. The draw backs of this process is that the product obtained in solution is not suitable for direct salt iodization as it contains impurities like the potassium hydroxide taken in excess, potassium iodide and dichromate. In order to use potassium iodate in salt iodization, the product has to be isolated and purified which makes the process costlier. The columbic efficiency of the cell is not more than 70% due to the reaction of potassium iodate and hypo iodite at the cathode. Potassium dichromate is a known carcinogen and health hazardous chemical. Its use can not be avoided as the products, potassium iodate and hypo iodite are reactive at the cathode. The operating temperature of the cells was 80-100 °C and inconvenient. L. Henry reported a method in the paper published in Chem. Ber. (Chernische Berichte) 1870, 3, 893, on the preparation of potassium iodate. The method involves the passing of chlorine gas into finely divided suspension of elemental iodine in water till it was dissolved. Latter on, one mol of potassium chlorate per gram atom of iodine was added to the resulting solution. The mixture was warmed to get potassium iodate with the evolution of chlorine gas. The drawbacks of this process are that it requires potassium chlorate as external oxidizing agent to convert all the iodine into potassium iodate. The evolved chlorine gas is acidic and corrosive, and it has to be scrubbed through alkali hydroxide or carbonate which enhances the process cost. Potassium chlorate is an explosive and needs special skills for handling. Further, potassium chlorate is a health hazardous chemical and needs to remove traces of it in the product, thereby limiting the use of this method. L. P. de St. Giles in his published paper cited in Compt. Rend. 1858, 46, 624 has reported the preparation of potassium iodate by the oxidation of potassium iodide with a solution of potassium permanganate. In this method, potassium iodide was reacted with potassium permanganate in 1:2 mole ratio under neutral conditions to give one mole of potassium iodate, two moles of manganese dioxide and two moles of potassium hydroxide. The drawback of this method is that it requires an additional step to purify the product, potassium iodate from manganese dioxide, potassium hydroxide and all other manganese impurities before recommending it for edible purposes. P. K. Ghosh et al. in their India patent application (1057/DEL/2000) have disclosed the preparation of solid alkali iodates from the corresponding alkali iodides using an ion exchange membrane flow reactor. In this method, an alkali iodide solution is passed through anode compartment and a 4-5% sodium hydroxide through cathode compartment of an anion exchange membrane cell. Iodide is oxidized to iodine and is disproportionated to iodate and iodide by the support of hydroxyl ions migrated from cathode compartment through the anion exchange membrane. The drawbacks of this method are that the method requires a sturdy and highly conductive anion exchange membrane having good thermal, mechanical and electrical properties. Moreover, the success execution of this method depends upon the cost and free availability an anion exchange membrane. The preparation of potassium iodate by this method is costly. P. K. Ghosh et al. in their Indian patent application (0479/DEL/2003) have further disclosed an improved process for the preparation of pure potassium iodate solution for direct salt iodization. In this method iodine is dissolved in potassium hydroxide in stoichiometric quantities and the resulting solution is passed through the anode compartment of an anion exchange membrane flow cell. A solution of 4-5% sodium hydroxide is passed through the cathode compartment. Iodide is oxidized to iodine and is disproportionated to iodate and iodide at an high current efficiency by the support of hydroxyl ions migrated from cathode compartment through the anion exchange membrane. The drawbacks of this method are that the method requires a sturdy and highly conductive anion exchange membrane having with good thermal, mechanical and electrical properties. Moreover, the success execution of this method depends upon the cost and free availability an anion exchange membrane. OBJECTS OF THE INVENTION The main object of the present invention is to provide a cost effective process for preparation of iodate salt solution for direct iodization of common salt which obviates the drawbacks as detailed above. Another object of the present invention is to provide a suitable method of preparing pure 3% (w/v) potassium iodate solution for direct salt iodization. Still another object of the present invention is to utilize chlorine gas to produce 3% (w/v) potassium iodate from iodine and potassium hydroxide. Yet another object of the present invention is to eliminate the hazardous impurities and reduce the possibility of adulteration in the iodization of salt. Yet another object of the present invention is to provide an alternate chemical route for the preparation of pure 3% (w/v) potassium iodate solution and to avoid the use of harmful catalysts/chemicals, to reduce the capital investment and eliminate the use of costly membranes. Yet another object of the present invention is to provide cost effective method for the preparation of highly pure 3% (w/v) potassium iodate solution. SUMMARY OF THE INVENTION Accordingly the present invention provides a cost effective process for preparation of iodate salt solution for direct iodization of common salt which comprises: i) preparing a solution of a mixture of analytical grade potassium hydroxide in the range of 1.375 to 1.381% (w/v) and sodium hydroxide in the range of 5.138 to 5.141% (w/v) in a water jacketed glass reactor and keeping the solution under continuous stirring, ii) maintaining the temperature of the solution in the range of 30 to 50 degree Celsius, iii) adding 99.9% pure iodine to the solution in step (ii) to have a concentration in the range of 3.109 to 3.125% (w/v) and stirring the solution to become colorless, iv) purging chlorine gas at a rate in the range of 5 - 15 g per min into the solution in step (iii) till the solution turns violet, v) adding sodium hydroxide to the solution in step (iv) in the concentration range of 0.063 to 0.078% (w/v), vi) again purging chlorine gas at a rate in the range of 0 to 3 g per min till the solution attaining the pH in the range of 5 to 8 and the solution is colorless, vii) continuing the stirring of solution obtained in step (vi) for a period in the range of 15 to 45 min while maintaining the temperature in the range of 30 to 50 degree Celsius, viii) diluting the reaction mixture obtained in step (vii) to make up the final volume with deionized water to obtain the desired concentration of potassium iodate solution, ix) obtaining the dilute potassium iodate solution in the concentration range of 2.9 to 3.1% (w/v). In an embodiment of the present invention wherein 3% potassium iodate solution for direct use in salt iodization is prepared using analytical grade 1.378% (w/v) of potassium hydroxide and 5.139% (w/v) of sodium hydroxide by dissolving together under stirring in de-ionized water. In another embodiment of the present invention wherein the reactor temperature was maintained between 30 to 40 degree Celsius by constant water circulation. In yet another embodiment of the present invention wherein 3.109 to 3.125% (w/v) iodine of 99.9% purity was added in two batches and stirred till the solution was colorless. In a further embodiment of the present invention wherein 0.063 to 0.078% (w/v) of NaOH was added to the violet color solution. In an embodiment of the present invention wherein for preparing pure 3% potassium iodate solution for direct use in salt iodization, the reaction mixture was diluted with deionized water to obtain 3% potassium iodate solution. DESCRIPTION OF THE INVENTION A method for preparing pure 3% potassium iodate solution for direct use in salt iodization which comprises of i) preparing solution of 32 liters of a mixture of analytical grade potassium hydroxide weighing in the range of 440 to 442 g and sodium hydroxide weighing in the range of 1644-1645 g in a 40 to 50 liter capacity round bottom water jacketed glass reactor and keeping the solution under continuous stirring; ii) maintaining the temperature of the solution in the range of 30 to 50 degree Celsius by circulating water at room temperature; iii) adding 99.9% pure iodine to the solution in step (ii) to have a concentration in the range of 995 to 1000 g and stirring the solution to become colorless; iv) purging chlorine gas at a rate in the range of 5 - 15 g per min into the solution in step (iii) till the solution turns violet; v) adding sodium hydroxide to the solution in step (iv) in the concentration range of 20 to 25 g; vi) again purging chlorine gas at a rate in the range of 0 to 3 g per min till the solution attaining the pH in the range of 5 to 8 and the solution is colorless; vii) continuing the stirring of solution obtained in step (vi) for a period in the range of 15 to 45 min while maintaining the temperature in the range of 30 to 50 degree Celsius; viii) diluting the reaction mixture obtained in step (vii) to make up the final volume in the range of 56 to 56.5 liters with deionized water; ix) obtaining the dilute potassium iodate solution in the concentration range of 2.9 to 3.1% (w/v). According to the present invention, elemental iodine dissolves in potassium hydroxide solution and stabilized itself in the form of potassium iodide and potassium iodate as shown in eq 1. (Equation Removed) The iodide produced in eq 1 can be oxidized to elemental iodine by employing chlorine (CI2) gas or hypochlorite (HCIO or OCP) eqs 2-4. The elemental iodine thus formed is sparingly soluble in water. However, it readily reacts with iodide ion and becomes itself highly soluble tri-iodide (eq 5). Tri-iodide ion is violet in color and imparts the same color to its aqueous solution inferring its presence. (Equation Removed) The h~ which is stable at pH becomes unstable at pH > 10. In alkaline conditions, l3 or l2 rapidly disproportionates to iodide and iodate ions (eqs 6 and 7). (Equation Removed) If T ion produced on right hand side (eqs 1, 6 and 7) is being constantly oxidized to l2 by Cl2, HOCI, or OCl, under basic conditions, all the iodine present in the solution would be converted completely into iodate. The standard r/l2-CI2, I7I2-HCI0 and I7I2-CICT cells could easily be constructed and their potentials can be derived from standard electrode (E°, V) potentials of iodide (-0.535 V), Cl2 (+1.359) HCIO (+1.50 V) and CICT (+0.880 V), as +0.824 V, 0.965 and 0.345 V (Wendell M. Latimer, The oxidation states of the elements and their potentials in aqueous solutions, 2nd edn., Prentice Hall, Inc. New York, 1952), respectively. Eqs 2 and 4 are applicable to basic or neutral conditions while Eq 3 is applied to acidic medium pH According to available thermodynamic data (Wendell M. Latimer, The oxidation states of the elements and their potentials in aqueous solutions, 2nd edn., Prentice Hall, Inc. New York, 1952), E°, +1.085 V in neutral and E°, -0.268 V in basic medium for I/ IO3" half cell, the standard l-Cl2 (eq 8), T-HCIO and r-CIO~ cells in both neutral (eqs 8-10) and basic (eqs 11-13) media for the direct conversion of iodide to iodate should also be considered. If the reaction medium is highly basic, the oxidation of iodide to iodate should only be considered through Eqs 11-13. Moreover, the existence of HCIO at and above pH 10.5 is meager; therefore the possibility of iodide oxidation to iodate as per the eq 12 may be ignored. Thus, the possibility of direct iodide to iodate oxidation would only occur through Eq 11 and 13. The sign and magnitude of these cells indicate that the iodide oxidation to iodate through Eq 13 is preferred to that of Eq 11. (Equation Removed) Overall, it is concluded that the iodide oxidation in highly alkaline solutions to give iodate is only possible through eqs 8, 10, 11 and 13. Among these four ways, the oxidation of iodide to iodate seems to proceed more likely through eq. 8 via iodine and eq 13 in basic solutions. Further oxidation of iodate to periodates, H3IO62- or H5IO6 by Cl2/HCIO in neutral, and Cl2/CIO in basic solutions are also feasible. From standard half-cell potentials of IO3-- H5IO6 or H3IO62- in (-1.6 V) neutral or (-0.70 V) basic solutions, the I037H5IO - CI2 (eq 14), I037H5IO6 - HCIO (eq. 15) and I037H5IO - CIO" (eq 16) cells in neutral medium; and IO7 H3IO2" - CI2 (eq 17) and I037 H3IO2~ - CIO- (eq 18) cells in basic medium reveal that the IO~ does not under go oxidation either by Cl2, HCIO or CIO" in neutral medium as the cell potentials are negative. However, CI2 and CIO" oxidize the IO3" to H3IO62~ in excess alkaline solutions. Comparison of potentials in Eq 18 with those in Eqs 8-13, shows that IO3- to H3IO62~ in alkaline solution is also expected to some extent. (Equation Removed) However, the H5IO6 -1~ cell (Wendell M. Latimer, The oxidation states of the elements and their potentials in aqueous solutions, 2nd edn., Prentice Hall, Inc. New York, 1952; Ju. Lurie Hand Book of Analytical Chemistry, Mur Publishers, Moscow, 1975, p300-313) (eq 19, E°, +2.685 V) in neutral and H3IO62" -1" cell (eq. 20, E°, +0.432 V) in alkaline medium indicate that the reaction between I" and H5IO6 or H3I062" are spontaneous. The reaction seems very rapid in neutral and slow in alkaline conditions, implying that i) the H5IO6 or H3I062" species is unstable in the presence of iodide, ii) I03~ undergoes oxidation if one equiv or more of alkali is present and iodide is absent. (Equation Removed) Accordingly, 3-5% potassium iodate solution was prepared in a 50 liter glass reactor fitted with a water circulating cooling bath, stirrer, a flow meter for purging Cl2 gas (1-10 g/min) and a pH meter provided with a combined glass electrode for monitoring the solution pH. A wide-mouth inlet for adding water and chemicals and an out let to take out the final KIO3 solution were also provided to the reactor. In the batch process of preparation of KIO3 solution which was standardized to 1.685 Kgs, 440.94 g of KOH and 1644.36 g of NaOH were weighed and dissolved under stirring in 32 liters of de-ionized water taken. To it, 1,000 g of lz was added in two batches under stirring. To this clear and colorless solution, Cl2 gas was purged till the solution turned slightly to violet. The solution was charged further with another 20 g of NaOH and CI2 gas was purged at slow rate till the pH becomes to 7.0. Stirring was continued for 30 min more to obtain approximately 5% colorless potassium iodate solution. The solution was taken out and diluted to 56.2 liters to obtain 3% potassium iodate solution. The solution thus obtained was analyzed for potassium iodate by volumetric procedure using standard sodium thiosulfate (Na2S2O3) and 10 ml of 2 N sulfuric acid and starch as an indicator (A. I. Vogel A Text-Book of Quantitative Inorganic Analysis, 3rd ed., The English Language Book Society, Longman, London 1969, 349) and proportionately diluted to give a 3% solution for direct salt iodization. The present invention relates to the preparation of highly pure potassium iodate solution useful for direct salt iodization. The potassium iodate solution in the required concentration range was prepared from iodine, potassium hydroxide, sodium hydroxide and chlorine gas. In this method, the calculated amount of iodine was dissolved in potassium hydroxide solution. The resultant solution was chlorinated in the presence of calculated amounts of sodium hydroxide under vigorous stirring at ambient temperature with water circulation. The chlorinated solution was diluted proportionately with distilled water for the ready use in the process of salt iodization. The inventive steps adopted in the present invention are (i) a calculated amount of iodine was dissolved in an appropriate amount of potassium hydroxide solution, (ii) the iodine solution was chlorinated under ambient temperature in the presence of calculated amount of sodium hydroxide which obviates the need of special membranes, chemicals that add impurities like lead, chromium, dichromate, iodides, potassium permanganate, manganese dioxide etc. explosive/health hazardous chemicals like potassium chlorate, (iii) the clear and colorless solution after passing required quantity of chlorine gas having pH in the range of 5 to 9 was diluted proportionately to obtain 3% potassium iodate solution suitable for direct salt iodization which eliminates cost involving steps like precipitation by chilling washing, centrifuging, drying and transport or using chemicals like acetic acid and alcohol, (iv) the temperature was maintained by simple water circulation (30-40 °C), (iv) commercially available liquid chlorine was used for the oxidation of alkaline iodine to potassium iodate; and (v) the dilution was affected using deionized water. The following example is given by the way of illustration of the present invention and should not be construed to limit the scope of the present invention. EXAMPLE 1: 440.94 g of potassium hydroxide and 1644.36 g of sodium hydroxide were dissolved under stirring in 32 liters of de-ionized water in a water-jacketed 50 liter capacity round bottom glass reactor. To it, 1,000 g of 99.9% pure iodine was added in two batches and stirred till the solution turns colorless. To this clear and colorless solution, chlorine gas was passed at about 10 g/min till the solution turned violet. The temperature of the solution was maintained at 37 degree Celsius. The purging of chlorine gas was stopped and the solution was charged with another 20 g of sodium hydroxide. The chlorine gas was purged once again at a controlled rate till the pH of the solution becomes to 8.33. The solution was stirred for about another 30 min. The final solution should look colorless indicating the absence of unreacted iodine as potassium iodide. The solution was taken out, measured and diluted to 56.2 liters to get 3% potassium iodate solution for further use in direct in salt iodization process. EXAMPLE 2: 220.5 g of potassium hydroxide and 822.4 g of sodium hydroxide were dissolved under stirring in 16 liters of de-ionized water in a water jacketed 50 liter flask. To it, 500 g of 99.9% pure iodine was added and the solution was stirred to become colorless. To this clear and colorless solution, chlorine gas was passed at about 10 g/min till the solution turned violet. The temperature of the solution was maintained at 40 degree Celsius. The purging of chlorine gas was stopped and the solution was charged with another 10 g of sodium hydroxide. The chlorine gas was purged once again at a controlled (-0.1 - 0.5 g/min) for -15 min till the pH of the solution becomes to 8.5. The solution was stirred for about another 30 min. The final solution should look colorless indicating the absence of unreacted iodine as potassium iodide. The solution measuring about 16.5 liters having 831.09 ± 1.36 was taken out and diluted to 27.70 liters to get 3% potassium iodate solution for further use in direct in salt iodization process. EXAMPLE 3: 661.41 g of potassium hydroxide and 2497.2 g of sodium hydroxide were dissolved under stirring in 50 liters of de-ionized water in a water-jacketed 50 liter capacity round bottom glass reactor. To it, 1,500 g of 99.9% pure iodine was added in three batches and the solution was stirred till it becomes colorless. To this clear and colorless solution, chlorine gas was passed at about 10 g/min till the solution turned violet. The temperature of the solution was maintained at 38 degree Celsius. The purging of CI2 gas was stopped and the solution was charged with another 20 g of sodium hydroxide. The chlorine gas was purged once again at a controlled rate till the pH of the solution becomes to 6.45. The solution was stirred for about another 30 min. The final solution should look colorless indicating the absence of unreacted iodine as potassium iodide. The solution was taken out, measured and diluted to 84.25 liters to get 3% potassium iodate solution for further use in direct in salt iodization process. EXAMPLE 4: 440.94 g of potassium hydroxide and 1644.36 g of sodium hydroxide were dissolved under stirring in 32 liters of de-ionized water in a water-jacketed 50 liter capacity round bottom glass reactor. To it, 1,000 g of 99.9% pure iodine was added in two batches and stirred till the solution turns colorless. To this clear and colorless solution, chlorine gas was passed at about 10 g/min till the solution turned violet. The temperature of the solution was maintained at 35 degree Celsius. The purging of chlorine gas was stopped and the solution was charged with another 20 g of sodium hydroxide. The chlorine gas was purged once again at a controlled rate till the pH of the solution becomes to 5.90. The solution was stirred for about another 30 min. The solution was taken out, measured and diluted to 56.2 liters to get 3% potassium iodate solution for further use in direct in salt iodization process. EXAMPLE 5: 3.4 ml of 3% KIO3 solution obtained as described in Example 4 was diluted to 30 ml with distilled water and mixed thoroughly with 1 Kg of high purity salt for obtaining a homogenized iodised salt. The iodine content in the iodized salt was estimated by dissolving 50 g of salt in about 200 ml of distilled water and titrating it against standard sodium thiosulphate immediately and after regular intervals of time of storage to assess the available iodine content in it. The amount of iodine content was found to be 58.43, 54.62, 52.74 and 51.55 ppm in immediately, 90, 181 and 216 days, respectively of storing the iodized salt. The main advantages of the present invention are: 1. The present method of preparation of potassium iodate uses chlorine gas as oxidizing agent which is available as a by product in plenty in the chloro-alkali industry. 2. The use of chemicals like dichromate, membranes, costly equipment such as DC power supplies, electrochemical cells with costly electrodes are not required. 3. The product, potassium iodate solution obtained in this method is of required concentration to be useful directly in salt iodization process. 4. The possibility of presence of associated impurities like potassium iodide and hepta valent oxides of iodine is minimized. We Claim: 1. A cost effective process for preparation of iodate salt solution for direct iodization of common salt which comprises: i) preparing a solution of a mixture of analytical grade potassium hydroxide in the range of 1.375 to 1.381% (w/v) and sodium hydroxide in the range of 5.138 to 5.141% (w/v) in a water jacketed glass reactor and keeping the solution under continuous stirring, ii) maintaining the temperature of the solution in the range of 30 to 50 degree Celsius, iii) adding 99.9% pure iodine to the solution in step (ii) to have a concentration in the range of 3.109 to 3.125% (w/v) and stirring the solution to become colorless, iv) purging chlorine gas at a rate in the range of 5 - 15 g per min into the solution in step (iii) till the solution turns violet, v) adding sodium hydroxide to the solution in step (iv) in the concentration range of 0.063 to 0.078% (w/v), vi) again purging chlorine gas at a rate in the range of 0 to 3 g per min till the solution attaining the pH in the range of 5 to 8 and the solution is colorless, vii) continuing the stirring of solution obtained in step (vi) for a period in the range of 15 to 45 min while maintaining the temperature in the range of 30 to 50 degree Celsius, viii) diluting the reaction mixture obtained in step (vii) to make up the final volume with deionized water to obtain the desired concentration of potassium iodate solution, ix) obtaining the dilute potassium iodate solution in the concentration range of 2.9 to 3.1% (w/v). 2. A process as claimed in claim 1 wherein 3% potassium iodate solution for direct use in salt iodization is prepared using analytical grade 1.378% (w/v) of potassium hydroxide and 5.139% (w/v) of sodium hydroxide by dissolving together under stirring in de-ionized water. 3. A process as claimed in claim 1 wherein the reactor temperature was maintained between 30 to 40 degree Celsius by constant water circulation. 4. A process as claimed in claim 1 wherein 3.109 to 3.125% (w/v) iodine of 99.9% purity was added in two batches and stirred till the solution was colorless. 5. A process as claimed in claim 1 wherein 0.063 to 0.078% (w/v) of NaOH was added to the violet color solution. 6. A process as claimed in claim 1 wherein for preparing pure 3% potassium iodate solution for direct use in salt iodization, the reaction mixture was diluted with deionized water to obtain 3% potassium iodate solution. 7. A cost effective process for preparation of iodate salt solution for direct iodization of common salt, substantially as herein described with references to the examples accompanying this specifications.

Full Text

FIELD OF THE INVENTION
This invention relates to a cost effective process for preparation of iodate salt solution for direct iodization of common salt
The present relates to the preparation of potassium iodate solution for direct salt iodization using chlorine gas, sodium hydroxide, potassium hydroxide and iodine.
BACKGROUND OF THE INVENTION
The daily intake of iodine recommended by the National Research Council of the US National Academy of Sciences in 1989 (Report of a joint FAO/WHO expert consultation Bangkok, Thailand, Chapter 12 in Human Vitamin and Mineral Requirements published by World Health Organization Food and Agriculture Organization of the United Nations Rome, 2002, http://www.fao.Org/DOCREP/004/Y2809E/v2809e0i.htm#bm18.5) was 40 ug/day for young infants (0-6 months), 50 ug/day for older infants (6-12 months), 60-100 ug/day for children (1-10 years), and 150 ug/day for adolescents and adults (US National Research Council, 1989, Recommended dietary allowances, 10th edition, Iodine Food and Nutrition Board, P. 213-217, Washington D.C., National Academy Press Publication), approximating to 7.5 ug/kg/day for age 0-12 months, 5.4 ug/kg/day for age 1-10 years, and 2 ug/kg/day for adolescents and adults. These amounts are proposed to allow normal T4 production without stressing the thyroid iodide trapping mechanism or rising TSH levels. The iodine deficiency for long time, leads to biological disorders like gout, mental retardation, deaf mutism, short stature, cretinism and risk of death during the childhood (Scientific Encyclopedia, Van Nostrand's, 8th ed. D. M. Considine, Ed. Van Nostrand Reinhold, New York, p1751-1755, 1995; Iodised salt for preventing iodine deficiency disorders, T. Wu, G. J. Liu and P. Li, C. Clar Cochrane Review in The Cochrane Library, Issue 3 2002. Oxford, Update Software; Iodine Deficiency Disorders in India Report of Nutrition and IDD Cell, Ministry of Health and Family Planning, October 1997, http://www.people.virginia.edu/~itd/iccidd/mi/ idd 075.htm; P. Pongpaew, S. Saowakontha, R. Tungtrongchitr, U. Mahaweerawat, F. P Schelp Nutrition Research (New York), 2002, 22(1/2), 137-144; K. A.McMonigal, L. E. Braverman, J. T. Dunn, J. B. Stanbury, M.L. Wear, P.B. Hamm, R. L. Sauer, R. D. Billica and S. L Pool in their
publication entitled 'Thyroid function changes related to use of iodinated water in the U.S. space program' in Aviation, Space and Environmental Medicine, 2000, 7f(11), 1120-1125; S. Muslimatun, R. Gross, D. H. S. Dillon, W. Schultink Asia Pacific Journal of Clinical Nutrition, 1998, 7(3/4), 211-216). It is supplemented by different ways of iodization of edible materials like salt, oil (capsule and injections), water, bread, soya sauce, iodoform compounds used in dairy and poultry, and certain food additives (World Health Organization. 1994. Iodine and health: A statement by WHO. WHO/NUT/94.4).
Iodized salt is normally recommended for edible purposes as most of the people consume it irrespective of religion, caste, creed and sex. Alkali iodides and iodates are known to be useful in the iodization of salt for edible purposes to prevent thyroid gland diseases. Both of these forms of iodine are absorbed as iodide ions and are completely bio-available (ICCIDD/MI/UNICEF/WHO, 1995. Salt iodisation for the elimination of iodine deficiency). Potassium iodate is preferred to other salts of iodine for the iodization of salt in all Asian countries including India because of weather conditions. Presently, the iodization of salt is done either by using potassium iodate or potassium iodide in amounts that ensure a minimum intake of 150 ug iodine/day/person.
Reference is made to Indian Patent No. 173, 008 (1994) assigned to S. Balagopalan et. al. has disclosed that a flow reactor with an externally insulated stainless steel tank as cathode and a cylindrical lead oxide coated graphite anode placed at a distance of 1.5 - 3 mm gap can be used for the preparation of potassium iodate from elemental iodine in a potassium hydroxide solution. The product is cooled and isolated. The drawbacks of this process is that the product obtained in solution form is not pure and to be isolated to avoid the impurities. The columbic efficiency of the cell gets reduced as the products, potassium iodate and hypo iodite are unstable at the cathode. Even, the isolated solid contains impurities like lead in ppm level, which affects the health in the long run.
J. von Liebig in his paper published in Ogg. Ann. 1832, 24,362 and G. S. Serullas in his paper published in Ann. Chim. Phys. 1830, 43, 125 have independently reported the preparation of sodium iodate and potassium iodate by a multi-stage method. The procedures comprise saturating chlorine gas in water containing a fine suspension of iodine, neutralizing the liquid with the respective carbonate; and again passing chlorine until the iodine is dissolved, and further neutralizing with the carbonate. The solution is to be evaporated to
one-tenth of its volume, mixed with half its volume of alcohol, and the sodium/potassium chloride was washed from the precipitate by means of aqueous alcoholic solutions. The sodium carbonate is to be removed by treatment with acetic acid, and the sodium acetate is then washed with alcohol. The drawbacks of this process are that it is a multi-stage process and involves the use of a weak base. Acetic acid is required to neutralize the excess sodium carbonate. Besides, it requires heating to concentrate the solutions and adding alcohol to precipitate the iodate salts which makes the process costlier.
J. L. Gay Lussac in his paper published in Ann. Chim. Phys. 1814, 91(1), 5, has reported a procedure for the preparation of potassium iodate from iodine and potassium hydroxide. In this method, iodine is dissolved in a preheated solution of potassium hydroxide to give 16.67% of potassium iodate and 83.33% of potassium iodide. Later on, the solution is concentrated and precipitated the potassium iodate by the addition of alcohol. The main drawback of this method is that only a part of the total iodine taken gets converted to potassium iodate and hence the yield of potassium iodate is equal to one-sixth of total iodine taken or less of it. The method requires an additional chemical step to convert the major portion of iodine left as potassium iodide to its iodate for improving the yields of potassium iodate.
0. Henry in his published paper in Journ. Pharm. 1862, 18, 345, has prepared potassium iodate by melting together an intimate mixture of potassium iodide and potassium chlorate between 450-500 degree Celsius, at which chlorate begins to decompose. The product is separated from the un-reacted potassium chlorate by the fractional crystallization. The drawbacks of this method are that potassium chlorate is an explosive and requires special equipment and intensive care to be taken to handle the reaction at higher temperature greater than 450 degree Celsius.
J. S. Stas in his paper published in Mem. Acad. Belgque, 1865, 35, 3, has disclosed a method for the preparation of potassium iodate on a laboratory scale. In this method elemental iodine or potassium iodide was heated with potassium chlorate between 450-500 degree Celsius, at which chlorate begins to decompose. The drawbacks of this method are that potassium chlorate is an explosive and requires special equipment and intensive care to handle the reaction.
Chinese patent no. CN 1,121,540 (1996) assigned to N. H. Hugo et al. reveals a method for preparing potassium iodate by electrolytic method. In this method iodine is reacted with 30-40 lit of potassium hydroxide in a cooling reactor and subjected to electrolysis in multistage series-connected electrolytic cells. The voltage of each cell is maintained at 2.0 -3.5 V and the flow rate at 5 - 10 lit/min. The current density was between 0.1 and 0.2 A/m2 while the temperature of the last cell was reported to be 80-100 °C. The potassium iodate is crystallized and separated. About 1 - 3 g/lit potassium dichromate was added to the electrolyte to prevent the reduction of iodates and/or hypo iodite at the cathode. The draw backs of this process is that the product obtained in solution is not suitable for direct salt iodization as it contains impurities like the potassium hydroxide taken in excess, potassium iodide and dichromate. In order to use potassium iodate in salt iodization, the product has to be isolated and purified which makes the process costlier. The columbic efficiency of the cell is not more than 70% due to the reaction of potassium iodate and hypo iodite at the cathode. Potassium dichromate is a known carcinogen and health hazardous chemical. Its use can not be avoided as the products, potassium iodate and hypo iodite are reactive at the cathode. The operating temperature of the cells was 80-100 °C and inconvenient.
L. Henry reported a method in the paper published in Chem. Ber. (Chernische Berichte) 1870, 3, 893, on the preparation of potassium iodate. The method involves the passing of chlorine gas into finely divided suspension of elemental iodine in water till it was dissolved. Latter on, one mol of potassium chlorate per gram atom of iodine was added to the resulting solution. The mixture was warmed to get potassium iodate with the evolution of chlorine gas. The drawbacks of this process are that it requires potassium chlorate as external oxidizing agent to convert all the iodine into potassium iodate. The evolved chlorine gas is acidic and corrosive, and it has to be scrubbed through alkali hydroxide or carbonate which enhances the process cost. Potassium chlorate is an explosive and needs special skills for handling. Further, potassium chlorate is a health hazardous chemical and needs to remove traces of it in the product, thereby limiting the use of this method.
L. P. de St. Giles in his published paper cited in Compt. Rend. 1858, 46, 624 has reported the preparation of potassium iodate by the oxidation of potassium iodide with a solution of potassium permanganate. In this method, potassium iodide was reacted with potassium permanganate in 1:2 mole ratio under neutral conditions to give one mole of
potassium iodate, two moles of manganese dioxide and two moles of potassium hydroxide. The drawback of this method is that it requires an additional step to purify the product, potassium iodate from manganese dioxide, potassium hydroxide and all other manganese impurities before recommending it for edible purposes.
P. K. Ghosh et al. in their India patent application (1057/DEL/2000) have disclosed the preparation of solid alkali iodates from the corresponding alkali iodides using an ion exchange membrane flow reactor. In this method, an alkali iodide solution is passed through anode compartment and a 4-5% sodium hydroxide through cathode compartment of an anion exchange membrane cell. Iodide is oxidized to iodine and is disproportionated to iodate and iodide by the support of hydroxyl ions migrated from cathode compartment through the anion exchange membrane. The drawbacks of this method are that the method requires a sturdy and highly conductive anion exchange membrane having good thermal, mechanical and electrical properties. Moreover, the success execution of this method depends upon the cost and free availability an anion exchange membrane. The preparation of potassium iodate by this method is costly.
P. K. Ghosh et al. in their Indian patent application (0479/DEL/2003) have further disclosed an improved process for the preparation of pure potassium iodate solution for direct salt iodization. In this method iodine is dissolved in potassium hydroxide in stoichiometric quantities and the resulting solution is passed through the anode compartment of an anion exchange membrane flow cell. A solution of 4-5% sodium hydroxide is passed through the cathode compartment. Iodide is oxidized to iodine and is disproportionated to iodate and iodide at an high current efficiency by the support of hydroxyl ions migrated from cathode compartment through the anion exchange membrane. The drawbacks of this method are that the method requires a sturdy and highly conductive anion exchange membrane having with good thermal, mechanical and electrical properties. Moreover, the success execution of this method depends upon the cost and free availability an anion exchange membrane.
OBJECTS OF THE INVENTION
The main object of the present invention is to provide a cost effective process for preparation of iodate salt solution for direct iodization of common salt which obviates the drawbacks as detailed above.
Another object of the present invention is to provide a suitable method of preparing pure 3% (w/v) potassium iodate solution for direct salt iodization.
Still another object of the present invention is to utilize chlorine gas to produce 3% (w/v) potassium iodate from iodine and potassium hydroxide.
Yet another object of the present invention is to eliminate the hazardous impurities and reduce the possibility of adulteration in the iodization of salt.
Yet another object of the present invention is to provide an alternate chemical route for the preparation of pure 3% (w/v) potassium iodate solution and to avoid the use of harmful catalysts/chemicals, to reduce the capital investment and eliminate the use of costly membranes.
Yet another object of the present invention is to provide cost effective method for the preparation of highly pure 3% (w/v) potassium iodate solution.
SUMMARY OF THE INVENTION
Accordingly the present invention provides a cost effective process for preparation of
iodate salt solution for direct iodization of common salt which comprises:
i) preparing a solution of a mixture of analytical grade potassium hydroxide in the range of 1.375 to 1.381% (w/v) and sodium hydroxide in the range of 5.138 to 5.141% (w/v) in a water jacketed glass reactor and keeping the solution under continuous stirring,
ii) maintaining the temperature of the solution in the range of 30 to 50 degree Celsius,
iii) adding 99.9% pure iodine to the solution in step (ii) to have a concentration in the range of 3.109 to 3.125% (w/v) and stirring the solution to become colorless,
iv) purging chlorine gas at a rate in the range of 5 - 15 g per min into the solution in step (iii) till the solution turns violet,
v) adding sodium hydroxide to the solution in step (iv) in the concentration range of 0.063 to 0.078% (w/v),
vi) again purging chlorine gas at a rate in the range of 0 to 3 g per min till the solution attaining the pH in the range of 5 to 8 and the solution is colorless,
vii) continuing the stirring of solution obtained in step (vi) for a period in the range of 15 to 45 min while maintaining the temperature in the range of 30 to 50 degree Celsius,
viii) diluting the reaction mixture obtained in step (vii) to make up the final volume with deionized water to obtain the desired concentration of potassium iodate solution,
ix) obtaining the dilute potassium iodate solution in the concentration range of 2.9 to 3.1% (w/v).
In an embodiment of the present invention wherein 3% potassium iodate solution for direct use in salt iodization is prepared using analytical grade 1.378% (w/v) of potassium hydroxide and 5.139% (w/v) of sodium hydroxide by dissolving together under stirring in de-ionized water.
In another embodiment of the present invention wherein the reactor temperature was maintained between 30 to 40 degree Celsius by constant water circulation.
In yet another embodiment of the present invention wherein 3.109 to 3.125% (w/v) iodine of 99.9% purity was added in two batches and stirred till the solution was colorless.
In a further embodiment of the present invention wherein 0.063 to 0.078% (w/v) of NaOH was added to the violet color solution.
In an embodiment of the present invention wherein for preparing pure 3% potassium iodate solution for direct use in salt iodization, the reaction mixture was diluted with deionized water to obtain 3% potassium iodate solution.
DESCRIPTION OF THE INVENTION
A method for preparing pure 3% potassium iodate solution for direct use in salt iodization which comprises of
i) preparing solution of 32 liters of a mixture of analytical grade potassium hydroxide
weighing in the range of 440 to 442 g and sodium hydroxide weighing in the range of
1644-1645 g in a 40 to 50 liter capacity round bottom water jacketed glass reactor and
keeping the solution under continuous stirring; ii) maintaining the temperature of the solution in the range of 30 to 50 degree Celsius by
circulating water at room temperature; iii) adding 99.9% pure iodine to the solution in step (ii) to have a concentration in the range
of 995 to 1000 g and stirring the solution to become colorless; iv) purging chlorine gas at a rate in the range of 5 - 15 g per min into the solution in step
(iii) till the solution turns violet; v) adding sodium hydroxide to the solution in step (iv) in the concentration range of 20 to
25 g;
vi) again purging chlorine gas at a rate in the range of 0 to 3 g per min till the solution
attaining the pH in the range of 5 to 8 and the solution is colorless; vii) continuing the stirring of solution obtained in step (vi) for a period in the range of 15 to
45 min while maintaining the temperature in the range of 30 to 50 degree Celsius; viii) diluting the reaction mixture obtained in step (vii) to make up the final volume in the
range of 56 to 56.5 liters with deionized water; ix) obtaining the dilute potassium iodate solution in the concentration range of 2.9 to 3.1%
(w/v).
According to the present invention, elemental iodine dissolves in potassium hydroxide solution and stabilized itself in the form of potassium iodide and potassium iodate as shown in eq 1.
(Equation Removed)
The iodide produced in eq 1 can be oxidized to elemental iodine by employing chlorine (CI2) gas or hypochlorite (HCIO or OCP) eqs 2-4. The elemental iodine thus formed is sparingly soluble in water. However, it readily reacts with iodide ion and becomes itself highly soluble tri-iodide (eq 5). Tri-iodide ion is violet in color and imparts the same color to its aqueous solution inferring its presence.
(Equation Removed)

The h~ which is stable at pH becomes unstable at pH > 10. In alkaline conditions, l3 or l2 rapidly disproportionates to iodide and iodate ions (eqs 6 and 7).
(Equation Removed)

If T ion produced on right hand side (eqs 1, 6 and 7) is being constantly oxidized to l2 by Cl2, HOCI, or OCl, under basic conditions, all the iodine present in the solution would be converted completely into iodate.
The standard r/l2-CI2, I7I2-HCI0 and I7I2-CICT cells could easily be constructed and their potentials can be derived from standard electrode (E°, V) potentials of iodide (-0.535 V), Cl2 (+1.359) HCIO (+1.50 V) and CICT (+0.880 V), as +0.824 V, 0.965 and 0.345 V (Wendell M. Latimer, The oxidation states of the elements and their potentials in aqueous solutions, 2nd edn., Prentice Hall, Inc. New York, 1952), respectively. Eqs 2 and 4 are applicable to basic or neutral conditions while Eq 3 is applied to acidic medium pH According to available thermodynamic data (Wendell M. Latimer, The oxidation states of the elements and their potentials in aqueous solutions, 2nd edn., Prentice Hall, Inc. New York, 1952), E°, +1.085 V in neutral and E°, -0.268 V in basic medium for I/ IO3" half cell, the standard l-Cl2 (eq 8), T-HCIO and r-CIO~ cells in both neutral (eqs 8-10) and basic (eqs 11-13) media for the direct conversion of iodide to iodate should also be considered. If the reaction medium is highly basic, the oxidation of iodide to iodate should only be considered through Eqs 11-13. Moreover, the existence of HCIO at and above pH 10.5 is meager; therefore the possibility of iodide oxidation to iodate as per the eq 12 may be ignored. Thus, the possibility of direct iodide to iodate oxidation would only occur through Eq 11 and 13. The sign and magnitude of these cells indicate that the iodide oxidation to iodate through Eq 13 is preferred to that of Eq 11.
(Equation Removed)

Overall, it is concluded that the iodide oxidation in highly alkaline solutions to give iodate is only possible through eqs 8, 10, 11 and 13. Among these four ways, the oxidation of iodide to iodate seems to proceed more likely through eq. 8 via iodine and eq 13 in basic solutions.
Further oxidation of iodate to periodates, H3IO62- or H5IO6 by Cl2/HCIO in neutral, and Cl2/CIO in basic solutions are also feasible. From standard half-cell potentials of IO3-- H5IO6 or H3IO62- in (-1.6 V) neutral or (-0.70 V) basic solutions, the I037H5IO - CI2 (eq 14), I037H5IO6 - HCIO (eq. 15) and I037H5IO - CIO" (eq 16) cells in neutral medium; and IO7 H3IO2" - CI2 (eq 17) and I037 H3IO2~ - CIO- (eq 18) cells in basic medium reveal that the IO~ does not under go oxidation either by Cl2, HCIO or CIO" in neutral medium as the cell potentials are negative. However, CI2 and CIO" oxidize the IO3" to H3IO62~ in excess alkaline solutions. Comparison of potentials in Eq 18 with those in Eqs 8-13, shows that IO3- to H3IO62~ in alkaline solution is also expected to some extent.
(Equation Removed)

However, the H5IO6 -1~ cell (Wendell M. Latimer, The oxidation states of the elements and their potentials in aqueous solutions, 2nd edn., Prentice Hall, Inc. New York, 1952; Ju. Lurie Hand Book of Analytical Chemistry, Mur Publishers, Moscow, 1975, p300-313) (eq 19, E°, +2.685 V) in neutral and H3IO62" -1" cell (eq. 20, E°, +0.432 V) in alkaline medium indicate that the reaction between I" and H5IO6 or H3I062" are spontaneous. The reaction seems very rapid in neutral and slow in alkaline conditions, implying that i) the H5IO6 or H3I062" species is unstable in the presence of iodide, ii) I03~ undergoes oxidation if one equiv or more of alkali is present and iodide is absent.
(Equation Removed)

Accordingly, 3-5% potassium iodate solution was prepared in a 50 liter glass reactor fitted with a water circulating cooling bath, stirrer, a flow meter for purging Cl2 gas (1-10 g/min) and a pH meter provided with a combined glass electrode for monitoring the solution pH. A wide-mouth inlet for adding water and chemicals and an out let to take out the final KIO3 solution were also provided to the reactor. In the batch process of preparation of KIO3
solution which was standardized to 1.685 Kgs, 440.94 g of KOH and 1644.36 g of NaOH were weighed and dissolved under stirring in 32 liters of de-ionized water taken. To it, 1,000 g of lz was added in two batches under stirring. To this clear and colorless solution, Cl2 gas was purged till the solution turned slightly to violet. The solution was charged further with another 20 g of NaOH and CI2 gas was purged at slow rate till the pH becomes to 7.0. Stirring was continued for 30 min more to obtain approximately 5% colorless potassium iodate solution. The solution was taken out and diluted to 56.2 liters to obtain 3% potassium iodate solution.
The solution thus obtained was analyzed for potassium iodate by volumetric procedure using standard sodium thiosulfate (Na2S2O3) and 10 ml of 2 N sulfuric acid and starch as an indicator (A. I. Vogel A Text-Book of Quantitative Inorganic Analysis, 3rd ed., The English Language Book Society, Longman, London 1969, 349) and proportionately diluted to give a 3% solution for direct salt iodization.
The present invention relates to the preparation of highly pure potassium iodate solution useful for direct salt iodization. The potassium iodate solution in the required concentration range was prepared from iodine, potassium hydroxide, sodium hydroxide and chlorine gas. In this method, the calculated amount of iodine was dissolved in potassium hydroxide solution. The resultant solution was chlorinated in the presence of calculated amounts of sodium hydroxide under vigorous stirring at ambient temperature with water circulation. The chlorinated solution was diluted proportionately with distilled water for the ready use in the process of salt iodization. The inventive steps adopted in the present invention are (i) a calculated amount of iodine was dissolved in an appropriate amount of potassium hydroxide solution, (ii) the iodine solution was chlorinated under ambient temperature in the presence of calculated amount of sodium hydroxide which obviates the need of special membranes, chemicals that add impurities like lead, chromium, dichromate, iodides, potassium permanganate, manganese dioxide etc. explosive/health hazardous chemicals like potassium chlorate, (iii) the clear and colorless solution after passing required quantity of chlorine gas having pH in the range of 5 to 9 was diluted proportionately to obtain 3% potassium iodate solution suitable for direct salt iodization which eliminates cost involving steps like precipitation by chilling washing, centrifuging, drying and transport or using chemicals like acetic acid and alcohol, (iv) the temperature was maintained by simple water
circulation (30-40 °C), (iv) commercially available liquid chlorine was used for the oxidation of alkaline iodine to potassium iodate; and (v) the dilution was affected using deionized water.
The following example is given by the way of illustration of the present invention and should not be construed to limit the scope of the present invention.
EXAMPLE 1: 440.94 g of potassium hydroxide and 1644.36 g of sodium hydroxide were dissolved under stirring in 32 liters of de-ionized water in a water-jacketed 50 liter capacity round bottom glass reactor. To it, 1,000 g of 99.9% pure iodine was added in two batches and stirred till the solution turns colorless. To this clear and colorless solution, chlorine gas was passed at about 10 g/min till the solution turned violet. The temperature of the solution was maintained at 37 degree Celsius. The purging of chlorine gas was stopped and the solution was charged with another 20 g of sodium hydroxide. The chlorine gas was purged once again at a controlled rate till the pH of the solution becomes to 8.33. The solution was stirred for about another 30 min. The final solution should look colorless indicating the absence of unreacted iodine as potassium iodide. The solution was taken out, measured and diluted to 56.2 liters to get 3% potassium iodate solution for further use in direct in salt iodization process.
EXAMPLE 2: 220.5 g of potassium hydroxide and 822.4 g of sodium hydroxide were dissolved under stirring in 16 liters of de-ionized water in a water jacketed 50 liter flask. To it, 500 g of 99.9% pure iodine was added and the solution was stirred to become colorless. To this clear and colorless solution, chlorine gas was passed at about 10 g/min till the solution turned violet. The temperature of the solution was maintained at 40 degree Celsius. The purging of chlorine gas was stopped and the solution was charged with another 10 g of sodium hydroxide. The chlorine gas was purged once again at a controlled (-0.1 - 0.5 g/min) for -15 min till the pH of the solution becomes to 8.5. The solution was stirred for about another 30 min. The final solution should look colorless indicating the absence of unreacted iodine as potassium iodide. The solution measuring about 16.5 liters having 831.09 ± 1.36 was taken out and diluted to 27.70 liters to get 3% potassium iodate solution for further use in direct in salt iodization process.
EXAMPLE 3:
661.41 g of potassium hydroxide and 2497.2 g of sodium hydroxide were dissolved under stirring in 50 liters of de-ionized water in a water-jacketed 50 liter capacity round bottom glass reactor. To it, 1,500 g of 99.9% pure iodine was added in three batches and the solution was stirred till it becomes colorless. To this clear and colorless solution, chlorine gas was passed at about 10 g/min till the solution turned violet. The temperature of the solution was maintained at 38 degree Celsius. The purging of CI2 gas was stopped and the solution was charged with another 20 g of sodium hydroxide. The chlorine gas was purged once again at a controlled rate till the pH of the solution becomes to 6.45. The solution was stirred for about another 30 min. The final solution should look colorless indicating the absence of unreacted iodine as potassium iodide. The solution was taken out, measured and diluted to 84.25 liters to get 3% potassium iodate solution for further use in direct in salt iodization process.
EXAMPLE 4: 440.94 g of potassium hydroxide and 1644.36 g of sodium hydroxide were dissolved under stirring in 32 liters of de-ionized water in a water-jacketed 50 liter capacity round bottom glass reactor. To it, 1,000 g of 99.9% pure iodine was added in two batches and stirred till the solution turns colorless. To this clear and colorless solution, chlorine gas was passed at about 10 g/min till the solution turned violet. The temperature of the solution was maintained at 35 degree Celsius. The purging of chlorine gas was stopped and the solution was charged with another 20 g of sodium hydroxide. The chlorine gas was purged once again at a controlled rate till the pH of the solution becomes to 5.90. The solution was stirred for about another 30 min. The solution was taken out, measured and diluted to 56.2 liters to get 3% potassium iodate solution for further use in direct in salt iodization process.
EXAMPLE 5: 3.4 ml of 3% KIO3 solution obtained as described in Example 4 was diluted to 30 ml with distilled water and mixed thoroughly with 1 Kg of high purity salt for obtaining a homogenized iodised salt. The iodine content in the iodized salt was estimated by dissolving 50 g of salt in about 200 ml of distilled water and titrating it against standard sodium thiosulphate immediately and after regular intervals of time of storage to assess the available iodine content in it. The amount of iodine content was found to be 58.43, 54.62, 52.74 and 51.55 ppm in immediately, 90, 181 and 216 days, respectively of storing the iodized salt.
The main advantages of the present invention are:
1. The present method of preparation of potassium iodate uses chlorine gas as oxidizing agent which is available as a by product in plenty in the chloro-alkali industry.
2. The use of chemicals like dichromate, membranes, costly equipment such as DC power supplies, electrochemical cells with costly electrodes are not required.
3. The product, potassium iodate solution obtained in this method is of required concentration to be useful directly in salt iodization process.
4. The possibility of presence of associated impurities like potassium iodide and hepta valent oxides of iodine is minimized.

We Claim:
1. A cost effective process for preparation of iodate salt solution for direct iodization of
common salt which comprises:
i) preparing a solution of a mixture of analytical grade potassium hydroxide in the range of 1.375 to 1.381% (w/v) and sodium hydroxide in the range of 5.138 to 5.141% (w/v) in a water jacketed glass reactor and keeping the solution under continuous stirring,
ii) maintaining the temperature of the solution in the range of 30 to 50 degree Celsius,
iii) adding 99.9% pure iodine to the solution in step (ii) to have a concentration in the range of 3.109 to 3.125% (w/v) and stirring the solution to become colorless,
iv) purging chlorine gas at a rate in the range of 5 - 15 g per min into the solution in step (iii) till the solution turns violet,
v) adding sodium hydroxide to the solution in step (iv) in the concentration range of 0.063 to 0.078% (w/v),
vi) again purging chlorine gas at a rate in the range of 0 to 3 g per min till the solution attaining the pH in the range of 5 to 8 and the solution is colorless,
vii) continuing the stirring of solution obtained in step (vi) for a period in the range of 15 to 45 min while maintaining the temperature in the range of 30 to 50 degree Celsius,
viii) diluting the reaction mixture obtained in step (vii) to make up the final volume with deionized water to obtain the desired concentration of potassium iodate solution,
ix) obtaining the dilute potassium iodate solution in the concentration range of 2.9 to 3.1% (w/v).
2. A process as claimed in claim 1 wherein 3% potassium iodate solution for direct use in salt iodization is prepared using analytical grade 1.378% (w/v) of potassium hydroxide and 5.139% (w/v) of sodium hydroxide by dissolving together under stirring in de-ionized water.
3. A process as claimed in claim 1 wherein the reactor temperature was maintained between 30 to 40 degree Celsius by constant water circulation.
4. A process as claimed in claim 1 wherein 3.109 to 3.125% (w/v) iodine of 99.9% purity was added in two batches and stirred till the solution was colorless.
5. A process as claimed in claim 1 wherein 0.063 to 0.078% (w/v) of NaOH was added to the violet color solution.
6. A process as claimed in claim 1 wherein for preparing pure 3% potassium iodate solution for direct use in salt iodization, the reaction mixture was diluted with deionized water to obtain 3% potassium iodate solution.
7. A cost effective process for preparation of iodate salt solution for direct iodization of common salt, substantially as herein described with references to the examples accompanying this specifications.

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Patent Number

270990

Indian Patent Application Number

176/DEL/2009

PG Journal Number

05/2016

Publication Date

29-Jan-2016

Grant Date

29-Jan-2016

Date of Filing

30-Jan-2009

Name of Patentee

COUNCIL OF SCIENTIFIC INDUSTRIAL RESEARCH

Applicant Address

ANUSANDHAN BHAWAN, 2, RAFI MARG, NEW DELHI-110001

Inventors:

#	Inventor's Name	Inventor's Address
1	PUSHPITO KUMAR GHOSH	CENTRAL SALT & MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVANAGAR 364002 GUJARAT. INDIA
2	GADDE RAMACHANDRALIAH	CENTRE SALT & MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVANAGAR 364002 GUJARAT. INDIA
3	SUNIL PRATAPRAI DAVE	CENTRAL SALT & MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVANAGAR 364002 GUJARAT. INDIA
4	SUSARLA VENKATARAMAKRISHNA SARMA	CENTRAL SALT & MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR 364002 GUJARAT. INDIA
5	MANISH PRAFULBHAI JOSHI	CENTRAL SALT & MARINE CHEMICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR 364002 GUJARAT. INDIA
6	MALLAMPATI SUBBA REDDY	CENTRAL SALT & MARINE CHEMKICALS RESEARCH INSTITUTE, GIJUBHAI BADHEKA MARG, BHAVNAGAR 364002 GUJARAT. INDIA

PCT International Classification Number

C04B 18/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA