Title of Invention

AN IMPROVED PROCESS FOR THE PREPARATION OF BISMUTH ORTHOVANADATE

Abstract

This invention relates to an improved process for the preparation of Bismuth orthovanadate. The product is useful for automotive finishes and coloring toys etc., because of its superior quality, eco-friendly nature and stability towards adverse atmospheric conditions and higher temperature for prolonged period. The precipitation of BiVO4 of specific crystal structure is Ph dependent and these forms undergo reversible colour changes indicating temperature dependency of equilibrium. In the present invention solution reaction is carried out wherein the crystal structure of the product is obtained by carefully controlling temperature and pH to obtain the desired product.

Full Text

This invention relates to an improved process for the preparation of Bismuth orthovanadate. More particularly this invention relates to an improved process for the preparation of Bismuth orthovanadate, useful for automotive finishes and colouring toys etc., because of its superior quality, eco-friendly nature and stability towards adverse atmospheric conditions and higher temperature for prolonged period. The molecular formula for Bismuth orthovanadate is BiVO4. The naturally occurring mineral 'pucherite' is of the same formula and was first discovered in the Pucher Mine in Schneeburg, Germany by Frenzel. Subsequently it was also found to occur in Brazil. The mineral as discovered was reddish brown in colour and had a specific gravity of 6.249 at 24.5°C and an orthorhombic crystal structure with lattice parameters of a=5.33, b=12.02andc=5.06A°. I.M. Gottlieb and D.P. Kelly (Proc. 4th Int. Natl. Conf. on Thermal Analysis, Budapest, P.675, 1974) attempted to synthesize bismuth orthovanadate and compare it with the mineral. Solid-state as well as solution-state syntheses were attempted. When equimolecular quantities of intimately mixed powders of Bi2O3 and X^Os were heated at a temperature of 800°C for a period of 16 h, a compound was obtained which was similar to that obtained by R.S. Roth and J.L. Waring (Amer. Mineral. Vol.48, PP 1348-1356, 1963). The compound BiVQ} is monoclinic, however the mineral is orthorhombic. The stability of the orthorhombic structure was attributed to the presence of impurities in the mineral, which however could not be conclusively proved. I.M. Gottlieb and Ch. R. Rowe (Thermal Analysis. Vol.2, Proc. 3rd ICTA Davos, 1971, P.303) reported that the synthesis from solution phase was very complex owing to the hydrolysis of Bi(NC>3)3 and polymerisation of VC>43" ion. The following were their observations. Atleast three different compounds exist over three pH ranges. The precipitation by adding bismuth nitrate to sodium vanadate at pH 13.7 resulted in a curdy white precipitate which was essentially bismuthyl nitrate, vanadate. When the pH of sodium vanadate was lowered to 12.5 to avoid polymerisation of the vanadate a bright yellow precipitate was formed. This material was orange in colour at high temperature (200°C) and yellow at room temperature. The yellow modification was found to be monoclinic. When the precipitation was carried out at pH less than or equal to one a tetragonal compound was the sole product. Thus, it is evident from the above studies that precipitation of BiVC>4 of a specific crystal structure is pH dependent. Also these forms undergo reversible colour changes indicating temperature dependency of equilibrium. Bismuth vanadate as a pigment was recognised only recently as can be seen from the patents : U.S. 4,026,722 (1977) by Hess, Richard William; U.S. 4,063,956 (1977) by Higgins, James Francis; Ger Offen 2,933,778 by Balducci, Luigi; Rustioni, Massimo and Ger Offen DE 3,315,851 by Koehler Peter; Ringe Peter and Heine Heinrich. A glance through the above cited patents indicates methods (1) in solid state between the constituent oxides followed by wet grinding and (2) mixing solutions of appropriate strengths of constituent salts at an appropriate pH followed by digestion, filtration, washing etc. One very important observation made in the case of solution reactions is that the crystal structure of the product is a function of temperature and pH which are to be carefully controlled. Otherwise mixture of phases will result. The main objective of the present invention is to provide an improved process for the preparation of Bismuth orthovanadate. Another objective of the present invention is to provide easily controllable experimental conditions. Still another objective of the present invention is to provide a method for preparation of an eco-friendly brilliant yellow pigment which can substitute the health hazardous chrome yellow and cadmium yellow pigments. Yet another objective of the invention is to provide a method for the preparation of a pigment which can withstand high temperature. The know-how for the preparation of this pigment is not available in this country and it has been developed for the first time. The conditions prescribed in this invention are not specified by any other invention so far. Accordingly the present invention provides an improved process for the preparation of Bismuth orthovanadate which comprises mixing aqueous solution of Bismuth nitrate, an alkali vanadate and an alkali in a molar ratio of 1:1:1 in a buffer solution particularly of sodium acetate and acetic acid at a pH in the range of 2 to 4, stirring by conventional method, filtering the solution to obtain residue, washing and drying the said residue by conventional methods, followed by heating at temperature in the range of 550 to 650°C for a period of 5 to 6 hrs and pulverizing by conventional methods to obtain bismuth orthovanadate. In an embodiment of the invention, the bismuth salt used may be bismuth nitrate. In another embodiment of the invention, the alkali vanadate solution used may be sodium orthovanadate, sodium metavanadate or ammonium metavanadate. In yet another embodiment of the invention the alkali used may be sodium hydroxide, sodium carbonate or ammonium hydroxide. In yet another embodiment of the invention the buffer solution used may be sodium acetate and acetic acid. In yet another embodiment of the invention the pH of the suspension may be maintained at 3.5. Example 1 Sodium vanadate solution containing 122g of NaVO3 in 1L, 7L of buffer solution containing 10 ml of glacial acetic acid and 200 g of sodium acetate are taken in a reactor. Bismuth nitrate solution containing 485g of Bi(NO3)3 . 5H2O in 1L of 1M nitric acid and 1M sodium hydroxide solution are simultaneously and separately added to the reactor over a period of 1h with constant stirring to obtain a suspension having pH of 3.5. The suspension is aged by stirring for another two hours after completion of the reagent addition. The slurry is then filtered, the residue is washed with water and the cake is dried at 200°C for 3h. The dried material is then heated at 550°C for 6h and is pulverised by conventioinal method to get the desired product. Example 2 Sodium vanadate solution containing 122g of NaVOa in 1L, a buffer of 7L containing 10 ml of glacial acetic acid and 200g of sodium acetate are taken in a reaction vessel and are heated at 70°C in a thermostat. Bismuth nitrate solution containing 485g of Bi(NO3)3 . 5H2O in 1L of 1M nitric acid and 1M sodium hydroxide solution are simultaneously and separately added to the reactor over a period of Ih with constant stirring, maintaining the temperature to obtain a suspension having pH of 3.5. The suspension is aged by stirring for another 2 hours after complete addition of the reagents. The slurry is cooled and filtered; the residue washed with water and the cake is dried at 200°C for 2.5 hours. The dried material is heated at 500°C for 6 hours and pulverised to get the desired product. Example 3 Sodium vanadate solution containing 122g of NaVOs in 1L, 7L of buffer solution containing 10 ml of glacial acetic acid and 200g of sodium acetate are taken in a reactor. Bismuth nitrate solution containing 485g of Bi(NO3)3 . 5H2O in 1L of 1M nitric acid and 1M NH4OH solution are simultaneously and separately added to the reactor over a period of 1h with constant stirring to obtain a suspension having pH of 3.5. The suspension is aged by stirring for another 2 hours after complete addition of the reagents. The slurry is then filtered and the residue is washed with water and then the cake is dried at 200°C for 2h. The dried material is then heated at 650°C for 6h and pulverised to get the desired product. We Claim: 1. An improved process for the preparation of Bismuth orthovanadate which comprises; mixing aqueous solution of Bismuth nitrate, an alkali vanadate solution selected from sodium orthovanadate, sodium metavanadate or ammonium metavanadate and an alkali such as herein described in a molar ratio of 1:1:1 in a buffer solution particularly of sodium acetate and acetic acid at a pH in the range of 2 to 4, stirring by convenţional method, filtering the solution to obtain residue, washing and drying the said residue by convenţional methods, followed by heating at temperature in the range of 550 to 650°C for a period of 5 to 6 hrs and pulverizing by convenţional methods to obtain bismuth orthovanadate. 2. An improved process as claimed in claim l wherein the alkali used is sodium hydroxide, sodium carbonate or ammonium hydroxide. 3. An improved process as claimed in claims l to 2 wherein the pH of the solution is maintained at 3.5. 4. An improved process for the preparation of Bismuth orthovanadate substantially as herein described with reference to the examples.

Documents:

281-del-2001-abstract.pdf

281-DEL-2001-Claims.pdf

281-del-2001-correspondence-others.pdf

281-del-2001-correspondence-po.pdf

281-del-2001-description (complete).pdf

281-del-2001-form-1.pdf

281-del-2001-form-18.pdf

281-del-2001-form-2.pdf

281-del-2001-form-3.pdf