Patent GB-801129-A (GB)
Title: Improvements in or relating to method of producing defluorinated phosphate material
IPC: C01B25/32
Filed: 1955-04-12
Abstract: Defluorinated calcium orthophosphate, suitable for an animal food supplement or fertilizer, is prepared by precipitating the impurities from a fluorine-containing acidic phosphate-bearing solution with calcium oxide, hydroxide or carbonate and separately recovering the filtrate and the precipitated solids, then preparing an impure fluorine-containing acidic phosphatebearing solution and at mixing this solution with the precipitated solids to adjust the CaO/P2O5 ratio to less than 1.2, calcining the mixture to remove moisture and evolve fluorine and finally hydrolysing the calcined product in the presence of steam to reconvert the P2O5 content to orthophosphate. The solution obtained after separating precipitated solids in the first stage may be treated with additional calcium carbonate to precipitate dicalcium phosphate substantially free from fluorine. The initial solution may be obtained by reacting ground phosphate rock at 65-100 DEG  C., with sulphuric acid for example 50-70 per cent strength in amounts between 101 and 115 per cent of the theoretical requirement to produce monocalcium phosphate.  The acid mix is allowed to set and then pulverized and leached at 72 DEG  to 82 DEG C. with water, preferably in counter current, to produce a phosphate solution containing 20 to 35 per cent by weight solids content.  This initial solution is diluted to 10 to 15 per cent P2O5 content and then reacted with the calcium compound preferably calcium carbonate in amounts between 5 to 8 lb. of carbonate per 100 lb. of solution. The precipitated solids containing substantially all the fluorine are then mixed with a solution obtained by leaching unaged superphosphate.  Such solution is obtained by reacting finely-ground phosphate with sulphuric acid in such proportions that on leaching with water the final acidic phosphate bearing solution will have a CaO/P2O5 ratio of less than 0.4.  The precipitated solids and acid solution are proportioned to produce a CaO/P2O5 ratio, preferably between 0.7 and 1.05 and after agitation the slurry mixture is dried at 110 DEG  to 200 DEG  C. and then heat treated at 325 DEG  to 800 DEG  C., whereupon substantially all of the fluorine is removed as gas.  The resulting dry calcium phosphate mixture has a fluorine content of less than 0.2 per cent.  This, after comminution, is heated in an atmosphere of steam at 5 to 50 p.s.i.g. to produce calcium orthophosphate containing a ratio of phosphorus to fluorine of about 180. Specifications 799,489 and 799,490 are referred to.ALSO:Defluorinated calcium orthophosphate, suitable for feed supplement is prepared by precipitating the impurities from a fluorine-containing acidic phosphate-bearing solution with calcium, oxide, hydroxide or carbonate and separately recovering the filtrate and the precipitated solids, then preparing an impure fluorine-containing acidic phosphate-bearing solution and at mixing this solution with the precipitated solids to adjust the CaO/P2O5 ratio to less than 1,2, calcining the mixture to remove moisture and evolve fluorine and finally hydrolyzing the calcined product in the presence of steam to reconvert the P2O5 content to orthophosphate. Specifications 799,489 and 799,490 are referred to.