PROCESS FOR THE PRODUCTION OF SODIUM TRIPOLYPHOSPHATE

摘要

1473404 Sodium tripolyphosphate SOC ITALIANA RESINE SIR SpA 18 March 1975 [25 March 1974] 11314/75 Heading C1A The sulphuric acid solution resulting from the sulphate process for the production of TiO 2 from ilmenite or Ti-bearing slags is concentrated to >40% by weight and contacted in stoichiometric excess with phosphate ores at elevated temperature to liberate phosphoric acid; F and SiO 2 are removed from the solution, the solution is purified from sulphate ions, free sulphuric acid, arsenic and organic substances, sodium hydroxide is added in an amount sufficient to precipitate V, Cr and Fe and also to cause salification of the acid and the sodium phosphates are converted to sodium tripolyphosphate. In the preferred procedure, titaniferous material is dried and ground and leached with H 2 SO 4 in amounts of 1À4-2 : 1 relative to the TiO 2 content, the porous solid obtained is dissolved in water or dilute acid and the Fe3+ is reduced to Fe2+, e.g. by the addition of metallic ion at a temperature of 50-80‹ C. The solution is clarified and then cooled to a temperature of 10-20‹ C. to precipitate FeSO 4 .7H 2 O, which is then separated. The residual solution is subjected to hydrolysis to precipitate Ti(OH) 2 which is separated and subjected to treatment to transform it to TiO 2 in rutile or anatase form. Both forms may be subjected to post-treatments, e.g. coating with Al 2 O 3 or SiO 2 . The solution remaining is concentrated to between 40-70% by weight H 2 SO 4 and contacted in stoichiometric excess with finely ground phosphatic minerals typically at 70-90‹ C. for 4-10 hours. The solution is filtered and F and SiO 2 are eliminated from the filtrate, e.g. as sodium fluorosilicate. The filtrate thus obtained is concentrated to a phosphoric acid solution with a P 2 O 5 strength of 45-55% by weight and organic substances are eliminated e.g. by adding active carbon and heating the suspension at 60-70‹ C. for 0À5 to one hour. B, Cr and Fe are eliminated by addition to the solution of NaOH. This is preferably done in a first step to adjust pH to 4 followed by a second step to adjust the pH to between 6À7 and 6À8. The mass is heated, e.g. at 85-95‹ C. and a precipitate formed is separated. The phosphate solution is preferably further purified by removal of any organic impurities and then dried by evaporation. The residue is suitably calcined at 540-560‹ C. for 0À5-2 hours to form a sodium tripolyphosphate. The tripolyphosphate has a greatly reduced V and Fe content and thus has improved whiteness.