High purity technical grade phosphoric acid preparation - from wet process phosphoric acid by formation of urea phosphate, purification and treatment with nitric acid

摘要

Process for the preparation of high purity technical phosphoric acid by following successive stages effected in continuous or batch mode; -a) crude wet process phosphoric acid, containing 50-54% P205, is diluted with water and/or an aqueous solution of phosphoric acid, optionally containing urea, until it contains 30-50% P205 and 0-8% of urea. Then this product is reacted with 1-4wt% of a composition previously formed from 1 part sodium carbonate and 3-5 parts of reduced phosphorite of particle size less than 150 microns, with a reaction content time of 1-3 hrs. and the product from the reaction is treated with 20-30 ppm of a flocculant in aqueous solution. The liquid phase is decanted from the insolubles and represents 50-95% of the initially introduced P205 and contains 31-50% P205 and 0-7%urea; b) the acid from stage a) is treated with urea and the formed urea phosphate crystallised by cooling or heating under reduced pressure to obtain urea phosphate of particle size 100-2000 microns. The mother liquors may be recycled to the first stage and the crystals are lixwated with an equivalent weight of a saturated solution of urea phosphate of recrystallised; c) in a third stage, the urea phosphate from b) is used to form an aqueous reaction product containing 35-50%phosphoric acid, 6-21% nitric acid and 4-15% of urea and when equilibrium is reached the urea nitrate and phosphoric acid formed in the reaction are seperated. The crystalline mass is washed with nitric acid and the washings and a fraction of the obtained phosphate acid are recycled to the reaction with a new lot of urea phosphate; d) the residual urea and nitric acid content of the phosphoric acid is reduced by concentrating at 90-220deg.C. and 110-760 High quality technical grade phosphoric acid contg. not more than 0.02 wt. parts of impurities per 100 wt. parts P205. This product is suitable for use in galvanic baths (cleaning baths), other industrial processes where ortho- and polyphosphates are used a.