METHOD OF PURIFYING WET-PROCESS PHOSPHORIC ACID Russian patent published in 2010 - IPC C01B25/234 

FIELD: chemistry.

SUBSTANCE: invention relates to a method of purifying wet-process sulphuric acid obtained via sulphuric acid decomposition of low-grade phosphate material, for example Karatau phosphorites, which can be used in fertiliser production. The purification method involves feeding initial weak phosphoric acid into a settling tank for mixing with evaporated acid to obtain a mixture of acids. Solid impurities are precipitated from the mixture of acids to obtain clear purified acid. A portion of the clear acid output as a product and the remaining portion is taken for evaporation. Evaporation of the clear acid is carried out under a vacuum at temperature 65 - 85°C until achieving P₂O₅ content of 42-48%. Concentration of the mixture of acids in the settling tank is kept at 35 - 40% P₂O₅. Settling is carried out until achieving solid phase residual content of 0.5-2.0% in the clear acid. The difference in densities of the evaporated and clarified phosphoric acid is kept between 0.08 and 0.18 g/cm³.

EFFECT: method enables to obtain purified wet-process phosphoric acid with low content of impurities of iron, aluminium, calcium, magnesium and fluorine from Karatau phosphorites with low cost and high efficiency of the process.

2 tbl, 1 dwg, 1 ex