METHOD OF PURIFYING WET-PROCESS PHOSPHORIC ACID Russian patent published in 2011 - 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, for use in fertiliser production. The method of purifying wet-process sulphuric acid involves feeding initial weak phosphoric acid into a settling tank 2 for mixing with acid being into pumped from a heating tank 1 by a pump 5 and pre-evaporated in an evaporator 3, precipitation of solid impurities from the mixture of acids to obtain clarified pure acid, outlet of a portion of the clarified acid as a product through a pump 6 and returning the remaining portion of acid under gravity for evaporation. The clarified acid is evaporated in evaporator 3 under a vacuum at temperature 65 - 85 °C until 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 residual content of the solid phase of 0.5-2.0% in the clarified acid. The difference in density of the evaporated and clarified phosphoric acid is kept in the range of 0.08 - 0.18 g/cm³.

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

2 tbl, 1 dwg, 1 ex