关键词: 湿法磷酸, 盐酸法, 溶剂萃取, 洗涤, 反萃取

Abstract:

The process of back extraction of phosphoric acid from tributyl phosphate（TBP） was studied.The quality of the different stripped phosphoric acid obtained by the one-step process（simultaneously precipitating CaCl₂ and stripping H₃PO₄ with H₂SO₄ solution） and by the two-step process（firstly precipitating and removing CaCl₂ with H₂SO₄,then stripping H₃PO₄ with deionized water） was investigated.The results showed that in the one-step process the purity of the stripped phosphoric acid was affected by the dissolution balance of calcium sulfate with high content of calcium,while in the two-step process,the contents of CaCl₂ in the stripped reduced to below 0.002 7%,and the value of n（H₃PO₄）/n（Ca²⁺） increased by more than 65 times,but the H₃PO₄ loss in organic phase caused by scrubbing process was about 20%.The focused beam reflectance measurement（FBRM） technology was used to monitor the crystallization of calcium sulfate on line in the organic phase during the scrubbing process.The morphology and phase composition of the calcium sulfate were analyzed by scanning electron microscope（SEM） and X-ray diffraction（XRD） methods.The results showed that after scrubbing for 10 min under the experimental conditions,Ca²⁺ in the system basically generated hemihydrate gypsum（CaSO₄·0.5H₂O）.Theoretical calcula-tion indicated that the production of the by-product gypsum（calculated as CaSO₄·2H₂O） in scrubbing step of the wet phosp-horic acid process by hydrochloric acid route was only equivalent to 8.7% of that by sulfuric acid route,significantly reduces the amount of gypsum treated in the wet process phosphoric acid process.

Key words: wet process phosphoric acid, hydrochloric acid route, solvent extraction, scrubbing, stripping