Existing form and distribution of fluorine and phosphorus in phosphate rock acid-insoluble residue

The phosphorus-sulfur two-step production process was developed in the wet-process phosphoric acid industry to solve phosphogypsum pollution. However, phosphate rock acid-insoluble residue is produced during this process as a new type of solid waste, which had a high potential for recycling. For process reasons, this type of residue still contains a certain amount of fluorine and phosphorus, which has a massive impact on the potential uses of phosphate rock acid-insoluble residue. Therefore, X-ray photoelectron spectroscopy, Raman, electron probe spectroscopy, and scanning electron microscopy were used to examine the existing form and distribution of fluorine and phosphorus in phosphate rock acid-insoluble residue. The mass fraction of F and P₂O₅ were 9.407% and 11.862%, respectively. Fluorine existed mainly in the form of fluorite, fluorapatite and metal fluoride. Phosphorus existed mainly in the form of fluoroapatite, phosphate, hydrogen phosphate, and dihydrogen phosphate. The total phosphate, hydrogen phosphate and dihydrogen phosphate contents were much higher than that of fluoroapatite, whereas the fluoroapatite content was higher than that of fluorite and metal fluoride. Fluorine and phosphorus were distributed in the form of agglomerates in the phosphate rock acid-insoluble residue. Fluorine and phosphorus were partially correlated, showing a weak relationship in the high phosphorus area.