Novel Synergistic Process of Impurities Extraction and Phophogypsum Crystallization Control in Wet-Process Phosphoric Acid.

ABSTRACT

Phosphogypsum, as a byproduct of wet-process phosphoric acid reaction, has caused many environmental pollution problems. To improve the property and purity of phosphogypsum in the wet-process phosphoric acid process, a liquid-solid-liquid three-phase acid hydrolysis synergistic extraction reaction system was established by adding a certain amount of extractant in the actual production process. In order to study the extraction effect and residue of impurities in the reaction system, the phase, morphology, and impurity occurrences of phosphogypsum were systematically analyzed. The results showed that when the reaction time was 7 h, the reaction temperature was 80 °C, the reaction speed was 200 r/min, the volume ratio of the extractant to diluent (dilution ratio) was 14 and the volume ratio of the oil phase/aqueous phase (O/A ratio) was 11, P2O5 conversion was the highest in phosphate rock, and the residual P2O5 content in phosphogypsum was as low as 0.36%. The morphology of the phosphogypsum crystal was uniform and coarse long strip. The main forms of residual impurities were silicate, aluminum fluoride with crystal water, aluminate, phosphate, and fluoride. Meanwhile, the residual amount of main impurities in phosphogypsum was significantly reduced. Through this novel method, the property of phosphogypsum can be improved through the generation process and is greatly beneficial for its utilization and the recycling development of the wet-process phosphoric acid industry.