Optimization of wet-process phosphoric acid for high-quality phosphogypsum

The chronical accumulation of phosphogypsum (PG) has caused serious environmental pollution problems in wet-process phosphoric acid (WPPA) industry. An innovation technical route for turning PG into a resource has been realized by introducing floc flotation and acid cleaning in WPPA. The floc flotation using cationic polyacrylamide as a flocculant and micro lotion which composed of dioctyl phthalate, nonaphenol polyethyleneoxy (10) ether, kerosene and n-octanol as a collector has been performed. The effect of floc flotation on the quality of products and its mechanism were investigated by XRF，FT-IR, SEM and 2-dimensional fractal dimension analysis. The optimal parameters have been determined by single factor experiment as followings: floc flotation temperature 65℃, cationic polyacrylamide 180 g/Mg, collector 1.08 kg/Mg, and flushing sulfuric acid concentration 20%. The obtained purified PG had a high grade of 95.61%, whiteness reached 70.8% with the yield of 82.15% and gypsum recovery of 95.33%. Moreover, the soluble phosphorus and soluble fluorine are less than 0.1%. In the flotation, polyacrylamide and collector combined fine organic matter and siliceous material with hydrophobic bubble to float up, separating from PG. The new WPPA with higher product quality and lower production cost can be widely used in the WPPA factory to improve benefits of enterprise, providing a green approach to produce phosphoric acid and high-quality PG.