Selective Leaching of Phosphorus from Phosphate Tailings and Extraction of Calcium Phosphates : Toward Comprehensive Utilization of Tailing Resources

To realize the high value-added utilization of phosphate tailings, hydrochloric acid leaching-chemical precipitation method was proposed to separate and recover phosphorus from phosphate tailings. Namely, the fluorapatite in phosphate tailings was leached selectively, and then the calcium phosphates were extracted from the leachate by chemical precipitation. The results showed that P was predominantly concentrated in the fluorapatite, and its dissolution ratio increased with the decrease in pH during selective leaching. At pH 1.0, the dissolution ratio of P reached 96.3%, and most of Mg and Ca were also dissolved, while Si was hardly dissolved. It demonstrated that almost all the fluorapatite and dolomite were dissolved while the quartz was difficult to dissolve in this case. Dolomite was more preferentially dissolved than fluorapatite. Improving temperature contributed to the dissolution of dolomite while suppressing fluorapatite dissolution. After leaching, the residue was mainly composed of 87.9% SiO2 (quartz) and its P2O5 content was only 0.25%, which can be used as a construction material. When the pH of leachate was adjusted to 7.0, the large majority of phosphate ions precipitated in the form of calcium phosphate. The obtained precipitate containing 56.10% CaO and 34.18% P2O5 could be used as the P raw material or a slow-released phosphate fertilizer. The high-efficient utilization of phosphate tailings was achieved via this process