Search

To achieve highly efficient extraction of phosphorus (P) and comprehensive utilization of phosphate tailings, a two-stage leaching-precipitation method was proposed. Phosphate tailings primarily consisted of dolomite, fluorapatite, and quartz. During the first-stage leaching, the large majority of dolomite was selectively dissolved and the leaching efficiency of Mg reached 93.1 % at pH 2.0 and 60 °C. The subsequent second-stage leaching of fluorapatite was performed and the P leaching efficiency was 98.8 % at pH 1.5 and 20 °C, while the quartz remained in the residue. Through two-stage leaching, a stepwise leaching of dolomite and fluorapatite was achieved. After chemical precipitation, calcium phosphate with a high purity of 97.9 % was obtained; and the total recovery efficiency of P exceeded 98 %. The obtained calcium phosphate can be a raw material in the phosphorus chemical industry, while the Mg-rich leachate and the final quartz-rich residue have the potential for Mg extraction and the production of mortars or geopolymers, respectively. The two-stage leaching-precipitation process could significantly reduce the leaching costs, and enhance the reaction rates. It is expected to realize a volume reduction and efficient resource utilization of the phosphate tailings by using this sustainable and promising solution. • A new method of P extraction and utilization of phosphate tailings was proposed. • A stepwise dissolution of dolomite and fluorapatite was achieved. • High-grade calcium phosphates were recovered from the phosphate tailings. • CaHPO 4 and Ca 10 (PO 4) 6 (OH) 2 were obtained at pH 6.0 and 8.0, respectively. [ABSTRACT FROM AUTHOR]

Phosphate tailing is an extremely fine by-product during phosphate ore flotation. Due to the large quantities and relatively higher P 2 O 5 content, the phosphate tailings have been considered as a potential P resource, compared to other P-bearing wastes. Besides, phosphate tailings also contain a large amount of available components, such as Ca, Mg, and Si. To explore a low-cost and efficient process for the utilization of phosphate tailings, the hydrochloric acid leaching-precipitation method was employed to recover phosphorus. The P in phosphate tailings can be selectively dissolved into leaching liquor, followed by the precipitation of calcium phosphates from the leaching liquor through pH adjustment. The results showed that P was predominantly concentrated in fluorapatite and its dissolution ratio increased with the decrease in pH. At pH 1.0, the P dissolution efficiency from phosphate tailings reached 96.3%, along with the majority of Mg and Ca. However, Si was hardly dissolved. It demonstrated that almost all the fluorapatite and dolomite were dissolved while the quartz was difficult to dissolve. Dolomite was more preferentially dissolved than fluorapatite. Increasing temperature contributed to the dissolution of dolomite while suppressing fluorapatite dissolution. The residue containing 87.9% SiO 2 (quartz) and only 0.25% P 2 O 5 has the potential as a building material. As the pH increased to 7.0, the collected precipitate consisted of 34.18% P 2 O 5 and 56.10% CaO, which can serve as a source of a slow-released phosphate fertilizer. The highly efficient utilization of phosphate tailings was achieved via this process. • Selective leaching of P from phosphate tailings can be achieved by HCl solution. • Calcium phosphates are obtained from leachate by the precipitation method. • The obtained precipitate can be used as a slow-released phosphate fertilizer. • The residue mainly composed of quartz has the potential to be a building material. • A method for resource utilization of phosphate tailings was proposed. [ABSTRACT FROM AUTHOR]