Phosphorus recovery from phosphate tailings through a two-stage leaching-precipitation process: Toward the harmless and reduction treatment of P-bearing wastes.

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.

Leaching of phosphorus from phosphate tailings and extraction of calcium phosphates: Toward comprehensive utilization of tailing resources.

Phosphate tailing is an extremely fine by-product during phosphate ore flotation. Due to the large quantities and relatively higher P2O5 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% SiO2 (quartz) and only 0.25% P2O5 has the potential as a building material. As the pH increased to 7.0, the collected precipitate consisted of 34.18% P2O5 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.

A review on the P enrichment and recovery from steelmaking slag: Towards a sustainable P supply and comprehensive utilization of industrial solid wastes.

Phosphorus (P) is one of the desirable nutrient elements for the growing of crops and is a non-renewable resource. The over-exploitation of high-grade phosphate rocks makes finding alternative P sources urgent for a sustainable and stable P supply. Steelmaking slag has been considered a potential P source due to its huge production and the increasing P content in slag with the utilization of low-grade iron ores. If the efficient separation of P from steelmaking slag is achieved, the obtained P can be used as the raw material for phosphate products, and the P-removal steelmaking slag can be reused as a metallurgical flux in steel plants, realizing the comprehensive utilization of steelmaking slag. To better understand the separation method and mechanism of P from steelmaking slag, this paper reviews: (1) the enrichment mechanism of P in steelmaking slag, (2) the methods of the P-rich phase separation from slag and P recovery, and (3) facilitating the enrichment of P in the mineral phase by cooling treatment and modification. Furthermore, some industrial solid wastes were selected as modifiers for steelmaking slag, which not only provided several valuable components but also significantly reduced treatment costs. Hence, a collaborative processing of steelmaking slag and other P-bearing industrial solid wastes is proposed, providing a new solution for P recovery and the comprehensive utilization of industrial solid wastes, achieving the sustainable development of steel and phosphate industries.

Magnetic resonance imaging assessment of temporomandibular joint soft tissue injuries of intracapsular condylar fracture.

We evaluated the soft tissue of the temporomandibular joint (TMJ) with magnetic resonance imaging (MRI) after intracapsular condylar fracture. Eighteen consecutive patients (19 TMJ) were diagnosed between 1 January 2010 and 30 October 2011. They were examined using bilateral sagittal and coronal MRI, which were obtained immediately after injury to assess the displacement of the disc, whether there was a tear in capsule or the retrodiscal tissue, and whether there was an effusion in the joint. On the affected side MRI showed disc displacement in 15 of 19, tears in the capsule in 9, and tears in the retrodiscal tissue in 16. All 19 had joint effusions. It also showed 2 joints with abnormalities on the unaffected side. We conclude that MRI is useful for diagnosis and for estimating the amount of damage to the TMJ, and is helpful in planning treatment.