Abstract

SOLTANI, F.; ABDOLLAHY, M.; JAVAD KOLEINI, S.M.  and  MORADKHANI, D.. Selection of an appropriate leaching method for light REEs from Esfordi flotation concentrate based on mineral characterization. J. S. Afr. Inst. Min. Metall. [online]. 2017, vol.117, n.5, pp.443-450. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2017/v117n5a6.

The objective of the study was to determine the type and distribution of rare earth elements (REEs) in the phosphate flotation concentrate from the Esfordi flotation plant in central Iran, in order to understand their leaching behaviour. Samples of the concentrate were prepared and analysed using XRF, XRD, ICP, and EMPA. The Ce, Nd, La, and Y contents were 5608, 2227, 1959, and 679.7 mg/kg, respectively. The main REE-bearing minerals in the concentrate are fluorapatite, monazite, and xenotime. Apatite is the chief mineral of the concentrate and the ratio of apatite to monazite is greater than 60. From EMPA analysis, monazite contains a much higher proportion of REEs than apatite, but more than 50% of the REE content of the concentrate is in apatite, as this is the main mineral constituent of the concentrate. During the leaching of REEs in the phosphoric acid production process, more than 99% of the total rare earth values report to the large amounts of phosphogypsum (CaSO₄2H₂O) formed during the dissolution reaction. Accordingly, two process options are suggested for treating the Esfordi concentrate. In the first option, the concentrate is treated with 98% H₂SO₄ at 200-300°C. After digestion and water leaching, phosphorus and REEs are precipitated out of solution. In the second option, the concentrate is treated in a pre-leach stage. The process residue from the pre-leach stage is then subjected to acid digestion at elevated temperature for phosphoric acid production.

Keywords : Esfordi phosphate; mineral characterization; rare earth elements; leaching.

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