Leachability of rare-earth, calcium and minor metal ions from natural Fluorapatite in perchloric, hydrochloric, nitric and phosphoric acid solutions: Effect of proton activity and anion participation

Abstract

A C C E P T E D M A N U S C R I P T C was conducted using particles of size range 150-180 µm, 5% (w/w) solids and a stirring rate of 1100 rpm. The similarities and differences in leaching efficiencies of metal ions are rationalised on the basis of proton activity of acids and the participation of anions due to complexation with metal ions. The leaching efficiency of calcium, phosphate, fluoride, sodium and strontium reached 80-100% after 5-10 min in hydrochloric, perchloric and nitric acid compared to lower leaching efficiencies (<40%) in phosphoric acid. Despite the low solubility products of phosphates of iron(III) and calcium (pK SP ≈ 24, 31), the higher pH, and lower proton activity of phosphoric acid, the higher leaching efficiencies of calcium and iron (≥80%) suggest the formation of complex species of these metal ions with phosphate ions. The leaching efficiencies of lanthanum, cerium and neodymium were low in all acids and showed a descending order: HClO 4 (54-63%) > HCl (21-13%) > HNO 3 (5-7%). The RE leaching efficiency in HClO 4 remained relatively unaffected with time, but the low leaching efficiencies in other acids after 30 min (<20%) indicates the precipitation of RE-phosphates and prospect of selective leaching of FAP. The slope of linear correlation of leaching efficiency of REs was close to unity in HClO 4 , HCl and HNO 3 indicating similar behaviour. A higher slope for La-Ce leaching efficiency correlation of 1.8 compared to 0.9 for Nd-Ce in H 3 PO 4 warrants further studies. ACCEPTED MANUSCRIPT

Application of Gettering Process on the Improvement of the Structural and Mineralogical Properties of Tunisian Phosphate Rock

“…Similar intensity bands are found at 1056, 1100, 1116 cm -1 which are assigned to ʋ3 PO 4 3-antisymmetric stretching vibration, the three bandes are attributed to a pure fluorapatite [18]. Low intensity Raman band at 1009 cm -1 is attributed to ʋ1 PO 4 3-symmetric stretching mode [28,33,34].…”

“…Compared to the reference phosphate are 2.4, treated phosphate (TP) is become 1.7 which is closer to the theoretical Ca/P molar ratio of pure FAP: 1.67. However, this proves the presence of carbonate-FAP and calcite in reference sample and the presence of calcium oxide in excess [28]. This difference in composition may take place by incorporation of ion present in the site of PO 4 2-group.…”

“…From this figure, we can't observe any vibrational mode for reference sample (RP). This is due to the fact that Raman bands are completely overlapped by the fluorescence background originated from organic matter, metal compouned and rare earth existing in natural phosphate rock (RP) [25][26][27][28][29]. As a result of this overlap, we can't differentiate between the different vibrational modes.…”

Selection of an appropriate leaching method for light REEs from Esfordi flotation concentrate based on mineral characterization

“…Iron phosphate coatings are also primarily used as base coatings for paint (Wikipedia, 2016). Finally, the REEs are converted to hydroxide with caustic soda (Li et al, 2009) ® Acid leaching of the concentrate with HNO3, HCl, or H 3 PO 4 to dissolve apatite prior to the acid digestion stage (Bandara and Senanayake, 2015). Hydrochloric acid could in principle be used, but is not in practice due to its high corrosivity.…”

Mining and Beneficiation of Phosphate Ore

“…20). RE phosphate minerals, such as monazite, florencite, xenotime, cheralite and britholite, are the most naturally abundant forms that are associated with fluorapatite [47], [61], [62], [63], [64].…”