Nitrophosphate Solution Purification by Calcium Precipitation as Gypsum
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https://doi.org/10.1007/s11837-020-04374-3 Ó 2020 The Minerals, Metals & Materials Society
ADVANCED COATING AND THIN FILM MATERIALS FOR ENERGY, AEROSPACE AND BIOLOGICAL APPLICATIONS
Nitrophosphate Solution Purification by Calcium Precipitation as Gypsum SEYED RAMIN BANIHASHEMI,1 BIJAN TAHERI,1,3 SEYED MOHAMMAD RAZAVIAN,1 and FARAZ SOLTANI2 1.—Department of Mining Engineering, University of Kashan, Kashan, Iran. 2.—Department of Mining Engineering, Arak University of Technology, Arak, Iran. 3.—e-mail: [email protected]
Phosphate ores are one of the most important secondary sources of rare earth elements (REEs). The Esfordi phosphate concentrate (Yazd Province, Iran) contains 13.1% phosphate, 34.6% calcium, and 1.09% REEs. After selective leaching of the concentrate with 35% nitric acid at 60°C for 70 min, a pregnant leach (nitrophosphate) solution containing 143.6 g/L calcium, 53.1 g/L phosphorus, and other impurities was obtained. Sulfuric acid was used to remove calcium from the pregnant leach solution in the form of gypsum, and the effect of the stoichiometric ratio of sulfate to calcium was investigated. The results showed that at a sulfate-to-calcium molar ratio of 1, 99.5% of calcium, 95.2% of cerium, 92.8% of La, and 96.5% of Nd were precipitated from the solution. Phosphate co-precipitation with gypsum was < 10%. As the stoichiometric ratio of sulfate to calcium increased, the co-precipitation rate of phosphate decreased. The results of the present study showed that in the two-stage leaching method of REE production from phosphate ores, calcium precipitation in the form of gypsum is an effective method for purifying the solution from calcium.
INTRODUCTION The rare earth elements (REEs) are a unique group of metals (lanthanide elements plus yttrium and scandium) and are among the most critical elements for their specialized applications in many modern technologies such as clean technology, hybrid cars, electronics, advanced military applications, metallurgy, surgical instruments, batteries, and nuclear energy.1 The major sources for REEs are classical minerals such as monazite, xenotime, and bastnasite.1 China has the main sources for REEs, and over 90% of the global REE production takes place in China.2 The demand for REEs has increased in recent years because of their increasing usage in numerous hightechnology applications. The challenge of the REE (Received July 4, 2020; accepted September 1, 2020)
supply due to the scarcity of mineral deposits and policies of China’s rare earth industry has encouraged other countries to find secondary sources of REEs.3 Phosphate deposits are one of the most important secondary sources containing REEs.4 Phosphate deposits are divided into igneous and sedimentary groups, with igneous deposits accounting for 10– 15% of the world’s total reserves.5 The REE grade in igneous phosphate ores is about 1–2%, which is higher than that of sedimentary phosphate ores.4,5 In most phosphate reserves, apatite with the chemical formula ðCa; REEÞ5 ðPO4 Þ3 ðF; Cl OHÞ is th
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