Rare Earths Extraction Enrichment From Low Concentration Of Rare Earth Solution And Oil Removing From Raffinate Aqueous Phase

Precipitation crystallization is the widely used method to draw rare earths from ion adsorption rare earth leaching solution containing low concentration of rare earths.However, for the low concentration of rare earth solution containing lots of impurities,precipitation method will face the challenge by solvent extraction due to the cost and product quality problems. The advantage of extraction method lies in its high efficiency for the separation of rare earth with most of the impurities, and is suitable for continuous mass production. Extraction for practical application, of course, also need to solve the following two questions: selecting a optimized extractant with superior performance, lowing the organic phase loss in raffinate aqueous phase to meet the recycling or discharge requirements. In the present study, we comparatively investigated the extraction performance of C272 produced by three different manufacturers first, and then focused on the organic phase loss during the extraction process of rare earths by P₅₀₇ and N₁₉₂₃ with respecting to the effect of the extraction and operate conditions on the oil concentration in raffinate aqueous phase as well as the methods to remove oil from the raffinate aqueous phase. The main contents are:The extraction performance for rare earth sulphate in solution with different initial pH values by 20%N₁₉₂₃-10% sec-octyl alcohols- 70% kerosene organic phase protonated directly with 1mol/L H2SO4?call as sulfuric acid protonated organic phase,SAPOP? or via a rare earth stripping process with 1.5 mol/L hydrochloric acid?call as hydrochloric acid protonated organic phase, HAPOP? were comparatively investigated. In the case of SAPOP, the extraction rate increases with the increase of initiate pH value of rare earth solution, and the optimal pH value is between 2-6; But for the HAPOP, the extraction rate decreases with the increase of initiate pH value of rare earth solution, evident extraction only occurred at pH lower than 1.Hydrochloric acid, sulfuric acid and their mixture solution with the corresponding ammonium salts were employed as stripping reagents from rare earths loaded organic phase. The result proves that the stripping ability depends on the type of cation and anion, and show sequences of H+ >NH4+ and Cl- > SO42-, The highest stripping rate when employing same concentration is found for hydrochloric acid.However, the remaining acid concentration is high, which is not beneficial for the following precipitation of rare earth. Therefore, a mixture solution with molar ratio of hydrochloric acid to ammonium chloride at 6:4 was determined as a suitable stripping solution, which shows high stripping rate with low free acid. Combined with the results previously, a principle process to enrich rare earth from ion adsorption rare earth leaching solution is proposed for the separation of rare earth from aluminum,iron, calcium and magnesium.A simple method for determining kerosene content in water was established and used to study the influence of extraction and operating conditions on the oil content in raffinate aqueous phase of P₅₀₇ and N₁₉₂₃ system. It was found that although the kerosene content in raffinate aqueous phase increased with the increase of aqueous pH and phase ratio A/O, prolonging phase separating time is the key to reduce oil content in aqueous phase, and can eliminate the impact of oscillation time and intensity. Furthermore, the kerosene content in raffinate aqueous phase of N₁₉₂₃ system is lower than that in P₅₀₇ system.A flocculation-precipitation method was employed to remove dissolve oil and emulsified oil from P₅₀₇ and N₁₉₂₃ raffinate aqueous phase using Al2?SO4?3 as flocculant. The relationship between process parameters and the actual effect were respectively studied. The results showed that the removal rate of kerosene from P₅₀₇ raffinate aqueous phase reaches more then 86%?dropped from 450mg/L to 63mg/L?under the optimal conditions with Al3+ dosage of 120.0mg/L, initial pH 9.4, stirring intensity 600r/min, stirring time 90 s, setting time 30 min. Meanwhile, the removal rate of kerosene from N₁₉₂₃ raffinate aqueous phase reaches more then 96%?dropped from1203mg/L to 45mg/L? under the optimal conditions with Al3+dosage of 120.0mg/L,initial pH 11.92, stirring intensity 800r/min, stirring time 120 s, setting time 30 min.Finally, a flocculation-air flotation method was used to remove oil from a N₁₉₂₃ raffinate aqueous phase containing oil more than 315.7 mg/L. And when assuming a dosage of flocculant 40 mg/L, the removal rate is 97.6% and the final oil content is below 7.5g/L, which can meet the emission requirements.