| With the increasing of social demand for phosphate, the phosphate rock resources will be depleted gradually. High quality phosphoric acid produced with low and medium grade phosphate rocks is developing fast. However, it contains varied impurities. Solvent extraction is the most widely used method to purify commercial wet process phosphoric acid. It is still lack of many raw points for industrial application. Liquid-liquid equilibrium data is important for designing extraction equipment, evaluating the important parameters of extraction process, enlarging the database of the simulation process. Also, it can be used for research on extraction mechanism.There are seven liquid-liquid equilibrium experiments of quaternary systems have been conducted in the paper. It contains concentrations, density and viscosity when the two phases reach equilibria. It calculates distribution coefficient, separation factor of every solute with the experimental data, which can reflect the extraction ability of tri-n-butyl phosphate (TBP) on different substances. NRTL equation and Pitzer’s equation are used to simulate the experimental data, Hand, Othmer-Tobias and Bachman equations are used for data fitting.Wet process phosphoric acid is produced by leaching phosphate with inorganic acids (HCl、H2SO4、 HNO3). Thus, it contains excess acid in the product which produces phosphoric acid-inorganic acid mixture. It obtains essential data of systems H3PO4-HC1/H2SO4/HNO3-H2O-TBP. According to the experimental data, it analyzes that in the same concentration of different inorganic acid solution, the sequence of distribution coefficient that TBP extracts H3PO4 is HC1> H2SO4> HNO3. It is also the sequence of ability that TBP extract H3PO4 in different acids. The sequence of these acids extracted by TBP is HNO3> H3PO4> HCl> H2SO4.Because of high content in phosphate, wet process phosphoric acid contains plentiful Ca2+. If it deals phosphate with nitric acid, there is Ca(NO3)2 in the wet process phosphoric acid. The quaternary extraction system H3PO4-Ca(NO3)2-H2O-TBP is investigated with H3PO4 concentration range from 2.5% to 17.5%, Ca(NO3)2 concentration is 0-15%. When the solute concentration increase in the initial mixture solution, it would separate out crystal Ca(H2PO4)2-H2O. The paper proproses a solvent extraction process to produce high-purity Ca(H2PO4)2-H2O according to the experimental result.In this paper, it tests the salting-out effect on H3PO4 extraction with TBP. It chooses Na2SO4 and K2SO4 as salting-out agent according to imnpurity in wet process phosphoric acid. The result shows that the existence of salt can promote the H3PO4 extraction with TBP. The higher salt concentration contributes to easier extraction on H3PO4. While different salt has different effect, the effect of Na+ is greater than K+. Na2SO4 and K2SO4 have a similar effect on TBP extraction. NaCl is greater than KCl.In addition, it accomplishes the process optimization which separates H3PO4-HNO3 with TBP. It chooses TBP as extraction agent, and water as stripping agent. The best extraction condition:shaking time is 5 min, temperature is 303.2K, and phase ratio A/O (aqueous phase/organic phase, mass) is 1:2; the extraction rate of HNO3 reaches 0.8 under this condition. The best stripping condition:shaking time is 10 min, temperature is 303.2K, and phase ratio O/A (organic phase/aqueous phase, mass) is 2:3; the stripping rate of H3PO4 is 1 while that of HNO3 reaches 0.8 under this condition.All results obtained in this experiment can provide basic data and further theoretical studies for solvent extraction process which is used on purification of wet process phosphoric acid, and be beneficial to optimization of technical condition in the industrial production. |
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