Since the conventional liquid-liquid extraction method suffered from a series of problems such as inefficiency of one stage extraction, vast device occupation and severe emulsification, we adopted microcapsule(MC) technique to change the former liquid-liquid extraction to liquid-solid extraction. Firstly, the piercing method was performed to prepare the empty polysulfone(PSF) microcapsules, which was easy to implement and control. Secondly, the ultrasonic approach was utilized to prepare the functional microcapsules containing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester(EHPNA). We focused on a key factor of the molar ratio of PSF over 1-Methyl-2-pyrrolidinone(NMP), attaining a loading ratio as high as 7.21 g-EHPNA/g-PSF. Thirdly, we examined the kinetics and thermodynamics of extraction. Kinetic results demonstrated that equilibrium was reached within two hours, with an extraction rate of Sm3+≈Er3+>La3+; Thermodynamic results showed that the extraction of lanthanides complied with the Langmuir law, with an extraction capacity of 0.25–0.30 mmol/g-microcapsule. Fourthly, stripping experiment indicated that three hours were required to accomplish equilibrium for La3+ and Sm3+ while longer hours for Er3+. Finally, seven extraction-stripping cyclic experiments were performed for three mixed elements, the results of which revealed that Sm3+ and Er3+ maintained constantly high extraction amount whilst La3+ leveled off at approximately 50%. This proposed polysulfone microcapsule containing EHPNA is suitable to be applied to extraction and concentration of rare earth metals.
A process to recover rare earth(RE) metals from spent fluid catalytic cracking(FCC) catalysts by solvent extraction was studied, using saponified 2-ethylhexyl phosphoric acid-2-ethylhexyl ester(EHEHPA or P507). The recovery process involved three steps:(1) leaching REs(mainly lanthanum and cerium);(2) solvent extraction by applying saponified P507-kerosene system;(3) stripping. Experiments to assure optimal operating conditions were conducted. Results indicated that RE metals could be recovered effectively from spent catalyst with saponified P507-kerosene-HCl system. At room temperature of 25 oC, 10 g spent catalyst with 110 m L of HCl(1 mol/L) could achieve a leaching efficiency of 85%. For extraction, initial pH value of 3.17, organic/aqueous ratio(O/A ratio) of 2:1 with an extractants' saponification rate of 20% could obtain 100% efficiency. In the stripping process, 1 mol/L HCl with O/A ratio of 1:1 led to a stripping efficiency of 96%. In the present study, RE metals from spent FCC catalysts were effectively recovered, which avoided wasting a large amount of RE resources. It provides a theoretical support for commercial recycling of RE resources.
The conventional rare earth solvent extraction equipments have many problems such as long mixing time,low processing capacity,large factory area occupation,high energy consumption and so on.In order to solve the problems,many types of equipments were brought out.In this work,studies were carried out on the La(III)extraction process with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester(EHEHPA)by membrane dispersion micro-extractor.Equilibrium studies showed that the initial aqueous pH value 4.15 with the saponification rate 40%was the optimal operation condition.The effects of membrane dispersion micro-extractor operational conditions such as dispersion mode,bulk flow rate and organic phase flow rate on the extraction efficiency were studied.The results showed that when the organic solution was the dispersed phase,the extraction efficiency was higher than that of others.Increasing bulk flow ratio could enhance the extraction efficiency greatly.When the ratio of organic phase flow rate to that of aqueous phase was 80:80,the extraction efficiency was over 95%.The effect of stripping phase acidity on the La(III)recovery was studied.The results showed that when the stripping phase pH was 2.0,organic phase flow rate to stripping phase flow rate was 20:80;the recovery efficiency of La(III)can reach 82%.
The experimental and numerical investigations of single drop in liquid/liquid extraction system have been reviewed with particular focus on experimental techniques and computational fluid dynamic simulation approaches.Comprehensive surveys of available experimental techniques and numerical approaches for single drop rising and falling were given.Subsequently,single drop mass transfer was also reviewed both experimentally and numerically.Additionally,single drop breakage and coalescence process and the influencing factors were summarized and compared,so as to establish sub-models for population balance model.Future directions on single drop mass transfer,drop breakage and coalescence were suggested.It is believed that the single drop is a powerful tool to assist extraction process design from lab-scale to pilot-scale.
The efficacy of polysulfone microcapsules encapsulating ionic liquid [trialkylmethylammonium][di(2-ethylhelxyl) orthophosphinate]([A336][P507]) for the extraction of La^(3+), Sm^(3+) and Er^(3+) from dilute aqueous solutions was investigated. Microcapsules were synthesized using coaxial microfluidic method, and subsequently encapsulated with extractant [A336][P507]. The kinetics data were fitted well by pseudo-second-order equation and Crank model, and the kinetics parameters were evaluated. The extraction rate had the order of Er^(3+)>Sm^(3+)>La^(3+). The isotherm data were analyzed by Langmuir model and shifted Langmuir model. The extraction capacities of La^(3+), Sm^(3+) and Er^(3+) were 58.4, 56.6 and 81.7 mg/g, respectively. The dependency of stripping performance on HNO3 concentration was measured. The regeneration of microcapsules was evaluated using cycling extraction experiments.
By using membrane dispersion micro-extractor, Ce(Ⅲ) solvent extraction experiments were conducted. Cerium chloride solution with certain acidity was used as aqueous phase and 2-ethylhexyl phosphoric acid-2-ethylhexyl ester(EHEHPA) kerosene solution as organic phase. The effects of system physicochemical properties and operational conditions, such as initial EHEHPA concentration, initial aqueous acidity, total flow rate and continuous phase flow rate, etc., on the extraction efficiency and the overall volume mass transfer coefficient were evaluated. As the total flow rate increased from 20 to 160 m L/min, the overall volume mass transfer coefficient was enhanced from 0.1 to 0.54 s–1. Under the optimal conditions, the Ce(Ⅲ) extraction efficiency could reach 99.92% in 2.98 s. A mathematical model was set up to predict the overall volume mass transfer coefficient, and the calculation results agreed well with the experimental results, most relative error was within ±10%.
