| The transport and separation for recovery of some kinds of rare earths through a dispersion supported liquid membrane (DSLM) consisting of polyvinylidene fluoride membrane (PVDF) as the liquid membrane support, dispersion solution including HCl solution as the stripping solution and organophosphates carrier in kerosene as the membrane solution, has been studied. The mathematical model of metal ions transport in liquid membrane systems was established by the analysis of mass transfer. The results are summarized as follows:1. The transport of La(Ⅲ), Ce(IV), Tb(III), Eu(Ⅲ), Dy(III) and Tm(Ⅲ) through a DSLM system with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC-88A) as the carrier was studied. Effects of volume ratio of membrane solution and HCl solution, HCl concentration in the dispersion phase, pH in the feed phase, initial concentrations of these rare earths, concentration of PC-88A and different stripping agents on transport of these rare earths have been studied respectively. As a result, the optimum transport conditons of La(III), Ce(Ⅳ), Tb(III), Eu(III), Dy(III) and Tm(III) were obtained as that volume ratio of membrane solution and HCl solution 30:30,40:20,30:30,30:30,40:20 and 40:20 in the dispersion phase respectively, concentration of HCl solution 4.0 mol/L in the dispersion phase, pH value in the feed phase 4.00,1.00,5.20,4.20,5.00 and 5.10 respectively, concentration of PC-88A 0.160mol/L,0.160 mol/L,0.100 mol/L,0.160 mol/L,0.100 mol/L and 0.160 mol/L in the membrane solution respectively. Under the optimum conditions, when initial concentration of La(Ⅲ), Ce(IV), Tb(III), Eu(III), Dy(III) and Tm(III) were 8.00×10-5mol/L,7.00x10-5 mol/L, 1.O0×10-4 mol/L,8.00x10-5mol/L,8.00×10-5 mol/L and 1.OOx10-4mol/L respectively, during the transport time of 125 min,75 min,95 min,130 min,95 min and 155 min the transport percentages of these rare earths are up to 93.9%,96.3%,95.2%,95.3%,96.2% and 92.2% respectively.2. The transport of La(Ⅲ), Ce(IV), Tb(Ⅲ), Eu(Ⅲ), Dy(Ⅲ) and Tm(Ⅲ) through a DSLM system with Di(2-ethylhexyl)phosphoric acid (D2EHPA) as the carrier was studied. Effects of volume ratio of membrane solution and HCl solution, HCl concentration in the dispersion phase, pH in the feed phase, initial concentrations of these rare earths, concentration of D2EHPA and different strip agents on transport of these rare earths have been studied respectively. As a result, the optimum transport conditons of La(Ⅲ), Ce(IV), Tb(Ⅲ), Eu(Ⅲ), Dy(Ⅲ) and Tm(Ⅲ) were obtained as that volume ratio of membrane solution and HCl solution 20:40,30:30,30:30, 30:30,20:40 and 40:20 in the dispersion phase respectively, concentration of HCl solution 4.00 mol/L in the dispersion phase, pH value in the feed phase 5.00,0.500,4.50,5.00,4.50 and 5.00 respectively, concentration of D2EHPA 0.160 mol/L,0.160 mol/L,0.100 mol/L,0.160 mol/L, 0.100 mol/L and 0.160 mol/L in the membrane solution respectively. Under the optimum conditions, when initial concentration of La(III), Tb(III), Eu(III), Dy(Ⅲ) and Tm(III) were all 1.00x10-4 mol/L, during the transport time of 35 min the transport percentages of these rare earths are up to 94.8%,99.1%,93.7%,98.2% and 99.2%, respectively, and the transport percentages of Ce(IV) is 78.3%.3. The transport of Tb(III), Eu(Ⅲ) and Dy(III) through a DSLM system with PC-88A and D2EHPA as the mixed carrier was studied. Effects of volume ratio of membrane solution and HCl, HCl concentration in the dispersion phase, pH in the feed phase, initial concentrations of these rare earths, concentration and ratio of mixed carrier and different stripping agents on transport of these rare earths have been studied respectively. As a result, the optimum transport conditons of Tb(Ⅲ), Eu(Ⅲ) and Dy(Ⅲ) were obtained as that volume ratio of membrane solution and HCl solution 20:40,40:20 and 40:20 in the dispersion phase respectively, concentration of HCl solution 4.00 mol/L in the dispersion phase, pH value in the feed phase 3.80,4.80 and 3.80 respectively, concentration of PC-88A 8.00×10-2 mol/L and D2EHPA 8.00×10-2 mol/L in the membrane solution respectively. Under the optimum conditions, when initial concentration of Tb(Ⅲ), Eu(Ⅲ) and Dy(III) were all 1.OO×1O-4 mol/L, during the transport time of 30 min the transport percentages of these rare earths are up to 95.4%,94.6% and 97.0%.4. According to the transport studies of every rare earths metal in DSLM system, separations of mixed rare earths were studied in DSLM. The results are sumrnarized as follows:(1) DSLM separation system with PC-88A as the carrier:Ce(IV) can be separated from other rare earths in 120 min with PC-88A as the carrier, when initial concentration of La(III), Ce(IV), Tb(Ⅲ), Eu(Ⅲ), Dy(III) and Tm(III) were all 1.00×10-4mol/L, acidity in the feed phase was 0.500 mol/L, volume ratio of membrane solution and HCl solution 30:30, concentration of HCl solution 4.00 mol/L in the dispersion phase, and concentration of PC-88A was 0.160 mol/L in the membrane solution. Then pH in the feed phase was adjusted to 2.80, in 300 min the separation factors of Tb(Ⅲ), Eu(Ⅲ) and Dy(Ⅲ) separated from La(Ⅲ) were 3.95,4.80 and 6.12 respectively. However, Tb(III), Eu(Ⅲ) and Dy(Ⅲ) separated from Tm(III) were 12.8,15.8 and 19.8 respectively.(2) DSLM separation system with D2EHPA as the carrier:In 80 min the separation factors of Tb(Ⅲ), Eu(III) and Dy(Ⅲ) separated from La(Ⅲ) were 9.24,4.81 and 1.80 respectively with D2EHPA as the carrier, when initial concentration of La(Ⅲ), Ce(IV), Tb(Ⅲ), Eu(Ⅲ), Dy(Ⅲ) and Tm(Ⅲ) were all 1.OO＋10-4 mol/L, pH in the feed phase was 2.80, volume ratio of membrane solution and HCl solution 30:30, concentration of HCl solution 4.00 mol/L in the dispersion phase, and concentration of D2EHPA was 0.160 mol/L in the membrane solution. However, Tb(Ⅲ), Eu(Ⅲ) and Dy(Ⅲ) separated from Tm(Ⅲ) were 64.4,33.5 and 12.6 respectively, so Tb(Ⅲ) and Eu(Ⅲ) can be separated from La(Ⅲ), Dy(III) and Tm(Ⅲ). When pH in the feed phase was adjusted to 2.00, in 160 min the separation factors of Dy(Ⅲ) separated from La(Ⅲ) and Tm(III) were 23.3 and 102.9 respectively, so Dy(Ⅲ) can be separated from La(Ⅲ) and Tm(Ⅲ). When pH in the feed phase was adjusted to 3.00, in mixed solution with La(III) and Tm(Ⅲ), in 250 min the separation factors of La(Ⅲ) separated from Tm(Ⅲ) was 19.1, so La(III) can be separated from Tm(III).(3) DSLM separation system with PC-88A and D2EHPA as the mixed carrier:In 80 min the separation factors of Tb(III) and Dy(Ⅲ) separated from Eu(Ⅲ) were 24.2 and 10.7 respectively with PC-88A and D2EHPA as the mixed carrier, when initial concentration of Tb(Ⅲ), Eu(Ⅲ) and Dy(III) were all 1.OOxlO-4mol/L, pH in the feed phase was 2.60, volume ratio of membrane solution and HCl solution 30:30, concentration of HCl solution 4.00 mol/L in the dispersion phase, and concentration of D2EHPA and PC-88A were all 8.00x 10-2 mol/L in the membrane solution. However, Tb(III) separated from Dy(III) was 2.26, so Tb(III) and Dy(III) can be separated from Eu(III). When pH in the feed phase was adjusted to 2.00, in 80 min the separation factors of Dy(III) and Eu(III) separated from Tb(III) were 28.9 and 19.1 respectively, so Eu(III) and Dy(III)can be separated from Tb(III).5. Through the analysis of mass transfer, the driving force of transportation is differences of concentration of hydrogen ion between feed phase and dispersion phase. The kinetics of transportation of metal ion through liquld membrane is studied and the results indicated that the transport kinetics could be analyzed in the formalism of concatenation reaction. The rate equation of transportation was obtained. The transport kinetics parameters are calculated including k1,k2, tmax, Rmax,Jfmax and Jsmax. The transport kinetics parameters Af,△m, df and Dm are calculated through the DSLM system. The osmotic coefficient equation is obtained through the DSLM. The osmotic coefficient equation is proved by transportation experiment.
|
PDF Full Text Request