Selective Concetration and Removal Using Nanofiltration Membranes Jungwon Kim 1

Introduction 1. Membrane Filration - the separation of particulate and colloidal matter 2. Membrane Process Classification - MF, UF, NF, RO, dialysis, and electrodialysis 3. Removal Mechanism - In MF and UF : Straining(sieving) - In NF and RO : Rejection by the water layer 4. Nanofiltration - Remove particle size : <1nm - Use : removal of selected dissolved constituents 2

3 Introduction FeedstreamPermeate Concentrate Retentate Reject The recovey is defined as (permeate flowrate / feedstream flowrate) The rejection is defined as (retentate conc. / feedstream conc.)

4 Selective Removal of Cobalt Species Using Nanofiltration Membranes (Choo,K.H.;Kwon,D.J.;Lee,K.W.; Choi,S.J. Environ. Sci. Technol. 2002, 36, ) (Choo,K.H.;Kwon,D.J.;Lee,K.W.; Choi,S.J. Environ. Sci. Technol. 2002, 36, ) Effect of feed cobalt concentration and pH on cobalt rejection when no boric acid (BA) and NaCl exist in the feed : membrane, NTR7250; operating pressure, 4.9 bar; tangential velocity, 1.0 m/s. ※ Fommation of CO(OH) 2

5 Effect of Feed pH Cobalt Concentraions on Cobalt Rejection The formation of Co(OH) 2 solids began from a pH of approximately 8 The CO 2 in the air might play a role in cobalt rejection

6 Effect of Feed pH Cobalt Concentraions on Cobalt Rejection the percentage of precipitates of initial cobalt at various pH levels : ( ) a system with no carbonate species; ( ) an open system with an equilibrium dissolved CO 2 concentration of M; (·) a closed system with a total carbonate concentration of M. The total cobalt concentration is mM. Co 2+ +CO  Co(CO) 3 Co 2+ +2OH  Co(OH) 2 ※ Fommation of CO(CO) 3

7 Effect of Membrane Types on Cobalt Rejection mebranePore radius(nm) R S (%) R NaCl (%) NTR (s)15 NTR (g)60 NTR729H F (g)92 NF (g)58 Feed composition : mM Co(NO 3 ) 2, operating pressure, 4.9 bar; tangential velocity, 1.0 m/s. Properties of the NF Membranes Used

8 Effect of Background Components on Cobalt Rejection Variation of feed turbidity with pH at different BA concentrations. The number in the parentheses of legend indicates the molar ratios of BA to cobalt. Examination of complexation reactions between cobalt and BA by near-infrared (NIR) spectroscopy.

9 Selective Concentration of Uranium from Seawater By Nanofiltration (Alain Favre-Reguillon, Gerard Lebuzit, Jacques Foos, Alain Guy, Micheline Draye, and Marc Lemaire* Ind. Eng. Chem. Res. 2003, 42, ) Distribution of uranium(VI) hydroxy and carbonate complexes as a function of the pH for [CO 3 2- ] = 2 ×10-3M, [NaCl] = 11g/L, and T = 25 ℃ built with CHESS software. 8.3 UO 2 (CO 3 ) 3 4- UO 2 (CO 3 ) 2 2- UO 2 (CO 3 ) 3 4- UO 2 (CO 3 ) 5.5

10 Retention Coefficient of U(VI Retention Coefficient of U(VI) with Simulated Seawater Dependence of the observed uranium retention coefficient as a function of the sodium concentration in the feed. Conditions: T = 20 ℃, △ P = 3 bar, pH 8.3, [UO 2 2 +] )= 1×10 -5 mol/L, [CO HCO 3 ] ) = 2×10 -3 mol/L, [NaCl] ) = 0~11 g/L. G50

11 Retention Coefficient of Na, Ca, and U(VI Retention Coefficient of Na, Ca, and U(VI) with Simulated Seawater coefficient of sodium, calcium, and uranium as a function of the operating membrane. Experimental conditions: T = 20 ℃, △ P = 3 bar, pH 8.3, [UO 2 2+ ] = 1×10 -5 mol/L, [CO HCO 3 ] = 2×10 -3 mol/L, [NaCl] = 11 g/L, [CaCl 2 ] = 1 g/L VI) High retention coefficient for U(VI) Low retention coefficient for Na and Ca

12 Retention Coefficient U(VI Retention Coefficient U(VI) with Actual Seawater(3.66μg/L) Concentration of U(VI) in the retentate versus initial concentration of U(VI) in the feed as a function of the nanofiltered volume ratio. Experimental conditions: prefiltered seawater, T = 20 ℃, △ P = 3 bar, G10 membrane, pH 8.3. ICP-MS (detection limit=3.66μg/L) ICP-OES (detection limit=2.38mg/L)

13 Flux Decline during Nanofiltration of Organic Componets in Aqueous Solution (Bart Van der Bruggen* and Carlo Vandecasteele, Environ. Sci. Technol. 2001, 35, ) Flux(J) = diriving force/(viscosity×total resistance) total resistance = R P + R A + R M + R G + R CP + R I + R D ≒ R P + R A + R M Influence of the concentration on the water flux for benzonitrile (membrane, NF70).

14 Mechanism of Flux Decline Flux decline for the used set of molecules (membrane, NF70) Flux decline as a function of concentration for benzonitrile (membrane, NF70) q = K f C n = △ J

15 Influence of Molecular Size and Dipole Moment PressureNF70(-)UTC-60(+)UTC-20(-)NTR 7450(-) 5bar bar bar bar bar Flux Decline (%) between Initial Water Flux and Water Flux after Filtration with the Last Component UTC-60 : fouling by electrostactic interaction NTR 7450 : fouling by hydrophobic interaction

16 Influence of Molecular Size and Dipole Moment Flux decline (%) as a function of effective diameter for (a) NF70 and (b) UTC-20 NF70 Standard deviation (variation of pore size) : 0.54nm UTC-20 Standard deviation (variation of pore size) : 0.34nm

Conclusion 1. Cobalt carbonates play a major role in the greater cobalt rejection with the increase of pH during NF instead of cobalt hydroxides. 2. NTR7410 membrane(large pore size) would be as attractive for cobalt removal as other moderately dense NF membranes along with pH adjustments. 3. Background components such as bonic acid affect cobalt rejection. 4. The G10 membrane shows a high retention for U( Ⅵ ) and low retention for Na and Ca, so this membrane is useful for the selcetive concentration of uranyl ion. 5. Molecules can get attached to the membrane pores or to the membrane surface by adsorption, so they cause flux decline. 6. Molecular size is an important factor for flux decline. 17