4 [ ] London -van der Waals physical adsorption electrostatic adsorption ( chemical adsorption
London -van der Waals Coulomb Fe, Mn
Freundlich Langmuir Linear isotherm m i(ads) = K d m i(soln) m i(ads) : i mole/kg) m i(soln) : i mole/l) K d : [L/kg] Linear distribution coefficient
m i(ads) = K f m i n (soln) Freundlich Freundlich isotherm m i(ads) : i mole/kg) m i(soln) : i mole/l) K f increase n: n increase K f : Freundlich K f decrease n decrease Langmuir Langmuir isotherm m i(soln) adsorption [mole/l] m vacant sites m i(ads)
Langmuir Langmuir isotherm vacant site + i = occupied site m vacant site m i(soln) m i(ads) K Lang = m i(ads) /(m i(soln) m vacant sites ) m i(ads, max) = m i(ads) + m vacant sites K m i(ads) = m Lang m i(soln) i(ads, max) 1 + K Lang m i(soln) 1 1 1 = + m i(ads) m i(ads, max) K Lang m i(ads, max) 1 m i(soln) K Lang m i(soln) 1 m i(ads) = m i(ads, max) K Lang m i(soln) m i(ads, max) K lang K d (linear isotherm) a) (b) H 2 O (c) -OH -OH
M z+ : 1 2 2- - - z+ (z -2)+ Acid-Base Equilibria S: surface S-OH = S-O - + H + deprotonation at high ph S-OH + H + = S-OH 2+ protonation at low ph ph ph zero point of charge (ZPC)
: insic S-OH 2+ = S-OH + H S + [ S-OH][H + ] S K a1 = [ S-OH2+ ] S-OH = S-O - + H S + [ S-O - ][H + ] S K a2 = [ S-OH] at ph = ph ZPC, [ S-OH 2+ ] = [ S-O - ] and Ψ x = 0 [H + ] location x = [H + ] bulk soln exp(-zfψ (x) /RT) z = +1, [H + ] location x < [H + ] bulk soln z: charge of ion F: Faraday s constant Ψ: electrical potential ph ZPC = 0.5 (pk a1 + pk a2 ) surface x bulk x =
pk a1 pk a2 ph meter Acid or Base (goethite, α-feooh) ph 1 kg Q (surface charge, mol/kg) ( CA CB + m - m ) OH- H + + - Q = = [ Fe - OH2 ] -[ Fe - O ] a C A, C B (mol/l m H+, m OH- H +, OH - a (kg/l) Q ph zpc = 7.9
Fe-OH 2+ = Fe-OH + H + Fe-OH = Fe-O - + H + K a1 = K a2 = [ Fe-OH][H + ] [ Fe-OH 2+ ] [ Fe-O - ][H + ] [ Fe-OH] [ TOT FeOH] = [ FeOH2 + ] + [ FeOH] + [ FeO + - ph < ph ZPC Q = [ Fe - OH2 ] -[ Fe - O ] = [ Fe - OH2 + ([TOT FeOH] Q)[H ] K a1 = Q + - ph > ph ZPC Q = [ Fe - OH ] -[ Fe - O ] = [ Fe - O ] K a2 2 + Q[H ] = [TOT FeOH] Q ] + ] Q pk a Q= 0 pk a pka 1 pk a2
ph Q = 0 ph zpc 1 ph zpc ph 1 ph ph ZPC ph NaCl γ-al 2 O 3
[ S-OH 2+ ], [ S-O - ] (1L C A, C B H +, OH - m H+, m OH- C A C B = {[ S-OH 2+ ] + m H+ } -{[ S-O - ] + m OH- } ph < ph zpc C A m H+ = [ S-OH 2+ ] ph > ph zpc C B m OH - = [ S-O - ] [ S-OH 2+ ], [ S-O - ] ph pk a1, pk a2 K a1, K a2 zpc pk a1, pk a2 pk a2 pk a1 zpc pk a1 pk a2
inner-sphere and outer-sphere complexes S-OH + M 2+ = S-O-M + + H + (1 K M = [ S-OM + ][H + ] [ S-OH][M 2+ ] exp(- zfψ (surface) /RT) S-OH S-OH S-O + M 2+ = M + 2H + (2 S-O β 2(M) = [( S-O) 2 M][H + ] 2 [( S-OH) 2 ][M 2+ ] exp(- zfψ (surface) /RT)
ph ph 0%~100% S-OH + L - + H + = S-L + H 2 O [ S-L] K L- = [ S-OH][L- ][H + ] exp(- zfψ (surface) /RT)
ph ph As(III)
Diffuse double-layer model (DDLM) Constant capacitance model (CCM) Triple-layer model (TLM) Electrical potential Gouy-Chapman model (Cl-, NO - 3, Na +, K + etc) Triple-layer model (TLM)
ph ph -log[m n+ ] Fe 3+ Al 3+ Cu 2+ Zn 2+ Fe 2+ Cd 2+ Mg 2+ Ag + Ca 2+ ph ph ph (zpc) 7.8~8.3 α-hfeo 2 8.45~9.27 α-fe 2 O 3 Fe 8.1 Fe(OH) 3 γ-al(oh) 3 7.8~9.5 Al 9.4 Al(OH) 3 Cu>Zn>Co>Mn Cu>Pb>Zn>Co>Cd Pb>Cu>Zn>Co>Cd Pb>Cu>Zn>Ni>Cd>Co Mg>Ca>Sr>Ba Cu>Pb>Zn>Ni>Co>Cd zpc: zero point of charge
Aromatic hydrocarbons (e.g., BTX (benzene, toluene, xylene)) Chlorinated hydrocarbons (e.g., TCE, DCE, DDT, PCB) Organic coatings mineral PAH (e.g., pyrene, phenanthrene) 0.1~1 % C (ads) = K d C (soln) K d -OH
Hydrophilic head Hydrophobic tail CH 3 e.g. R-N + (CH 3 ) 3 e.g. R-SO - 3 e.g. R-O-CH 2 -CH 2 (-O-CH 2 -CH 2 ) n -O-CH 2 -CH 2 -OH T O T T O T 2 1 T O T Al 13 O 4 (OH) 28 3+ 500
Al 13 O 4 (OH) 28 3+ CO 2 + H 2 O + HX