1 humic substances seminar vii march 1 7 - 19, 200 4 northeastern university boston, ma, usa...

1

Humic Substances Seminar VIIMarch 17-19, 2004

Northeastern UniversityBoston, MA, USA

Physical and Chemical Kinetics in Humic Dispersions

Martina Klučáková

Miloslav Pekař

Institute of Physical and Applied Chemistry

Brno University of Technology

Czech Republic

2



Kinetics is nature‘s way of preventing everything from happening all at once (S. E. LeBlanc)

3



studied material

lignitic humic acid

raw material: South-Moravian lignite (Mikulčice)

isolation: alkalic extraction (NaOH)

C H N S O COOH

[wt. %] [meq/g]

58.6 5.0 2.4 1.4 32.6 4.45

4



studied systems

solid humic acids (adsorption)

humic acids in sols (chemical interaction)

humic gels (diffusion & chemical reaction)

interaction with metal ions interaction with metal ions (Cu(Cu2+2+))

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Northeastern UniversityBoston, MA, USAsolid humic acids:

adsorption

equilibrium studies = adsorption isotherms

adsorbed amount = f (equilibrium concentration)

Langmuir model: bc

bcaa

eq

eqeq

1max

6



adsorption

pH = 2

0.0

0.2

0.4

0.6

0.8

1.0

0 0.2 0.4 0.6 0.8 1

concentration [mol/dm3]

adso

rbed a

mount

[mm

ol/g]

pH = 4.5

0.0

0.5

1.0

1.5

2.0

0 0.2 0.4 0.6 0.8 1

concentration [mol/dm3]

adso

rbed a

mount

[mm

ol/g]

experimental data fitted by Langmuir model

0.72 2.4410-3

b [dm3/mol] amax [mol/g]

2.47 2.9310-3

b [dm3/mol] amax [mol/g]

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adsorption

experimental results: kinetics

pH = 2

0.00

0.05

0.10

0.15

0 100 200 300 400

time [min]

adso

rbed

am

ount

[m

mol

/g]

0

0.1

0.2

0.3

0.4

0.5

0 100 200 300 400

time [min]

adso

rbed

am

ount

[m

mol

/g]

pH = 4.5

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adsorption

reaction rate inherent in Langmuir‘s description

r = kads cadsorbate cfree sites – kdes coccupied sites

b = kads / kdes

1 – at / amax

at / amax

cmetal ions

adsorption rate desorption rate

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adsorption

b

x

bxyxx

tkx 0

002 )

1(

dd

ads x … c (Cu2+) x0 … initial c (Cu2+)

xeq … equilibrium c (Cu2+)

y0 … initial c (binding

sites)

b = kads / kdesconstts

xx

xx

eq

eq ln

42 adsks

10



adsorption

experimental data fitting

pH =4.5pH = 2

5

6

7

8

9

10

0 100 200 300 400

time [min]

5

6

7

8

9

10

0 100 200 300 400

time [min]

11



how to explain ?

binding of Cu2+ ions by carboxylic and phenolic groups

liberation of H+ ions

summary (reversible) reaction:CuCu2+2+ + H + H22R CuR + 2HR CuR + 2H++

low initial pH-value = backward reaction

adsorption on „other“ binding site

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how to explain ?

comparison of spectrometry and potentiometry

40

42

44

46

48

50

0 100 200 300 400

time [min]

x [m

mol

/dm

3 ]

0

1

2

3

4

5

pH

UV/VIS

potentiometry

0

1

2

3

4

5

6

0 0.1 0.2 0.3 0.4 0.5

equilibrium concentration [mol/dm3]

adso

rbed a

mount

[mm

ol/g]

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Northeastern UniversityBoston, MA, USAinteraction

in humic sol

classic theory

increase of acidity and conductivity

as long as the studied system is not in equilibrium

CuCu2+2+ + H + H22R CuR + 2HR CuR + 2H++

CuCu2+2+ + + 22HR CuR + 2HHR CuR + 2H++

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in humic sol

experimental data

3.5

4.0

4.5

5.0

0 20 40 60

time [s]

pH

13

13.5

14

14.5

conduct

ivit

y [m

S]

minimum on pH curve

temporal liberation followed by further consumptionanalogy to consecutive reactions

complex mechanism

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how to explain ?

CuCu2+2+ + HR CuR + HR CuR++ + + HH++

2CuR2CuR+ + CuR CuR22 + Cu + Cu2+2+

CuCu2+2+ + H + H22O Cu(OH)O Cu(OH)22 + + 2H2H++

Cu2+ ions hydrolysis

„simple“ complex mechanism

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in humic sol

0

0.5

1

1.5

0 100 200 300 400 500 600

time [s]

(cla

ssic

mechanis

m)

0

0.05

0.1

0.15

0.2

0.25

(

com

ple

x m

echanis

m)

0

0.05

0.1

0.15

0 0.02 0.04 0.06 0.08 0.1 0.12

initial concentration of Cu2+

[mol/dm3]

rate

con

stan

t [1

/s]

0

0.05

0.1

0.15

rate

con

stan

t [m

S/s]

comparison of classic and complex mechanism

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comparison solid-sol

interaction interaction rate: rate: sol sol >>>> solsolidid HA HA

diffusion effect in heterogeneous system

humic gel = model system for diffusion study:

experimentally more tractable

simple suppression of convective and thermal mixing

close to water environment

relation to real (natural) systems

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Northeastern UniversityBoston, MA, USAdiffusion

in humic gel

one-dimensional diffusion

T, p = const.; D D (c)

Fick law211

x

cD

t

c

total flux into gel

concentration profile in gel

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from constant source

initial and boundary conditions

t = 0 x 0; L c1 = 0

t 0 x = 0 c1 = c1,s = const.

t 0 x = L / 2 c1 / x = 0

total flux:

Dt

cm s,12

calculation of diffusion coefficientcalculation of diffusion coefficient

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from constant source

1.4310-9 1.0710-9

Dpub [m2/s] Dnum [m2/s]

y = 1.5909x

R2 = 0.9994

0

100

200

300

400

500

0 100 200 300

time1/2 [s1/2]

tota

l flux

[mol

/m2]

fitting of experimental data

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from time-variable source


concentration profile

t = 0 x 0; L c1 = 0

t = 0 x < 0; x > L c2 = c2,0

t 0 x = 0 D1 c1 / x = D2 c2 / x

t 0 x = L / 2 c2 / x = 0

t x = 0 = c1 / c2

tD

xerfc

DD

cc

121

0,21

4/1

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from time-variable source

0.0E+00

2.0E-04

4.0E-04

6.0E-04

8.0E-04

1.0E-03

1.2E-03

1.4E-03

1.6E-03

0 10 20 30 40 50

x [mm]

c [m

ol/g

HK]

30 min 2 h 24 h

0.0E+00

2.0E-04

4.0E-04

6.0E-04

8.0E-04

1.0E-03

1.2E-03

1.4E-03

1.6E-03

0 10 20 30 40 50

x [mm]

c [m

ol/g

HK]

0.02M 0.20M 0.40M

experimental data

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with chemical reaction

1st order reaction: A products


Fick law modification:

t = 0 x 0; L c1 = 0

t 0 x = 0 c1 = c1,0 exp -kt

t 0 x = L / 2 c1 / x = 0

121

21 kc

x

cD

t

c

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with chemical reaction

211

x

cD

t

c

1,1 cc im

t

c

x

cD

t

c im

,1

21

21

21

21

1 x

cD

t

c

1

DDef

assumption of local equilibrium

connecting with Fick law

modified Fick law

resultant equation

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diffusion with chemical reaction

comparison theory & experimental data

imobilization of Cu2+ ions

rate transport in gel lower, even under influence of reaction

simple & effective model

0

1

2

3

4

5

0 0.5 1 1.5 2 2.5

x [cm]

c [

mol/dm

3]

Dpub (no reaction)

Dnum (reaction Cu2+ + HA)

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Northeastern UniversityBoston, MA, USAcomparison

of the three systems

0.00001

0.0001

0.001

0.01

0.1

0 1000 2000 3000

time [s]

c(Cu-

HA) [m

ol/g

]

sol

gel

solid HA

interaction rate

sol > gel + solution >> diffusion in gel > solid HA

binding capacity lowest in solid state

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conclusions

complex interaction mechanism HA-metal in all systems

non-ideal kinetics

dynamic in diluted, mobile systems

strongly diffusion-effected interaction with solid HA

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thank

Grant Agency of Czech Republic for financial support (project No. 10402D036)

You for your attention

1 humic substances seminar vii march 1 7 - 19, 200 4 northeastern university boston, ma, usa...

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