Physical and Chemical Kinetics in Humic Dispersions

1
Physical and Chemical Kinetics in Humic
Dispersions
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA
Martina Klucáková Miloslav Pekar
Institute of Physical and Applied Chemistry Brno
University of Technology Czech Republic
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Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA
Kinetics is natures way
of preventing everything
from
happening all at once (S.
E. LeBlanc)
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studied material
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• lignitic humic acid
• raw material
  South-Moravian lignite (Mikulcice)
• isolation alkalic extraction (NaOH)

4
studied systems
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• solid humic acids (adsorption)
• humic acids in sols (chemical interaction)
• humic gels (diffusion chemical
  reaction)

interaction with metal ions (Cu2)
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solid humic acids adsorption
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• equilibrium studies adsorption isotherms
• adsorbed amount f (equilibrium concentration)
• Langmuir model

6
solid humic acids adsorption
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• experimental data fitted by Langmuir model

7
solid humic acids adsorption
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• experimental results kinetics

pH 4.5
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solid humic acids adsorption
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• reaction rate inherent in Langmuirs description

adsorption rate
desorption rate
r kads cadsorbate cfree sites kdes coccupied
sites
cmetal ions
? at / amax
? 1 at / amax
b kads / kdes
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solid humic acids adsorption
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA
x c (Cu2) x0 initial c (Cu2) xeq
equilibrium c (Cu2) y0 initial c (binding
sites) b kads / kdes
?
?
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solid humic acids adsorption
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• experimental data fitting

pH 4.5
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how to explain ?
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• binding of Cu2 ions by carboxylic and phenolic
  groups
• liberation of H ions
• summary (reversible) reaction

Cu2 H2R CuR 2H

• low initial pH-value backward reaction
• adsorption on other binding site

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how to explain ?
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• comparison of spectrometry and potentiometry

UV/VIS
potentiometry
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interaction in humic sol
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• classic theory
• increase of acidity and conductivity
• as long as the studied system is not in
  equilibrium

Cu2 H2R CuR 2H
Cu2 2HR CuR 2H
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interaction in humic sol
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• experimental data

• minimum on pH curve
• temporal liberation followed by further
  consumption

• analogy to consecutive reactions
• complex mechanism

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how to explain ?
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA
Cu2 H2O Cu(OH)2 2H

• Cu2 ions hydrolysis

Cu2 HR CuR H 2CuR CuR2 Cu2

• simple complex mechanism

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interaction in humic sol
Humic Substances Seminar VIIMarch 19-21,
2003Northeastern UniversityBoston, MA, USA

• comparison of classic and complex mechanism

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comparison solid-sol
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• interaction rate sol gtgt solid 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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diffusion in humic gel
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• one-dimensional diffusion
• T, p const. D ? D (c)
• Fick law

• total flux into gel
• concentration profile in gel

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diffusion from constant source
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• initial and boundary conditions

• total flux

calculation of diffusion coefficient
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diffusion from constant source
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• fitting of experimental data

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diffusion from time-variable source
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• initial and boundary conditions
• concentration profile

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diffusion from time-variable source
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• experimental data

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diffusion with chemical reaction
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• 1st order reaction A ? products
• initial and boundary conditions
• Fick law modification

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diffusion with chemical reaction
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• assumption of local equilibrium
• connecting with Fick law
• modified Fick law
• resultant equation

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diffusion with chemical reaction
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• comparison theory experimental data
• imobilization of Cu2 ions
• rate transport in gel lower,
  even under influence
  of reaction
• simple effective model

Dpub (no reaction) Dnum (reaction Cu2 HA)
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comparison of the three systems
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• interaction rate
• sol gt gel solution gtgt diffusion in gel gt solid
  HA
• binding capacity lowest in solid state

sol
gel
solid HA
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conclusions
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• complex interaction mechanism HA-metal in all
  systems
• non-ideal kinetics
• dynamic in diluted, mobile systems
• strongly diffusion-effected interaction with
  solid HA

28
thank
Humic Substances Seminar VIIMarch 17-19,
2004Northeastern UniversityBoston, MA, USA

• Grant Agency of Czech Republic for financial
  support (project No. 10402D036)
• You for your attention