1 Humic Substances Seminar VII March , Northeastern University Boston, 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 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA Kinetics is nature‘s way of preventing everything from happening all at once ( S. E. LeBlanc)

3 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA studied material lignitic humic acid raw material: South-Moravian lignite (Mikulčice) isolation: alkalic extraction (NaOH) CHNSOCOOH [wt. %][meq/g]

4 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA studied systems solid humic acids (adsorption) humic acids in sols (chemical interaction) humic gels (diffusion & chemical reaction) interaction with metal ions (Cu 2+ )

5 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA solid humic acids: adsorption equilibrium studies = adsorption isotherms adsorbed amount = f (equilibrium concentration) Langmuir model:

6 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA solid humic acids: adsorption experimental data fitted by Langmuir model  b [dm 3 /mol] a max [mol/g]  b [dm 3 /mol] a max [mol/g]

7 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA solid humic acids: adsorption experimental results: kinetics pH = 4.5

8 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA solid humic acids: adsorption reaction rate inherent in Langmuir‘s description r = k ads c adsorbate c free sites – k des c occupied sites b = k ads / k des  1 – a t / a max  a t / a max c metal ions adsorption rate desorption rate

9 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA solid humic acids: adsorption x … c (Cu 2+ ) x 0 … initial c (Cu 2+ ) x eq … equilibrium c (Cu 2+ ) y 0 … initial c (binding sites) b = k ads / k des 

10 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA solid humic acids: adsorption experimental data fitting pH =4.5

11 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA how to explain ? binding of Cu 2+ ions by carboxylic and phenolic groups liberation of H + ions summary (reversible) reaction: Cu 2+ + H 2 R CuR + 2H + low initial pH-value = backward reaction adsorption on „other“ binding site

12 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA how to explain ? comparison of spectrometry and potentiometry UV/VIS potentiometry

13 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA interaction in humic sol classic theory increase of acidity and conductivity as long as the studied system is not in equilibrium Cu 2+ + H 2 R CuR + 2H + Cu HR CuR + 2H +

14 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA interaction in humic sol experimental data minimum on pH curve temporal liberation followed by further consumption analogy to consecutive reactions complex mechanism

15 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA how to explain ? Cu 2+ + HR CuR + + H + 2CuR + CuR 2 + Cu 2+ Cu 2+ + H 2 O Cu(OH) 2 + 2H + Cu 2+ ions hydrolysis „simple“ complex mechanism

16 Humic Substances Seminar VII March 19-21, 2003 Northeastern University Boston, MA, USA interaction in humic sol comparison of classic and complex mechanism

17 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA comparison solid-sol interaction rate: sol >> 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

18 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA diffusion in humic gel one-dimensional diffusion T, p = const.; D  D (c) Fick law total flux into gel concentration profile in gel

19 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA diffusion from constant source initial and boundary conditions t = 0 x  0; L  c 1 = 0 t  0 x = 0c 1 = c 1,s = const. t  0 x = L / 2  c 1 /  x = 0 total flux: calculation of diffusion coefficient

20 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA diffusion from constant source 1.43   D pub [m 2 /s] D num [m 2 /s] fitting of experimental data

21 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA diffusion from time-variable source initial and boundary conditions concentration profile t = 0 x   0; L  c 1 = 0 t = 0x Lc 2 = c 2,0 t  0 x = 0 D 1  c 1 /  x = D 2  c 2 /  x t  0 x = L / 2  c 2 /  x = 0 t  t   x = 0  = c 1 / c 2

22 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA diffusion from time-variable source experimental data

23 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA diffusion with chemical reaction 1 st order reaction: A  products initial and boundary conditions Fick law modification: t = 0 x  0; L  c 1 = 0 t  0 x = 0c 1 = c 1,0 exp -kt t  0 x = L / 2  c 1 /  x = 0

24 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA diffusion with chemical reaction assumption of local equilibrium connecting with Fick law modified Fick law resultant equation

25 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA diffusion with chemical reaction comparison theory & experimental data imobilization of Cu 2+ ions rate transport in gel lower, even under influence of reaction simple & effective model D pub (no reaction) D num (reaction Cu 2+ + HA)

26 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA comparison of the three systems sol gel solid HA interaction rate sol > gel + solution >> diffusion in gel > solid HA binding capacity lowest in solid state

27 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA conclusions complex interaction mechanism HA-metal in all systems non-ideal kinetics dynamic in diluted, mobile systems strongly diffusion-effected interaction with solid HA

28 Humic Substances Seminar VII March , Northeastern University Boston, MA, USA thank Grant Agency of Czech Republic for financial support (project No D036) You for your attention