Diffusion studies in humic gels Marek Burian Martina Klučáková Miloslav Pekař Institute of Physical and Applied Chemistry Faculty of Chemistry Brno University of Technology Purkyňova Brno Czech Republic

why study diffusion of metal ions in humic gels? àHA form very easily complexes with ions of transition metals àrate of interaction in sol >> rate of interaction in solid àstrongly diffusion-effected interaction with solid HA àdiffusion effect in heterogenous system

model system for diffusion study = humic gel àexperimentally more tractable àsimple suppression of convective and thermal mixing àclose to water environment àrelation to real (natural) systems

non-stationary diffusion Fick law: one-dimensional problem; D  D (c 1 )

diffusion of Co 2+ ions into humic gels (experimental arrangement)

diffusion from constant source t = 0 x  0; L  c 1 = 0 t  0t  0t  0t  0 x = 0 c 1 = const. t  0 x = L / 2  c 1 /  x = 0

diffusion from constant source (supersaturated solution) D num, m 2 /s D pub, m 2 /s 7.98   10 -9

diffusion from time-variable source t = 0 x   0; L  c 1 = 0 t = 0 x L c 2 = c 2,0 t  0t  0t  0t  0 x = 0 D 1  c 1 /  x = D 2  c 2 /  x t  0t  0t  0t  0 x = L / 2  c 2 /  x = 0 t  t  t  t   x = 0  = c 1 / c 2

diffusion from time-variable source (decrease of solution concentration)

diffusion with chemical reaction first order reaction: A  products t = 0 x  0; L  c 1 = 0 t  0t  0t  0t  0 x = 0 c 1 = c 1,0 exp -kt t  0t  0t  0t  0 x = L / 2  c 1 /  x = 0

interaction Co 2+ with humic gel summary reaction: Co 2+ + H 2 R  CoR + 2H +

diffusion with chemical reaction

conclusions àsimple but effective method àeffect of chemical reaction! ànumerical analysis inevitable future directions àother elements àdiffusion from saturated gel