A. Amirbahman et Tm. Olson, DEPOSITION KINETICS OF HUMIC MATTER-COATED HEMATITE IN POROUS-MEDIA IN THE PRESENCE OF CA2+, Colloids and surfaces. A, Physicochemical and engineering aspects, 99(1), 1995, pp. 1-10
Column filtration experiments were conducted to determine the depositi
on kinetics of the humic matter-coated hematite (alpha-Fe2O3) colloids
on quartz grains in the presence of Ca2+. Three well-characterized hu
mic substances were used. Our results indicate that several mechanisms
are responsible for the differences in the attachment efficiencies of
these particles. The relative importance of each mechanism varies dep
ending upon the type of humic matter used. Systems coated with the pea
t humic acid, which is the least acidic, the most hydrophobic and has
the highest molecular size of all the samples used here, had the highe
st stability at approximately [Ca2+] < 0.002 M, despite their lower el
ectrophoretic mobilities. This behavior may be attributed to the great
er electrosteric interactions brought about by the adsorbed humic acid
. At higher Ca2+ concentrations, however, the stability of the peat hu
mic acid-coated systems was drastically reduced owing to the effect of
cation bridging and/or hydrophobic interactions. Our experimental set
up does not allow unequivocal determination of the underlying cause o
f the observed differences between the attachment efficiencies of the
particles coated with the two fulvic acids used here. Such differences
may be controlled by electrostatic, hydrophobic or electrosteric inte
ractions, or a complex combination of these.