Ff. Peng et Pk. Di, EFFECT OF MULTIVALENT SALTS CALCIUM AND ALUMINUM ON THE FLOCCULATION OF KAOLIN SUSPENSION WITH ANIONIC POLYACRYLAMIDE, Journal of colloid and interface science, 164(1), 1994, pp. 229-237
The effects of calcium and aluminum ions on the interaction behavior o
f anionic polyacrylamide (anionic PAM or HPAM) and kaolin are importan
t in determining the efficient flocculation of kaolin. While kaolin su
rfaces are negatively charged in media such as water, they exhibit the
positive surface charge characteristic at pH below 3.2 in the solutio
n of calcium cation, and at pH below 9.2 in the solution of aluminum c
ation. The experimental results show that both calcium and aluminum io
ns suppress the kaolin flocculation process. The results are analyzed
and explained by molecular orbital theory, solution chemistry, infrare
d spectra, and electronic probe examination of kaolin treated with and
without anionic PAM. Analysis results indicate that the specific adso
rption of Ca2+, Al3+ and their hydroxo complexes on anionic PAM causes
the loss of anionic character in the low pH range and leads to a low
flocculation efficiency. In the high pH range, the poor kaolin floccul
ation can be attributed to precipitation of calcium and aluminum hydro
xides on active functional groups, which inhibits the hydrogen bonding
between anionic PAM and kaolin surfaces. At neutral pH values, the tr
ivalent aluminum ion has more significant adverse effect on the kaolin
flocculation than the divalent calcium ion. (C) 1994 Academic Press,
Inc.