A Caltech Library Service

Effects of Surface Chemistry on Kinetics of Coagulation of Submicron Iron Oxide Particles (α-Fe₂O₃) in Water


Liang, Liyuan (1988) Effects of Surface Chemistry on Kinetics of Coagulation of Submicron Iron Oxide Particles (α-Fe₂O₃) in Water. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/4XGW-4G55.


Particles in the colloidal size range, i.e. smaller than 10⁻⁶ meter, are of interest in environmental science and many other fields of science and engineering. Since aqueous oxide particles have high specific surface areas they adsorb ions and molecules from water, and may remain stable in the aqueous phase with respect to coagulation. Submicron particles collide as a result of their thermal energy, and the effective collision rate is slowed by electric repulsion forces. A key to understanding particle stability and coagulation is the role of simple chemical changes in the water altering the electrostatic repulsion forces between particles.

Experiments using hematite particles (α-Fe₂O₃, 70nm in diameter) reveal important features of coagulation dynamics. Three experimental techniques are employed: (1) Light scattering measurements to yield quantitative information on the rate of the initial coagulation process; (2) electrokinetic measurements to provide information about the sign and magnitude of the electrical charge on the aqueous oxide particles; (3) acid-base titration and equilibrium adsorption to obtain the intrinsic equilibrium constants for surface species.

The acid-base titration data indicate that the pHzpc of the synthesized hematite colloid is 8.5. This is also supported by the electrophoretic mobility measurements. In the presence of non-specific adsorbing ions (such as Na⁺ and Ca²⁺, etc.), the coagulation of a hematite colloid is achieved mainly by the compression of diffuse layer and Schulze-Hardy Rule is exhibited for non-specific electrolytes. Specifically adsorbed counter ions (such as phosphate) are able to reduce the surface charge of aqueous oxide particles, and the critical coagulation concentrations are dependent on the value of the pH, and are much less than those predicted by DLVO theory. In inorganic media, we found that the order of the effectiveness in causing hematite particles to coagulate is:

phosphate > sulfate > chloride at pH < pHzpc


magnesium > calcium > sodium~potassium at pH < pHzpc

The adsorption study reveals that phthalate ions specifically adsorb on hematite particles. The process is most likely due to carboxylic group bonding to the surface. The hematite coagulation rates in the presence of poly-aspartic acid (PAA) demonstrate that the polyelectrolyte is very effective in causing the colloid to coagulate. When the PAA concentration is increased beyond the critical coagulation concentration, the particles are stabilized; this is attributed to the reversal of surface potential as a result of the adsorption of PAA. Similar features are observed in the initial coagulation rates when naturally occurring organics (fulvic and humic acid from Suwannee River) are used.

The adsorption of lauric acid on hematite was investigated and the results interpreted in terms of the energy contributed by the specific chemical, electrostatic and hydrophobic interactions. The initial coagulation rates of hematite particles and the electrophoretic mobilities with respect to fatty acid concentration both show systematic variations as a function of the numbers of carbons in the acid. Hydrophobic interaction may account for these observations since the specific chemical energy appears to be the same for all the fatty acids studied, and the electrostatic contribution is also similar at the same extent of adsorption.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Iron oxide, hematite, colloid, coagulation, kinetics, humic acid, surface chemistry
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Environmental Science and Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Morgan, James J.
Thesis Committee:
  • Morgan, James J. (chair)
  • Brooks, Norman H.
  • Hoffmann, Michael R.
  • Flagan, Richard C.
  • Rossman, George Robert
Defense Date:20 May 1988
Funding AgencyGrant Number
Jessie Smith Noyes FoundationUNSPECIFIED
Mellon FoundationUNSPECIFIED
Record Number:CaltechETD:etd-11072007-110812
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4448
Deposited By: Imported from ETD-db
Deposited On:27 Nov 2007
Last Modified:01 Feb 2020 00:31

Thesis Files

PDF - Final Version
See Usage Policy.


Repository Staff Only: item control page