Colloid Stability of Clays Using Photon Correlation Spectroscopy

Abstract

Abstract--Photon correlation spectroscopy (PCS), a dynamic light-scattering technique for particle size measurement, was used to determine the coagulation rates of aqueous dispersions of relatively monodisperse South Carolina Peerless kaolinite, Silver Hill, Montana, illite, Wyoming montmorillonite, and Florida palygorskite. This technique allows quantitative measurement of the rate of coagulation for clay particles where the traditional turbidity method gives only a qualitative measure. The critical coagulation concentrations for KC1 at pH = 10.0 were: 0.199 M for kaolinite, 0.202 M for illite, 0.290 M for montmorillonite, and 0.034 M for palygorskite. The effective Hamaker constants, calculated using DerjaguinLandau-Verwey-Overbeek theory, were: 3.1 • 10 -20 J for kaolinite, 2.5 x 10 -2o J for illite, 2.2 x 10 -20 J for montmorillonite, and i.63 x 10 -19 J for palygorskite. Stern potentials at the critical coagulation concentration at pH 10.0 were: -42.7 mV for kaolinite, -40.7 mV for illite, -21.2 mV for montmorillonite, and -66.9 mV for palygorskite.

Hysteresis in the Binary Exchange of Cations on 2:1 Clay Minerals: A Critical Review

“…The existence of such a relationship would account for the effect of the total normality of the solution on the hysteresis associated with cation exchange reactions, observed for example by Van Bladel and Laudelout (1967). Indeed, the experimental results obtained by Fitzsimmons et al (1970) and Greene et al (1978) via optical density measurements and by Novich and Ring (1984) using photon correlation spectroscopy indicate that the average number of clay platelets per quasi-crystal increases significantly with the total electrolyte content of the solution in which the clay is suspended. The fact that air drying of smectite suspensions causes an increase in the average size of quasi-crystals (Shainberg and Otoh, 1968;Blackmore and Miller, 1961), in conjunction with the observations of hysteresis made by Tabikh et al (1960), lends credence to Van Bladel and Laudelout's (1967) hypothesis.…”

“…Similar results were obtained by Frenkel and Shainberg (1981) using a stopped flow spectrophotometer and mixtures of Na-saturated and, respectively, Ca-, Mg-, Al-, Fe-, and Al-saturated Wyoming bentonite. These results are however sharply contradicted by the observations made by Greene et al (1973) and, more recently, by Novich and Ring (1984). Greene et al (1973) used light scattering techniques and monitored the development of flow birefringence to follow the rearrangement of elementary platelets of Ca-saturated Wyoming bentonite into quasi-crystals.…”

“…They present data for illite indicating that the rate of quasi-crystal or domain formation remained constant over a 20 min period after the beginning of the experiment. Both Green et al's (1973) and Novich and Ring's (1984) data refer to the formation of quasi-crystals, while Shainberg and Kaiserman's (1969) evidence relates to both formation and breakdown processes. Undoubtedly, further research is needed in this area.…”

“…At the highest shaking rate, the optical density of the clay suspensions, directly related to the size of the quasicrystals, was still steadily increasing four weeks after the beginning of the experiments. Novich and Ring (1984), on the other hand, used photon correlation spectroscopy to monitor the coagulation of suspensions of a number of clay minerals. They present data for illite indicating that the rate of quasi-crystal or domain formation remained constant over a 20 min period after the beginning of the experiment.…”

On the Applicability of DLVO Theory to the Prediction of Clay Colloids Stability

“…The coagulation kinetics was studied by means of the timeresolved dynamic light scattering technique (6), which was recently demonstrated as being a valuable tool for the study of the coagulation kinetics of clays (7).…”