Surface properties and modeling potentiometric titration of aqueous illite suspensions

Abstract

The potentiometric titration behavior of complex illitic clay minerals provided from different origins (two Tunisian illite samples and an American illite sample) was investigated and interpreted according to the surface complexation theory. In the present investigation, the focus is on the surface charge characteristics. The proton surface charge can be calculated by subtracting the supernatant titration curves from those of the illite suspension at ambient temperature with an aerated medium. The points of zero charge (PZC), which were determined using the Gran plot method and the fast titration technique, were in the range of ∼8.5–9.2. Our potentiometric titration curves were modeled using derived parameters of the Gran method. The surface ionization constants were determined by implementing the theory of surface complexation models (SCMs): the NEM, the constant capacitance model (CCM), and the triple layer model (TLM). The pKas values determined from derived parameters of the Gran plot data were in the range of pKa1 = 4.5–5.52 and pKa2 = 9.78–10.4 and are compared to those obtained by SCMs.