The titration of clay minerals

Temperature effect on the acid–base behaviour of Na-montmorillonite

“…In addition, the temperature does not significantly impact the net consumption below pH 8, so that a constant surface charge is reached in this pH region. This result indicates that acid-base surface site reactions in the studied pH domain (4)(5)(6)(7)(8) are not significantly dependant on the temperature which can be interpreted either by very low enthalpy and entropy values or by an absence of proton affinity constants for the surface site reactions in this pH region. The latter interpretation agrees with our previous studies that suggested this proton affinity constant below 5 [19,20].…”

“…Roughly speaking, the initial bentonite suspension was first centrifuged to recover the smallest size fraction (<2 μm), which was then decarbonated in 1 mol/L sodium acetate/acetic acid solution (pH 5, 80 • C, 2 h). The Na-montmorillonite particles were then sodium-saturated by exchange in 1 mol/L NaClO 4 water. The resulting solid was stored in ultra pure water as a stock suspension (38.2 g/L) to prevent experimental artifact due to the drying procedure [19].…”

“…Therefore, accurate knowledge of the temperature dependence of the surface properties of clays is fundamental in order to predict the long-term stability and performance of such complex barriers. In particular, the acid-base characteristics of the broken-bond surface sites at the edges of the clay platelets remain key parameters in order to understand complexation processes [2][3][4].…”

pH-dependent surface charging and points of zero charge II. Update

“…A recent version of the MUSIC model, originally introduced for metal (hydr)oxides, was recently applied to interpret the surface charging of montmorillonite [13]. The surface area of montmorillonite is dominated by basal and interlayer contributions, and the contribution of the edge is about 1%.…”

Acid–base properties of bentonite rocks with different origins

“…Consequently, the acid/base properties of the edge sites of bentonite can be studied. Titrations were made in the range pH 4-8, so the disturbing processes (e.g., dissolution, precipitation, ion pair formation) can be minimized [29,30].…”