Apophyllite (001) surface alteration in aqueous solutions studied by HAFM

Basal plane reactivity of phyllosilicates studied in situ by hydrothermal atomic force microscopy (HAFM)

“…Natural fluoroapophyllite (Poona, India; for microprobe analysis see Aldushin et al, 2004a) and phlogopite Fig. 1.…”

“…At pH 5.6 and temperatures above 110°C, Aldushin et al (2004a) reported dissolution via step retreat i.e., detachment of material at the steps of the silicate layers. In this study, therefore, we focus on moderate to neutral pH conditions at temperatures below 110°C.…”

“…2a). In such a way, the reaction can proceed layer by layer into the bulk crystal (Aldushin et al, 2004a). Investigations of the reaction mechanism (Aldushin et al, 2004b) showed that the protonation and ion release within an interlayer takes place in two different sequences of individual transformations.…”

Kinematics of apophyllite leaching—A terrace–ledge–kink process within phyllosilicate interlayers

“…In previous studies [6,15,16], the mechanisms and kinetics of the alteration of apophyllite in aqueous solutions have been investigated in wide ranges of pH (1.5-10) and temperature (20-130 1C). At acidic conditions (pH 1.5-3), hydronium ions replace the interlayer ions and form silanol groups at the nonbridging tetrahedral apexes.…”

Dissolution of anisotropic colloidal mineral particles: Evidence for basal surface reactivity of nontronite

“…Positive correlations between dissolution rate of smectite and nonequivalent cation substitution indicate that proton attack occurs at the sites of isomorphic substitution [14,16,17] and that basal faces actively participate in the dissolution process. More recently, the dissolution of basal surfaces of apophyllite, phlogopite, and chlorite has been documented by microscopic observation of the formation of shallow etch pits [18][19][20]. Formation of etch pits was attributed to surface defects or compositional inhomogeneities [18].…”