Electrophoretic and potentiometric signatures of multistage CaCO3 nucleation

Abstract

Highlights:• time-dependent electrokinetic potential shows signatures of multistage nucleation process • changes in z-potential, solution pH, saturation indexes, and particle morphology are consistent with vaterite to calcite transformation via dissolution of the former and recrystallization of the latter starting a few minutes after reagents are mixed • z-potential measurements can be used to monitor polymorphic transformations of carbonate phases in-situ

Unseeded, spontaneous nucleation of spherulitic magnesium calcite

“…SEM images of carbonate precipitates were taken three hours after the reagents had been mixed using FEI Nova NanoSEM 450 with an accelerating voltage of 2 kV. A more detailed discussion about the experimental protocol can be found elsewhere [48]. The crystal structure of carbonate precipitates was characterized by Bruker D8 Advance X-ray diffractometer equipped with Cu K (l=0.154 nm) lamp and Lynx Eye Array detector.…”

“…In Fig. 1 we show the time-evolution of electrokinetic potential (-potential) during spontaneous unseeded precipitation experiment from a slightly supersaturated solution (SI calcite ~2 [48]). We observe a rapid change in pH from 5 to 11 after reagents were mixed, followed by a slow decrease to around 10.…”

“…Besides, the (time) curve appears to be shifted towards lower absolute values (i.e., less negative) if the Mg 2+ ions are present. Because the ionic strength of the solution is kept constant by using the background electrolyte, this reduction in -potential must be related to the evolution of particle size [70] and morphology [48] along the precipitation pathway. The absolute value of -potential, which is a measure of suspension-stabilizing repulsive electrical double layer forces, is correlated with polymorph free energy (i.e., |-vaterite < |-aragonite < |-calcite) [30,31,48].…”

“…Prus et al [48] showed that the transformation of vaterite to calcite in an unseeded spontaneous precipitation experiment could be studied by monitoring solution composition and electrokinetic potential [48]. Here, by using a similar experimental approach, we try to answer the question of how growth rate and solid composition are changing along the magnesian calcite nucleation, growth, and transformation pathways.…”

Investigations of mechanism of Ca2+ adsorption on silica and alumina based on Ca-ISE monitoring, potentiometric titration, electrokinetic measurements and surface complexation modeling

“…The surface charge σ H was calculated in the way presented by Piasecki et al (2019). Next, the samples were subjected to Ca 2+ uptake experiments in which the concentration of free calcium ions was checked every 0.5 pH unit by Ca-ISE used also in our previous study (Prus et al 2019) as well as applying the spectrophotometric method (Kendrick et al 1977) as a reference. In a separate experiment the dependence of the electrokinetic potential (ζ) of the dispersions with and without 1 mM Ca 2+ in 0.01 M KCl as a function of pH at 25 °C was determined using the Malvern Zetasizer Nano ZS equipped with the MPT-2 autotitrator and a high concentration zeta cell.…”