Effect of pH and Type of Stirring on the Spontaneous Precipitation of CaCO3 at Identical Initial Supersaturation, Ionic Strength and a(Ca2+)/a(CO32−) Ratio

Abstract

CaCO3 precipitation is physical-chemical basis of biomineral formation of hard tissue (shells, skeletons) in marine calcifying organisms (=biomineralization). Processes controlling biomineralization are still not fully clarified, so the study of influence of pH on basic processes of CaCO3 precipitation should contribute to better understanding of biomineralization under climate change. This paper reports on the effect of initial pH (pH0) and type of stirring (mechanical and magnetical) on spontaneous precipitation and phase composition, size and morphology of spontaneously precipitated CaCO3 formed at the identical initial supersaturation, ionic strength and a(Ca2+)/a(CO32−) ratio. The initial pH varied in a range 8.50 ≤ pH0 ≤ 10.50 and included values relevant for mimicking the conditions related to biomineralization in marine organisms. In all systems two CaCO3 polymorphs were found: calcite and/or vaterite. The increase of pH0 favoured the formation of rhombohedral calcite no matter the type of stirring. This was exclusively influenced by the systems’ pH0 (other relevant initial parameters were identical). Furthermore, increase of pH0 caused change of vaterite morphology from cauliflower-like spheroids to regular spherulites. The mechanically stirred systems produced larger calcite and vaterite particles and higher content of calcite.

Calcium carbonate: controlled synthesis, surface functionalization, and nanostructured materials

“…88,120–122 To this aim, Trofimov et al 95 suggested that an increase in pH from 7 to 11 may lead to the precipitation of vaterite, which was explained by the observations of alterable supersaturation and increased CO 3 2− content, but that the addition of negatively-charged inorganic or organic substances appeared to have the same effect. Moreover, Džakula et al 122 showed that in systems in which the supersaturation, ionic strength, ratio of the activity of the constituent ions ( a (Ca 2+ )/ a (CO 3 2− )), and the type of stirring were identical that the calcite content increased with an increase in the pH from 8.5 to 10.5, while in the same systems that were magnetically stirred with the pH controlled at 8.5 and 9.0, the precipitated product was almost entirely vaterite. The morphology of the resultant vaterite was observed to continuously change with increasing pH.…”

Inducing Inorganic Carbon Accrual in Subsoil through Biochar Application on Calcareous Topsoil

“…44 The ratio of bicarbonate/carbonate can decrease as the soil pH becomes alkaline, which can cause higher nucleation rates and faster precipitation of CaCO 3 crystals with smaller size. 44,45 If there are sufficient CO 2 , CO 3 2−…”

Green Approach in Synthesis of Bio-Inspired Materials

“…Kontrec et al [1] in their paper indicate a significant contribution of initial pH to the overall effect of all parameters relevant to precipitation processes and biomineralization. This paper reports on the influence of initial pH and type of stirring on the kinetics, phase composition, size, and morphology of spontaneously precipitated calcium carbonate (CaCO 3 ).…”