Heterogeneous growth of cadmium and cobalt carbonate phases at the 101¯4 calcite surface

Abstract

The ability of surface precipitates to form heteroepitaxially is an important factor that controls the extent of heterogeneous growth. In this work, the growth of cadmium and cobalt carbonate phases on 1014 calcite surfaces is compared for a range of initial saturation states with respect to otavite (CdCO 3 ) and sphaerocobaltite (CoCO 3 ), two isostructural metal carbonates that exhibit different lattice misfits with respect to calcite (−4% and −15%, respectively, based on 1014 surface areas). Calcite single crystals were reacted in static conditions for 16 h with CdCl 2 and CoCl 2 aqueous solutions with initial concentrations 0.3 ≤ [Cd 2+ ] 0 ≤ 100 μM and 25 ≤ [Co 2+ ] 0 ≤ 200 μM. The reacted crystals were imaged in situ with atomic force microscopy (AFM) and analyzed ex situ with X-ray photoelectron spectroscopy (XPS). AFM images of Cd-reacted crystals showed the formation of large islands elongated along the 421 h i direction, clear evidence of heteroepitaxial growth, whereas surface precipitates on Co-reacted crystals were small round islands. Deformation of calcite etch pits in both cases indicated the incorporation of Cd and Co at step edges. XPS analysis pointed to the formation of a Cd-rich (Ca,Cd)CO 3 solid solution coating atop the calcite substrate. In contrast, XPS measurements of the Co-reacted crystals provided evidence for the formation of a mixed hydroxy-carbonate cobalt phase despite supersaturation with respect to CoCO 3 . The combined AFM and XPS results suggest that the lattice misfit between CoCO 3 and CaCO 3 is too large to allow for heteroepitaxial growth of a pure cobalt carbonate phase on calcite surfaces in aqueous solutions and at ambient conditions. The use of the satellite structure of the Co 2p 3/2 photoelectron line as a tool for determining the nature of cobalt surface precipitates is also discussed.

Epitaxial Growth and Frictional Response of Otavite and Spherocobaltite on Dolomite (10.4) Surfaces

“…The misfits between the overgrowths and the substrates can also explain the different formation behavior observed in the otavite/dolomite and otavite/calcite systems and in the spherocobaltite/dolomite and spherocobaltite/calcite systems. As explained above, when otavite grows on calcite, it shows a preferential orientation along the [42.1] direction, 13,16 whereas on dolomite, otavite does not have any preferential orientation. Growing on calcite, the otavite structure has to expand to accommodate the deformation, leading to misfits of 1.42% and 3.05% for the [01.0] and [42.1] directions, respectively.…”

“…Our observations of spherocobaltite growing on dolomite surfaces contrast with the previously reported formation of an amorphous Co-bearing hydroxy-carbonate phase on calcite (10.4) surfaces. 16 The formation of different phases on dolomite and calcite (10.4) surfaces from Co-bearing solutions can be due to both the different supersaturations with respect to the spherocobaltite in the solutions and the different substrates used. As in the case of otavite, spherocobaltite lattice parameters were estimated on the high-resolution images ( Figures 3C and S5, Supporting Information).…”

Investigation of interaction of Co, Mn and Fe atoms with the calcite by X-ray photoelectron spectroscopy

“…Показано, в частности, что двухвалентные катионы металлов в одном случае образуют поверхностные гидратированные комплексы, в другом -проникают в решетку кальцита с образованием поверхностных слоев карбонатов. В недавних работах (Xu et al, 2017;Xu et al, 2015) показано, например, что при адсорбции Mn 2+ , Cd 2+ из водного раствора на поверхности CaCO 3 (1014) образуется ИССЛЕДОВАНИЕ ВЗАИМОДЕЙСТВИЯ АТОМОВ Co, Mn, Fe С КАЛЬЦИТОМ МЕТОДОМ РЕНТГЕНОВСКОЙ ФОТОЭЛЕКТРОННОЙ СПЕКТРОСКОПИИ структурно согласованный с подложкой упорядоченный тонкий слой карбонатов металлов, несмотря на несогласованность постоянных решеток подложки и адсорбата. Формирование таких упорядоченных структур происходит в результате релаксации напряжений при росте пленки из раствора и образовании твердых растворов на границе раздела, имеющих состав, отличающийся от термодинамически стабильных фаз соответствующих массивных материалов.…”

“…Особенность для кобальта заключается в том, что рост поверхностных соединений не происходит вдоль какого-либо кристаллографического направления. Это, по мнению авторов (Xu et al, 2015), свидетельствует о том, что твердый раствор (Са,Со)СО 3 на поверхности не образуется. Вместо этого происходит образование смешанной гидрокси-карбонатной кобальтовой фазы Co 2 (OH) 2 CO 3 на кальцитовом субстрате.…”

Dissolution and Sorption Processes on the Surface of Calcite in the Presence of High Co2+ Concentration

“…Recently, González-López et al [17] reported the thermochemistry of (Ca,Co)CO 3 solid solutions from density functional theory simulations and concluded that many Ca 1−x Co x CO 3 mineral solid solutions (with observed compositions of up to x = 0.027, and above x = 0.93) are metastable with respect to phase separation. Finally, Xu et al [18] studied the interaction of calcite with solutions with a very low Co 2+ concentration ([Co aq ] initial = 1-10 ppm) using AFM and XPS. They suggested that that the lattice misfit between CoCO 3 and CaCO 3 is too large to allow heteroepitaxial growth of a pure cobalt carbonate phase in ambient conditions.…”