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Nano precipitates formed during the dissolution of calcite incorporated with Cu and Mn
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Calcite, because of its strong chemical activity, is often doped with impurity ions that will affect the dissolution behavior of calcite-water interface. Solid solutions of (Ca, Cu)CO3 and (Ca, Mn)CO3 were synthesized by co-precipitation to study its dissolution in acidic solution (pH=5) at 25℃. This experiment aims to study the dissolution pattern of impurity ions in calcite, and reveals the effect of impurity ions in calcite on its dissolution process. ICP-OES results shown that the aqueous concentrations of Cu2+ and Mn2+ increased first and then decreased with the extension of dissolution time. It indicated that some of the aqueous Cu2+ and Mn2+ had been removed by re-adsorption or precipitation from the solution in the secondary stage. SEM and TEM observation revealed that new precipitates with needle or prism morphology formed on the surface of calcite. The size of the precipitates were 1~2μm in length and 10~20 nm in width for (Ca, Mn)CO3 and 50 ~ 200 nm for (Ca, Cu)CO3. The EDS data shown that the new formed precipitates were rich in Mn and Cu, respectively, comparing to their parents minerals. HRTEM the new formed Mn-rich precipitate was close to MnCO3. It suggested that the dissolution and precipitates of carbonates might be changed due to the presence of impurity ions. Our results provided new insights on the behaviour of carbonate minerals and heavy metals such as Mn and Cu in the environment.

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Biomineraization in Sarcocornia pruinosa growing in the tidal area of Río Tinto, an extreme acidic environment.

We present the localization of Na, Ca, Mg and Fe biominerals in Sarcocornia pruinosa (Chenopodiacaeae), a halophyte species that grow in the estuarine area of the Río Tinto basin. The estuarine soils of the Tinto basin are characterized by an extreme low pH, a slightly high salinity and high concentration of S and Fe, together with Na, Mg, P, Cu and Zn salts. It is exposed to the daily tides, with the correspondent increase in the pH and the concentrations of Na and Mg.

The aim of this work was to characterize the elemental composition and identify the biominerals and their distribution in different organs and tissues of S. pruinosa.

Analytical techniques (ICP-MS), X-Ray diffraction and microscopy such as OM (optical microscopy) with histochemical staining (Prussian blue stain), SEM and TEM (scanning and transmission electronic microscopy) coupled with EDX (energy dispersive X-ray) have been used to analyze the plant tissues, for mineral characterization.

A high accumulation of salts has been observed in all the analyzed parts, highlighting the high content of Na and K between the major elements, followed by Ca, Mg, together with a high concentration of Fe, Cu, Zn and Mn.

We documented the occurrence of halite, silvite, whewellite, weddellite, glushinkite and Fe oxides as biominerals in S. pruinosa. We highlight the scarcity of data related to the presence of these biominerals in plants. Our data suggest the importance of plants in the biogeochemical cycles in the estuarine areas.

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