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Pb2+–Calcite Interactions under Far-from-Equilibrium Conditions: Formation of Micropyramids and Pseudomorphic Growth of Cerussite

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posted on 04.01.2018 by Ke Yuan, Vincent De Andrade, Zhange Feng, Neil C. Sturchio, Sang Soo Lee, Paul Fenter
The presence of impurity ions is known to significantly influence mineral surface morphology during crystal growth from aqueous solution, but knowledge on impurity ion–mineral interactions during dissolution under far-from-equilibrium conditions remains limited. Here we show that calcite (CaCO3) exhibits a rich array of dissolution features in acidic Pb-bearing solutions. During the initial stage, calcite exhibits nonclassical surface features characterized as micropyramids that developed spontaneously. Subsequent pseudomorphic growth of cerussite (PbCO3) was observed, where nucleation occurred entirely within a pore space created by dissolution at the calcite/substrate interface. Uneven growth rates yielded a cerussite shell made of lath- or dendritic-shaped crystals. The cerussite phase was separated from the calcite by pores of less than 200 nm under transmission X-ray microscopy, consistent with the interface-coupled dissolution–precipitation mechanism. These results show that impurity metal ions exert significant control over the microscale dissolution features found on mineral surfaces and provide new insights into interpreting and designing microstructures observed in natural and synthetic carbonate minerals by dissolution. In addition, heterogeneous microenvironments created in transport limited reactions in pore spaces may lead to unusual growth forms during crystal nucleation and precipitation.