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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 2018-01-04, 00:00 authored by Ke Yuan, Vincent De Andrade, Zhange Feng, Neil C. Sturchio, Sang Soo Lee, Paul FenterThe
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.
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calcite exhibits nonclassical surface featuresimpurity metal ionsfar-from-equilibrium conditionsPseudomorphic Growthcrystal growthcrystal nucleationtransmission X-ray microscopyresults showpore spacespore spacePbCO 3microscale dissolution featuresSubsequent pseudomorphic growthFar-from-Equilibrium Conditionscarbonate mineralsdendritic-shaped crystalsdissolution features in acidic Pb-bearing solutionsCaCO 3impurity ionscerussite shellinfluence mineral surface morphologymineral surfaces200 nmUneven growth ratesgrowth formscerussite phase
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