Bromate incorporation in calcite and aragonite

The presence of bromine as a trace-element in calcium carbonate speleothems constitutes a useful proxy of past volcanic activity, thus helping to provide input parameters for climate model simulations and risk assessment. However, the chemical nature of bromine-containing impurities in the calcium carbonate phases forming speleothems is not understood, which limits interpretation of experimental measurements on speleothems. We present here a computer simulation study, based on quantum mechanical calculations, of the incorporation of bromine as BrO3- oxyanions in CaCO3 polymorphs calcite and aragonite. We discuss how the relative distribution of bromate anions and charge-compensating alkali-metal cations is determined by the interplay between an impurity binding effect (which is stronger for aragonite than for calcite, and changes in the order Li