The growth of CaCO3 polymorphs in the presence of As(V): The stabilization of vaterite phase.

Abstract

Calcium carbonate (CaCO3) polymorphs are some of the most abundant minerals in natural environments on Earth’s surface. They are normally linked to fields including biomineralization, global CO2 exchange or pollutants remediation due to the strong surface interaction with heavy metals in the environment. The aim of this work is to study the crystallization of CaCO3 through precipitation experiments from aqueous solutions in the presence of different amounts of As(V), thus evaluating the capacity of the precipitating phases to remove As from solutions. Surprisingly, the results confirmed that the uptake mechanism operates relatively well, decreasing the initial concentration of arsenic in all the experiments conducted. On the other hand, the presence of this element controls the crystallization of calcite by inhibiting it, and stabilizing the less stable phase, vaterite, which under As-free conditions acts as a transient intermediate phase during the crystallisation process of amorphous calcium carbonate to the most stable polymorph, calcite. Different characterization techniques, including X-ray diffraction and ICP spectroscopy, were used to corroborate that the formation and stabilization of vaterite is linked to the presence of that pollutant. This phenomenon should be taken into account since natural CO2 sink, in the form of carbonate rocks, must be affected by the presence of this element, even at low concentrations, thus being the arsenic element even more poisoning than we thought until now.