Sanchez-Pastor, Nuria; Gigler, Alexander M.; Cruz, Juncal A.; Park, Sohyun; Jordan, Guntram; Fernandez-Diaz, Lurdes
Growth of Calcium Carbonate in the Presence of Cr(VI).
In: Crystal Growth and Design, Vol. 11, No. 7: pp. 3081-3089
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The extended use of hexavalent chromium Cr(VI) compounds in industrialprocesses caused a significant increase of the concentration of thishighly toxic heavy metal in natural environments. In order toinvestigate the influence of Cr(VI) in the formation of CaCO3,crystallization experiments were carried out in a double diffusionsystem, using silica hydrogel with different Cr(VI) contents as thegrowth medium. Crystalline products were examined by scanning electronmicroscopy, Raman spectroscopy, electron microprobe analysis, and singlecrystal X-ray diffraction. Increasing Cr(VI) concentration causedinhibition of the nucleation and growth of calcite and promoted theformation of the metastable polymorphs aragonite and vaterite. Thiseffect correlated with a decrease of crystal size. Furthermore, thehabit of calcite crystals changed with increasing Cr(VI) concentrationsfrom 51046 to forms increasingly elongated parallel to the c-axis.Raman spectroscopy, single crystal X-ray diffraction (XRD), and electronmicroprobe analysis (EMPA) gave strong indications of an isomorphicanion substitution of trigonal planar carbonate by the tetrahedralchromate within the calcite lattice. The apparent partitioningcoefficients of Cr(VI) into calcite determined in this work suggest thatthe fate of this pollutant in natural environments can be significantlyinfluenced by CaCO3 precipitation processes.