SEM images showing the crystal morphology of the sorbents
precipitated out with Na2CO3 are given in Fig. 3. In all samples
spherical structures, which may be assigned to vaterite or
amorphous calcium carbonate, were present. Only in CaAl-ac-
Na2CO3-pH9.7 some rhombohedral calcite crystals are shown.
However, XRD measurements showed that for CaAl-ac-Na2CO3-
pH9.7 calcium carbonate is only present as calcite. It has been
reported that, in the presence of a second species during precipitation,
calcite can form spherules in addition to its “conventional”
rhombohedral morphology