The heterogeneous catalyst was prepared by calcining eggshell
waste at high temperature. The textural structure of eggshell calcined
at different temperatures can be observed from the scanning
electron micrograph (SEM) images. Natural eggshell had macropores
and a generally irregular crystal structure. The SEM images
indicated that the structure of eggshell changed with calcination
temperature. Below 700 C, the size and shape of particles was
similar to that of natural eggshell. Above 800 C, the size of particles
decreased and the particle shape became more regular. The
change of structure of eggshell may be resulted from the change
of composition.
In order to explain the effect of calcination temperature, we
investigated the calcination process of eggshell with thermal gravity
analysis (TGA) technology. TGA result showed the temperatures,
at which the eggshell precursors decomposed when heated
in a controlled environment. Water and organics was removed
from the precursors below 600 C, whereas carbon dioxide was lost
between 700–800 C.
The thermal pre-treatment resulted in a change in the X-ray diffraction
(XRD) pattern, caused by the removal of CO2 from the
starting material (Fig. 1). The diffraction patterns of the samples
heated at temperatures 700 C displayed diffraction
reflections characteristic of CaO. Samples calcined at 700 C for
2 h contain CaCO3 as the major phase and CaO as a minor phase.