Mineralogical and spectroscopic characterization, and potential environmental use of limestone from the Abiod formation, Tunisia

Limestone beds of the Late Cretaceous Abiod formation (Campanian-Maastrichtian system) are fundamentally important for the economic growth of the raw material sector in Tunisia. However, little attention has been paid to the detailed physical and chemical properties of the Abiod limestone. Nine limestone samples collected from the Abiod formation outcropping in the areas of Bizerte, Gafsa and Gabes, Tunisia, as well as their separated clay fractions, were characterized using different techniques, such as XRF, XRD, FTIR and TG/DTA. XRF showed the chemical composition of the limestone in which calcium carbonate was the main constituent, and silica, iron and magnesium were the impurities. XRD also confirmed the presence of small amounts of clay minerals and quartz along with sharp peaks of calcite. FTIR spectra indicated that the limestone was mainly composed of CaCO3 in the form of calcite, as identified by its main characteristic absorption bands. These data were in agreement with XRD and XRF analysis data. The TG/DTA curves of the limestone samples, showing a close similarity to that of pure calcium carbonate, exhibited an endothermic peak between 600 and 760A degrees C, with the maximum near 750A degrees C. Moreover, FTIR spectra of clay fraction samples indicated high silica content in some samples. Especially the samples SD1 and SD2 collected in the northern area showed higher amounts of silica compared with those of AS1, AS2, CHB, ZNC, SND, MKM and GBS collected from southern districts. However, among the latter seven samples, one could recognize two groups based on the clay mineral investigations: (1) limestone with minor amounts of smectite and mixed layer minerals of smectite/illite (AS1 and 2, CHB, ZNC, SND and GBS) and (2) limestone with smectite, kaolinite and apatite (SND and MKM). Differences in these mineralogical and chemical characteristics should be considered when limestone from the Abiod formation is utilized as a medium for heavy metal removal from wastewater.