ABSTRACT
In this paper diatomite samples taken from the Leizhou Peninsula have been studied by chemical analysis(24 samples), DTA(23 samples), TG(23 samples), XRD(>100 samples), IR(26 samples), SEM(21 samples), X-ray Energy Spectroscopy (37 samples, >200 photos), EPR (22 samples), and MAS NMR Techniques (13 samples). The study shows that the diatomaceous genera and their organic contents are variable with buried depth, from Melosira to stephanodiscus and then to Cyclotella. Various impurities in the samples, such as quartz, kaolinite and montmorillonite indicate different sedimentary environments. When heated, the diatom would change in shape due to the phase transformation in which amorphous silica crystallized from disordered opal to ordered cristobalite. The temperatures of phase transformation are different for various diatoms due to the presence of different impurities and constituents of diatomaceous genera and species. There are two existing forms of iron in diatomite: Fe3+ in oxide and hydroxide adsorbed on the outer and inner surfaces of diatomite, and Fe3+, which is isomorphously substituted for Al3+ in clay minerals such as montomorillonite. The 29Si MAS NMR spectra of diatomites show several signal with different chemical shifts at −110 to −112, −102, −91 and −107 ppm and intensity. These signals belong to 29Si resonances of siliceous sheel of diatoms, kaolinite and quartz.
