Chemical Activation of Spent Diatomaceous Earth by Alkaline Etching in the Preparation of Mesoporous Adsorbents

This work was to study the activation regeneration of spent diatomaceous earth (SDE) for the preparation of mesoporous silica adsorbents by using alkaline activation method. Under the experimental conditions investigated, it was found that the alkaline activation method by sodium hydroxide under the controlled conditions significantly etched to proceed inwardly to the interior of the existing pore structure in the clay minerals, leaving a framework possessing a large Brunauer−Emmett−Teller surface area (over 100 m2/g) and total pore volume (over 0.3 cm3/g). The results indicated that these samples are type IV with a hysteresis loop. This observation was also in close agreement with the examinations on the scanning electron microscopy, X-ray diffraction, and Fourier transform infrared. Further, the adsorption rate of methylene blue onto the resulting clay adsorbent can be well described with the pseudo-second-order reaction model. The physical properties of the diatomaceous earth and resulting adsorbent were also consistent with the parameters obtained from the fittings of the common isotherms (Langmuir and Freundlich).