STRUCTURAL AND CHEMICAL ALTERATION OF GLAUCONITE UNDER PROGRESSIVE ACID TREATMENT

Abstract

Boiling glauconite from the El-Gideda area of Egypt in different concentrations of HCl and H2SO4 for different periods led to a modified structure. Treatment resulted in progressive destruction of the structure, leaving X-ray amorphous silica and only relics of the original mineral. The glauconitic material was modified structurally in order to increase its adsorption activity. The glauconite was evaluated in terms of mineralogy, chemistry, morphology, structural modification, octahedral cation leaching rate, surface area and cation exchange capacity using X-ray diffraction, infrared spectroscopy, X-ray fluorescence, scanning electron microscopy and surface area analysis. The ratio of extracted octahedral cations to the total octahedral cations in the untreated glauconite was taken as a measure of octahedral sheet decomposition. A progressive decrease in crystallinity and the formation of X-ray amorphous silica Si-O vibration bands at 1100, 800 and 494 cm−1 accompanied octahedral cation depletion. Acid activation using 2 M and 4 M HCl for 6 h destroyed 30% and 61% of the octahedral sheet, respectively. In contrast, similar treatment using 2.9 and 5.5 M H2SO4 destroyed 48% and 93% of the octahedral sheet, respectively. Depending on the extent of cation depletion, the 4 M HCl product surface areas were as high as 259 m2/g, whereas the surface area of the 5.5 M H2SO4 product was only 63 m2/g. The progressive increase in surface area was due to glauconite morphology alteration. Acid-induced dissolution of Al, Fe, Mg cations from octahedral sheet edges led to a wedge-like splitting of the glauconite crystals, mesopore creation, and greater access to interlayer galleries.