Chemical Activation of a Kaolinite under Acid and Alkaline Conditions

Abstract

Four metakaolins were prepared by calcination of a natural Spanish kaolin (Navalacruz deposit, Zamora province) at 600, 700, 800, and 900 °C. These four metakaolins, more reactive than the parent kaolin, were submitted to acid and alkaline activations. Acid activation was carried out with 6 M HCl at room temperature and at 90 °C under reflux conditions, with times of treatment of 6 and 24 h. Treatment at room temperature did not produce any alteration in the structure or in the properties of the metakaolins. Treatment under reflux conditions for 6 h led to the removal of most of the octahedral Al 3+ cations, and the formation of an amorphous silica phase, with surface area up to 219 m 2 /g, because of a high development of both the internal and the external surface of the solids. Acid treatment under stronger conditions (reflux, 24 h) also removed the octahedral cations, but provoked an amorphization of the silica obtained (S ≈ 23 m 2 /g). The metakaolin prepared by calcination at 900 °C showed a lower reactivity than those synthesized at the other temperatures considered. The alkaline treatments were carried out with 1 M and 5 M KOH solutions, the treatments with the concentrated solution, both at room temperature and, especially, under reflux, led to the dissolution of the metakaolins and to the formation of well-crystallized K-F zeolite. The solids obtained by acid treatments are promising as adsorbents and catalyst supports, while treatment in alkaline conditions may be a good method for preparing K-F zeolite.

Facile Preparation of Biocomposite from Prawn Shell Derived Chitosan and Kaolinite-Rich Locally Available Clay

“…Kaolinite is the major mineral component of kaolin, which usually contains quartz and mica. It also contains small percentages of feldspar, illite, montmorillonite, ilmenite, anastase, haematite, bauxite, zircon, rutile, kyanite, sillimanite, graphite, attapulgite, and halloysite [15,16]. Bijoypur clay (187 km from Dhaka city, located in Netrokona District of Mymensingh Division) is one of the best quality clay types available in Bangladesh.…”

Gas Phase Oligomerization of Isobutene over Acid Treated Kaolinite Clay Catalyst

“…The well resolved high-intensity lines in the range of 1109 cm -1 (Si-O stretch) and 1040 (Si-O stretch), correspond to the vibrations (Si-O) [19]. The bands at 526 cm -1 (Si-O-Al deformation), 469 cm -1 (Si-O bending) cm -1 are typical of kaolinite clay mineral [15,20,21]. The band at 1629 cm -1 corresponds to the quartz phase.…”

Distribution of Clay Minerals in Light Coal Fractions and the Thermal Reaction Products of These Clay Minerals during Combustion in a Drop Tube Furnace

“…The soluble aluminium fraction of the 1050˝C DTF ash of the WX light coal is less than that of the WX raw coal ash at the same DTF temperature. The acid-solubility of aluminium in the dehydroxylation products of kaolinite is related to the degree of dehydroxylation [26]. The dehydroxylation reactions of the clay minerals in WX light coal should be incomplete at a DTF temperature of 1050˝C.…”

“…Aluminium in coal is basically derived from its clay minerals, which are the most abundant minerals in many coals. When aluminosilicates are treated by acids, the chemical structures of the aluminosilicates determine the solubility of the aluminium [22][23][24][25][26]. Tian et al, analysed coal ash samples prepared at different temperatures in a drop-tube furnace (DTF) system using a chemical separation method with hot concentrated hydrochloric acid (denoted as boiling acid separation).…”