Study of ground and unground leached vermiculite

• Published in: Applied clay science Vol. 44; no. 1; pp. 178 - 184
• Main Authors: Maqueda, Celia, Perez-Rodriguez, José Luís, Šubrt, Jan, Murafa, Natalia
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.04.2009; Elsevier
• Subjects: Acid leaching; Akaganeite; Amorphous silica; Earth sciences; Earth, ocean, space; Electron microscopy; Exact sciences and technology; Grinding; Mineralogy; Porosity; Silicates; Vermiculite; Iberian Peninsula; Southern Europe; Andalusia Spain; Huelva Spain; Europe; Spain; Amorphous silica; Akaganeite; Vermiculite; Acid leaching; Porosity; Electron microscopy; Grinding; chain silicates; oxides; silica; grinding; specific surface; acids; solution; pyroxene; sheet silicates; silicates; electron microscopy; transmission electron microscopy; clinopyroxene; particles; X-ray diffraction analysis; high resolution; vermiculite; morphology; iron oxides; porosity; concentration; leaching; materials; akaganeite; clay minerals; iron
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2009.01.019

Grinding of clays modifies their surfaces and can significantly affect their leaching behaviour. The acid reaction of vermiculite from Santa Olalla (Huelva, Spain) with HCl at various concentrations was affected by grinding and acid concentration. The acid leaching of ground vermiculite for 3 min with 1 M HCl solution at 80 °C for 24 h removed MgO and Al 2O 3 almost completely, leaving a residue containing SiO 2 and Fe 2O 3. X-ray diffraction analysis showed the presence of akaganeite (β-FeOOH) and an amorphous phase (silica). Porosity studies showed a very high specific surface area for ground samples compared with unground vermiculite samples, attributed to the presence of iron in the residue coming from structural iron. High resolution transmission electron microscopy (HRTEM) confirmed the presence of iron oxyhydroxides embedded in the silica material. The particle morphology of the iron oxides corresponded well to akaganeite microcrystals precipitated from solution. The leached vermiculite residue also contained Cl − and a small amount of Ti 4+, which were accumulated into the akaganeite microcrystals.