Exfoliation of vermiculites with chemical treatment using hydrogen peroxide and thermal treatment using microwaves

This paper presents the investigation about chemical and thermal exfoliation of vermiculites from Santa Olalla (Huelva, Spain), Libby (Montana, USA) and Goias (Brasil). Four experiments were made: 1) Reaction of each sample from Santa Olalla, Libby and Goias with hydrogen peroxide solution of 30% and 50% respectively, at different times for each sample. 2) Irradiation of Libby and Goias samples with microwaves for 20 s.3) Reaction of Goias samples with hydrogen peroxide solutions of 30 and 50 mass%, respectively, into microwave oven for 20 s. 4) Abrupt heating of Libby vermiculite at 1000 degrees C for 1 min in an oven once stabilized (similar to 2 h). The original and treated vermiculite samples were characterized by X-ray diffraction (XRD) and thermogravimetry; their chemical composition was obtained by electron microprobe and their morphology was examined with the scanning electron optical and microscopy. The results of this study, in relation to the treatments with hydrogen peroxide, showed that: 1) The purest samples like those from Santa Olalla suffered minor changes (slight structural disorder) and the exfoliation was lower; while others like Libby, with higher content of iron and interlayer potassium, could suffer major changes with the formation of a new phase through interstratified phases, and the exfoliation grade was higher. 2) The exfoliation speed of the samples increased with the peroxide hydrogen concentration and might be attributed to higher dissolution of dissolved and/or exchanged amounts of cations such as sodium, potassium, magnesium and iron. In relation to the microwave irradiation: 1) No major structural changes in the investigated samples were observed as no major changes were observed in the XRD patterns of the treated samples in relation to the untreated ones. 2) Samples like those from Goias, which did not exfoliate when irradiated with microwaves, exfoliate when treated with hydrogen peroxide and simultaneously irradiated with microwaves for a few seconds. (C) 2013 Elsevier B.V. All rights reserved.