Remoção de impurezas não esmectíticas da bentonite de boane

Abstract

Bentonite is a plastic and colloidal clay consisting essentially of clay minerals from group of smectites (montmorillonite), presenting more than 140 industrial applications. Mozambique has a bentonite mine in Maputo Province, Boane District. That bentonite is highly contaminated by cristobalite. The existence of α-cristobalite in bentonites it is dangerous to human health and reduces its commercial value. Due to the similarity between well-ordered XRD patterns, C-opal and CT-opal have been confused with α-cristobalite in many publications. This is important, because α-cristobalite is probably a human carcinogen and opals are not. In this work, the bentonite digestion method was applied in H 3 PO 4 followed by XRD, for confirm whether the silica present in Boane's bentonite is actually cristobalite, tridimite, opal or mixture of these. Additionally, the crude bentonite was separated by colloidal fractionation and subsequent chemical treatment in order to separate it from impurities. The bentonites obtained in all stages, including the crude (untreated) bentonite used as reference, were characterized by XRD to determine the mineralogical composition. At were used to determine CTC, SE and only a few samples of non-bentonite treated and chemically treated benefited from the determination of the chemical composition with FRX. The result of bentonite digestion in H 3 PO 4, confirmed the presence of cristobalite in bentonite of Boane instead of the other polymorphic forms of silica. X-ray diffractograms and FRX results showed the loss of the mineral of interest (MMT) in the supernatant fraction and much more after chemical treatment compared to untreated. You CTC and SE values ​​were within the parameters of a smectite clay with values ​​in the order of 50.8 to 105.5meq / 100g of clay for CTC and 396.44 to 823.37 m 2 / g for SE, having higher values ​​in the supernatant fraction.