This study reports the geological and physicochemical characterization of Monoun plain alluvial clays. The field was profiled using an auger corer in three localities (Njimbet, Bangourain, Ngwenfon). The present results reveal good indices of alluvial clay deposits with thicknesses ranging from 0 to 620 centimeters and are made up of various facies. The clay samples were collected from six representative profiles at different localities and they indicated silty clay texture except NJB1_2 and BGR2_2, i.e., a sandy clay texture. In all sample, quartz, kaolinite, goethite, illite and chlorite are the major minerals, while gibbsite, hematite, anatase, and K-feldspar are the minor minerals. Chemical analysis revealed the silico–aluminous character of samples with various iron products (1%<Fe2O3<14%) and small alkali and alkaline earth oxides (0%<Na2O+K2O+CaO+MgO <3%). The physical parameters of alluvial clays exhibit a wide spread granulometry (gravel: 0.0–6.3%; sand: 19.6–79.5%; silt: 12.4–67.4% and clay: 1.5–49.0%) with relatively high plastic index (11–49%). The comparison of Monoun alluvial clay with the others alluvial clays in the country and European clay used in ceramic production indicated similarities in mineralogy, chemical and grain size composition. The reference diagrams of classification of raw clay material for ceramic production also confirm that these alluvial clays can be used in structural ceramics like red stoneware tiles, tiles, roofing tiles, firing bricks and pottery.
A new reference sample of “hydrobiotite” mined at Palabora, the Republic of South Africa distributed by the Clay Science Society of Japan (CSSJ), was characterized by XRD, SEM, Mӧssbauer spectroscopy and TG-DTA. The XRD indicated that the sample was predominantly composed of the relatively regular interstratification of biotite- and vermiculite-layers, but segregated packets of vermiculite- and biotite-layers also existed, respectively. Diopside (Di75Hd25–Di80Hd20), wollastonite, apatite and titanite, were identified as impurity minerals. Mӧssbauer spectroscopy indicated that ∼83% of iron was ferric on average. Chemical compositions, especially the amount of K, were significantly varied among individual grains, while the compositional variance inside each grain was relatively small. The TG-DTA showed two sharp endothermic reactions at around 100 and 230°C, possibly corresponding to the two stages of dehydration of the interlayer region of the vermiculite-layer. In the range from 300 to 800°C, a gentle weight loss (about 2.5 wt%) was observed, corresponding to the dehydroxylation and/or the slow dehydration of water molecules tenaciously held in the interlayer. The total weight loss from 85 to 800°C was ∼7.0%. One-dimensional XRD profile simulation for mixed-layer structure was attempted for quantitative characterization of the mixed layer structure. At least four different stacking sequences were suggested for the major diffraction peaks; two types of relatively regular interstratified biotite- and vermiculite-layers (49.7% and 18.8% of the total number of layers), a biotite-layer rich stacking sequence (29.8%) and an almost pure vermiculite-layer stacking sequence (1.7%).
Aflatoxin B1 (AfB1) is one of the main contaminant of grains such as corn and wheat, causing damage to livestock through ingestion of contaminated feed. Recently, various clays have been added to the feed to adsorb mycotoxins and to prevent mycotoxicosis of animals. However, the effect of kind of clays is still unclear. In this study, several kinds of natural clays such as bentonite and sepiolite, as well as the synthetic two-dimensional talc as a reference, were tested as an adsorbent for AfB1 in aqueous solutions. All of the clays used here was found to have high adsorption performance for AfB1. Especially, five kinds of the bentonite samples indicated the larger adsorption capacity and the faster adsorption rate of AfB1 in spite of their relatively lower specific surface area. The adsorption capacity of the sepiolite sample was almost similar to the bentonite samples, but the adsorption rate was somewhat smaller because of its intrinsic smaller pore structure. Moreover, the adsorption capacity of these clay for AfB1 was hardly influenced by the solution pH of 3–9 and temperature of 25–40°C, and the desorption of AfB1 from these clay samples in water was almost negligible. In these cases, AfB1 molecules are thought to be captured by the chelating of two carbonyl groups with metal cation at the destruction face of the clay basal layer. In conclusion, these natural and acid-treated clays can be used as the practical adsorbent to prevent mycotoxicosis of animals.