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In this work a fast and environmentally friendly method for the extraction and quantification of soluble sulphates in red clay using microwave assisted extraction (MAE) and determination by turbidimetry was developed and validated. The favorable conditions for the extraction of soluble sulphates in red clay by MAE were: 1 g of sample, with particle size of 63μm, dissolved in 50 mL of distilled water, it was extracted using a microwave oven with 70% of power during 5 min, later the sample was centrifuged during 5 min and then filtered. The soluble sulphates in red clays were quantified at 420 nm. The procedure proposed showed linear behaviour in the tested rank (5-7000 mg SO42-/kg of clay) with R2 0.9993. The limits of detection and quantification were 4.30 and 14.33 mg/kg, respectively, with a variation coefficient of 1.41%. The method proposed in this work allows to determine soluble sulphates in red clay with a recovery of 94%. ResumoNeste trabalho foi desenvolvido e validado um método rápido e inofensivo ao ambiente para a extração e quantificação de sulfatos solúveis em argilas vermelhas usando extração assistida por microondas (MAE) e determinação por turbidimetria. As condições favoráveis para a extração de sulfatos solúveis de argilas vermelhas por MAE foram: 1 g de amostra, com tamanho de partícula de 63 µm, dissolvido em 50 mL de água destilada, foi extraida em um forno micro-ondas a 70% de potência durante 5 min e então filtrada. Os sulfatos solúveis em argilas vermelhas foram quantificados em 420 nm. O procedimento proposto apresentou comportamento linear na faixa testada (5-7000 mg SO42-/kg de argila), com R2 0,9993. Os limites de detecção e de quantificação foram 4,30 e 14,33 mg/kg, respectivamente, com um coeficiente de variação de 1,41%. O método proposto neste trabalho permite determinar sulfatos solúveis em argila vermelho com uma recuperação de 94%.

Heavy-mineral analysis is a sensitive technique in constraining provenance of sandstone, but has rarely been applied to loess. Here we report a heavy-mineral study of selected samples from the Luochuan, Xifeng and Caoxian loess-Red Clay sections on the Chinese Loess Plateau, based on the novel QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) technique. We found that heavy mineral assemblages of loess deposited through the past 500. kyr are similar and unchanged by post-depositional chemical dissolution. In contrast, in samples deposited from 900. ka to 3. Ma, the relative proportion of stable minerals tends to increase down section. In addition, the Xifeng samples consistently display higher contents of unstable ferromagnesian minerals than the Luochuan samples. Detailed analysis of surface textures displayed by different minerals by optical methods indicates that such a compositional difference can be ascribed to more effective diagenetic dissolution for the Luochuan section, explained by more extensive percolation of interstitial waters in wetter climatic conditions. Interestingly, heavy-mineral assemblages in the underlying upper Miocene Red Clay from Xifeng (deposition age. ~. 7. Ma) are similar to those of recent loess deposited since 500. ka. This similarity indicates that climate and/or local preservation conditions hampered dissolution reactions, thus helping to preserve an original provenance signal that remained largely unchanged throughout the considered time period. Our study demonstrates that climatically- and time-controlled diagenesis plays a key role in determining the composition of heavy-mineral assemblages contained in loess deposited several hundreds of thousands years ago. We also show that by using both QEMSCAN and traditional optical techniques on the same samples we can obtain fundamental complementary information for a correct interpretation of the heavy-mineral assemblage. © 2013 Elsevier B.V.

X-ray fluorescence, themogravimetric-differential thermal analysis, Fourier Transform Infrared spectroscopy, X-ray diffraction, particle size analysis and Atterberg limits were used to study physico-chemical, mineralogical and thermal properties of two types of clays from four different locations of Tamilnadu, India. The chemical and mineralogical compositions of these clays differ considerably. The mineralogy indicated that the alluvial clays (G1 and G2) comprise highly quartz, illite, kaolinite, plagioclase and small amount of chlorite. The red clays (R1 and R2) were also rich in quartz, well-ordered kaolinite and abundant Fe-bearing minerals such as goethite and hematite. With respect to chemical composition, the G1 and G2 clays contained high amount of SiO2, low amount of Al2O3 and low loss on ignition, however, the R1 and R2 clays contain moderate amount of SiO2, Al2O3, and high amount of Fe2O3 and high loss on ignition. The results indicate that clays from alluvial deposit have adequate characteristics for common brick fabrication. However, clays collected from red clay deposit possessing adequate properties for roofing tile manufacturing and can be used for the manufacturing of common brick with some modification. As técnicas de fluorescência de raios X, análise termogravimétrica-térmica diferencial, espectroscopia no infravermelho com transformada de Fourier, difração de raios X, análise de tamanho de partículas e limites de Atterberg foram utilizadas para o estudo de propriedades físico-químicas, mineralógicas e térmicas de dois tipos de argilas de quatro diferentes localizações em Tamilnadu, India. As composições químicas e mineralógicas dessas argilas diferem consideravelmente. A mineralogia indica que argilas aluviais (G1 and G2) são compostas principalmente de quartzo, ilita, caulinita, plagioclases e pequenas quantidades de cloretos. As argilas vermelhas (R1 and R2) são também ricas em quartzo, caulinita bem ordenada, e minerais abundantes em ferro tais como goetita e hematita. Com relação à composição química, as argilas G1 e G2 contém alto teor de SiO2, baixo teor de Al2O3 e baixa perda ao fogo; as argilas R1 e R2, entretanto, contém teor moderado de SiO2, Al2O3, e alto teor de Fe2O3 e alta perda ao fogo. Os resultados indicam que argilas de depósitos aluviais tem características adequadas para a fabricação de tijolos. Entretanto, as argilas coletadas de depósitos de argilas vermelhas com propriedades adequadas para fabricação de telhas podem ser utilizadas na fabricação de tijolos após algumas modificações.

Uranium is a very toxic and radioactive element. Removal of uranium from wastewaters requires remediation technologies. Actual methods are costly and ineffective when uranium concentration is very low. Little is known about the enhancement of sorption of uranyl ions by phosphate ions on aluminosilicates. Here, we studied sorption of uranyl acetate on red clay in the presence of phosphates. The concentration of U(VI) ranged 0.0001–0.001 mol/L, whereas the concentration of PO43− was constant at 0.0001 mol/L. We designed a new method for the analysis of ternary surface complexes. We observed for the first time a remarkable improvement of U(VI) sorption on red clay under the influence of phosphates. We also found that at least two different ternary surface complexes U(VI)–phosphate–clay are formed in the sorbent phase. The complexation of UO22+ cations by phosphate ligands in the sorbent phase was confirmed by the X-ray photoelectron spectra of U 4f electrons.