Paulo César Corrêa da Costa

Adsorption of arsenic ions on Brazilian sepiolite: Effect of contact time, pH, concentration, and calorimetric investigation

The original sepiolite clay mineral has been collected from Amazon region, Brazil. The compound 2-aminomethylpyridine (AMP) was anchored onto Amazon sepiolite surface by heterogeneous route. The natural (SPT) and modified (SPT(AMP)) sepiolite samples were characterized by elemental analysis, SEM, N(2) adsorption, and nuclear magnetic nuclei of (29)Si and (13)C. The well-defined peaks obtained in the (13)C NMR spectrum in the 0-160 ppm region confirmed the attachment of organic functional groups as pendant chains bonded into the porous clay. The ability of these materials to remove As(V) from aqueous solution was followed by a series of adsorption isotherms at room temperature and pH 4.0. The maximum number of moles adsorbed was determined to be 7.26×10(-2) and 11.70×10(-2) mmol g(-1) for SPT and SPT(AMP), respectively. In order to evaluate the clay samples as adsorbents in dynamic system, a glass column was fulfilled with clay samples (1.0 g) and it was fed with 2.0×10(-2) mmol dm(-3) As(V) at pH 4.0. The energetic effects caused by metal cations adsorption were determined through calorimetric titrations. Thermodynamics indicated the existence of favorable conditions for such As(V)-nitrogen interactions.

Petrografia e química mineral dos diques máficos da região Crixás-Goiás, estado de Goiás

No Bloco Arqueano de Goias (Centro-Oeste do Brasil) ocorrem diques maficos paleoproterozoicos orientados preferencialmente segundo NE e NW. Em funcao dos aspectos petrograficos foram classificados em: diabasio, metabasito e anfibolito. Sob o ponto de vista quimico tratam-se de toleitos, situando-se a grande maioria deles no campo do basalto, sendo que alguns, principalmente o diabasio, situam-se no campo do andesito basaltico. Diabasio, metabasito e, pelo menos parte dos anfibolitos parece ser cogenetica. Os diques de diabasio e metabasito contem piroxenios de composicoes ricas (augita) e pobres (enstatita e pigeonita) em calcio. Nesses diques verifica-se que, tanto para os piroxenios ricos quanto pobres em calcio, os conteudos de wollastonita (Wo) decrescem dos nucleos para as bordas dos graos acompanhados de um aumento dos teores de ferrossilita (Fs). Nos piroxenios pobres em calcio, ha um fraco incremento em Wo, e moderado enriquecimento em Fs. As analises de nucleos e bordas dos graos de plagioclasio mostraram composicoes que variam de labradorita a bytownita no diabasio e metabasito e andesina a oligoclasio nos anfibolitos. As temperaturas de cristalizacao obtidas no diabasio e metabasito, segundo varios geotermometros, indicam os mesmos intervalos de temperatura, quer utilizando-se os piroxenios, cuja variacao media vai de 1100oC a 1200oC, quer usando-se plagioclasio, cuja variacao media situa-se em 1100oC. Existem dois tipos de anfibolios calcicos: primarios e secundarios. Suas composicoes sao muito variadas, principalmente no que concerne aos elementos de Mg e Fe. Analises quimicas de opacos revelaram a presenca de magnetita e ilmenita.

Mafic Dykes: Petrogenesis and Tectonic Inferences

The main mafic dyke swarms of the Sao Francisco craton range in age from Late Archean to the Early Neoproterozoic, and record extensional and transpression tectonic events. The Uaua and Lavras regions include norite (2.73 and 2.66 Ga) and tholeiite swarms (2.62 and 1.97 Ga) respectively. Other swarms are made up of tholeiites: Paraopeba (2.10 Ga), Para de Minas (1.71 Ga), Curaca and Chapada Diamantina (1.5 Ga), Diamantina (0.93 Ga) and Salvador-Olivenca (0.92 Ga). Geochemical and Sr–Nd isotopic data indicate variable scales of mantle heterogeneity, caused by recurrent metasomatic effects since Archean times. The main processes are attributed to the action of slab fluids from recycling of oceanic crust and overlying sediments on the sub-lithospheric mantle in continental settings, and by upwelling of OIB-like material. These processes are consistent with the protracted geologic history of the country rocks, given by episodic juvenile accretion and successive continental amalgamations from Archean to ca. 2.0 Ga. The adopted mixing geochemical model permits to evaluate the variation range of N-MORB melts, OIB and slab fluids and melts, which are considered to represent the main components of the parental mantle composition of the studied dykes.