Flávio Machado de Souza Carvalho

Formation of Aluminum Titanate with Small Additions of MgO and SiO2

The formation of aluminum titanate was investigated by isothermal treatments of samples obtained from equimolar mixtures of alumina and titania, containing small amounts of silica and magnesia. Results of differential thermal analysis and Rietveld refinements of data collected by X-ray powder diffraction (XRPD) showed that additions of silica in amounts used in this work did not influence the formation of aluminum titanate. However, the presence of magnesia favored the formation of aluminum titanate in two steps, first one by incorporating Mg2+ into Al2TiO5 lattice during its initial formation, and the second one by accelerating the Al2TiO5 formation, contributing to large quantities of this phase. MgO doped samples have also developed a more suitable microstructure for stabilizing of Al2TiO5, what make them promising for applications such as thermal barriers, internal combustion engines and support material for catalyst.

As Jazidas de Talco no Contexto da História Metamórfica dos Metadolomitos do Grupo Itaiacoca, PR

Four main types of talc occurrences have been recognized in the Proterozoic metadolomites of the Itaiacoca Group, Parana State, southern Brazil: a) talc schists along transcurrent shear zones; b) incipient talc formation along fractures and bedding planes; c) irregular pockets of fine-grained, massive talc; d) retrometamorphic talc associated with lenses of olivine, diopside, tremolite, calcite and quartz in the contact zone with the neighbouring granites. Of these, only types (a) and (c) form ore deposits. The Itaiacoca Group underwent four metamorphic episodes: 1) greenschist facies regional metamorphism during the Neoproterozoic Brasiliano orogeny; 2) thermal metamorphism along the contact with the Neoproterozoic Cunhaporanga granite batholith; 3) hydrothermalism related to transcurrent shear zones, that formed large volumes of talc schists and irregular pockets of fine-grained massive talc; 4) small-scale thermal metamorphism related to Mesozoic diabase dikes. The Itapirapua transcurrent shear zone marks the contact between the Itaiacoca Group and the Proterozoic Tres Corregos granite batholith, and the main talc deposits are aligned along its branches. Enhanced permeability due to shearing provided channels for percolation of the silica-rich aqueous solutions that reacted with the metadolomite to form the talc deposits. Minor amounts of talc occur along fractures and sedimentary layering. The massive pockets of talc (type c) that replaced the metadolomite probably formed statically at lower temperatures by the activity of hydrothermal fluids introduced through a network of microfractures.

Produtos metamórficos de sistemas high-sulfidation oceânicos mesoproterozoicos, grupo Serra do Itaberaba, SP

In the central portion of the Ribeira fold belt, southeastern Brazil, the Mesoproterozoic volcanosedimentary Serra do Itaberaba Group was affected by two medium-grade regional metamorphic events and by a third low-grade retrometamorphic event. This succession was deposited in an ocean basin having N-MORB type basalts that evolved to a back-arc environment. Within the group four occurrences of alumina-rich rocks are now known (Guavirituba, Pedra Branca, Itaberaba and Pico Pelado), which crop out as small lenses intercalated between metabasites and metamorphosed volcanoclastic rocks, tuffs and pelites. Their genesis is related to oceanic magmatic-hydrothermal activity in the backarc environment that was associated with the emplacement of small rhyolitic bodies and high-sulfidation gold mineralization. X-ray diffraction analysis (XRD) of 15 very fine-grained alumina-rich samples permitted corundum, topaz, margarita, rutile and an undifferentiated mica (possibly sericite) to be identified. Mineral associations allow recognition of two advanced argillic alteration events and a third carbonation or retrometamorphic event that affected rocks of the Serra do Itaberaba Group: the first event generated protolith 1 rich in aluminum oxides ± alunite that after metamorphism produced dark blue lithotypes composed of corundum ± sericite; the second event was a silicification event that produced protolith 2 composed of topaz + zunyite + alunite ± rutile or of andalusite + alunite, with metamorphic products corresponding to brown and whitish lithotypes (Pico Pelado occurrence); during carbonatization or retrometamorphism, margarite crystalized after andalusite, cyanite or sillimanite. The sum of these three events produced, after the metamorphism or retrometamorphism, brown, whitish, and heterogeneous lithotypes composed of margarite or of margarite + sericite ± corundum (Guavirituba and Pedra Branca occurrences). The identification of similar lithotypes during field work represents a potentially very valuable tool in mineral exploration works as they comprise rock guides for finding gold deposits in medium-grade metamorphosed volcanosedimentary sequences.

ALTERAÇÃO EXPERIMENTAL DE ROCHAS CARBONÁTICAS, CAVERNA DAS PERÓLAS, IPORANGA (SP)

Experimental studies were performed to study the chemical weathering of carbonate rocks from the Perolas Cave, Iporanga municipality, State of Sao Paulo. Soxhlet extractors were used to accelerate the leaching process in two different ways: continuous and intermittent. The leaching solution obtained from the continuous test was chemically analyzed at the end of the process (about 454 hours), and the precipitates were separated and mineralogically analyzed by X-ray diffraction (XRD). In the intermittent leaching process, solutions and precipitates were collected after a predetermined period of time and chemically analysed to determine the number of ions removed from the weathered rocks. It was found that the ions mainly leached in the beginning of the experimental weathering were Na+ and Mg2+; however, when the leaching process was accelerated, Sr2+, Ba2+ and Ca2+ became the most remobilized ions, along with Na+, leading to the precipitation of calcite. In the continuous leaching test, it was observed that the concentrations of Sr2+ and Ba2+ were lower compared to the intermittent test, showing that these ions were probably co-precipitated with calcite. The low Mg/Ca ratio in the experimental leaching solutions may have caused the precipitation of calcite instead of aragonite. It was noted that there was a higher rate of remobilization of the constituents of the carbonate rocks on the level where the samples were subjected to fluctuations of the water table in the compartment of the Soxhlet equipment. Kaolinite is the main secondary mineral in the weathered rock.

Efeito da adição de lama vermelha nas propriedades eletroquímicas e de adsorção de um latossolo vermelho

This study aimed to characterize the waste generated in the production of alumina from bauxite refining process (red mud) and to analyze its effect on the electrochemical and adsorption properties of a tropical soil (Oxisol). The red mud (LM) is a highly alkaline residue (pH around 12), which is rich in iron oxide/hydroxides. To study the effect of red mud and calcium carbonate (CaCO3) - commonly used in agriculture to correct soil pH - on the soil, these substances were added in different proportions to Oxisol samples for 60 days. The addition of CaCO3 and LM to the soil increased the pH and the point of zero charge (PZC). However, the pH H 2 0 value of the soil with LM was greater than its PCZ, enabling dispersion of soil particles. Moreover, such addition increases cation exchange capacity in soils, as observed in removal tests of Pb 2+ in solution. It was observed that the minimal addition of 0.5% of CaCO3 and 10% of LM to the soil increased the Pb 2+ retention capacity from 37% to 100%. The same results were observed in tests performed only with red mud. Even when subjected to an acid leaching (solution with pH 4.9), soils incubated with 1% CaCO3 and 1% LM released 7.5% and 11% of retained Pb 2+ , respectively. This low Pb 2+ leaching rate is due to the increase in soil pH, favoring the adsorption of Pb 2+ by Fe and A1 oxy-hydroxides present in the soil and red mud composition. It can be concluded, therefore, that the addition of red mud can change the electrochemical conditions of the soil, dispersing more clay and colloidal particles. However, by increasing the pH of the system and introducing iron and aluminum oxides and hydroxides, such material can increase the retention of heavy metals, such as Pb 2+ , in the soil.