Paulo Roberto Gomes Brandão

Adsorption of oleate and octyl-hydroxamate on to rare-earths minerals☆

The adsorption of sodium oleate and potassium octyl-hydroxamate onto the rare-earths minerals monazite and bastnaesite was investigated through microflotation experiments, zeta potential determinations and infrared spectroscopy. The monazite and bastnaesite samples were purified in the laboratory reaching, respectively, final grades of 68.7 and 45.3 % RE2O3 + ThO2. The results confirm that sodium oleate chemisorbs onto bastnaesite and suggest a physical adsorption mechanism of this reagent onto monazite. Despite the lack of a full confirmation from FTIR spectrometry, there is a possibility of oleate chemisorption onto monazite in the pH range above the isoelectric point. A chemical adsorption mechanism was established for the interaction between octylhydroxamate and both minerals.

Dental enamel around fixed orthodontic appliances after fluoride varnish application

Poor oral hygiene has been considered one of the main problems routinely faced in the orthodontic treatment. Orthodontic appliance creates an environment that provides mineral loss from the dental enamel. Such condition is clinically seen as white spot lesions and cavitations in the most severe cases. The aim of this study was to evaluate the effects of a fluoride varnish application as a caries prevention method for clinical orthodontics. The experiment analyzed dental enamel adjacent to orthodontics accessories after treatment. In addition, it was observed the calcium, phosphorus and fluoride contents on enamel treated with a fluoride varnish. The results showed that fluoride varnish application is a simple and fast technique that could be useful in preventing enamel demineralization associated to orthodontic treatment. Scanning electron microscopy revealed significant amount of calcium fluoride-like material deposited on enamel and energy dispersive x-ray analysis demonstrated a large incorporation of calcium and fluoride to the enamel of the treated specimens. It was concluded that fluoride varnish could indeed be considered an efficient preventive method to enhance enamel resistance against the cariogenic challenges during orthodontic therapy.

Césarferreiraite, Fe2+Fe23+(AsO4)2(OH)2·8H2O, from Eduardo mine, Conselheiro Pena, Minas Gerais, Brazil: Second arsenate in the laueite mineral group

Abstract Césarferreiraite, Fe2+Fe23+(AsO4)2(OH)2·8H2O, is a new laueite-group mineral (IMA 2012-099) of triclinic symmetry, from Eduardo pegmatite mine, Conselheiro Pena municipality, Minas Gerais, Brazil. Intimately associated minerals are pharmacosiderite, scorodite, and earlier arsenopyrite, and probably césarferreiraite replaces the latter. It occurs as fibrous-to-tabular aggregates up to 2 mm. Single crystals, up to 10 μm long with a thickness of about 1-2 μm, are elongated along [001] and flattened on (100). The fibers have almost rectangular cross-section apparently bound by the {100} and {010} pinacoid forms. Color and streak are pale to greenish yellow. Luster is vitreous; individual crystals are transparent and masses are translucent. Cleavage is distinct, presumably on {010} and {100}. Calculated density is 2.934 g/cm3. The mineral is biaxial (+), n (min) = 1.747(3), n (max) = 1.754(3) (589 nm). IR spectrum of césarferreiraite is unique and can be used for the identification of the mineral. Chemical composition (n = 4, WDS, calculated for the condition Fe2+:Fe3+ = 1:2, H2O for the ideal structural formula, wt%) is: FeO 11.50, Fe2O3 25.56, CaO 15.41, As2O5 33.51, H2O 26.01, total 100.12. The empirical formula (based on 18 O apfu) is Fe2+0.98Fe3+1.96[(AsO4)1.79(PO4)0.31](OH)1.52·8.08H2O. The strongest eight X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 9.85(95)(010), 6.35(100)(001), 3.671(29)(1̅21), 3.158(32)(13̅0), 2.960(39)(022̅), 2.884(35)(1̅31), 2.680(29)(2̅11), and 2.540(23)(2̅10). Unit-cell parameters refined from powder data indexed by analogy with related laueite-group minerals (space group: P1̅) are: a = 5.383(2), b = 10.363(3), c = 6.878(2) Å, α = 96.42(4), β = 109.19(3), γ = 102.30(2)°, V = 347.1(2) Å3, and Z = 1. Gladstone-Dale compatibility is -0.020 (excellent). Césarferreiraite is the arsenate analog of ferrolaueite.

Statistical validation of standardless and standard-based analysis by X-ray fluorescence spectrometry in iron ores characterisation☆

An X-ray fluorescence (XRF) study comparing the performances of standardless or semiquantitative analysis in relation to the traditional standard-based or quantitative analysis technique is presented. This comparison using precision lines and simultaneous confidence intervals provides reliable information about the precision and trueness that each technique can achieve. This study enables the comparison of the results obtained with two different analytical approaches for iron ore samples in terms of precision and accuracy of results, sample preparation and availability of standards. A new technique for assessing the accuracy of an analytical method using linear regression is presented, wherein the results of both analyses are regressed against certified reference materials. The statistical test performed is based on the joint confidence interval for the slope and the intercept of the regression line calculated considering the uncertainties in both axes or in both analytical methods. The slope, intercept and variances associated with the regression coefficients are calculated with bivariate least-squares regression. Some chosen standard-samples were analysed for statistical validation of the methods. These samples had sufficient replicates to perform the calculations and later statistical comparison between the accuracy (precision and trueness) of each analytical method and evaluation of its precision lines.

Vegetable lipid oil-based collectors in the flotation of apatite ores

Apatite ores of igneous carbonatite origin are the most important phosphorus source in Brazil. Most of these ores are deeply or partially weathered, having complex chemical and mineralogical compositions. Rice bran oil and soybean oil were the vegetable lipid oils evaluated as raw materials for saponified fatty acids collectors, in the flotation of apatite ores; linseed oil was included, for comparison reasons. They were characterized by chemical wet methods and gas chromatography. Flotation was studied by two approaches: a) microflotation tests using pure apatite and reagent grade fatty acids; b) bench scale flotation tests, using a typical weathered apatite ore; the collectors were the vegetable oils, after saponification; the tests ran under realistic conditions, at pH = 10. The microflotation tests showed that, at basic pH, linoleic acid was the best collector for apatite, followed by linolenic and oleic acids. These results were fully confirmed by the bench scale flotation tests with the apatite ore; the best natural oils, as collectors for apatite ores, were those richer in linoleic acid. Soybean oil was the best collector, considering P2O5 grade and recovery, and Fe2O3 content (as a measure of gangue minerals contamination). However, linseed oil yielded excellent results, too. Although being a practical collector for apatite flotation, rice bran oil always gave the worst results, among the three vegetable lipid oil-based collectors tested.

The influence of crystal chemistry properties on the floatability of apatites with sodium oleate

Abstract Several apatites from Brazilian deposits of different origins (igneous, metamorphic and sedimentary) had their crystal chemistry properties determined. The main goal was to establish correlations with their froth flotation behavior. X-ray diffraction studies were carried out, with computer support and a high degree of analytical detail, to determine precisely the a and b crystal lattice parameters, and the crystallinity level of the apatite samples. A thorough chemical analysis of these minerals was also conducted. Microflotation tests were carried out, using sodium oleate as collector. Metamorphic and sedimentary apatites were the most chemically heterogeneous, mainly for the substitution of phosphate ions by carbonate. Parameter a showed a broader variation than c . Crystallinity level values ranked from 10.0 to 4.4. A marked correlation was observed between this crystallinity sequence and floatability; the latter dropped drastically for crystallinity values lower than 8.0.

Kimberlito Canastra-1 (São Roque de Minas, MG): geologia, mineralogia e reservas diamantíferas

The research on the primary diamond sources in Brazil started in the 1960 years and had its highest achievement with the discovery of the mineralized Canastra-1 kimberlite which is the first Brazilian primary deposit having economic contents. This pipe surfaces in the Serra da Canastra (Canastra Range) near the sources of the Sao Francisco River. The intrusion is made up of two blows lined along NE-SE, which is the regions structural trend defined in the metasedimentary rocks of the Canastra Group. The smaller blow is nearly circular with an area of approximately 0.8 ha and has only negligible diamond content. The SE blow has almost 1.0 ha and is mineralized with an average content of 12 to 18 ct/100 tonnes of rock. There are also significant differences in the petrographic facies of the two bodies, which is homogeneous in the NW blow while the SE blow is heterogeneous, with the occurrence of a mixture of several facies. The short distance between the blows justifies the assumption that they join in depth, therefore being apophyses of the same intrusion. The mineral chemistry of the indicators showed a strong resemblance with some diamondiferous African kimberlites. Data from experimental mining indicated an excellent quality for this kimberlites diamonds, with US

Reologia de suspensões minerais: uma revisão

180-200/ct estimated average value.

Infrared-spectroscopy analysis of zinc phosphate and nickel and manganese modified zinc phosphate coatings on electrogalvanized steel

Mineral processing is often carried out on suspensions (usually a mixture of solid particles and liquid). The process is influenced by the resistance to flow resulting from a shear stress or pressure applied in the fluid (suspension). Therefore, the viscosity of suspensions will affect the mineral process. This paper reviews the applications of rheology in mineral processing. This review focuses on conceptual aspects such as fluid classification, variable of rheology and measurements with concentric viscometer.

Piso intertravado produzido com rejeito de sinter feed

Hopeite-type phosphate coatings in which zinc is partially replaced by other metals like manganese and nickel are of great interest for the automotive and home appliance industries. Such industries use phosphate conversion coatings on galvanized steels in association with cataphoretic electropainting. Zinc phosphates modified with manganese and nickel are isomorphic with the hopeite, and the phase identification using X-ray diffraction is difficult. In this paper, the phosphate coatings are identified using the Fourier transform infrared spectroscopy (FTIR).