Extração de ferro de esmectita brasileira com emprego do método ditionito-citrato-bicarbonato

A natural clay from Campina Grande region (Paraíba, Brazil), with 8.57% of Fe2O3, was used to study the most appropriate condition to carry out the iron extraction, without altering the clay structure in a significant way. Samples were treated with the Dithionite-Citrate-Bicarbonate method (DCB) for 30 and 120 minutes (pH=9.1), and also with citric acid (pH=1.8; time=15min), at 75°C. Conductivity measurements, X-ray fluorescence, X-ray diffraction, energy-dispersive spectrometry, electron-diffraction with transmission electron microscopy and textural evaluation by nitrogen adsorption were done. The treatment in a basic medium was more selective for iron removal than in acid condition. The time of 30 minutes, with 1.6 g Na2S2O4/10 g clay, was the best condition for the iron extraction.

Modification of a Brazilian smectite clay with different quaternary ammonium salts

In this work, a smectite clay from the State of Paraiba, Brazil, was treated with six different types of ammonium salts, which is an usual method to enhance the affinity between the clay and polymer for the preparation of nanocomposites. The clays, before and after modification, were characterized by X ray diffraction. The conformation of the salts within the platelets of the clay depended on the number of long alkyl chains of the salt. The thermal stability of the clays was also studied. The ammonium salts thermal decomposition was explained in light of their position within the organoclays.

Kinetics of K release from soils of Brazilian coffee regions: effect of organic acids

Kinetic studies on soil potassium release can contribute to a better understanding of K availability to plants. This study was conducted to evaluate K release rates from the whole soil, clay, silt, and sand fractions of B-horizon samples of a basalt-derived Oxisol and a sienite-derived Ultisol, both representative soils from coffee regions of Minas Gerais State, Brazil. Potassium was extracted from each fraction after eight different shaking time periods (0-665 h) with either 0.001 mol L-1 citrate or oxalate at a 1:10 solid:solution ratio. First-order, Elovich, zero-order, and parabolic diffusion equations were used to parameterize the time dependence of K release. For the Oxisol, the first-order equation fitted best to the experimental data of K release, with similar rates for all fractions and independent of the presence of citrate or oxalate in the extractant solution. For all studied Ultisol fractions, in which K release rates increased when extractions were performed with citrate solution, the Elovich model described K release kinetics most adequately. The highest potassium release rate of the Ultisol silt fraction was probably due to the transference of "non-exchangeable" K to the extractant solution, whereas in the Oxisol exchangeable potassium represented the main K source in all studied fractions.

Phosphorous forms in cultivated indian black earth (anthrosols) of varying texture in the brazilian Amazon

Despite the agricultural importance of Indian Black Earth (IBE) in the Amazon region, there are few studies that report on the relation between soil texture and chemical fertility of IBE. These soils of pre-Colombian origin, with high contents of P, Ca and other nutrients are found across the Amazon valley. IBE profiles were studied to evaluate the total contents of P, its primary chemical forms and the P transformation phases in areas with IBE soils of variable texture and in adjacent reference soils. The soil texture strongly influenced soil fertility, changing in terms of transformation of the primary P forms and, consequently, predominant P forms in IBE. Soils with texture varying between clay and heavy clay had higher total P contents and primary Ca-P forms. Highest P-Al and lowest total P amounts were observed at the site Rio Preto da Eva, where texture varies from sandy loam to sandy clay loam. In the IBE with clay texture the amounts of soluble P, extracted with NH4Cl were highest, although different from Mehlich 1-extractable amounts.

Aluminum hydroxy-interlayered minerals and chemical properties of a subtropical Brazilian Oxisol under no-tillage and conventional tillage

No tillage systems significantly influence the soil system, but knowledge about the effects on the mineralogy of tropical and subtropical soils is limited. This study evaluated the long-term effects (26 years) of no-tillage (NT) on aluminum hydroxy-interlayered minerals of a subtropical Oxisol in Southern Brazil (Guarapuava, PR), compared to the same soil under conventional tillage (CT). The clay fraction (< 2 µm) in soil samples of the surface horizons of a field experiment under both management systems was analyzed by X-ray diffraction (XRD) to identify and characterize Al hydroxy-interlayered minerals before and after treatment with sodium citrate to remove intra-layer material. Soil liquid (solution) and solid phases were also characterized. The contents of total organic C, exchangeable cations, P, and the values of extractable acidity and cation exchange capacity as well as electrical conductivity and levels of dissolved organic C, basic cations, aluminum, Si, and sulfur in the soil solution were higher in the NT soil. Under both soil management systems, more than 90 % of the total soluble Al was complexed with organic compounds, with similar Al activity. No significant changes were detected by 2:1 clay mineral XRD analyses in terms of extension or intercalation of Al-hydroxy-polymers in the no-tilled in comparison to the conventionally tilled soil. In both soil management systems, Al and Si activities in the soil solution indicated thermodynamic stability of 2:1 clay minerals with partially occupied by hydroxy-Al, suggesting deceleration in the intercalation process and a tendency of transforming clay minerals from extensive into partial intercalation.

Water-dispersible clay in soils treated with sewage sludge

A by-product of Wastewater Treatment Stations is sewage sludge. By treatment and processing, the sludge is made suitable for rational and environmentally safe use in agriculture. The aim of this study was to assess the influence of different doses of limed sewage sludge (50 %) on clay dispersion in soil samples with different textures (clayey and medium). The study was conducted with soil samples collected from native forest, on a Red Latosol (Brazilian classification: Latossolo Vermelho distroférrico) loamy soil in Londrina (PR) and a Red-Yellow Latosol (BC: Latossolo Vermelho-Amarelo distrófico) medium texture soil in Jaguapitã (PR). Pots were filled with 3 kg of air-dried fine earth and kept in greenhouse. The experiment was arranged in a randomized block design with six treatments: T1 control, and treatments with limed sewage sludge (50 %) as follows: T2 (3 t ha-1), T3 (6 t ha-1), T4 (12 t ha-1), T5 (24 t ha-1) and T6 (48 t ha-1) and five replications. The incubation time was 180 days. At the end of this period, the pots were opened and two sub-samples per treatment collected to determine pH-H2O, pH KCl (1 mol L-1), organic matter content, water-dispersible clay, ΔpH (pH KCl - pH-H2O) and estimated PZC (point of zero charge): PZC = 2 pH KCl - pH-H2O, as well as the mineralogy of the clay fraction, determined by X ray diffraction. The results showed no significant difference in the average values for water-dispersible clay between the control and the other treatments for the two soil samples studied and ΔpH was the variable that correlated best with water-dispersible clay in both soils.

Chemical dispersants and pre-treatments to determine clay in soils with different mineralogy

Knowledge of the soil physical properties, including the clay content, is of utmost importance for agriculture. The behavior of apparently similar soils can differ in intrinsic characteristics determined by different formation processes and nature of the parent material. The purpose of this study was to assess the efficacy of separate or combined pre-treatments, dispersion methods and chemical dispersant agents to determine clay in some soil classes, selected according to their mineralogy. Two Brazilian Oxisols, two Alfisols and one Mollisol with contrasting mineralogy were selected. Different treatments were applied: chemical substances as dispersants (lithium hydroxide, sodium hydroxide, and hexametaphosphate); pre-treatment with dithionite, ammonium oxalate, and hydrogen peroxide to eliminate organic matter; and coarse sand as abrasive and ultrasound, to test their mechanical action. The conclusion was drawn that different treatments must be applied to determine clay, in view of the soil mineralogy. Lithium hydroxide was not efficient to disperse low-CEC electropositive soils and very efficient in dispersing high-CEC electronegative soils. The use of coarse sand as an abrasive increased the clay content of all soils and in all treatments in which dispersion occurred, with or without the use of chemical dispersants. The efficiency of coarse sand is not the same for all soil classes.

Chemical and mineralogical changes in a Brazilian Rhodic Paleudult under different land use and managements

Changes in land use and management can affect the dynamic equilibrium of soil systems and induce chemical and mineralogical alterations. This study was based on two long-term experiments (10 and 27 years) to evaluate soil used for no-tillage maize cultivation, with and without poultry litter application (NTPL and NTM), and with grazed native pasture fertilized with cattle droppings (GrP), on the chemical and mineralogical characteristics of a Rhodic Paleudult in Southern Brazil, in comparison with the same soil under native grassland (NGr). In the four treatments, soil was sampled from the 0.0-2.5 and 2.5-5.0 cm layers. In the air-dried fine soil (ADFS) fraction (∅ < 2 mm), chemical characteristics of solid and liquid phases and the specific surface area (SSA) were evaluated. The clay fraction (∅ < 0.002 mm) in the 0.0-2.5 cm layer was analyzed by X-ray diffraction (XRD) after treatments for identification and characterization of 2:1 clay minerals. Animal waste application increased the total organic C concentration (COT) and specific surface area (SSA) in the 0.0-2.5 cm layer. In comparison to NGr, poultry litter application (NTPL) increased the concentrations of Ca and CECpH7, while cattle droppings (GrP) increased the P and K concentrations. In the soil solution, the concentration of dissolved organic C was positively related with COT levels. With regard to NGr, the soil use with crops (NTM and NTPL) had practically no effect on the chemical elements in solution. On the other hand, the concentrations of most chemical elements in solution were higher in GrP, especially of Fe, Al and Si. The Fe and Al concentrations in the soil iron oxides were lower, indicating reductive/complexive dissolution of crystalline forms. The X-ray diffraction (XRD) patterns of clay in the GrP environment showed a decrease in intensity and reflection area of the 2:1 clay minerals. This fact, along with the intensified Al and Si activity in soil solution indicate dissolution of clay minerals in soil under cattle-grazed pasture fertilized with animal droppings.

Potential of Spectroradiometry to Classify Soil Clay Content

ABSTRACT Diffuse reflectance spectroscopy (DRS) is a fast and cheap alternative for soil clay, but needs further investigation to assess the scope of application. The purpose of the study was to develop a linear regression model to predict clay content from DRS data, to classify the soils into three textural classes, similar to those defined by a regulation of the Brazilian Ministry of Agriculture, Livestock and Food Supply. The DRS data of 412 soil samples, from the 0.0-0.5 m layer, from different locations in the state of Rio Grande do Sul, Brazil, were measured at wavelengths of 350 to 2,500 nm in the laboratory. The fitting of the linear regression model developed to predict soil clay content from the DRS data was based on a R2 value of 0.74 and 0.75, with a RMSE of 7.82 and 8.51 % for the calibration and validation sets, respectively. Soil texture classification had an overall accuracy of 79.0 % (calibration) and 80.9 % (validation). The heterogeneity of soil samples affected the performance of the prediction models. Future studies should consider a previous classification of soil samples in different groups by soil type, parent material and/or sampling region.

Remaining phosphorus and sodium fluoride pH in soils with different clay contents and clay mineralogies

The remaining phosphorus (Prem) has been used for estimating the phosphorus buffer capacity (PBC) of soils of some Brazilian regions. Furthermore, the remaining phosphorus can also be used for estimating P, S and Zn soil critical levels determined with PBC-sensible extractants and for defining P and S levels to be used not only in P and S adsorption studies but also for the establishment of P and S response curves. The objective of this work was to evaluate the effects of soil clay content and clay mineralogy on Prem and its relationship with pH values measured in saturated NaF solution (pH NaF). Ammonium-oxalate-extractable aluminum exerts the major impacts on both Prem and pH NaF, which, in turn, are less dependent on soil clay content. Although Prem and pH NaF have consistent correlation, the former has a soil-PBC discriminatory capacity much greater than pH NaF.

Sorption of fomesafen in Brazilian soils

The study of the dynamics of a herbicide in the soil focus on the interactions with environmental components to obtain agronomic efficiency, ensuring selectivity to the culture and risk reduction of environmental impact. This study evaluated the sorption process of fomesafen in the Brazilian soils Ultisol, Cambisol, and Organosol. Besides soil, washed sand was used as an inert material for determination of the sorption ratio of fomesafen in the soil. The bioassay method was applied, using Sorghum vulgare plants as bio-indicator of herbicide presence. Plant poisoning evaluation and harvest for dry matter determination were carried out 21 days after sorghum sowing. To calculate C50, the nonlinear log-logistic model was applied and sorption ratios of the herbicide were obtained in different soils. The decreasing sorption ratio of formesafen in the soils was: Organosol > Ultisol > Cambisol. It was concluded that the contents of organic matter and clay in the soils were the attributes that most influenced fomesafen sorption.

Going Global: an organizational study of Brazilian foreign policy

This study analyzes the impact of globalisation on the organization and strategies outlined by the Brazilian Ministry of Foreign Affairs. The study intends to understand how countries from the periphery deal with new institutional challenges resulting from globalization, using the case of the Brazilian diplomatic service.

Brazil: an emerging military power? The problem of the use of force in Brazilian international relations in the 21st century

The central goal of this paper is thinking about the Brazilian military power and its linking to the international ambitions of the country in the 21st century. After a comparative analysis to other BRICs and with a historical one about Brazil's strategic irrelevance, we aim to establish what the minimum military capacity Brazil would need in order to meet the country's latest international interests. Similarly, it will be discussed if the National Strategy of Defense, approved in 2008, and the recent strategic agreements signed with France represent one more step toward this minimum military capacity.

Rendering peacekeeping instrumental? The Brazilian approach to United Nations peacekeeping during the Lula da Silva years (2003-2010)

The article analyses how Brazilian state actions and policies regarding peace operations during the Presidency of Lula da Silva relate to the country's positions and attitudes towards United Nations peacekeeping. It argues that the inconsistencies identified on the Brazilian positions reflect the lack of a clear strategic horizon guiding the country's participation in UN peacekeeping, which consequentially hinders the country emergence as a great power.

The Brazilian Business World: the difficult adaptation to globalization

The article deals with the internationalization of Brazilian businesses in the current decade. In the 1990s, Brazil embraced economic neoliberalism and promoted a huge opening up of its economy. At that time, Brazilian companies had to adapt rapidly. Twenty years later, the country has reinforced its presence in Latin America and has ensured a better position in the global markets, especially by through agricultural exports.