Fate of nickel ion in (II-III) hydroxysulphate green rust synthesized by precipitation and coprecipitation

In order to investigate the efficiency of sulfate green rust (GR2) to remove Ni from solution, GR2 samples were synthesized under controlled laboratory conditions. Some GR2 samples were synthesized from Fe(II) and Fe(III) sulfate salts by precipitation. Other samples were prepared by coprecipitation, of Ni(II), Fe(II) and Fe(III) sulfate salts, i.e., in the presence of Ni. In another sample, Ni(II) sulfate salt was added to pre-formed GR2. After an initial X-ray diffraction (XRD) characterization all samples were exposed to ambient air in order to understand the role of Ni in the transformation of the GR2 samples. XRD was repeated after 45 days. The results showed that Nious GR2 prepared by coprecipitation is isomorphous to Ni-free GR2, i.e. Ni is incorporated into the crystalline structure. Fe(II) was not replaced by Ni(II) in the crystalline structure of GR2 formed prior to exposure to solution-phase Ni. This suggests Ni was adsorbed to the GR2 surface. Sulfate green rust is more efficient in removing Ni from the environment by coprecipitation.

Nickel incorporation in Fe(II, III) hydroxysulfate Green Rust: effect on crystal lattice spacing and oxidation products

Ni(II)-Fe(II)-Fe(III) layered double hydroxides (LDH) or Ni-containing sulfate green rust (GR2) samples were prepared from Ni(II), Fe(II) and Fe(III) sulfate salts and analyzed with X ray diffraction. Nickel is readily incorporated in the GR2 structure and forms a solid solution between GR2 and a Ni(II)-Fe(III) LDH. There is a correlation between the unit cell a-value and the fraction of Ni(II) incorporated into the Ni(II)-GR2 structure. Since there is strong evidence that the divalent/trivalent cation ratio in GR2 is fixed at 2, it is possible in principle to determine the extent of divalent cation substitution for Fe(II) in GR2 from the unit cell a-value. Oxidation forms a mixture of minerals but the LDH structure is retained if at least 20 % of the divalent cations in the initial solution are Ni(II). It appears that Ni(II) is incorporated in a stable LDH structure. This may be important for two reasons, first for understanding the formation of LDHs, which are anion exchangers, in the natural environment. Secondly, this is important for understanding the fate of transition metals in the environment, particularly in the presence of reduced Fe compounds.

Mineralogy of the clay fraction of Alfisols in two slope curvatures: III - spatial variability

A good knowledge of the spatial distribution of clay minerals in the landscape facilitates the understanding of the influence of relief on the content and crystallographic attributes of soil minerals such as goethite, hematite, kaolinite and gibbsite. This study aimed at describing the relationships between the mineral properties of the clay fraction and landscape shapes by determining the mineral properties of goethite, hematite, kaolinite and gibbsite, and assessing their dependence and spatial variability, in two slope curvatures. To this end, two 100 × 100 m grids were used to establish a total of 121 regularly spaced georeferenced sampling nodes 10 m apart. Samples were collected from the layer 0.0-0.2 m and analysed for iron oxides, and kaolinite and gibbsite in the clay fraction. Minerals in the clay fraction were characterized from their X-ray diffraction (XRD) patterns, which were interpreted and used to calculate the width at half height (WHH) and mean crystallite dimension (MCD) of iron oxides, kaolinite, and gibbsite, as well as aluminium substitution and specific surface area (SSA) in hematite and goethite. Additional calculations included the goethite and hematite contents, and the goethite/(goethite+hematite) [Gt/(Gt+Hm)] and kaolinite/(kaolinite+gibbsite) [Kt/(Kt+Gb)] ratios. Mineral properties were established by statistical analysis of the XRD data, and spatial dependence was assessed geostatistically. Mineralogical properties differed significantly between the convex area and concave area. The geostatistical analysis showed a greater number of mineralogical properties with spatial dependence and a higher range in the convex than in the concave area.

Variability of root traits in common bean genotypes at different levels of phosphorus supply and ontogenetic stages

Selection of common bean (Phaseolus vulgaris L.) cultivars with enhanced root growth would be a strategy for increasing P uptake and grain yield in tropical soils, but the strong plasticity of root traits may compromise their inclusion in breeding programs. The aim of this study was to evaluate the magnitude of the genotypic variability of root traits in common bean plants at two ontogenetic stages and two soil P levels. Twenty-four common bean genotypes, comprising the four growth habits that exist in the species and two wild genotypes, were grown in 4 kg pots at two levels of applied P (20 and 80 mg kg-1) and harvested at the stages of pod setting and early pod filling. Root area and root length were measured by digital image analysis. Significant genotype × P level and genotype × harvest interactions in analysis of variance indicate that the genotypic variation of root traits depended on soil nutrient availability and the stage at which evaluation was made. Genotypes differed for taproot mass, basal and lateral root mass, root area and root length at both P levels and growth stages; differences in specific root area and length were small. Genotypes with growth habits II (upright indeterminate) and III (prostrate indeterminate) showed better adaptation to limited P supply than genotypes of groups I (determinate) and IV (indeterminate climbing). Between the two harvests, genotypes of groups II and III increased the mass of basal and lateral roots by 40 and 50 %, respectively, whereas genotypes of groups I and IV by only 7 and 19 %. Values of the genotypic coefficient of determination, which estimates the proportion of phenotypic variance resulting from genetic effects, were higher at early pod filling than at pod setting. Correlations between shoot mass and root mass, which could indicate indirect selection of root systems via aboveground biomass, were higher at early pod filling than at pod setting. The results indicate that selection for root traits in common bean genotypes should preferentially be performed at the early pod-filling stage.

Desempenho de novos clones de seringueira: III. seleções promissoras para a região de Votuporanga, Estado de São Paulo

É apresentado o resultado da primeira seleção de 25 clones de seringueira (Hevea brasiliensis (Willd. ex Adr. de Juss.) Müell. Arg.), a maior parte constituída de introduções de diferentes origens. Após multiplicados, foram avaliados em experimentos do tipo pequena escala, obedecendo ao delineamento de blocos ao acaso, instalado na Estação Experimental de Votuporanga, SP. Os caracteres avaliados foram: produção de borracha seca, vigor expresso pelo perímetro do caule, espessura de casca e número de anéis de vasos laticíferos. Com relação à produção de borracha seca, destacaram-se os clones IAN 3156, IAC 40, 7/6, 3/5 e 3/1, produzindo 124%, 105%, 27%, 26% e 19% superiores em relação ao RRIM 600, recomendando-se seu plantio em pequena escala na região de Jaú. Caracteres secundários tais como o vigor, espessura de casca e número de anéis de vasos laticíferos dos clones testados são também discutidos. Sugere-se sua avaliação em experimentos do tipo grande escala com o objetivo de avaliar, além da produção, outros caracteres secundários para futuras recomendações no Estado de São Paulo.