Nestor Kämpf

Avaliação da estimativa de substituição de Fe por Al em hematitas de solos

Hematites from nine soils and one from itabirite rock were concentrated with 5 mol L-1 NaOH, and analyzed by XRD (step scanning 0.02o2θ/20 s), to determine the unit cell parameters. The samples were dissolved by extraction with DCB to determine the Fe (Fed) and Al (Ald) content. Al substitution was estimated from a0 using established regressions currently in use based on hematites synthesized at 25°C (Al25) and 70°C (Al70). The a0 values ranged from 0.50380 to 0.50200 nm, corresponding to values of zero to 0.125 mol mol-1 Ald. The estimated values by the regression between a0 and Ald deviated from the Al70 regression by -0.003 to + 0.009 mol mol-1 Al, whereas the Al25 regression overestimated the substitution by an average of 0.03 mol mol-1 Al. Thus, for soil hematites, Al substitution is best estimated by the regression based on hematites synthesized at 70°C (Al mol mol-1 = 31.09 - 61.714a0).

Mineralogia, química e micromorfologia de solos de uma microbacia nos tabuleiros costeiros do Espírito Santo

Soils of the coastal plains of the EspIrito Santo state, Brazil, were studied with the objective of investigating and interrelationing their mineralogical, chemical and micromorphological characteristics and to furnish subsides for the pedogenetic environment reconstruction. Eleven soil profiles were described, collected and analysed. Less crystalline Fe by acid ammonium oxalate and amorphous Si by NaOH 0.5 mol L -1 were also determined. On mottles and nodules samples the proportion of hematite and goethite and Al substitution in goethite were analysed. Mineralogical analyses were performed through optical methods, X-ray diffraction and differential thermal analysis. From undisturbed samples of subsuperficial horizons thin sections were prepared for micromorpho- logical analysis. It was found that the present pedogenetic environment is favoring kaolinite stabiliza- tion and goethite formation, removing hematite and being probably responsible for the yellowing (xanthization) of superficial horizons. The process of iron segregation is evidenced by its accumulation in nodules and mottles in relation to soil matrix, probably by diffusion, the source being the matrix. The red nodules and mottles are in process of destruction instead of formation. The iron droplets which frequently occur in the interior of nodules and concretions constitute a stage of the process of develop- ment of these structures.

Mineralogia e fontes de potássio em solos no Rio Grande do Sul cultivados com arroz irrigado

Lowland soils cultivated with flooded rice in the State of Rio Grande do Sul, Brazil, show a lack of response to potassium fertilization in this culture, even in soils with a low level of available potassium. This study was carried out with the objective to verify the contribution of soil mineralogy as a potential potassium source for rice cultivation. Four representative soils from regions of the State of Rio Grande do Sul (Planossolo Hidromorfico, Planossolo Haplico, Gleissolo Haplico and Chernossolo Ebanico), cultivated with flooded rice, were selected. These soils have low exchangeable potassium contents and do not respond to potassium fertilization. In horizon samples A and B of the four soils, the particle-size distribution and chemical composition were analyzed. The mineralogy of sand, silt and clay fractions was identified by X-ray diffraction. Main mineral potassium sources were: feldspars and micas in the sand fraction, and in the silt and clay fractions feldspars, micas, smectites and smectites with interlaying hydroxy-Al. The total potassium in the particle-sized fractions differed between soils. Silt and clay fractions had higher values of total K, except for the Planossolo Haplico, where there was a higher total K in the sand fraction. The mineral K sources identified in these four soils can help explain the lack of response of flooded rice to potassium fertilization.

Balanço geoquímico de solos derivados de rochas básico-ultrabásicas no ambiente subtropical do Rio Grande do Sul

The mass balance of weathering of soils derived from basic-ultrabasic rocks under the subtropical climate of southern Brazil, the least weathered soils found to date in the Rio Grande do Sul state, showed a higher relative concentration of the mobile elements in the surface horizons than in the subsurface horizons. These features, associated to the soil mineralogy and morphology, indicate the occurrence of erosive-depositional events in a pedogenetically recent past as well as a main contribution from less weathered materials to the mineral composition of the surface horizons. These erosive events and the profiles surface renewal explain the early stage of development of these soils and their chemical and mineralogical similarity to soils derived from basic-ultrabasic rocks of temperate regions.

Cinética da dissolução redutiva da goethita e hematita em solos poligenéticos

Two mathematical models were used to evaluate the reductive dissolution kinetics of goethite and hematite. The Kabais model described dissolution as a single linear segment, not discriminating the dissolution of different phases of the same iron oxide or different iron oxides in a sample. Consequently, this model can only compare crystal stability between distinct samples. The Avrami-Erofejevs model described dissolution as a set of linear segments for most of the samples. This model discriminated different phases of the same iron oxide and allowed classification of the degree of stability of these minerals in each sample. Both models indicated that hematite is less stable than goethite against reductive dissolution, mainly when goethite combines low Al+3 substitution and high specific surface area. The evaluation of these mineralogical parameters on the crystal stability in the reductive dissolution showed dependecy of the model used for determining the dissolutive kinetic.