Caracterização mineralógica de concreções de ferro por efeito Mössbauer e difratometria de raios x

Abstract

The mineralogy of a variety of concretionary materials from two different classes of Paraná soil was studied. The series of natural samples consisted of six different concretions of a NITOSSOLO VERMELHO Latossólico (horizons A and BW) and six other concretions of a LATOSSOLO VERMELHO férrico (horizons and BWC). The samples were characterized by chemical analysis, X-ray diffraction and Mössbauer spectroscopy at room temperature and at 25 K. The results indicated that iron is the most common metallic element at all concretions, although other metals such as aluminum, manganese and others exist in minimal fractions (<1%). From a structural point of view, goethite was present as the main phase, but kaolinite and hematite were identified at two concretions. For the majority of the natural samples, the Mössbauer spectra obtained at room temperature simultaneously exhibited a doublet and a hyperfine magnetic field distribution, both belonging to the goethite phase. In two samples, a discrete sextet was overlapped, with hyperfine parameters comparable to those of hematite to make the adjustment. It was observed that the spectra obtained at 25 K presented magnetic splitting and was fitted with two discrete sextets. These two sextets were assigned to regions of magnetically different goethite. Considering the iron, other metals contents and the mineral phases identified in the concretions, which varied little from sample to sample, it was not possible establish any correlation between the mineralogy and the class or horizon of the soil where they were collected.