Mineralogical characterization of a highly-weathered soil by the Rietveld Method

Abstract

The mineralogical characterization through mineral quantification of Brazilian soils by X-ray diffraction data using the Rietveld Method is not common. A mineralogical quantification of an Acric Ferralsol from the Ponta Grossa region, state of Paraná, Brazil, was carried out using this Method with X-Ray Diffraction data to verify if this method was suitable for mineral quantification of a highly-weathered soil. The A, AB and B 3 horizons were fractioned to separate the different particle sizes: clay, silt, fine sand (by Stokes Law) and coarse sand fractions (by sieving), with the procedure free of chemical treatments. X-ray Fluorescence, Inductively Coupled Plasma Atomic Emission Spectrometry, Infrared Spectroscopy and Mössbauer Spectroscopy were used in order to assist the mineral identification and quantification. The Rietveld Method enabled the quantification of the present minerals. In a general way, the quantitative mineralogical characterization by the Rietveld Method revealed that quartz, gibbsite, rutile, hematite, goethite, kaolinite and halloysite were present in the clay and silt fractions of all horizons. The silt fractions of the deeper horizons were different from the more superficial ones due to the presence of large amounts of quartz. The fine and the coarse sand fractions are constituted mainly by quartz. Therefore, a mineralogical quantification of the finer fraction (clay and silt) by the Rietveld Method was successful. Key words: Acric Ferralsol, clay fraction, silt fraction, mineralogical quantification, X-ray diffraction Caracterização mineralógica de um solo altamente intemperizado pelo Método de RietveldRESUMO: A caracterização mineralógica por meio da quantificação dos minerais presentes em solos brasileiros por difração de raios X usando o Método de Rietveld é, ainda, pouco comum. Neste trabalho foi realizada a quantificação mineralógica de um Latossolo Vermelho ácrico da região de Ponta Grossa, Paraná, Brasil, utilizando o Método de Rietveld com dados de Difração de Raios X e também verificado se o método foi adequado na quantificação mineral de um solo altamente intemperizado. Os horizontes A, AB e B 3 foram separados fisicamente nas frações: argila, silte, areia fina (por meio da Lei de Stokes) e areia grossa (por peneiramento) sem qualquer tratamento químico. As técnicas de Fluorescência de raios X, Espectroscopia de Emissão Atômica com Fonte de Plasma Induzido, Espectroscopia de Infravermelho e Espectroscopia Mössbauer foram utilizadas para auxiliar na identificação e quantificação dos minerais. O Método de Rietveld possibilitou a quantificação dos minerais presentes nas frações argila e silte de todos os horizontes: quartzo, gibbsita, rutílio, hematita, goethita, caulinita e haloisita. Na fração silte os horizontes mais profundos são diferentes do mais superficial devido à presença de grandes quantidades de quartzo. As frações areia fina e grossa são constituídas principalmente de quartzo. Portanto, o Método de Rietveld foi adequado para quantificação dos minerais, princ...

X‐ray Diffraction and Rietveld Refinement in Deferrified Clays for Forensic Science

“…3), refinement index: S (1.24-1.58), R F 2 (1.96-6.54%), and R wp (7.26-10.30%) ( Table 2). These difference curves and index values were low and similar to other studies that analyzed soil clays using RM-XRD (20)(21)(22)(23).…”

“…The Rietveld method (RM) is a refinement adjust based on least squares calculus between observed and calculated diffraction patterns by mathematical models of optic phenomena and instrumental factors of diffractometer, crystalline structures, crystallite size, microstrain and other sample characteristics (18,19). Thus, by employing refinement through RM with XRD data (RM-XRD), it is possible to quantify the proportions of minerals and refine the crystalline structure of minerals present in the soils and soil fractions (8,9,11,(20)(21)(22)(23).…”

Influence of mineral composition of siliceous rock on its volume change

“…On the other hand, in recent years determination of mineral composition using XRD (X-ray diffraction)-Rietveld analysis has started to become established as a method in rock and soil engineering fields [16][17][18]. When minerals that shrink during drying can be determined with the XRD-Rietveld method, it may become a simple and useful method for the quality evaluation of aggregate because some expansive clay minerals that shrink in relation to the dehydration of interlayer water could have detrimental effects on the shrinkage of aggregate [13,19,20].…”

Tropical Soil Toposequence Characterization via pXRF Spectrometry

“…Soils formed from quartzite are normally poor in nutrients and rich in sand since ∼90% of the parent material is composed of quartz (SiO 2 ). As a mineral with a hardness of 7.0 on the Mohs scale, quartz is very resistant to weathering when it occurs in coarse fractions and is predominantly found in the sand size fraction of soils (Kämpf et al, 2009; Brinatti et al, 2010; Skorupa et al, 2016). However, scarce information exists about the dynamics of other elements in soils formed from quartzite.…”