S.A.C. Furquim
University of São Paulo
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Featured researches published by S.A.C. Furquim.
Clays and Clay Minerals | 2008
S.A.C. Furquim; Robert C. Graham; Laurent Barbiero; José Pereira de Queiroz Neto; Vincent Valles
Smectite formation in alkaline-saline environments has been attributed to direct precipitation from solution and/or transformation from precursor minerals, but these mechanisms are not universally agreed upon in the literature. The objective of this work was to investigate the mineralogy of smectites in the soils surrounding a representative alkaline-saline lake of Nhecolândia, a sub-region of the Pantanal wetland, Brazil, and then to identify the mechanisms of their formation.Soils were sampled along a toposequence and analyzed by X-ray diffraction, transmission electron microscopy-energy dispersive X-ray analysis, and inductively coupled plasma-mass spectrometry. Water was collected along a transect involving the studied toposequence and equilibrium diagrams were calculated using the databases PHREEQC and AQUA.The fine-clay fraction is dominated by smectite, mica, and kaolinite. Smectites are concentrated at two places in the toposequence: an upper zone, which includes the soil horizons rarely reached by the lake-level variation; and a lower zone, which includes the surface horizon within the area of seasonal lake-level variation. Within the upper zone, the smectite is dioctahedral, rich in Al and Fe, and is classified as ferribeidellite. This phase is interstratified with mica and vermiculite and has an Fe content similar to that of the mica identified. These characteristics suggest that the ferribeidellite originates from transformation of micas and that vermiculite is an intermediate phase in this transformation. Within the lower zone, smectites are dominantly trioctahedral, Mg-rich, and are saponitic and stevensitic minerals. In addition, samples enriched in these minerals have much smaller rare-earth element (REE) contents than other soil samples. The water chemistry shows a geochemical control of Mg and saturation with respect to Mg-smectites in the more saline waters. The REE contents, water chemistry, and the presence of Mg-smectite where maximum evaporation is expected, suggest that saponitic and stevensitic minerals originate by chemical precipitation from the water column of the alkaline-saline lake.
Trace Metals and other Contaminants in the Environment | 2007
Laurent Barbiero; S.A.C. Furquim; Vincent Valles; S. Furian; A. Sakamoto; A.R. Filho; Monique Fort
A distinctive feature of Nhecolândia, a sub-region of the Pantanal wetland in Brazil, is the presence of both saline (alkaline) and freshwater lakes. Saline lakes were attributed to a past arid phase during the Pleistocene, but recent studies have shown that the geochemistry of the saline lakes arises from the current concentration process of fresh waters that is supplied to the Pantanal every year. The region is mainly used for cattle farming, and more recently eco-tourism is becoming widespread and water conservation agencies have begun to worry about As contents in surface and shallow groundwater. The study was carried out along a 600-m-long transect that linked a freshwater lake to a saline lake. The spatial distribution of As is studied, based on soil morphology, according to pH, redox conditions (Eh) and dissolved organic carbon, and also compared to distribution of major elements. Three main processes, responsible for the chemical variability, were identified: (1) the concentration of the solution under the influence of evaporation and the associated precipitations (Mg-calcite, illite, sodium carbonate); (2) oxidation of sulphides included in clay layers and subsequent development of acid conditions and (3) buffering of acid conditions by clay dissolution. Arsenic contents are not affected by the last two processes (2 and 3), but evolve in proportion to the concentration. Arsenic concentrations in water ranged from 0.11 μg/l to 3.68 mg/l, i.e., 368 times higher than the World Health Organization guidelines for drinking water. The As speciation, as calculated from field conditions, indicated that the As(V) redox state dominated in the groundwater and in the lakes, whereas some proportion of As(III) could occur on the shore and in the sediments of the saline lake. Arsenic(III) from the sediment can be remobilized and dispersed into the water following the disturbance of the sediments by cattle that come to drink water. Arsenic contents increased with most of the other dissolved species; hence, competitive adsorption prevents dissolved As regulation by solid phase reaction. Moreover, the pH values increased above 8 with increasing As, favouring As(V) desorption. As a consequence, the good correlation established between As contents and electrical conductivity (r2 = 0.97) should help to indirectly evaluate the As contents in shallow groundwater and lakes of the region.
Geoderma | 2010
S.A.C. Furquim; Robert C. Graham; Laurent Barbiero; J.P. Queiroz Neto; Pablo Vidal-Torrado
Geoderma | 2008
Laurent Barbiero; A. Rezende Filho; S.A.C. Furquim; S. Furian; A.Y. Sakamoto; Vincent Valles; Robert C. Graham; Monique Fort; Rosely Pacheco Dias Ferreira; J.P. Queiroz Neto
Geoderma | 2010
S.A.C. Furquim; Laurent Barbiero; Robert C. Graham; José Pereira de Queiroz Neto; Rosely Pacheco Dias Ferreira; S. Furian
Catena | 2013
S.A.C. Furquim; Lylian Coltrinari; Rosely Pacheco Dias Ferreira; Selma Simões de Castro; Gabriel R. Pugliese
Archive | 2004
S.A.C. Furquim; J.P. Queiroz Neto; S. Furian; Laurent Barbiero; Robert C. Graham
Catena | 2019
Jairo Calderari de Oliveira Junior; S.A.C. Furquim; Alexandre Ferreira do Nascimento; Raphael Moreira Beirigo; Laurent Barbiero; Vincent Valles; Eduardo Guimarães Couto; Pablo Vidal-Torrado
Águas Subterrâneas | 2013
Fernanda Campos de Oliveira; Renata de Mello Rollo; S.A.C. Furquim; Claudio A. O. Nascimento; Juliana Gardenalli de Freitas
Geoderma | 2008
Laurent Barbiero; S.A.C. Furquim; Robert C. Graham; A. Rezende Filho; Vitor Bacani; S. Furian; Monique Fort; R.P. Dias Ferreira; J.P. Queiroz Neto; A.Y. Sakamoto
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Alexandre Ferreira do Nascimento
Empresa Brasileira de Pesquisa Agropecuária
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