Geochemistry of natural chromium occurrence in a sandstone aquifer in Bauru Basin, Sao Paulo State, Brazil

Autor(es)

Bertolo, Reginaldo ^[1] ; Bourotte, Christine ^[2] ; Hirata, Ricardo ^[1] ; Marcolan, Leonardo ^[1] ; Sracek, Ondra ^{[3, 4]}

Afiliação do(s) autor(es)

^[1] Univ Sao Paulo, Inst Geosci, CEPAS Groundwater Res Ctr, BR-05508080 Sao Paulo - Brazil

^[2] Univ Sao Paulo, Sch Arts Sci & Humanities EACH, BR-03828000 Sao Paulo - Brazil

^[3] Palacky Univ, Fac Sci, Dept Geol, Olomouc 77146 - Czech Republic

^[4] OPV Sro Protect Ground Water Ltd, Prague 16900 6 - Czech Republic

• Tipo de documento: Artigo Científico
• Fonte: APPLIED GEOCHEMISTRY; v. 26, n. 8, p. 1353-1363, AUG 2011.
• Citações Web of Science: 13

Resumo

Anomalous concentrations of Cr(VI) occur in groundwaters of the Adamantina Aquifer, in a large region in the western state of Sao Paulo, sometimes exceeding the potability limit (0.05 mg L(-1)). To identify the possible geochemical reactions responsible for the occurrence of Cr in groundwater in Urania, borehole rock samples were collected in order to carry out mineralogical and chemical analyses. In addition, multilevel monitoring wells were installed and groundwater samples were analyzed. Analyses of the borehole rock samples show the occurrence of a geochemical anomaly of Cr in the quartzose sandstones (average concentrations of 221 ppm). Chrome-diopside is one of the main minerals contributing to this anomaly, having an average Cr content of 1505 ppm. Sequential extraction experiments indicated weakly adsorbed Cr in the order of 0.54 ppm, and this quantity is enough to provide the Cr concentrations observed in groundwater. Groundwaters from the monitoring wells proved to be stratified, with the highest concentrations of Cr(VI) (0.13 mg L(-1)) being associated with high redox and pH values (over 10) and high concentrations of Na. Geochemical reactions that may explain the release of Cr from the solid phase to groundwater involve the release of Cr(III) from minerals (like chrome-diopside and Cr-Fe hydroxide), followed by oxidation of Cr(III) to Cr(VI), probably related to the reduction of Mn oxides present in the aquifer. Then cation exchange occurs and dissolution of carbonates which increases the pH of groundwater, resulting in the desorption and mobilization of Cr(VI) into groundwater. (C) 2011 Elsevier Ltd. All rights reserved. (AU)

• Processo FAPESP: 97/13879-6 - Os mecanismos controladores da partição do cromo no sistema rocha-solo-água no aquífero Bauru, Noroeste do estado de São Paulo
• Beneficiário: Ricardo César Aoki Hirata
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 98/15340-0 - Hidrogeologia e modelagem hidrogeoquímica da zona não saturada do Aquífero Adamantina
• Beneficiário: Reginaldo Antonio Bertolo
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 05/60502-3 - Complementação da investigação hidrogeoquímica do cromo no Aquífero Adamantina em Urânia, SP
• Beneficiário: Reginaldo Antonio Bertolo
• Modalidade de apoio: Auxílio à Pesquisa - Regular