Transformation of Kaolinite into Smectite and Iron-Illite in Brazilian Mangrove Soils

Author(s)

Pugliese Andrade, Gabriel Ramatis ^[1] ; de Azevedo, Antonio Carlos ^[1] ; Cuadros, Javier ^[2] ; Souza, Jr., Valdomiro Severino ^[3] ; Correia Furquim, Sheila Aparecida ^[4] ; Kiyohara, Pedro K. ^[5] ; Vidal-Torrado, Pablo ^[1]

Affiliation

^[1] Univ Sao Paulo, ESALQ, Dep Ciencia Solo, BR-13418900 Piracicaba, SP - Brazil

^[2] Nat Hist Museum, Dept Earth Sci, London SW7 5BD - England

^[3] Univ Fed Rural Pernambuco UFRPE, Dept Agron, BR-51171900 Recife, PE - Brazil

^[4] Univ Fed Sao Paulo UNIFESP, Inst Ciencias Ambientais Quim & Farmaceut, BR-09972270 Diadema, SP - Brazil

^[5] Univ Sao Paulo, Inst Fis, BR-05314970 Sao Paulo - Brazil

• Document type: Journal article
• Source: Soil Science Society of America Journal; v. 78, n. 2, p. 655-672, MAR-APR 2014.
• Web of Science Citations: 10

Abstract

This study investigated soil clay mineralogy of mangrove forests along the Brazilian coast in eight regions of different environmental characteristics, with a focus on the crystallochemical features and genesis of 2: 1 phyllosilicates. Samples from two different depths (0-30 and 60-90 cm) and two clay size fractions (<2 and <0.2 mu m) were studied. The analytical tools used were X-ray diffraction, Fourier-transform infrared spectroscopy, and transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS). A complex assemblage was found in both fractions, including high proportions of kaolinite, illite (Fe-illite/glauconite), and smectite (Fe-beidellite, Fe-montmorillonite), minor amounts of gibbsite and quartz, and traces of K-feldspar, halloysite, and amphibole crystals (TEM-EDS data). Evidence of illite-smectite and possibly kaolinite-smectite mixed-layer phases was found in the <0.2-mu m fraction. An authigenic transformation process likely taking place, from kaolinite to Fe-illite/glauconite, through transitory kaolinite- smectite and illite-smectite phases. The reaction is triggered by high Fe activity in solution generated by dissolution of Fe oxides and pyrite present in the sediment, at approximately neutral pH and high salt content in the water. Smectite illitization takes place by substitution of Al3+ for Si4+ in the tetrahedral sheet, of Fe and Mg2+ for Al3+ in the octahedral sheet, and progressive Fe reduction, all of which produces an increase in the layer charge and K uptake. The sequential nature of the transformation (kaolinite-smectite-illite) suggests a solid-state transformation process. Two unusual kaolinite-rich mangroves were found, indicating low reactivity or high deposition rate of continental sediments of soils derived from the Barreiras Group, dominated by kaolinite. (AU)

• FAPESP's process: 09/51453-0 - Mineralogy of mangrove soils of Brazilian coast
• Grantee: Pablo Vidal Torrado
• Support Opportunities: Regular Research Grants