Environmental monitoring of magnetic iron phases of urban water reservoir lake sediments (Taiaçupeba Lake, metropolitan region of São Paulo, Brazil) by using Mossbauer spectroscopy

In the present work, we investigate the iron oxides and oxyhydroxides behavior and evolution, related to the geochemical behavior of some metals, which could be retained as solid phases in the sediments from an urban water reservoir lake, placed in Taiaçupeba, Great São Paulo, Brazil. These tasks were performed by the establishment of a proceduring setting for environmental monitoring analysis through Mössbauer spectroscopy measurements associated to hysteresis loops measurements and chemical analysis [X-ray fluorescence (XRF)]. We inferred the possibility of goethite occurrence in broad particle size distribution (5–50 nm), and related to ferrihydrite, and small grain-size hematite (about 8 nm). The magnetometry results pointed to the paramagnetic/superparamagnetic behavior of the magnetic phases present in the samples and also suggested the occurrence of small grain-size magnetite. We also verified the presence of clay minerals related to Fe, as well as the occurrence of Fe3+ and/or Fe2+ in short-range structural order. Through a straight correlation among Mössbauer spectra data gained at T = 77 K and Al-metal, metal-Fe molar ratios, provided through XRF data, we found remarkable indications of interference on meta-stable phases evolution to its final products. Such results can be pointing for evidences about the possible isomorphic replacing and/or adsorption of Al and other metals in goethite and hematite.