Transformação de fases e estabilidade de arsênio (As) coprecipitado com(hidr)óxidos de Fe eAI

Abstract

Arsenic (As) is an element that can cause risks to human health when present in large amounts in the environment. According to the World Health Organization, As is carcinogenic in high concentrations, and the tolerable value in drinking water is up to 10 μg L-1. Among the treatment strategies for As-contaminated effluents, co precipitation with Fe and Al (hydro)oxides stands out. Geochemical barriers formed by these (hydro)oxides are also considered efficient to immobilize As, due to the high affinity of this element by Fe. To verify the stability and efficiency of these barriers, phase changes caused by temperature changes, thermogravimetry tests and infrared spectrometry by Fourier transform were carried out. A selection of samples was also carried out for a mineralogical analysis by X-ray Diffraction. As contents were evaluated through oral (atomic absorption) and pulmonary (atomic fluorescence spectrophotometry) bioaccessibility tests. XRD analysis identified the following mineral phases; hematite (Hm), goethite (Gt), magnetite (Mn), ferrihydrite (Fh), iron sulfide (FeS), maghemite (Mg), alunite (Al), gibbsite (Gb), lepidocrocite (Lp) and bayerite (Ba ). With infrared spectrometry, it was possible to demonstrate the differences between samples with and without heating, whose vibrational peaks were different, in the samples, as a function of temperature. Thermogravimetric analyzes:thermogravimetry (TG), derived thermogravimetry (DTG) and differential exploratory calorimetry (DEC)allowed identifying endo and exothermic peaks resulting from phase transformations. The increase in temperature influenced the phase changes. The iron valences (Fe2+ and Fe3+), the presence of Al, as well as the valences and arsenic concentrations (As3+ and As5+) exerted influence on the phase change process. the thermal treatment does not provide a greater trapping of As in the crystal lattices, and may increase the As content available on the surface of the minerals.