Main chemical and mineralogical components of the Rio Doce sediments and the iron ore tailing from the Fundão Dam disaster, Southeastern Brazil.

Since the Fundão Dam rupture in Southeastern Brazil caused an enormous amount of iron ore tailing (IOT) to be discharged into the Doce River Catchment, various works have been published on the soil, water, and biota contamination by potentially hazardous trace metals. However, the objective of this study is to investigate changes in the main chemical composition and the mineral phases, which has not been studied yet. We present an analysis of sediment samples collected in the Doce River alluvial plain, before and after the disaster, as well as the tailing deposited. Granulometry, main chemical composition by X-ray fluorescence spectrometry, mineralogy by X-ray diffractometry, quantification of mineral phases using the Rietveld method, and scanning electron microscope imaging are shown. We conclude that the Fundão Dam rupture introduced fine particles into the Doce River alluvial plain, increasing the Fe and Al content in the sediments. The high Fe, Al, and Mn contents in the finer iron ore tailing fractions represent environmental risks for soil, water, and biotic chains. The IOT mineralogical components, mainly the muscovite, kaolinite, and hematite present in the finer particles can increase the sorption and desorption capacity of harmful trace metals depending on the natural or induced redox conditions, which are not always predictable and avoidable in the environment.

Trace metals in Rio Doce sediments before and after the collapse of the Fundão iron ore tailing dam, Southeastern Brazil.

The collapse of the Fundão Dam, in Southeastern Brazil, caused about 50 million m³ of iron ore tailings to sluice down the mountain to Rio Doce, in what is considered the greatest environmental disaster in Brazilian history. The fluvial system received an intense and sudden mudflow that was transported for more than 650 km, before reaching the Atlantic Ocean. Because the area was already impacted by the mineral activities in the region, it becomes essential to evaluate the environmental conditions before the disaster to correctly assess the disaster real damage. This study compares the concentration of trace metals in the sediments of the Rio Doce alluvial plain, before and after the dam collapse, as well as the newly deposited iron ore tailings that became part of the sedimentary framework. The data indicate that the fine particles deposited have since been incorporated into the sandy river sediments. The cadmium and arsenic contents in the sediments increased to levels above the National Environment Council thresholds. The comparison between the levels of trace metals in the situations before and after disaster shows that the mining mud is the source of cadmium while the arsenic was present before the environmental disaster, and its concentration increased due to sediment remobilization. The iron ore tailings deposited on the alluvial sediments also affected the physical parameters since the formed ferruginous crusts waterproofed the ground surface and may, gradually, release toxic metals when exposed to weathering and river reworking.