Efeitos da lama de rejeito de mineração da Samarco sobre o crescimento e composição mineral de braquiárias

Abstract

The breach of a Samarco dam in 2015 resulted in the release of nearly 50 million cubic meters of tailings mud, causing severe socio-environmental damage. The subsequent outcry in the society for a sustainable destination of that mud was intense, with special reference to the possible application in agriculture. This research aimed to chemically characterize the mud and assess its impacts on the growth and mineral composition of brachiaria grasses, using samples collected one year after the incident at the Risoleta Neves Hydroelectric Reservoir. Scanning Electron Microscopy (SEM) morphological analyses revealed the tailings showed lesser agglomeration, more irregular texture, and less uniform shape than the soil. Energy Dispersion Spectroscopy (EDS) indicated distinct compositions, with high levels of Al, Fe, O, and Si in the tailings, and Al, Ca, Fe, Mg, O, P, Si, and S in the soil. X-ray Diffraction (XRD) showed the presence of quartz, goethite, and hematite in the tailings, and quartz, goethite, gibbsite, kaolinite, feldspar, and mica in the soil. Microwave acid digestion was applied to soil and tailings samples, and the element concentrations analyzed by Inductively Coupled Plasma Optical Emission Spectrometry (ICPOES), revealing higher levels of Al, Ca, Cr, Cu, Mg, Ni, and Zn in the soil. In contrast, the tailings exhibited elevated levels of Fe and Mn, with Cd concentration exceeding regulatory limits. In order to verify the feasibility of using the mud in agriculture, brachiaria seedlings were grown in different proportions of tailings and soil (0%, 25%, 50%, 75%, and 100%), among the physiological variables, an increase in the dry weight of the roots was observed. There was a decrease in K concentration in the roots and Ca in the aboveground part, an increase in Mn throughout the plant, and an increase in Fe in the roots with increasing tailings. Al, Cr, Cu, Na, Mg, and Zn were not significantly affected. Since N levels in the mud were very inferior to those in the soil, the effects of different nitrogen sources on the absorption of other elements were examined in Brachiaria seedlings, and it was verified that all nitrogen sources caused a slight increase in Cu and K in the whole plant and significant absorptions of Al, Fe, and Mg in the roots. The study suggested the feasibility of using Samarco's tailings mud for the cultivation of brachiaria grass, with recommendations for a gradual approach in the mud-soil ratio, constant monitoring, and controlled N addition.