Avaliação do potencial de sorção de corantes e elementos potencialmente tóxicos em rejeito da mineração de ferro

Abstract

While mining generates a lot of wealth, the activity also results in major environmental impacts, such as the large amount of tailings stored in dams. Without an environmentally and economically viable destination, it becomes necessary to carry out new constructions of these structures subject to accidents. Due to the characteristics of the material, rich in Fe, Al and Mn oxhydroxides, the iron ore tailings could, for example, be used in the sorption of contaminants. Thus, the present study aimed to characterize the iron ore tailings extracted from a dam in the Iron Quadrangle and evaluate its potential sorbent of dyes and potentially toxic elements. The characterization of the tailings included scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), textural analysis and also physical, chemical and physical-chemical evaluations of the material. In the tests with dyes, two dyes were used, one cationic (methylene blue) and the other anionic (Congo red), submitted to different pH, concentrations and contact times. The tests with potentially toxic elements included the elements arsenic, lead and manganese, chemical elements found in relatively higher concentrations in waterways near areas of iron ore mining in Minas Gerais. Based on the results obtained, it was observed that the tailings present characteristics of a material with high specific mass, low porosity, high sand content, heterogeneous, with predominance of the mineralogical fractions hematite, magnetite and quartz; high presence of Fe and Mn; low CEC and good base saturation; Zero Load Point (PCZ) of 6.5; and can be classified as Class IIA waste. Based on these characteristics, the residue can be used as sorbent (important presence of Fe and Mn oxyhydroxides). There was a better sorption efficiency for the cationic dye at alkaline pH (above the PCZ), while for the anionic dye, the efficiencies were higher at acid pH. The efficiencies reached 96% for methylene blue (initial concentration = 50 μmol L-1, pH = 10 and 48 h contact time) and 94% for congo red (50 μmol L-1, pH = 3 and 48 h). Regarding potentially toxic elements, the adsorption of Pb was the highest among the contaminants evaluated, obtaining maximum efficiency of 45% (pH = 6.5 and contact time of 48 h), presenting 30 and 15% removal of As and Mn, respectively, in the same conditions. Based on results, it can be seen that the tailings have constituents with potential use in the removal of contaminants from wastewater from textile industries and effluents that contain potentially toxic elements. Thus, it can be better used, as was the case with other solid industrial wastes, such as steel mill slag. It is hoped that this work can contribute to the development of adsorptive technologies that can be inserted into the production chain, acting as a secondary destination for ore tailings, thus valorizing the by-product.