Utilização da lama de aciaria em um sistema de barreiras reativas permeáveis para remoção de cr(vi) de águas subterrâneas

Abstract

When soil or groundwater contaminations are identified, remedial action should be carefully investigated and implemented. Among these, permeable reactive barriers (PRB) technique is an interesting option. This technique consists on introducing reactive materials into the ground, perpendicularly to groundwater flow direction, aiming at the reaction of this material with contaminants present in groundwater and leading to their retention and/or transformation into less harmful species. This work proposes the use of steel waste, which is rich in iron, in order to obtain alternative materials for hexavalent chromium removal. Residues such as Basic Oxygen Furnace Coarse sludge (BOFCS) and the Basic Oxygen Furnace Fine Sludge (BOFFS), reduce contaminants through redox reactions, in which the present iron residue donates electrons to the contaminant. Firstly, batch tests were held, where fine and coarse sludge doses were added in suspension in known volumes of K2Cr2O7 solution in a concentration of 50 mg.L-1. Test results showed that the use of coarse sludge and fine sludge at a ratio equals 10 g.L-1, with no adjustments, can reduce up to 50% of hexavalent chromium present in the solution. However, when pH was reduced to 5.0 the efficiency increased to 58%. This indicates that Cr(VI) reducing activity was completely restored and that the pH strongly affects compounds activity and the reaction kinetics. After efficiency evaluation, column tests were performed, using coarse sludge only, which proved to be effective in Cr(VI) reduction and showed a favorable granulometry for the experiment. The reactive media (70% LGA + 30% sand) has achieved 100% removal, up to 12.2 percolated pore volumes (PV). It was possible to remove 0.213 mg of Cr(VI) for each coarse sludge gram. The bench reactor, which was developed in order to simulate real conditions of BRP implementation, has provided 100% removal efficiency for the first 19 days, which reduced to 95% after 71 days. The presence of iron and manganese oxides in the soil used in the assembly of the bench reactor, as shown by the chemical characterization analyzes, may have influenced chromium natural attenuation through reactions which form Cr, Fe and Mn complexes, and oxy-hydroxides of these metals, which precipitate in the soil. The use of BOF sludge as a permeable barrier reactive media, was proved to be a technological innovation which allows for both: waste reuse, which is currently hardly tapped and groundwater decontamination.