Estabilização in loco de rejeito de mineração de urânio em matriz cimentícia

Abstract

The Decommissioning Unit of Caldas from Indústrias Nucleares Brasileiras (DUC-Caldas) shows a strong reason for environmental concern due to the phenomenon of acid mine drainage (AMD) that occurs. AMD is a chemical process in which sulphide minerals are subjected to the action of water and oxygen, being oxidized and consequently producing an acidic solution that damages soils and aquatic systems. However, the problem mentioned has an aggravating factor, because the solution produced has a radioactive character and this is due to the fact that the residue exposed to the action of AMD is configured as uranium ore waste. Currently, the only mitigation action used in the installation is the treatment of acidic water with hydrated lime, aiming at the precipitation of contaminants. However, this neutralization results in another problem which is the formation of the residual compound known as CADU (calcium diuranate containing metal hydroxides). This residue indicate a danger for the AMD mitigation solution because, besides contaminating soil and water, it can also resolve the contaminants that have already precipitated during the treatment of acidic water. Therefore, a resource for this problem is the immobilization and stabilization of this residue in Portland cement, a proposal which this work aims to study. This solution aims to reduce the contamination potential, reducing mobility, solubility and toxicity of waste. This can be achieved when the residue is encapsulated in a matrix that has high structural integrity. Thus, this study has as main objective the determination of a viable formulation using Portland cement, acid lagoon water, CADU and superplasticizer additive, which is capable of mechanically immobilizing the waste. Furthermore, to evaluating the mechanical resistance to compression and resolubilization of contaminants through leaching tests. Then, 6 specimens were made for 4 compositions that differ in relation to the proportions of the components. The specimens were subjected to submerged curing for a period of 14 days and then to a compression test in accordance with the ABNT-NBR 5739 standard. The leaching tests followed the ABNT-NBR 10005 standard. The minimum mechanical resistance shown was 6.41 ± 0.43MPa, while the highest was 8.98 ± 0.74MPa. In the leaching tests, the pure residue presented 5.33 ± 0.33mg/L of uranium and the best result obtained was 0.0127 ± 0.0016mg/L of leached uranium, thus being below the permitted limits. Therefore, it can be said that Portland cement is a viable alternative for the described problem.