Environmental risk assessment following Brazilian mining dam collapse: A diffusion approach

An iron mining waste containment dam in southeastern Brazil has collapsed, causing devas- tating impacts on the Doce River Basin. This study examines the long-term effects of sludge on the mobility of potentially toxic elements (PTE) in soil. For this purpose, soil samples were subjected to diffusion tests. The planar source method predicts the behavior of species in a single direction using the diffusion coefficients in the environment. Fick’s laws provide a viable mathematical approach to analyzing diffusion data and have been modified to account for porous media. The migration of the PTE is modeled using a Gaussian profile to determine the diffusion coefficients for the species. Herein, the aim is to provide a comprehensive assess- ment of the effects of sludge on the mobility of PTEs within the soil environment. The planar source method was carried out in horizontal columns over 7 days, with the sludge serving as the central head of PTE. The PTE concentration in 1.0 mm sections and the distances were processed according to Fick’s laws using MatlabTM. The data set and algorithms are described below for both one-Gaussian and double-Gaussian models. Diffusion coefficients for Pb, Ni, Cr, and As were found to be around 10−12 m2 s−1 for porous media from Gaussian modeling, indicating the potential of sludge-soil migration. Additionally, three-dimensional surface modeling was simulated for PTE diffusion in soil using experimental diffusion coefficients covering a period of 10,000 years and a migration distance of 5 m to obtain an S-surface and characterize more than one step in the migration kinetics. The 3D-Surface algorithm is also described in the sequel. The proposed diffusion process, which unfolds in three steps over time, supports the concept of species interconversion related to the release of PTE and the heightened associated risk.

Keywords: mining disaster, potentially toxic element, ion mobility, Doce River basin, mining sludge