Environmental factors and metals mobilisation in alluvial sediments - Minas Gerais, Brazil

Abstract

In areas contaminated by potentially toxic elements (PTEs), knowledge of processes of metal mobilisation is the basis for the choice of appropriate remediation methodologies. The mobilisation of metals is a function of several factors and the response to these factors must be well known during the planning of remediation strategies. The activity of an ore metallurgical plant in SE Brazil resulted in major contamination by several heavy metals. Reverting the contamination´s negative impact required the geochemical assessment of the area including the physicochemical characterization, quantification, and delimitation of PTEs and the rating of the solubilization/mobilisation capacity of these elements. The definition of spatial patterns for PTEs´ distribution allowed the construction of contamination risk maps working as a tool for the mitigation and control of the contamination plume. The chemical analysis of interstitial water and selective and sequential extraction methodologies showed that elements that occur in the environment in critical concentrations (Zn-Cd-Pb-As) are mostly associated with easily mobilised forms (soluble, exchangeable cations, associated with Mn-oxides). Given the great mobility of the contamination plume, any process of removal of contaminated material becomes unfeasible, so the strategy of remediation for the stream and associated alluvial deposits must be based on methods of in situ decontamination.