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 South-East Brazil resulted in major contamination by several heavy metals. Reversing the contamination’s negative impact required geochemical assessment of the area, including the physicochemical characterisation, quantification, and delimitation of PTEs, and the rating of the solubilisation/mobilisation capacity of these elements. The definition of spatial patterns for PTEs’ distribution allowed the construction of contamination risk maps which work 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, thus the strategy of remediation for the stream and associated alluvial deposits must be based on methods of in situ decontamination.
Highlights
Mineral extraction and processing activities around the world contribute significantly to solute loads in receiving streams and aquifers [1]
The slightly more alkaline environment especially identified in the deeper layers of the alluvium after the rainy season might be a result of the increased leaching rate of sulphates accumulated in areas closer to the plant, with the subsequent accumulation in the lower less porous and impermeable deposits
The activity of an ore metallurgical plant in South-East Brazil (Minas Gerais State) has resulted in contamination by several heavy metals, which extends through the alluvial plain of a small stream (Consciência creek) and its affluent (Grota Seca creek)
Summary
Mineral extraction and processing activities around the world contribute significantly to solute loads in receiving streams and aquifers [1] In these streams, sediments are, more often than soils, contaminated with multiple chemicals [2] becoming potential sources of pollution with adverse effects on water resources through the mobilisation of contaminated particles and the release of contaminants into the water phase after natural or artificial resuspension of sediments. Sediment may act as an intermediate or permanent repository, using the ability of a sedimentary body to immobilise potentially hazardous substances over the long term [3] Both distinct functions make risk assessment and sediment management decision-making challenging and complex [3,4]. The other two parameters are the sill (C1) and the Range (a), which define correspondingly the inertia used in the interpolation process and the variable structure influence zone (Table 1)
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