PROCESS OF GENERATING ACID MINE DRAINAGE AND HEAVY METAL CONTAMINATION IN PROFILES OF REBUILT SOIL IN A COAL MINING AREA

Dioni Glei Bonini Bitencourt Luiz Fernando Spinelli Pinto Eloy Antonio Pauletto Mariana Tavares Silva Gabriel Furtado Garcia About the authors

ABSTRACT

Soils rebuilt after coal strip mining is composed of topsoil and, or, overburden, and their chemical properties differ from those of natural soils mainly due to the sulfurization process. The objective of this study was to evaluate the potential for acidification from sulfides and heavy metal contamination across profiles of soils rebuilt after coal mining, in areas of different ages, with and without concomitant environmental reclamation during mine operations. Mining areas of different ages were selected: areas I and II, without environmental reclamation during extraction and composed only from overburden, representing the oldest areas; and areas IV and VII, containing topsoil and, in some profiles, a clay layer (B and BC horizons from the natural soil) between the topsoil and the overburden, constituting the younger rebuilt mine soils. Soil pits were opened and disturbed samples were collected up to a depth of 2 m. Determinations were made of soil particle size, particle density, pH, Ca, Mg, Al, K, Na, P, H+Al, acidity potential, neutralization potential, net potential, organic C content, and electrical conductivity in saturated paste. In addition, potentially bioavailable metals were extracted by the USEPA 3050B method (Fe, Al, Mn, Ba, Cu, Zn, C, Cr, Co, Cd, Pb, Mo, As, and Se), and the results were compared to the guideline values of prevention and investigation for soils. In univariate analysis, descriptive statistics and the Kolmogorov-Smirnov test were applied. The degree of dispersion of each variable, expressed by the coefficient of variation, was qualitatively evaluated and classified as low, moderate, or high. Multivariate principal component analysis (PCA) was carried out for the constructed mine soils of areas I and II, and IV and VII, and then biplots were applied to the first principal components. The rebuilt mine soils from the oldest areas (I and II) showed lower pH (<3.2) and higher acidification potential. The topsoil and clay layers in areas IV and VII, in spite of providing favorable chemical conditions for surface vegetation, did not prevent acid mine drainage from developing in the subsurface. The sulfurization process and its relationship to release of metals was best characterized by principal component analysis performed in soils from areas IV and VII because the correlation between pH and base saturation in overburden layers is only expressed in base saturation above 40 %, which was not observed in rebuilt mine soils from areas I and II.

degraded mining areas; pyrite; metal contamination; principal component analysis

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