Waste and Destination of Hazardous Contaminants in Some Pile

7/27/2019 Waste and Destination of Hazardous Contaminants in Some Pile

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WASTE AND DESTINATION OF HAZARDOUS CONTAMINANTS IN SOME PILEOF ANTHRACITE MINING IN PORTUGAL AND MINERAL SPECIATION.

Felipe Leo, Marcio A. Kronbauer, Marcos L.S. Oliveira, Csar M. N. L. Cutruneo, Joana Ribeiro, Luis F.

O. Silva

University Center La Salle, Master in Environmental Impact Assessment in Mining, Av. Victor Barreto, 2288, Canoas-RS, Brazil

E-mail: [email protected]

ABSTRACT

The coal (anthracite A) in Douro Coalfield (NW of Portugal) has been exploited for many years and has been mainly used as

fuel supply by a thermal power plant. The mining activities inevitably impacted the environment, which includes a large numberof coal waste piles emplaced over the old mine sites and adjacent areas of the Douro Coalfield. The disposal of coal mining

residues represents significant environmental concerns due to their potential influence on soils and sediments, as well as on the

surface and groundwater of the surrounding areas. In the present study, the development of sequential extraction combined with

various advanced analytical techniques was performed to provide an improved understanding of the complex processes related

with sulfide-rich coal waste oxidation, sequences of mineral formation, and the transport mechanisms of hazardous elements by

specific neoformed soluble minerals. The results showed the presence of amorphous iron (oxy-) hydroxides and goethite with

various degrees of crystallinity, containing hazardous elements, such as As, Cr, Hg, Mo, Se, Pb, U, and others. Some of the

neoformed minerals found in the coal waste material are the same as those commonly associated with coal acid drainage, in which

oxidation of sulfides plays an important role. The precipitated neoformed minerals include pickeringite, bldite, and a mixture

of epsomite, pickeringite, and hexahydrite. As these sulfates may dissolve after the first rain, they may release above-mentioned

elements into surrounding water bodies.

KEYWORDS: Coal mining residues; Sequential extraction; Sulfide oxidation; Sulfate potential environment effects.

1. INTRODUCTION

Coal mining activities sometimes have adverse impacts on environment and human health, despite

their undeniable benefits to the economic and social sectors of many countries (Orem and Finkelman, 2004;

Surez-Ruiz and Crelling, 2008; Surez-Ruiz et al., 2012; Younger, 2004). The potential environmental

impact and health problems related to coal mining, processing and utilization depends on many factors,

such as coal composition, geological setting, local hydrology, climate, topography, mining methods and

combustion technologies, and local regulations, among others (Dai et al., 2004, 2008, 2012, 2013; Querol etal., 2008, 2011; Surez-Ruiz and Crelling, 2008).

In general, the environmental risks associated with coal mining, both developed by open-cut mining

or underground techniques, may include changes in landscape and land use, soil erosion, increased noise

generation, production of solid wastes, air pollution, surface and groundwater pollution, soil and sediment

pollution, land instability and subsidence, coal mine fires and several impacts on local biodiversity (Bell

et al., 2001; Surez-Ruiz and Crelling, 2008; Surez-Ruiz et al., 2012; Younger, 2004). The generation

and disposal alone of solid wastes, which are essentially made up of discarded and overburdened material

resulting from coal mining/utilization activities (Izquierdo et al., 2007, 2008, 2011; Medina et al., 2010),

may cause various environ-mental problems from those mentioned above and others such as atmospheric

dispersion of particles, spontaneous combustion of waste piles, landslides and mass movements in the waste

piles, mobilization of material, leaching of elements, and formation of acid drainage caused by weatheringand/or oxidation processes (Huggins et al., 2012; Querol et al., 2008, 2011; Ribeiro et al., 2010a,b, 2011,


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2012; Surez-Ruiz et al., 2012). For these reasons, the coal waste piles from anthracite mining in Portugal

are worthy of investigation.

1.1 Case study and objectives

The Douro Coalfield (NW of Portugal) is the most significant terres-trial Carboniferous (Upper

Pennsylvanian [Lower Stephanian C]) coal basin in Portugal (Eagar, 1983; Fernandes and de Jesus,

1997; Lemos de Sousa and Wagner, 1983), with NWSE alignment, a variable width (30250 m) and

approximately 53 km in length (Pinto de Jesus, 2001).Fig. 1illustrates the geographical and geological

setting of the Douro Coalfield.

The coal-bearing deposits of anthracite A (ISO, 11760, 2005) from the Douro Coalfield had been

exploited for many years (17951994), and the mining activities have inevitably impacted the environment

because coal mining started at the end of the 18th century when there was no great concern about

environmental issues. A large number of coal waste piles (28 were identified) found emplaced over theold mine sites and adjacent areas of the Douro Coalfield represent significant environmental concerns

due to their potential influence on soils and sediments, as well as on the surface and groundwater of the

surrounding areas (Ribeiro et al., 2010a, 2011, 2012).

The Serrinha waste pile, the object of the present study, was accumulated by simple discharge in a

topographical depression of overburdened material from the Pejo mining area in Douro Coalfield. The

waste pile is essentially made up of 2 million tones of shale and carbonaceous shale. These materials

are heterogeneous, dark in color, and with variable particle size, from a few m to some cm (Gama and

Arrais, 1996). Previous studies about the Serrinha coal waste pile revealed the petrography, mineralogy,

and geochemistry of the waste material, soils from surrounding areas, and sediments and waters from the

drainage system (Ribeiro et al., 2010b).

For further information for the assessment of environmental impact associated with the Serrinha coalwaste pile and for the remediation of affected soils and waters, the study on the impacts that these materials

are causing on the environment and their urban extent are required. Therefore, the objectives of this work

are: (i) to identify and characterize the primary and neoformed mineral phases present in coal mining

residues from the Serrinha waste pile; (ii) to define the fate and the leaching potential of some hazardous

elements; and, (iii) to assess potential effects on environment and human health.

2. SAMPLING AND ANALYTICAL METHODOLOGY

The samples collected from the Serrinha coal waste pile include precipitated neoformed minerals

and the underlying material. The neoformed minerals were found at the base of the waste pile where aninefficient drainage system exists (broken and overflowing decanting basin; Fig. 2). The underlying material

consists of coal mining residues, which are a mixture of shale and carbonaceous shale with disseminated

coal.

The analytical methods applied in this study include X-ray powder diffraction (XRD), field emission

scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and

mineral sequential extraction. To obtain an appropriate geochemical interpretation, it is very important to

combine the application of XRD, FE-SEM, and HR-TEM mineralogical analyses to coal mining residues

with mineral sequential extraction, because it provides an improved understanding of the retention behavior

of mobile elements by specific neoformed soluble minerals and crystallization properties. The following

paragraphs give a brief description of the procedures which were fully presented in previous works

(Cerqueira et al., 2011; Oliveira etal., 2012; Quispe et al., 2012; Ribeiro et al., 2010c; Tian et al., 2008).


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3. CONCLUSIONS

A large number of coal waste piles emplaced over the old mine sites and adjacent areas of the Douro

Coalfield (NW of Portugal) represent significant environmental concerns due to their potential influence on

soils and sediments, as well as on the surface and groundwater of the surrounding areas.

Some of the neoformed minerals found in the studied coal waste material (such as epsomite, jarosite,

hematite, and others) are the same as those commonly associated with coal acid mine drainage or coal waste

acid drainage, in which oxidation of sulfides plays an important role. Oxidation of sulfides in the coal waste

pile materials generates sulfuric acid, which aggressively attacks aluminosilicates. This weathering process

introduces considerable Al, Fe, Mg, and K into solution.

The sulfates precipitated at the base of the Serrinha waste pile, e.g., pickeringite, bldite, and a

mixture of epsomite, pickeringite, and hexahydrite, may dissolve after the first rain, and then may release

some hazardous elements into surround water bodies.

The potential environmental impacts associated with the coal waste disposal comprise air pollutioncaused by gas emissions and particles dispersion; soil, surface and groundwater pollution caused by

mobilization of solid particles, leaching of hazardous elements, dissolution of neoformed minerals, and

deposition of atmospheric particles; and deterioration of vegetation caused by acid drainage. The effects on

human health are related with the particle dispersion of the waste materials, and the pollution of soils and

waters which may affect human health through water consumption and land use for agriculture.

4. FIGURES

Figure 1


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Figure 1 - Geographical and geological setting of Douro Coalfield (modified fromPinto de Jesus, 2001) and

location of the Serrinha coal waste pile.

Figure 2

Figure 2 - Serrinha waste pile: decanting basin in the bottom of the waste pile; note the white precipitated

neoformed minerals and the partial destruction of the basin structure.

Figure 3


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Figure 3 - FE-SEM secondary electron image of alunogen and gypsum in the neoformed minerals after the

first step of sequential extraction.

Figure 4


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Figure 4 - (A) FE-SEM secondary electron images and EDS spectra of mixed jarosite group (natrojarosite

and jarosite) containing Cr and aluminum silicates. (B) Natrojarosite EDS element mapping.


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