Abstract
Coal mine waste rocks produced during mining and beneficiation can affect the environment due to land degradation and acid mine drainage generation. However, proper characterization and treatment of mineral processing wastes creates options for safe disposal, enhancing the environmental performance. The aim of this study was to use static and kinetic tests to assess properties of coal waste produced at the Moatize Mine in Mozambique, one of the largest "world-class" coal deposits. The study included sampling and characterization of coarse and fine wastes generated during coal beneficiation. Both materials were analyzed in terms of granular properties, static procedures - immediate composition, sulfur forms, mineralogical composition, elemental composition, acid-base balance - and kinetic behavior in humidity cell tests. The conjugation of these techniques indicates that these wastes have a low water acidification potential and low geochemical mobility of toxic elements. Therefore, it was concluded that fine and coarse wastes could be used in land shaping procedures.
Highlights
The extraction of coal is an activity practiced around the world, as it is used to generate thermal energy and metallurgical coke
Considering the apparent density, 1.18 g cm-3 with an empty space among particles of 39% was found for the coarse material
The acid-base accounting of the coal waste from the Chipanga seam of the Moatize Mine, both coarse and fine waste, have a slightly alkaline behavior, which is explained by the low concentration of pyrite and the presence of carbonates
Summary
The extraction of coal is an activity practiced around the world, as it is used to generate thermal energy and metallurgical coke. In most coal mines, the extracted material does not present adequate specifications for use, and must undergo a beneficiation process. The pyrite (FeS2) oxidation is the main cause of Acid Mine Drainage (AMD) generation. Sulfide oxidation occurs whenever water in the presence of oxygen percolates through pyrite bearing rocks, acquiring high acidity and high concentrations of Fe (as Fe2+ and/or Fe3+) and sulfates (Kontopoulos, 1998; Simate and Ndlovu, 2014). Due to its low pH, the AMD can solubilize and mobilize other metals present in the waste, compromising the quality of surface and ground water (Akcil & Koldas, 2006; Grande et al, 2018) and soils that it might contact (Chen et al, 2015; Yang et al, 2016)
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