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The aim of this work was to study the use of coal waste to produce concrete paving blocks. The methodology considered the following steps: sampling of a coal mining waste; gravity separation of the fraction with specific gravity between 2.4 and 2.8; comminution of the material and particle size analysis; technological characterization of the material and the production of concrete paving blocks. The results showed that the coal waste considered in this work can be used to replace conventional sand as a fine aggregate for concrete paving blocks. This practice can collaborate in a cleaner coal production.

The presence of sulfur in coal processing wastes can lead to environmental impacts, such as acid rock drainage (ARD). However, not all sulfur species are acid-forming, and the implications of sulfur speciation when assessing acid rock drainage potential by means of static chemical tests are not well understood. This study set out to evaluate the implications of different sulfur forms on the assessment of acid rock drainage potential using static laboratory-scale tests and to investigate the reliability of methods for the analysis of such forms for the case of three South African coal processing wastes. Both the International Organization for Standardization (ISO) 157:1996 and Australian Coal Association Research Program (ACARP) C15034 protocols were found to be suitable tools for analyzing the different forms of sulfur. Acid-generating sulfur forms constituted between 53% and 64% of the total sulfur in the wastes evaluated, with the maximum potential acidity (MPA) and net acid-producing potential (NAPP) values calculated on the basis of acid-forming sulfur being significantly lower than those calculated on the basis of total sulfur content. Results also showed that the partial conversion of sulfur species under the relatively aggressive conditions of the acid-neutralizing capacity (ANC) and net acid generation (NAG) tests may overestimate the potential acid generating potential in the case of coal. These findings highlight the uncertainties associated with standard ARD static tests and the importance of taking sulfur speciation into account when calculating the MPA for coal processing wastes.

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Coal wastes contain many minerals, including the pyrite, which oxidize and generates the acid mine drainage (AMD), a highly polluting effluent. Currently, the Brazilian coal mining operations emphasise AMD control using waste water treatment systems which consume substantial amounts of reagents and generate large amounts of sludge. The aim of this work was to study the acid mine drainage control by another approach, the sulphide exclusion preventive method. The method comprises in removing the pyrite form coal tailings, reducing the acid generation and minimizing the metals load in wastewater treatment plants. Accordingly, a typical coal waste sample was submitted to a density separation process to divide the sample in the following relative density ranges: below 2.2, from 2.2 to 2.7 and above 2.7. All density fractions were submitted to ultimate and proximate analysis. Static and kinetic tests were carried with the raw waste and the pyrite-free fraction. The results showed that, by gravity processing of coal tailings, it is possible to decrease 30% the volume of wastes. The remaining material presents an acid generation potential of about 80-90% lower than the raw waste. Furthermore, it is expected a reduction in costs of reagents of approximately 85% in acid mine treatment plants.

ResumoO carvão mineral brasileiro contém altos teores de impurezas (pirita e minerais de rochas sedimentares), sendo necessário seu beneficiamento. Os rejeitos do beneficiamento demandam uma grande área física para a sua disposição, modificam a topografia e geram a drenagem ácida de minas (DAM). O objetivo desse trabalho foi caracterizar um típico depósito de rejeitos na região carbonífera de Santa Catarina, buscando a separação de três frações para uso futuro: (a) uma fração para a geração de energia; (b) uma fração enriquecida em silicatos; e (c) uma fração com alto teor de enxofre. A metodologia do trabalho consistiu na amostragem e caracterização do material. A caracterização incluiu análise granulométrica, estudos densimétricos, medidas do teor de cinzas e enxofre, análise mineralógica por DRX, estudos petrográficos em lupa e medidas de contabilização de ácidos e bases. Os resultados granulométricos indicaram que 68% do material é composto por partículas grossas, 15%, por partículas finas e 17%, pelo lodo das bacias de sedimentação. Com o beneficiamento gravimétrico dos resíduos é possível uma recuperação teórica do material de 33,7% para geração de energia e 10,3% para produção de um concentrado rico em pirita. O material restante, com menor quantidade de enxofre e rico em silicatos, tem seu potencial de geração de acidez reduzido em 60% e apresenta possibilidade de uso na construção civil. Palavras