This work evaluates the benefits of a complementary treatment step of acid mine drainage (AMD) using the algae Scenedesmus sp. in terms of algae biomass production, residual metal removal, and the toxicity of the discharged water. Conventional treatment by neutralization/precipitation of an AMD from a coal mine in Brazil was conducted with Ca(OH)₂ at pH 8.7. Algal growth studies were performed in the treated AMD, with and without a nutrient supply. The raw effluent and treatments were compared in terms of residual concentration of metals and sulfate, conductivity, and toxicity with the Allium cepa and Daphnia magna test organisms. The results show that the conventional treatment allowed a major metal removal, reduction in the conductivity, and good indices in the toxicological parameters evaluated. The biosorption with in vivo microalgae improved the quality of the effluent for residual metals. No significant toxicity was observed to Allium cepa in all treatments performed, while the Daphnia magna test indicated a reduction in toxicity after the biosorption step. It was concluded that algae growth can be carried out in treated mine waters, providing algae biomass and helping to achieve the standards for water discharge.

O 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.

The treatment of fine particles dispersed in liquids is common in several industries and especially important in mineral processing. The efficiency of settling operations can be substantially increased by flocculation. The aim of this work was to study the flocculation of fine fluorite particles by the bacterium Corynebacterium xerosis. Flocculation tests, microelectrophoresis measurements and optical microscopy were used to evaluate flocculation. The results showed that C. xerosis cells adhere to the fluorite surfaces promoting the aggregation of the particles. High quality flocs can be obtained rapidly at pH 7.0 using a cell concentration of 40 mg/l, considerably lower than previously reported in the literature. The results are discussed with reference to the surface characteristics of the mineral and of the microorganism.

Algae growth can be carried out in treated mine waters, providing biomass and helping to achieve the standards for water discharge. However, efficient separation of algae from the aqueous medium is crucial. The present work investigated the stability of Scenedesmus sp. in treated acid drainage from coal mining and assessed the harvesting of microalgae via coagulation/flocculation and dissolved air flotation (DAF). Successful algae growth was achieved, with cells remaining suspended in the water at a wide range of pH values, requiring the use of reagents for destabilization/aggregation. Algae coagulation/flocculation was attained with the use of tannin or ferric chloride associated with an anionic polymer flocculant at a pH of 8.0 ± 0.1. When combined with the flocculant, both tannin and the inorganic coagulant proved effective in enhancing floc stability and hydrophobicity for the DAF process. In summary, this operational approach facilitated algae biomass recovery and significantly reduced turbidity in the treated water. Finally, a schematic diagram illustrating the algae cultivation and harvesting process is presented, offering a practical alternative to acid mine drainage (AMD) treatment refinement associated with algae biomass production.