Métodos de análise de sulfetos em amostras de rochas e sedimentos

SUMMARYMining in the State of Minas Gerais-Brazil is one of the activities with the strongest impact on the environment, in spite of its economical importance. Amongst mining activities, acid drainage poses a serious environmental problem due to its widespread practice in gold-extracting areas. It originates from metalsulfide oxidation, which causes water acidification, increasing the risk of toxic element mobilization and water resource pollution. This research aimed to evaluate the acid drainage problem in Minas Gerais State. The study began with a bibliographic survey at FEAM (Environment Foundation of Minas Gerais State) to identify mining sites where sulfides occur. Substrate samples were collected from these sites to determine AP (acidity potential) and NP (neutralization potential). The AP was evaluated by the procedure of the total sulfide content and by oxygen peroxide oxidation, followed by acidity titration. The NP was evaluated by the calcium carbonate equivalent. Petrographic thin sections were also mounted and described with a special view to sulfides and carbonates. Based on the chemical analysis, the acid-base accounting (ABA) was determined by the difference of AP and NP, and the acid drainage potential obtained by the ABA value and the total volume of material at each site. Results allowed the identification of substrates with potential to generate acid drainage in Minas Gerais state. Altogether these activities represent a potential to produce between 3.1 to 10.4 billions of m 3 of water at pH 2 or 31.4 to 103.7 billions of m 3 of water at pH 3. This, in turn, would imply in costs of US$ 7.8 to 25.9 millions to neutralize the acidity with commercial limestone. These figures are probably underestimated because some mines were not surveyed, whereas, in other cases, surface samples may not represent reality. A more reliable state-wide evaluation of the acid drainage potential would require

Section: Acid Base Accountingmentioning

confidence: 99%

Preliminary evaluation of acid mine drainage in Minas Gerais State, Brazil

Mello

Dias

Daniel³

et al. 2006

Caracterização de rejeito de mineração de ouro para avaliação de solubilização de metais pesados e arsênio e revegetação local

Silva

Procopio²,

Queiroz³

et al. 2004

RESUMODepósitos de rejeitos e pilhas de estéril, decorrentes de atividades de mineração, podem ser fontes de contaminação ambiental, por causa da presença de metais pesados e arsênio, principalmente quando esses materiais contêm minerais sulfetados e teores elevados de metais. O objetivo deste trabalho foi caracterizar o rejeito proveniente do beneficiamento de minério de ouro de uma mineração no estado de Minas Gerais, para avaliação de problemas de drenagem ácida e solubilização de metais e para planejamento da revegetação do local. Amostras de rejeito foram coletadas na camada superficial (0-20 cm), sendo submetidas a análises químicas de rotina da fertilidade do solo e a uma caracterização química específica de Ni, Cu, Pb, Cd, Fe, Zn, Cr, As e S extraídos em Água Régia, Mehlich-1, EDTA e água deionizada. Foram determinados o potencial de acidez (PA), o potencial de neutralização (PN) e equilíbrio ácido-base (EAB); além da realização de análise granulométrica e difração de raios-X. As amostras analisadas apresentaram baixos teores de matéria orgânica, P e K, alta acidez e salinidade, além de alto teor de As, o que indica sérias restrições ao estabelecimento de espécies vegetais. O rejeito apresentou potencial de geração de acidez e solubilização de elementos como As, Fe e S, o que pode acarretar problemas ambientais, como a drenagem ácida e a contaminação de solos e cursos d'água, bem como a incorporação desses elementos na cadeia trófica.Termos de indexação: drenagem ácida, extratores químicos, poluição ambiental.

Induction of a geochemical barrier for As, Fe and S immobilization in a sulfide substrate

Assis

Dias

Ribeiro

et al. 2012

SummarYacid mine drainage (amd) is an environmental concern due to the risk of element mobilization, including toxic elements, and inclusion in the food chain. In this study, three cover layers were tested to minimize as, fe and S mobilization from a substrate from former gold mining, containing pyrite and arsenopyrite. for this purpose, different layers (capillary break, sealant and cover layer) above the substrate and the induction of a geochemical barrier (GB) were used to provide suitable conditions for adsorption and co-precipitation of the mobilized as. thirteen treatments were established to evaluate the leaching of as, fe and S from a substrate in lysimeters. the ph, as, fe, S, na, and K concentrations and total volume of the leachates were determined. mineralogical analyses were realized in the substrate at the end of the experimental period. lowest amounts of as, fe and S (average values of 5.47, 48.59 and 132.89 g/lysimeter) were leached in the treatments that received na and K to induce GB formation. mineralogical analyses indicated jarosite formation in the control treatment and in treatments that received na and K salts. however, the jarosite amounts in these treatments were higher than in the control, suggesting that these salts accelerated the GB formation. high amounts of as, fe and S (average values of 11.7, 103.94 and 201.13 g/lysimeter) were observed in the leachate from treatments without capillary break layer. the formation of geochemical barrier and the use of different layers over the sulfide substrate proved to be efficient techniques to decrease as, fe and S mobilization and mitigate the impact of acid mine drainage. Index-terms: jarosite, arsenic, cover layers, gold mining, rehabilitation.(1) Part of mSc dissertation of first author presented at the Soil Science Post-Graduation Program of federal university of Viçosa, ufV. this work received financial support from fapemig and Inct-aqua (cnPq