Volume 186, Issue 1, 15 February 2011, Pages 516–525 Brazilian coal mining residues and sulphide oxidation by Fenton's reaction: An accelerated weathering procedure to evaluate possible environmental impacta b c Received 23 July 2010, Revised 16 October 2010, Accepted 8 November 2010, Available online 13 November 2010Fenton's reaction is proposed as an accelerated weathering test for sulphides associated with Brazilian Coal Mining Residues (CMR), that are exposed to oxygen and water during the mining of coal. TEM and SEM/EDX were used to evaluate the nature, occurrence and distribution of minerals in remaining coals and other lithological units, before and after applying the test. Oxidation of CMRs was examined by analyzing soluble sulphur (sulphate) and dissolved metals by ICP-MS or ICP OES. As dissolved sulphate increases, dissolved Zn, Cd, Cu and Co concentrations increase, leading to undetectable amounts in the remaining solid phases; dissolved Ni and Mn also increase with the mobilized sulphur, but the remainder in the solids is the most important fraction;

Fe and Pb are not mobilized due to precipitation as jarosite or hematite in the case of Fe or as sulphate in the case of Pb. Agreement between the observed results and the predictions by geochemical modelling is discussed.3m filtrete ultra clean large air purifier fap031. IntroductionPetroleum crises during the last few years have increased the significance of researching coal. holmes air purifier aldiAlthough abundant, existing coal reservoirs throughout the world could supply energy requirements for a long time, efficient use is limited by the coal's high sulphur content, as found in Brazilian coal, for example. airpura r600 all purpose air purifiers reviewsThe abundant presence of sulphide minerals associated with coal causes great concern as to the environmental impact of oxidation [1], [2], [3] and [4], together with the know CO2 production after coal firing.

Significant environmental problems associated with coal mining arise from interaction between the sulphides from coal and the immediate environment, especially atmospheric compounds, surrounding surface and ground waters [5].Most high-sulphur coals contain, among the different metal sulphides, high concentrations of pyritic sulphur. During the past two decades numerous studies have concentrated on understanding the mechanism of pyrite oxidation [6], [7], [8], [9] and [10], due in part to the environmental impact of acid mine drainage [11], [12] and [13]. Pyrite oxidation is an electrochemical process that consists of three distinct steps: (a) cathodic reaction, (b) electron transport and (c) anodic reaction [9].Two chemical reactions are responsible for the first oxidation step: (a) aqueous pyrite oxidation by O2, represented by the following overall reactions:(1)2222+42−+and (b) the own Ferric iron (Fe3+), itself a powerful oxidant of pyrite in highly acidic conditions [13], which reacts with pyrite according to the following reaction:(2)23+22+42−+This cathodic reaction (the predominant one

, (1) or (2), depends on the concentration of O2 and Fe3+) is the rate-determining step for sulphide mineral oxidation [10]. It oxidizes the sulphide to sulphate but maintains the iron in a state of ferrous oxidation. Studies on the oxidation of galena, sphalerite, chalcopyrite and arsenopyrite [9] concluded that the cathodic reaction (1) “is also true for these minerals, and is likely to be generally true”.Then, the ferrous iron (Fe2+) released into solution is chemically oxidized to ferric iron by the dissolved oxygen:(3)2+2+3+2Oa reaction kinetically enhanced by the presence of anaerobic microorganisms like iron-oxidizing bacteria [14]. Bearing in mind the partial reactions (1), (2) and (3), the global oxidation reaction is:(4)2223+42−4−where a highly buffered acid solution (pH ≈ 2) is formed being equimolar with the amount of dissolved Ferric ion released. In these conditions all the Ferric ion remains dissolved in the water solution.While oxidative surface reactions on Fe sulphide minerals have been studied [9], far fewer studies have focused on the dissolution of other sulphide minerals.

The direct oxidation of such cation divalent sulphides, like sphalerite(5)22+42−does not lead to acidification. At low pH (<3), the oxidative dissolution of sphalerite can be catalyzed by abiotic Fe3+ reduction and subsequent oxidation of Fe2+ by Thiobacillus ferrooxidans [15]. If the Fe2+ is not completely reoxidized or if it is leached by the soil water, Fe3+-mediated sphalerite oxidation results in a net acid release [16].Dissolved cations and sulphate anions, released as acidic solutions from the oxidation of metal sulphides associated with coals, can interact among themselves (dissolved lead and sulphate can precipitate lead sulphate even in acidic solutions) or with the dissolved ions in waters (mainly bicarbonate) or the minerals in the river sediments (mainly carbonates) leading to the formation of secondary sulphate minerals and/or different metal oxides, (oxy)hydroxides or carbonates. These complex interactions must be thoroughly understood to assess potential risks for the environment and even to the human health.

This study investigated the nature of the coal mining residues (CMRs) and attempts to quantify the extent to which interaction has taken place or could take place between the coal or coalbearing strata and the surrounding environment, by using an accelerated weathering procedure based on the Fenton's reaction, i.e. using H2O2 as the oxidant to examine experimentally the oxidation of metal sulphide mineral phases associated with Brazilian coals.The purpose is to evaluate the process of oxidation of the sulphides material in order to deduce the environmental fate of Fe, Ni, Cu, Pb, Mn, Zn, Co, Cd, H+ and SO42− in the Santa Catarina coal mining region. The results of such research are of great use in the design of prevention and remediation strategies for mine-affected regions.2. Background of the accelerated weathering by Fenton's reactionHydrogen peroxide (H2O2) has strong oxidizing properties and has been suggested as an appropriate chemical for clean desulphurization treatments of high-sulphur coals.