Browsing by Author "Paulo, Carlos"

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    Final report: selenium removal from coal mine valley ; fill effluents using Chara ARIES subtask 2.2.3
    (Boojum Research Ltd., 2013-11-21) Boojum Research Limited; Scribalo, Robin; Paulo, Carlos; Kalin, Margarete A.; Wheeler, William H.
    Potential Alternate Treatment Systems. Final Report: Se Removal from Coal Mine Valley Fill Effluents: ARIES Subtask 2.2.3 The Appalachian Research Initiative for Environmental Science (ARIES), under the direction of the Virginia Center for Coal and Energy Research at Virginia Tech was funded to coordinate a project to look into finding alternative treatment systems for selenium removal from coal mine valley fill ponds. In 2012, Boojum Research was was engaged to carry out a pre-feasibility study to assess, if biological polishing, one of the ecological engineering processes, would lower selenium concentrations in coal mine valley fill ponds. The University of Kentucky and 4 coal mining companies participated in the study. The main objective was to determine if, and how much, selenium could be accumulated by the aquatic vegetation found in the valley fill ponds. Periphytic or attached algae are known to be effective ‘polishers’ which adsorb and absorb contaminants from waste water. Selenium is one such waste water contaminant, although its structure is more complicated than most. Periphytic algae with associated ad/absorbed contaminants become buried in the sediment upon death. Phytoplankton (free-floating algae) generally leave the pond or sink to the sediment surface and decay, releasing selenium again to the water. Rooted vegetation can also sequester selenium, but mostly from the sediment and not from the water. The most effective algal group for biological polishing in alkaline water is the Characeae. This family of attached algae is one of the first invaders of freshly- dug ponds and ditches. These algae form dense perennial underwater meadows. These characteristics are especially suited for valley fill ponds, where mining companies have to remove the sediments periodically to maintain a certain water volume. Hence colonization by Characeae is likely. Many of the ponds visited and sampled had some Characeae growth. Only one pond had an abundant underwater meadow. Some ponds were ‘choked’ with rooted emergent vegetation. In one pond with the extensive underwater meadow of Characeae selenium concentrations were lower by 7 µg L‐1 when outflow concentrations were compared to inflow concentrations. Concentrations of in the biomass ranged from 2.2 to 8.0 mg.kg‐1. It was essential that part of the feasibility study determine whether selenium was enriched in the sediment in ponds colonized by the Characeae. This was assessed by collecting sediment cores and dividing them into vertical horizons. The surface sample (0‐2 cm) contained 17 µg. g‐1, decreasing to 7 µg.g‐1 at a depth of 2‐4 cm and further to 1.37 µg.g‐1. The deeper portions and those below in 6 cm, concentrations of around 0.6 µg. g‐1 were reported. These selenium concentration decreases with depth are a strong indication that the use of characean algae should be further studied. The challenge will be to determine the conditions needed to support the growth of an underwater meadow of the algae. Seeding the ponds after dredging with biomass or oospores (a type of seed) would likely be enough to ensure a healthy population. Using this relatively cost-effective approach would likely lead to reductions in the selenium concentration of the effluents leaving valley fill ponds.
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    Sulphide oxidation passivation technique
    (Boojum Research LTD: Collaborative Research with U of Toronto University of Toronto, 2009-04) Paulo, Carlos
    It is known that once exposed to an oxidizing environment (water or oxygen) as series of reactions occur at the surface of sulfide minerals, as pyrite, and lead to acid drainage generation.The major steps of pyrite oxidation are: (1) Oxidation of sulfur in presence of atmospheric oxygen [1] FeS2 + 7/2O2 + H2O 􀃙 Fe2+ + 2SO42‐ + 2H+ (2) Oxidation of ferrous iron Fe(II) (production of ferric iron Fe(III)). At low pH Fe the reaction rates strongly increased by microbial activity (e.g.,Acidithiobacillus ferrooxidans). Bacteria use the reaction as an energy‐generating process, acting as a catalyze Fe2+ oxidation to Fe3+, with rates 5 or 6 times higher than in sterile conditions, increasing acid generation. The soluble Fe3+ formed under these conditions, can effectively scavenge electrons from S(‐1) in pyrite, generating more Fe2+ once again, and this process is recycled. [1,2] Fe2+ + 1/4O2 + H+ 􀃙 Fe3+ + 1/2H2O FeS2 + 14 Fe3+ + 8H2O 􀃙 15 Fe2+ + 2SO42‐+ 16H+ (3) Hydrolysis and precipitation of ferric complexes and minerals (ferryhidrite, schwertmannite, goethite or jarosite) when the acid mine water, rich in ferric iron , reaches the surface. Most of the acid is produced at this stage [1]. Fe3++ 3 H2O 􀃙 Fe(OH)3(s) + 3H+ The development of a feasible, low cost and long‐term inhibition of Fe2+ oxidation process at sulfide surface in solid waste accumulations could drive the mining industry towards a more sustainable future. Such technology should be focused on the understanding of the chemical and biological processes occurring on the surface of the sulphide minerals, as pyrite and pyrrhotite. Different strategies to this problem have been proposed in the literature in the last years. Among them, the technologies designed to generate a physical barrier between pyrite surface and the oxidants agents seem to be the most promising techniques. Iron‐phosphate or silicate coatings [3,4,5], complexation of ferric iron [6,7] and, more recently, the effect of lipids with two hydropobic tails on pyrite surface [8,9] prove to be effective in laboratory studies. All the techniques require the addition of specific chemical solutions to the waste rock as, phosphate or silicate rich solutions, H2O2, chemical complexing agent, lipids and organic solvents. However, none of these methodologies has been validated on field conditions mainly because of scale factor, which makes difficult to estimate the cost and environmental impact that these solutions may have. Boojum Research LTD has been actively trying to address this problem since 1992, developing simultaneously laboratory (waste rock drums) and field tests (Inco, Buchans, Stanrock, etc) where natural phosphate rock (NPR), alone or combined with other components (horse manure, straw, etc) was added to waste rock and tailings, respectively. This technology is proposed by this company has being suitable to groundwater and seepage treatment but, most of all, as a long‐term AMD passivation technique. Some parameters of this technology are not fully optimized but, field and lab demonstration tests have shown that a long‐term inhibition technique may be possible due to the chemical properties of NPR plus the initiation of a biofilm coating on pyritic surfaces. However, the passivation mechanisms still need to be clarified in order to develop a final commercial product. In this report we evaluate, for the first time, the surface of a complete set of rocks use by Boojum in two exposure periods of the Waste Rock Experiment (WRD) in order to gather more basic information for the passivation concept comprehension.