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The passivation of calcite by acid mine water. Column experiments with ferric sulfate and ferric chloride solutions at pH 2

AuthorsSoler, Josep M. ; Boi, Marco; Mogollón, José Luis; Cama, Jordi ; Ayora, Carlos ; Nico, Peter S.; Tamura, Nomubichi; Kunz, Martin
KeywordsAcid mine drainage
Issue Date29-Aug-2008
CitationApplied Geochemistry 23(12): 3579-3588 (2008)
AbstractColumn experiments, simulating the behavior of passive treatment systems for acid mine drainage, have been performed. Acid solutions (HCl or H2SO4, pH 2), with initial concentrations of Fe(III) ranging from 250 to 1500 ppm, were injected into column reactors packed with calcite grains at a constant flow rate. The composition of the solutions was monitored during the experiments. At the end of the experiments (passivation of the columns), the composition and structure of the solids were measured. The dissolution of calcite in the columns caused an increase in pH and the release of Ca into the solution, leading to the precipitation of gypsum and Fe-oxyhydroxysulfates (Fe(III)-SO4-H+ solutions) or Fe-oxyhydroxychlorides (Fe(III)-Cl-H+ solutions). The columns worked as an efficient barrier for some time, increasing the pH of the circulating solutions from 2 to ~ 6-7 and removing its metal content. However, after some time (several weeks, depending on the conditions), the columns became chemically inert. The results showed that passivation time increased with decreasing anion and metal content of the solutions. Gypsum was the phase responsible for the passivation of calcite in the experiments with Fe(III)-SO4-H+ solutions. Schwertmannite and goethite appeared as the Fe(III) secondary phases in those experiments. Akaganeite was the phase responsible for the passivation of the system in the experiments with Fe(III)-Cl-H+ solutions.
Description10 pages, 8 figures, 1 table.-- Printed version published Dec 2008.
Publisher version (URL)http://dx.doi.org/10.1016/j.apgeochem.2008.08.011
Appears in Collections:(IDAEA) Artículos
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