|
|||||
|
|
Dissolution of lead- and lead-arsenic-jarosites at pH 2 and 8 and 20 °C: Insights from batch experiments |
|
| Authors: | Adrian ML Smith William E Dubbin Karen A Hudson-Edwards |
| Institution: | a Department of Mineralogy, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK b Davy Faraday Research Laboratory, The Royal Institution of Great Britain, 21 Albemarle Street, London, W1S 4BS, UK c Research School of Earth Sciences at UCL-Birkbeck, Birkbeck, University of London, Malet Street, London, WC1E 7HX, UK d Now at Entec UK Ltd, Canon Court North, Abbey Lawn, Abbey Foregate, Shrewsbury, SY2 5DE, UK e Now at Nanochemistry Research Institute, Department of Applied Chemistry, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia |
| Abstract: | Lead- and Pb-As-jarosites are minerals common to acidic, sulphate-rich environments, including weathering zones of sulphide ore deposits and acid rock or acid mine drainage (ARD/AMD) sites, and often form on or near galena. The structures of these jarosites are based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, comprised of slightly distorted FeO6 octahedra and SO42− (-AsO43− in Pb-As-jarosites) tetrahedra. To better understand the dissolution mechanisms and products of the break down of Pb- and Pb-As-jarosite, preliminary batch dissolution experiments were conducted on synthetic Pb- and Pb-As-jarosite at pH 2 and 20 °C, to mimic environments affected by ARD/AMD, and at pH 8 and 20 °C, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)2). All four dissolutions are incongruent. Dissolution of Pb-jarosite at pH 2 yields aqueous Pb, Fe and SO42−. The pH 8 Pb-jarosite dissolution yields aqueous Pb, SO42− and poorly crystalline Fe(OH)3, which does not appear to resorb Pb or SO42−, possibly due to the low solution pH (3.44-3.54) at the end of the experiment. The pH 2 and 8 dissolutions of Pb-As-jarosite result in the formation of secondary compounds (poorly crystalline PbSO4 for pH 2 dissolution; poorly crystalline PbSO4 and Fe(OH)3 for pH 8 dissolution), which may act as dissolution inhibitors after 250 to 300 h of dissolution. In the pH 2 dissolution, aqueous Fe, SO42− and AsO43− also form, and in the pH 8 dissolution, Fe(OH)3 precipitates then subsequently resorbs aqueous AsO43−. The dissolutions probably proceed by preferred dissolution of the A- and T-sites, which contain Pb, and SO42− and AsO43−, respectively, rather than Fe, which is sterically remote, within the T-O-T Pb- and Pb-As-jarosite structures. These data provide the foundation necessary for further, more detailed investigations into the dissolution of Pb- and Pb-As-jarosites. |
| Keywords: | Pb-jarosite Pb-As-jarosite Fe hydroxide Pb sulphate Acid mine drainage Dissolution |
| 本文献已被 ScienceDirect 等数据库收录！ | |