Smith et al.(2006)による〔『Dissolution of lead- and lead-arsenic-jarosites at pH 2 and 8 and 20℃: Insights from batch experiments』(344p)から〕

『pH 2と8および20℃における鉛-ヒ素-鉄明礬石の溶解:バッチ実験からの洞察』


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℃, to mimic environments affected by ARD/AMD, and at pH 8 and 20℃, 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』

1. Introduction
2. Methods and materials
 2.1. Synthesis of Pb- and Pb-As-jarosites
 2.2. Characterization of synthetic Pb- and Pb-As-jarosites
 2.3. Dissolution experiments
3. Results
 3.1. Characterization of synthetic Pb- and Pb-As-jarosites
 3.2. Dissolution at pH 2
  3.2.1. Solution chemistry
  3.2.2. Residual solids
 3.3. Dissolution at pH 8
  3.3.1. Solution composition
  3.3.2. Residual solids
4. Discussion
 4.1. Pb-jarosite
  4.1.1. Dissolution at pH 2
  4.1.2. Dissolution at pH 8
 4.2. Pb-As-jarosite
  4.2.1. Dissolution at pH 2
  4.2.2. Dissolution at pH 8
 4.3. Comparison of Pb-jarosite and Pb-As-jarosite dissolutions, and environmental implications
5. Conclusions
Acknowledgements
References



戻る