Mineralogical control of the form of ferric/ferrous precipitates for effective treatment of acid mine drainage

Chiharu Tokoro*, Yugo Mitani, Tatsuya Kato, Abdullah Al Mamun

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Acid mine drainage (AMD), which is a major source of mining pollution, often contains ferric and/or ferrous ions together with several toxic elements. The ferric and ferrous ions in AMD precipitate in several mineralogical forms after neutralization, and the ferric/ferrous precipitates become the main component of the sludge generated after AMD treatment. The precipitates are also good absorbents for several toxic elements. To avoid generation of voluminous sludges and the re-dissolution of toxic elements from the sludge, it is very important to generate well-draining and efficiently adsorbing sludges by controlling the mineralogical form of the ferric/ferrous precipitates. Green rust, which is ferric and ferrous hydroxide, is a double layer hydroxide which is able to sorb several toxic elements. The green rust transforms to goethite or lepidocrocite by rapid oxidation, whereas it transforms to magnetite at ambient temperature by slow oxidation. The magnetite is also good absorbent especially for toxic cations and it makes a compact sludge due to its magnetic properties. We investigated the magnetite generation process at ambient temperature in detail. The magnetite generation process can be divided into three steps; (i) oxidation of Fe(II), (ii) Fe(II) surface complexation to Fe(III) hydroxide, and (iii) crystallization of magnetite. More magnetite can form when the oxidation rate is slower than the crystallization rate, and optimum conditions for its formation are at pH 9.5 with mild agitation. Ferrihydrite is the most common precipitate and it is able to sorb many different toxic elements. However, it drains badly and its solid/liquid separation properties are poor. We investigated the removal mechanism of several toxic elements by co-precipitation with ferrihydrite. We confirmed that the removal mechanism by co-precipitation partly involved surface precipitation when the initial ratio of toxic elements to ferric ion was high, although the main mechanism was always surface complexation. When surface precipitation occurred, highly efficient toxic element removal with ferrihydrite could be achieved.

Original languageEnglish
Title of host publicationIMPC 2016 - 28th International Mineral Processing Congress
PublisherCanadian Institute of Mining, Metallurgy and Petroleum
ISBN (Electronic)9781926872292
Publication statusPublished - 2016
Event28th International Mineral Processing Congress, IMPC 2016 - Quebec City, Canada
Duration: 2016 Sept 112016 Sept 15

Publication series

NameIMPC 2016 - 28th International Mineral Processing Congress


Other28th International Mineral Processing Congress, IMPC 2016
CityQuebec City


  • Acid mine drainage
  • Co-precipitation
  • Ferrihydrite
  • Green rust
  • Magnetite

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geotechnical Engineering and Engineering Geology
  • Mechanical Engineering
  • Earth-Surface Processes


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