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Investigating monomineralic and polymineralic reactions during the oxidation of sulphide minerals in seawater: Implications for mining seafloor massive sulphide deposits

Investigating monomineralic and polymineralic reactions during the oxidation of sulphide minerals in seawater: Implications for mining seafloor massive sulphide deposits
Investigating monomineralic and polymineralic reactions during the oxidation of sulphide minerals in seawater: Implications for mining seafloor massive sulphide deposits
Seafloor massive sulphide (SMS) deposits are rich in metals, particularly Cu and Au, and are attracting the attention of mining companies. However, there are various environmental concerns associated with the potential extraction of these deposits, which includes the release of heavy metals following the crushing and grinding of these deposits on the seafloor as sulphide mineral surfaces are exposed to, and oxidised by seawater. A series of monomineralic and polymineralic sulphide mineral, batch reactor, abiotic oxidation experiments were completed in an effort to assess the geochemical impacts of mining SMS deposits in situ. Pyrite, chalcopyrite, sphalerite, and mixtures thereof, were reacted with synthetic seawater under conditions similar to that of the seafloor at between 2 and 3 km depth (2 °C, pH 8.2), but under atmospheric pressure and equilibrated with air. Galvanic effects are evident in the polymineralic experiments, predominantly the cathodic protection of pyrite by the preferential oxidation of chalcopyrite and sphalerite. However, the reaction between sphalerite and chalcopyrite remains unclear. Rates of reaction could not be quantitatively calculated due to the precipitation of iron oxyhydroxides that sequester Fe, Zn, and possibly minor Cu from solution. These experiments demonstrate that chalcopyrite represents the largest geochemical concern for the in situ mining of SMS deposits due to its continuous oxidation and Cu release, its preferential dissolution in galvanic cells, and the known toxicity of Cu relative to Fe and Zn.
0883-2927
63-74
Knight, Robert D.
04d3bfd0-6c52-495f-954f-aa605ee9be2e
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
Cooper, Matthew J.
54f7bff0-1f8c-4835-8358-71eef8529e7a
Knight, Robert D.
04d3bfd0-6c52-495f-954f-aa605ee9be2e
Roberts, Stephen
f095c7ab-a37b-4064-8a41-ae4820832856
Cooper, Matthew J.
54f7bff0-1f8c-4835-8358-71eef8529e7a

Knight, Robert D., Roberts, Stephen and Cooper, Matthew J. (2018) Investigating monomineralic and polymineralic reactions during the oxidation of sulphide minerals in seawater: Implications for mining seafloor massive sulphide deposits. Applied Geochemistry, 90, 63-74. (doi:10.1016/j.apgeochem.2017.12.027).

Record type: Article

Abstract

Seafloor massive sulphide (SMS) deposits are rich in metals, particularly Cu and Au, and are attracting the attention of mining companies. However, there are various environmental concerns associated with the potential extraction of these deposits, which includes the release of heavy metals following the crushing and grinding of these deposits on the seafloor as sulphide mineral surfaces are exposed to, and oxidised by seawater. A series of monomineralic and polymineralic sulphide mineral, batch reactor, abiotic oxidation experiments were completed in an effort to assess the geochemical impacts of mining SMS deposits in situ. Pyrite, chalcopyrite, sphalerite, and mixtures thereof, were reacted with synthetic seawater under conditions similar to that of the seafloor at between 2 and 3 km depth (2 °C, pH 8.2), but under atmospheric pressure and equilibrated with air. Galvanic effects are evident in the polymineralic experiments, predominantly the cathodic protection of pyrite by the preferential oxidation of chalcopyrite and sphalerite. However, the reaction between sphalerite and chalcopyrite remains unclear. Rates of reaction could not be quantitatively calculated due to the precipitation of iron oxyhydroxides that sequester Fe, Zn, and possibly minor Cu from solution. These experiments demonstrate that chalcopyrite represents the largest geochemical concern for the in situ mining of SMS deposits due to its continuous oxidation and Cu release, its preferential dissolution in galvanic cells, and the known toxicity of Cu relative to Fe and Zn.

Text App_Geochem_Accepted_MS
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Accepted/In Press date: 27 December 2017
Published date: 1 March 2018

Identifiers

Local EPrints ID: 417176
URI: https://eprints.soton.ac.uk/id/eprint/417176
ISSN: 0883-2927
PURE UUID: 1df75b2f-17ea-49c8-9266-6054ea0cccbe
ORCID for Stephen Roberts: ORCID iD orcid.org/0000-0003-4755-6703
ORCID for Matthew J. Cooper: ORCID iD orcid.org/0000-0002-2130-2759

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Date deposited: 23 Jan 2018 17:30
Last modified: 16 Apr 2018 16:31

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