Toxic chromium release from nickel mining sediments in surface waters, New Caledonia

Peggy Gunkel-Grillon (1) , Christine Laporte-Magoni (1) , Monika Lemestre (1) , Nicolas Bazire (1)

1 PPME - Pôle Pluridisciplinaire de la Matière et de l'Environnement

Mining sediments are excavated from nickel ore exploitation in New Caledonia. In those sediments, chromium (Cr) occurs as Cr(III), but Cr(III) can be oxidized to the toxic Cr(VI) under oxic conditions, for instance in overlying water. Here, we aimed to determine whether mining sediments could release available Cr(VI) in surface waters. Water samples were collected in a mine and in the village downstream, and then were analysed for Cr. Batch leaching experiments were performed on mining sediments in order to determine their exchangeable and their water-soluble Cr content as a function of pH. Results show that mine waters contain high concentrations of total dissolved Cr, of up to 0.73 mg/L. Moreover, Cr(VI) concentration in village waters increases with the rainfall rate upto 0.34 mg/L. Cr is released from sediments solely as Cr(VI). Desorption of chromate complexes is the main process involved in Cr release. We conclude that drainage of sediments mobilized by opencast Ni mines is a source of toxic Cr(VI) for surface waters.

Mots clés: Ni mines; Mining sediments; Chromium; Surface water; Ophiolitic substrate

Domaines: Biodiversité et Ecologie; Autre

Peggy Gunkel-Grillon, Christine Laporte-Magoni, Monika Lemestre, Nicolas Bazire. Toxic chromium release from nickel mining sediments in surface waters, New Caledonia. Environmental Chemistry Letters, 2014, 12 (4), pp.511-516. ⟨10.1007/s10311-014-0475-1⟩. ⟨hal-02520889⟩