Impact of past and present opencast Ni mining on the lagoon environment of New Caledonia

Transcription

1 Impact of past and present opencast Ni mining on the lagoon environment of New Caledonia Belhandouz A, Colombier T, Dolbecq M, Fernandez JM, Lamoureux JP, Moreton B IRD-Nouméa, Promenade Laroque, Noumea, New Caledonia jean-michel.fernandez@noumea.ird.nc 2 nd Assises de la Recherche Française dans le Pacifique. 11 ème Inter-congrès des sciences du Pacifique Papeete (Tahiti) 2-6 mars 9

2 5 Contexte The objective of this study was to examine the distribution of dissolved d and particulate forms of a number of metals (Co,( Cu, Cr, Fe, Mn, Ni and Zn ) in three distinct bays of the south western lagoon of New Caledonia : Saint Vincent Bay: : Exposed to a watershed where nickel extraction is currently active 21 5'S (???) Bay: : Exposed to a watershed where mines were exploited up until recentlty (198) 22 'S St Vincent Bay 5 Tontouta river (519) Bay: : Very limited exposure to mining activities 22 'S river (858) Sampling sites are located in the area influenced by the respective river mouths 22 'S Sampling locations River catchment area Mine locations (519) Total quantity of extracted ore (tonnes) 3 Bay Coulée river Bay 166 'E 166 'E 166 4'E

3 Methodology Dissolved metals: 72 Seawater and 18 riverwater samples were collected, immediately pre-concentrated on-site on an iminodiacetate chelating resin (OnGuard II M, Dionex), eluted at laboratory and then analysed by ICP-OES Portable pre-concentration unit (Moreton et al, 9): A pre-concentration/elution unit was used for all routine determinations. The unit consisted of a clear Perspex support to which the filter holders and resin cartridges were attached. A 16 channel peristaltic pump was automatically operated using either battery or mains power Schematic diagram of the fully automated resin conditioning unit for the simultaneous treatment (conditioning/elution) of up to 6 samples Schematic diagram of the portable preconcentration unit capable of treating upto 16 samples simultaneously

4 Methodology Particulate metals: In each bay, a sequential sediment trap (Technicap, model PPS 4/3) was moored at about 15 m depth, the SPM collect being performed 3 m above the sea floor. Traps are equipped with twelve vials which were filled with 5% formaldehyde seawater solution before mooring in order to preserve the particles (Heussner et al., 1989) from microbiological activity. Samples were collected at a frequency of 48h. 72 suspended particles samples were collected. Flux (mg/m²/d) = Mass (mg) / (Section area (m²) * Collecting time (d) per flask) Mineralogy, particulate fluxes and metal concentrations (ICP-EOS) were determined.

5 Results Dissolved and particulate Ni forms : times series concentrations collected from /11 to 15/12/7 simultaneously in the 3 sampling stations Dissolved Ni concentration (µg/l) Particulate Ni concentration (mg/kg) 8 4 StVincent StVincent /11 25/11 3/11 5/12 /12 15/12 /11 25/11 3/11 5/12 /12 15/12 StVincent : 1.9 to 7.1 µg/l : 1.3 to 4.5 µg/l : 1, to 3.9 µg/l Dissolved Ni(II) concentration Particulate Ni concentration StVincent : to 3 mg/kg : 18 to 133 mg/kg : 8 to 116 mg/kg BOULARI n=212 Fe Co Cr Mn Ni Cu Fe 1,998,994,995,993,8 Co,998 1,996,998,994,116 Cr,994,996 1,992,992,117 Mn,995,998,992 1,991,126 Ni,993,994,992,991 1,5 Cu,8,116,117,126,5 1 St VINCENT n=212 Fe Co Cr Mn Ni Cu Fe 1,986,963,869,95,57 Co,986 1,941,93,866,67 Cr,963,941 1,754,853, Mn,869,93,754 1,833,53 Ni,95,866,853,833 1,85 Cu,57,67,,53,85 1 DUMBEA n=212 Fe Co Cr Mn Ni Cu Fe 1,998,985,946,988,443 Co,998 1,986,948,99,437 Cr,985,986 1,888,986,479 Mn,946,948,888 1,912,33 Ni,988,99,986,912 1,453 Cu,443,437,479,33,453 1 Goethite ( -FeO-OH ) and Serpentine (Lizardite) Mg 6 [Si 4 O (OH) 2 ](OH) 6 are the main carriers of Co, Cr, Mn and Ni

6 Some conclusions Kd (ml/g) Ni flux (mg/m²/j) StVincent St Vincent /11 25/11 3/11 5/12 /12 15/12 /11 25/11 3/11 5/12 /12 15/12 St Vincent - Fine particles continuously enter the lagoon due to mining activities in the watershed of the La Tontouta River - Extremely high particulate fluxes up to 25 times those of the 2 other bays are recorded - Sorption/desorption cycles of Ni (Co and Cr) are observed - Progressive metal sorption phenomena increasing with time are observed - Change in the particles composition (organic coating) increases their metal complexing ability which can be attributed to advective inputs in organics during trade winds periods - Increasing sorption phenomena with time occurs with the reduction in suspended particles size - Finest suspended particles from the former mining forms aggregates with organics complexing nickel (and others metals).

7 Thank you for your attention