Metal fluxes from a sea deposit site for mine tailings

Transcription

1 Metal fluxes from a sea deposit site for mine tailings Morten T. Schaanning, Kuria Ndungu, Sigurd Øxnevad, Hilde C. Trannum Norwegian Institute for Water Research (NIVA) NRC Project ES32333 New knowledge on submarine tailings disposal (NYKOS) WP 4: Effects of mine tailings and associated chemicals on marine, benthic ecosystems Funded 80 % by the Norwegian Research Council. 20% from industry partners Titania As, Rana Gruber As, Omya Hustadmarmor As, Sibelco Nordic As, Sydvaranger Gruve As, Nordic Mining Asa, Nussir Asa 1

2 Subsea deposition challenges Far field Transition zone Nearfield Little or no impact Little to large impact Large impact Chemicals Cu +, Ni 2+, Zn 2+ 2

3 Titania AS 7% of world production of ilmenite Exploiting the Tellenes ore in South Norway ~ 30-40% ilmenite FeTiO 3 ~18% titanoxide TiO 2 pigment for paint, cosmetics, food design and more <2% sulfide minerals Tailings (µg g 1 ) Discharge water (µg L 1 ) Cobolt 83 Cadmium <0.0 Lead <0.20 Copper Chromium 49 <8 Nickel Zinc 1 84 Mercury

4 Location Knubedalsdjupet ? Jøssingfjorden m 28 Titania land deposit Dam height 8 m E. Ramirez-Llodra et al. Marine Pollution Bulletin 97 (201) / / /9 29/3 26 2/19 Dyngadjupet m 4

5 Titania land deposit? 6 kg Ni day 1 1. kg Ni day 1

6 Titania sea deposit From Gravdahl, Stability of heavy metals in submarine mine tailings. MSc thesis, UiB. Model after Konhauser, 2007: Morten Schaanning SedNet, Genova June

7 Sampling and set-up Jøssingfjorden (JF) box cores 2 fauna stations Dyngadjupet (DD) 4 box cores 2 fauna stations Reference (REF) 3 box cores 1 fauna stations 7

8 DGT-probes; Fe & Mn REF DD JF Fe&Mn redox transition zone C*10 = ng cm 2 Morten Schaanning SedNet, Genova June

9 Oxidation, precipitation and acidification JF Mn /2O 2 + H 2 O = MnO 2 + 2H + Fe /4O 2 + /2H 2 O = Fe(OH) 3 + 2H O2 7,1 7,2 7,3 7, ph 20 Fe 2+ Mn 2+ Fe&Mn redox transition zone Morten Schaanning SedNet, Genova June

10 DGT-probes; Metals in Jøssingfjorden deposit Microelectrodes O2 7,1 7,2 7,3 7, ph 20 Fe Co Ni Cu Zn Cd Pb / Morten Schaanning SedNet, Genova June

11 Sediment (0 1 cm) Cluster analyses of Ni, Cu, Co, Zn and Cd in various matrixes Pore water (0 1 cm) Flux from sediment to water Snails (Hinia reticulatae) /9 29 Air Seawater from 60m depth in adjacent fjord 26 2 Box core sample transferred from sea deposit site 11

12 Surface sediment (0-1 cm) ph %<63 µm µg g 1 dry wght. JF DD REF Nickel Copper Cobolt Fines ph JF DD REF H 2 O TOC /

13 Sediment, pore water and fluxes to overlying water H 2 O SEDIMENT ph %<63 µm µg g 1 dry wght. ph Nickel Copper Cobolt Fines JF DD REF SEDIMENT TOC JF DD REF / PORE WATER (µg L 1 ) FLUX (µg m 2 day 1 ) JF DD REF Nickel Copper Cobolt Nickel Copper Cobolt JF DD REF Cadmium 13

14 Summary of EQS exceeded Copper Nickel JF deposit Sediment Acute Chronic JF deposit Pore water vs EQS for Coastal water Acute Acute DD deposit Sediment Chronic Chronic DD deposit Pore water vs EQS for Coastal water Acute Chronic REF Sediment Chronic No REF Pore water vs EQS for Coastal water Acute Chronic 14

15 Benthic fauna (>1mm) N S 11 «Very good» «Good» H ES100 NQI

16 Fluxes from sediment to water g day 1 REF KN DD JF NICKEL COPPER COBOLT µg m 2 day 1 Nickel Copper Cobolt km km km / Cadmium JF DD REF 16

17 Conclusions EQS for Ni and Cu were exceeded in sediments in all deposit sites for mine tailings (i.e. Jøssingfjorden, Dyngadjupet and Knubedalsdjupet) Quality criteria for benthic communities were reduced compared with reference station, but within acceptance criteria of Norwegian legislation Leakage of nickel from all deposit areas was ~% of leakage from land deposit No evidence for upwards diffusion of metals from deep deposit layers (DGT probes) =>Leakage of metals to the overlying seawater is proportional to area rather than volume of deposit Concentration of metals in surface sediments was enough to sustain observed fluxes for ~200 years => natural sedimentation will slowly reduce leakage after deposition is ended 17

18 Recommendations If leakage of metals is proportional to deposit area rather than volume, =>sea deposit should be confined within clear boundaries by natural bathymetry (semienclosed basins) or subsea dam constructions If concentration of metals in surface sediments are enough to sustain observed fluxes for ~200 years => enhancement of natural recovery by postdeposition capping may be a good option That s all, thank you for your attention! 18