1. Trace elements dispersion from a tailings dam and speciation in surrounding agricultural soils Kombat Mine, Otavi Mountainland, Namibia Marta Mileusnić, Stanko Ružičić University of Zagreb, Croatia Benjamin Siyowi Mapani, Akalemwa Fred Kamona Isaac Mapaure, Percy Maruwa Chimwamurombe University of Namibia, Namibia

2. STUDY AREA - Kombat Grootfontein district latitude 19  43´S longitude 17  43´E altitude of 1.590 metres 2 000 inhabitants Agriculture: (1) livestock production (2) maize, potatoes, vegetables and subtropical fruits

3. Kombat Cu mine mining: 1962 – 2008 (46 years) 24,550,280 t of copper ore tailing dam (about 300 million T) Area: 20 haHeight: 3-4 m

4. winter summer Sub tropical climate Summers -very hot -heavy downpours -northeastery winds Winters (May –June) -mild -dry winters - easterly winds

5. Main agents of material transfer from tailings into surrounding areas WINTER - WINDSUMMER - RAIN WATER (as run-off in episodes of heavy downpours

6. RESEARCH GOALS (1) to determine lateral distribution and seasonal variability of trace metals, as well as dominant metal binding mechanisms in the agricultural soil (2) to identify dominant type of metal dispersion from the tailings impoundment (mechanical or chemical) (3) to carry out preliminary assessment of environmental risk associated with tailings dam

7. SAMPLING - after results of Kribek et al. (2006) 2) polluted soil 3) control soil 1) tailings -2 sampling campaigns: -Wet season – march -Dry season – august

8. Analytical work (1) bulk mineralogy of soils and tailings (XRD) (2) Pseudototal metal content of soils and tailings (aqua regia digestion, AAS) (3) Binding sites of metals (sequential leaching, AAS)

9. FractionLabelReagent ExchangeableADS/EXCAmmonium acetate Acid (carbonates) CARBAcetic acid ReducibleFEMNHydroxylamine hidrochloride OxidisableOR/SULHydrogen peroxide Modified after: TESSIER et al. (1979) and SULKOWSKI et al. (2006)

10. RESULTS Mineral content tailings: calcite and dolomite, quartz, micaceous material, +/-gypsum soil: quartz, calcite, dolomite, K-feldspar, plagioclase, clay minerals. pH tailings: circum-neutral (7.0-7.7) soil: alkaline (8.1-8.6)

11. Pseudototal metal concentrations (median values in mg/kg) - no seasonal variation in concentrations Canadian soil quality guidelines (CECME, 1999) for agricultural soils Eleme nt TailingsPolluted farmland soil Control soils Cu132811218 Pb94611717 Zn1074927 Cr162027 Ni3912 Co655 Cd3BDL

12. Metals binding forms in polluted soils Cu Pb

13. CONCLUSIONS (1) Cu and Pb showed significantly high concentration in tailings. (2) Cu and Pb in all analysed samples of farmland soils west of the tailings dam exceed maximal allowed values for agricultural soils. (3) Seasonal variations - not observed. (4) The main binding site for Cu and Pb is oxide fraction

14. (5) mechanical dispersion of elements from tailings dam prevails (6) carbonate minerals dominate in tailings - drainage is neutralized - lead and copper immobile (7) Pb and Cu relatively strongly bound to the soils + high pH of soil- small risk for their release in soil water and to groundwater (8) study by Casteel et al. (2006) - lead associated with iron oxide shows intermediate bioaccesibility while ingested (9) Rehabilitation of tailings dam necessary

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