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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 KamonaIsaac Mapaure, Percy Maruwa Chimwamurombe
University of Namibia, Namibia
STUDY AREA - Kombat
Grootfontein districtlatitude 1943´Slongitude 1743´Ealtitude of 1.590 metres
2 000 inhabitants
Agriculture:(1) livestock production(2) maize, potatoes, vegetables and subtropical fruits
Kombat Cu mine mining: 1962 – 2008 (46 years) 24,550,280 t of copper ore
tailing dam (about 300 million T)
Area: 20 ha Height: 3-4 m
winter
summer
Sub tropical climate
Summers-very hot-heavy downpours-northeastery winds
Winters (May –June)-mild-dry winters - easterly winds
Main agents of material transfer from tailings into surrounding areas
WINTER - WIND SUMMER - RAIN WATER
(as run-off in episodes of heavy downpours
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
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
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)
Fraction Label Reagent
Exchangeable ADS/EXC Ammonium acetate
Acid (carbonates)
CARB Acetic acid
Reducible FEMN Hydroxylamine hidrochloride
Oxidisable OR/SUL Hydrogen peroxide
Modified after: TESSIER et al. (1979) and SULKOWSKI et al. (2006)
RESULTS
Mineral content tailings: calcite and dolomite, quartz, micaceous material, +/-gypsum
soil: quartz, calcite, dolomite, K-feldspar, plagioclase, clay minerals.
pHtailings: circum-neutral (7.0-7.7)soil: alkaline (8.1-8.6)
Pseudototal metal concentrations (median values in mg/kg)
- no seasonal variation in concentrations
Canadian soil quality guidelines (CECME, 1999) for agricultural soils
Element
Tailings Polluted farmland soil
Control soils
Cu 1328 112 18
Pb 946 117 17
Zn 107 49 27
Cr 16 20 27
Ni 3 9 12
Co 6 5 5
Cd 3 BDL BDL
Metals binding forms in polluted soils
0
50
100
150
200
250
300
350
400
450
500
ADS-EXC CARB FEMN OR/SUL RES
soil fraction
mg/
kg
Cu
0
100
200
300
400
500
600
ADS-EXC CARB FEMN OR/SULF RES
soil fraction
mg/
kg
Pb
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
(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
THANK YOU FOR YOUR ATTENTION
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