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
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
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
Sub tropical climate
summer
winter
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)
1) tailings
2) polluted soil
3) control soil
-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
Exchangeable
Label
ADS/EXC
Reagent
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.
pH
tailings: 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
Eleme
nt
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
Canadian soil quality guidelines (CECME, 1999) for agricultural soils
Metals binding forms in polluted soils
500
600
450
Cu
400
Pb
500
400
300
mg/kg
mg/kg
350
250
300
200
200
150
100
100
50
0
0
ADS-EXC
CARB
FEMN
soil fraction
OR/SUL
RES
ADS-EXC
CARB
FEMN
soil fraction
OR/SULF
RES
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