dc.description.abstract |
This research project focused on the environmental impact of mining and
smelting nickel-copper (Ni-Cu) at the Selebi Phikwe area, south-eastern
Botswana. Physico-chemical properties, mineralogical identification and
characterisation, and heavy metals concentrations of elements for samples
of tailings dump, soils, particulate air matter (PAM), Colophospermum
mopane (mopane plant), and Imbrasia belina (phane caterpillar) were
investigated. Physico-chemical properties studied on tailings dump and soil
samples included soil texture and colour, particle size distribution (PSD), pH,
electrical conductivity (EC), cation exchange capacity (CEC) and descriptive
petrography. Identification and characterisation of minerals contained in
tailings dump, soil, and PAM samples were performed employing X-ray
powder diffraction (XRPD) techniques which included clay size and heavy
minerals fractionation. Chemical analyses for heavy metals (cadmium, Cd;
cobalt, Co; chromium, Cr; nickel, Ni and selenium, Se) concentrations in
tail ings dump, soils, PAM, mopane leaves and phane caterpillar were
measured with a graphite furnace atomic absorption spectrometer (GFAAS)
whereas the flame atomic absorption spectrometer (FAAS) measured
copper, Cu; iron, Fe and zinc, Zn concentration levels.
The clay and silt soil components made up to 50 wt % of soil. Very acidic
soils were located close to the smelter/concentrator plant, and both soil EC
and CEC va lues were significantly low. Physical tests revealed albite,
NaAISi30 s; cristobalite, a- Si02; chalcopyrite, CuFeS2; pyrrhotite, Fe1_xS; tremolite, Ca2MgsSis022(OHh; and pentlandite, (Fe,Ni)9Ss; to be contained
in tailings dump. Soil colour varied from pale yellow, reddish yellow to dark
reddish brown. The tailings dump comprised of nickelbloedite,
Na2(Ni(S04h.4H20; pyrrhotite; quartz, Si02; pentlandite;
malachite,Cu2C03(OHh; chalcopyrite; actinolite, Ca2(Mg,Fe)sSis022(OHh;
cristobalite; tremolite; kaolinite, AI2SbOs(OH)4; mica and albite. The PAM
consisted of quartz, Si02; pyrrhotite; chalcopyrite, CuFeS2; albite, and
djurleite, CU31 S16. Bulk soil samples consisted of actinolite, albite, quartz,
microciine, KAISi30 s; pyrrhotite, silicon sulphide, SiS; and cobalt oxide, CoO
whereas the < 2 f.In fraction was made of kaolinite, smectite,
Nao.3(AI,MghSi4010(OH)2.xH20; anorthite, CaAI2Si20 s; illite,
KAI2(Si~1010)(OH)2 and quartz. Ojurleite polymorphs (CU31S16 and CU193S)
were formed from secondary mineralisation of chalcopyrite and the S02
released from concentration/smelting processes. Ambient temperature and
an acidic milieu created favourable conditions for the formation of
nickelblodite and malachite from the primary ore minerals: pentlandite,
chalcopyrite and pyrrhotite in tailings dump. Cobalt oxide and silicon
sulphide identified in surface soils were indicative of environmental chemical
alteration of mining waste deposited on surface soils.
High concentrations of heavy metals recorded in different environmental
media had affected the physical environmental quality at Selebi Phikwe.
Heavy metals including Cd, Co, Cr, Cu, Fe, Ni, Se and Zn, which are
deleterious to the environment, and pose as health hazards to humanbeings, were associated with these minerals. Contamination of waterbodies
around Selebi Phikwe might have been possible by the heavy ions in
solution. Consumption of stunted phane might pose as health hazard. In
overcoming pollution problems at Selebi Phikwe, aspects of pollution
management such as phytoremediation and phytomining, environmental
desulphurisation, phytostabilisation, and biotechnology could be introduced
as pollution control measures. |
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