2.2 Laboratory analyses
The potential of soil nutrient sources in spoils and tailings was
assessed by analyzing the primary mineralogical compositions of 50-250
µm sized sand fraction. Mineral types were identified using a polarizing
microscope (Carl Zeiss Microscopy, Germany). The number of each mineral
type was counted from 300 grains by line count traverses.
X-ray diffraction (XRD) analysis for tin ores and white clay sediment
was carried out using a Rigaku (SmartLab, Japan). Tin ores and white
clay were analyzed to determine host-mineral of Sn and that white clay
for type of clay minerals. The refused white clay layer during tin
mining could be potential to be used as ameliorant for sandy tailing.
The tin ores were collected from re-mined tailing by local miners nearby
the study site. The tin ores were dried and finely ground as powder to
pass through a 50 µm sieve and kept for XRD analysis. For white clay
sediment, it was collected from the spoil profile, dried and finely
ground as powder to pass through a 50 µm sieve. The powder specimen was
mounted on glass slides and run on X-ray diffractometer, using Cu-alpha
radiation target, operated at 40 kV and 25 mA. The powder specimens were
scanned from 3 to 45º 2θ at 1°/min. XRD data were collected and stored
by IBM compatible PC.
The scanning electron microscope (SEM) analysis was performed for finely
ground tin ores (< 50 µm) using an EVO MA10 (Carl Zeiss
Microscopy, Cambridge, England) to observe their morphological features
and resistance to weathering processes. The specimens were oven dried
prior to gluing into an aluminum stub and then coated with carbon and
gold/palladium in a vacuum evaporator. The specimens were viewed at 11.0
and 15.0 kV, using a secondary electron detector. The chemical surface
compositions of specimens were analyzed using energy dispersive X-ray
(EDX).
The particle sizes of soil were determined by the pipette method (Soil
Survey Staff, 1992). The sand fraction was separated from the clay and
silt fractions by wet sieving. The silt- and clay-sized fractions were
measured by sedimentation according to Stokes law. The pH and electrical
conductivity (EC) were measured in water with a 1:5 soil:solution ratio
using an Orion pH meter and a conductivity meter, respectively. The
total organic C content was measured according to Walkley and Black wet
oxidation method (Soil Survey Staff, 1992). Total N was determined by
the Kjeldhal method (Bremner and Mulvaney, 1982). Soil cation exchange
capacity (CEC) was determined using a leaching column. The soil of 2 g
was transferred into a leaching column followed by leaching with 50 ml
of 1 M NH4OAc at pH 7.0 for an hour, then the cations
were measured in the supernatant (Soil Survey Staff, 1992) using an
atomic absorption spectrometer (AAS). The CEC was determined in 1 M
NH4OAc (buffered at pH 7.0) after extraction of
NH4+ as a measure of CEC by 10% NaCl.
The Bray 1 method was used to determine soil available P, and that
exchangeable Al was extracted by 1 M KCl as described by Van Reeuwijk
(1993).
Total elemental analysis of native soil, spoil and tailing was
determined using X-ray fluorescence (XRF). Soil, spoil and tailings were
finely ground using a ball mill/ pulverizer to pass through a 100-200
mesh sieve as powder. Measurements of major and trace elements were
carried out on pressed pellets, prepared following the procedure of
Norrish and Chappell (1977). The sample powder was mixed with carboxyl
methyl cellulose (CMC) as a binder by lightly ground. Samples were
pressed into pellets with boric acid backing in a ring stainless steel,
and oven dried at 55°C for about half hour. Elemental composition was
determined using X-Ray Fluorescence (Thermo Scientific ARL 9900 Series,
2011 Germany) with a Be tube operating at 60 kV, 40 mA for Ba,Sn, Cd,
Ag, Rb,Mo, Zr, Y, Pb, As, Se, Hg, Zr and Y; at 40 kV, 60 mA for Ni, Cu,
Co, Si, Al, Fe, Mn, V, Cr, Ti, Ca, K; and at 30 kV, 80 mA for Mg and Na
using scintillation counter. The available heavy metals were extracted
by 0.05 M CaCl2. The use of CaCl2 in
place of 1 M MgCl2 as used by Tessier et al. (1979) was
due to native conditions of tailing contain higher Ca than Mg, hence the
use of CaCl2 extractant solution is more closely
represent the native conditions.