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.