Analytical Methods Materials and Methods

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2.2.3 Analytical Methods

Identification for physicochemical properties of the milled rocks was carried out in their original condition without any pre-treatment as that might be used in practices. However, an exception was made for the measurement of particle size by using Malvern Mastersizer that the rock powders were ultrasonically dispersed prior to measurement. This treatment was applied due to concern to the possibility of scratching on the detection lens of the instrument by coarse agglomerated particles being measured. Care should be taken, therefore, in interpreting the results of this measurement as such pre-treatment to the samples may result underestimate values of particle size relative to those for the untreated SRFs. The concentrations of major elements in the initially milled T0 and milled T10 – T120 silicate rocks were determined by XRF Philips PW 1400 after fusing the samples with lithium metaborate Karathanasis and Hajek 1996. The determination of Fe was done in spite of the potential risk for sample contamination due to the use of Fe-steel ball mill, and hence of overestimation of the actual dissolution rate. An extracting solution of 1M ammonium acetate CH 3 COONH 4 buffered at pH 7.0 was used to measure the quantities of exchangeable basic cations Ca, Mg, K, and Na in the milled rocks. A subsample 250 mg of rock powder each was added to 20 mL extracting solution in a 30mL plastic container, and then shaken for 1 h on an end-over end shaker. This step was repeated three times for the same sample and the filtrates from each extraction were combined. The concentrations of Ca and Mg in the filtrates were measured using Atomic Absorbance Spectrophotometry AAS, K and Na were measured using flame emission. The lanthanum solution LaCl 3 was added to suppress interferences for Ca determination, and Cs solution was added to overcome ionization interference for K determination. The quantity of each exchangeable cation was calculated in units of centimole charge per kg rock dust cmol c kg and of total in rock i.e., the amount of each exchangeable element relative to the total content of the element in rock powder for each milling time and condition. The quantity of amorphous constituents was determined as Fe + Al + Si soluble in 0.2M ammonium oxalate-oxalic acid buffered at pH 3.0 using the procedure described by Rayment and Higginson 1992. The concentrations of Fe 8 and Al in the filtrate were measured using AAS and Si was determined using the molybdate blue method Strickland and Parsons 1968. In addition, the concentrations of Mg and K in the filtrates for milled basalt, dolerite, and gneiss, and K and Na in the filtrate for milled K-feldspar were measured using AAS for Mg and flame emission for Na and K. The concentration of Ca in the filtrate was not measured due to the present of white precipitate in the filtrate when lanthanum solution was added as a suppressing agent for measurement of Ca with AAS. Further identification of the precipitate was not carried out. It was presumed that the precipitate might be La-oxalate complex as such precipitate only present when La solution was added to oxalate filtrates, but there was no precipitate caused by adding La to the other filtrates e.g., filtrates of ammonium acetate, acetic-citric acids, and CH 3 COONH 4 extractions. The pH H 2 O 1 : 5 and electric conductivity 1 : 5 of water extracts of the milled rocks were measured with pH Cyberscan 2000 and EC Cyberscan 2000 meters. The particle size distribution of rock powders was measured in duplicate by using a Malvern Mastersizer the lowest detection limit is Ø 0.02 µm. The sample was ultrasonically dispersed in water for 5 min prior to measurement and stirred continuously during measurement. Specific surface area of duplicate samples without dispersion was measured by the BET-N 2 method Brunauer et al. 1938 using a Micromeritics Gemini III 2385 Surface Area Analyser. Before measurement of specific surface area, subsamples of the rocks that had been dry-milled with NaCl and KCl were washed with deionized water twice to dissolve free NaCl and KCl that may have remained in the rock powders. Mineralogical characteristics of rock powders were derived through analysis of XRD patterns by applying a X-ray Powder Diffraction Analysis Software XPAS V.3.0 described by Singh and Gilkes 1992. The XRD patterns were collected with a Philips PW-3020 diffractometer using monochromatised Cu K α radiation, generated at 50 kV and 20 mA. The diffraction intensity was recorded between 5 and 70° 2 θ at a scanning rate of 0.02° per second. 9

2.3. Results and Discussion