Soil Characterization and Quaternary Pedology Laboratory
The laboratory is equipped with two laser particle size analyzers: A Malvern Mastersizer 3000 and a Micrometrics Saturn Digisizer 5200. The lab is also equipped with an Accumet pH Meter 915, Accumet Excel XL30 Conductivity Meter, Thermolyne 1400 Muffle Furnace, Ro-Tap Sieve Shaker, a tensimeter, and more. Sample prepatory equipment includes a Quantachrome Sieving Riffler, Sampletek 200 Vial Rotator, SPEX 8000 Ball Mill, Gilson Performer III, precision analytical balances, high speed/high capacity centrifuges, shaking tables, large ovens, a microscope, and more.
The lab is also equipped with two chemical fume hoods with facilities for storage and disposal of chemicals. Instruments in other labs that we have access to include a Bruker D8 Advance X-Ray Diffractometer (XRD) and a Dionex ICS 1500 Ion Chromatography System.
Laser Particle Size Analysis
The laser particle size analysis (LPSA) procedure is used to determine the percentage of size-class fractions in soil or sediment samples, as well as water-sediment mixtures. The procedure is based on ASTM-C-1070-01 to determine particle size distribution analysis (PSDA) of alumina and quartz powders by laser light scatter (ASTM, 2000).
Based on the Mie theory of light scattering, laser diffraction measures particle size distributions by measuring the angle and intensity of light scattered as a laser beam passes through a dispersed particulate sample. Large particles scatter light at small angles and small particles scatter light at large angles. The angular scattering intensity data is then analyzed to calculate the size of the particles responsible for creating the scattering pattern, using the Mie theory. The method assumes that all particles are spheres, and the reported size class percentages are volume based.
Samples undergoing laser particle size analysis can be prepared in several ways. The two most commonly used in our lab are:
- External dispersion (shaking overnight in a surfactant), followed by wet sieving to remove the entire sand fraction (>62.5 μm) and laser analysis of the fine (silt and clay) fraction only.
- Dry sieved to remove the coarse sand particles (>2mm, >1mm, or >0.5mm depending on the project objectives and analyzer being used), and laser analysis of the remaining sample using internal dispersion in the laser analyzer using ultra-sonication.
Method 1 has the advantage of added resolution to the fine end by removing larger sand-sized particles, thereby reducing multiple light scatter. Method 2 has the advantage of having more of an entire sample being analyzed in a single technique. If the entire sample of interest is analyzed by laser diffraction, a mean, mode, and kurtosis of the entire particle size distribution can be determined.
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