Abstract
It is expected in the future that soil particle size distribution (PSD) measurements by laser diffraction method (LDM) may replace sieve-pipette sedimentation methods (SPM) as they are faster, require less sample, and are accurate and reproducible. LDM measurement result is a continuous function of PSD, which can facilitate the conversion between the various limits (by countries, by scientific field) of the calculated particle size fractions (PSF – e.g. clay, silt, sand). Currently, there is no standard method for LDM PSD measurement. Many different types of instruments and preparation devices are currently used in laboratories, with various sample preparation, pre-treatment and measurement methods (duration, chemical and/or mechanical dispersion, settings, etc.). In soil LDM PSD measurements, researchers put relatively little emphasis on the choice of the type of aqueous media used. Thus, it is still questionable to what extent the results of the LDM measurement depend on the selection of the dispersion method and the aqueous media. For our research, eight soil samples with various physical and chemical properties were collected in Hungary. The particle size fractions (clay, silt, sand) determined with LDM (Malvern Mastersizer 3000) measured in three types of aqueous media (distilled, deionized and tap water), in different combinations of two dispersion methods (no treatment, ultrasonic or chemical dispersion with Calgon and their combination) were compared. For the comparison, PSF results of the conventional sieve pipette method (SPM) were used as a reference. Our results showed that LDM measurement can achieve various degrees of dispersion with different preparations, in many cases only partial dispersion, disaggregation, sometimes re-aggregation, and flocculation of soil particles were observed as compared to full preparation (in SPM). The “disaggregation pattern” of the soil samples also depended on the quality of the aqueous media and the properties of the soil investigated, because several types and degrees of interactions could occur in the various soil-liquid-dispersant/disaggregation effect systems.
Published Version
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