EFFECTS OF PRETREATMENT ON LASER DIFFRACTION PARTICLE SIZE ANALYSIS OF FLUVIAL SEDIMENTS IN DESERT REGIONS

Abstract

The choice of pretreatment methods in laser diffraction analysis of mineralogical grain size composition in fluvial sediments can significantly influence measurement outcomes, yet published data on this topic remain limited. This study systematically investigates the effects of four different pretreatment methods—sieving only, physical dispersion only, removal of organic matter only, and combined removal of carbonate and organic matter—on grain size measurements, using typical fluvial sediments from the terminal oasis of the Keriya River in the central Tarim Basin, Taklamakan Desert. Results showed that samples treated by sieving alone tend to yield overestimated median grain sizes, with particle size variation rates exceeding 70% in some cases. We concluded that carbonate acts as the primary cementing agent between sediment particles in this region, and acid digestion plays a crucial role in disaggregating micro-aggregates and releasing fine-grained fractions. Physical dispersion is mainly effective in breaking down loosely structured macro-aggregates. Furthermore, the removal of organic matter is essential for eliminating organic cementation and minimizing interference from water absorption and swelling in certain samples.