Lake sediment should be prctreated before particle size analysis. It is necessary to eliminate the error caused by floccula-tion phenomenon of fine grain of sediment samples at the same time of effectively removing organic matter and carbonate particles. Surface sediment sample from the Lake Sanjiao in Wuhan was used for X-ray powder diffraction (XRD) to identify its mineral composition and clay species and automatic laser granulometer for grain size analysis. The XRD result demonstrated that the main non-clay minerals in sample were quartz and feldspar; while the clay minerals were primarily illite, kaolinite, chlorite. Furthermore, the result of grain size analysis showed that the grain size of 94. 5% of component in sample was less than 30 μm. These characteristics made the sample easy to form flocculation at the pretreatment process of grain size analysis. Based on the results above, for the sample which are composited primarily with illite, kaolinite, chlorite, a single factor optimization method including ultrasonic concussion, dispersing agent and acid washing was used to check the optimum condition for eliminating flocculation. Results indicate that the optical condition for eliminating flocculation are ultrasonic concussion time; 6-8 min, dispersing agent concentration: 20 g/L, with acid washing before particle size analysis.%采用激光粒度仪对湖泊沉积物进行粒度分析时需要进行必要的前处理.在有效去除有机质与碳酸盐颗粒的同时,需要消除细粒泥沙质样品中絮凝现象对粒度分析结果造成的误差或错误.本文以武汉三角湖表层沉积物样品为例,采用X射线粉晶衍射(XRD)对其矿物组成和粘土矿物种属进行鉴定,并采用全自动激光粒度仪对样品进行粒度分析.X射线粉晶衍射结果表明样品中非粘土矿物主要为石英与长石,粘土矿物以伊利石、高岭石、绿泥石为主；粒度分析结果显示样品中小于30 μm组分占94.5％.这些特征表明该样品易于在前处理过程中形成絮凝.本次研究采用单因素寻优法探讨了超声震荡、分散剂、洗酸对于以伊利石、高岭石、绿泥石为主、平均粒径较小的样品消除絮凝现象的最佳条件.研究结果表明,针对此类样品消除絮凝现象的最佳条件为:超声震荡时间应选择6～8 min,分散剂浓度为20 g/L左右,同时在粒度分析之前需要对样品进行洗酸.
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