前处理过程对汉江上游谷地“古土壤”粒度测试结果的影响研究

Pretreatment Methods and Their Influences on Grain-size Measurement of Palaeosol in the Upper Reaches of the Hanjiang River Valley, China

对汉江谷地的古土壤用6种方法分别进行了前处理,A处理为样品H2O2和盐酸处理后,烧杯注满水静置72 h后加5 mL分散剂。B处理在A基础上再用超声波再震荡10 min。C在A基础上再用超声波再震荡20min。D处理为H2O2和盐酸处理后,烧杯注满水静置72 h后加10 mL分散剂,再用超声波再震荡20 min。E处理为H2O2和盐酸处理后再搅拌15 min,烧杯注满水静置72 h后再加入10 mL分散剂,用超声波振荡20 min。F处理为H2O2和盐酸处理后,搅拌30 min,余与E相同。用Beckman公司生产的LS1320型激光粒度仪进行测量。结果表明,样品前处理过程中,超声波震荡及振荡时间是影响粒度测量结果的最主要因素。针对汉江上游谷地的样品而言,类黄土的沉积样品(黄土、表土、河漫滩沉积物等)使用前处理方法A后,颗粒可得到充分的分散,能获得了较好的粒度测量效果。而成壤强烈和黏结性较高的古土壤样品,不同的前处理方法对粒度测量结果影响非常大,平均粒径和众值粒径可出现数倍几倍的变化,其中前处理方法C对古土壤样品较合适,样品颗粒能得到较好的分散,测量效果要好于其它方法(A、B、D、E和F)。

The grain size of sediment is an important tool for the extraction of paleo-climate and paleo-environment change information. This article attempts to study the influence of sample pretreatment methods on particle size analysis result. Loess and paleosol sample were chosen from the Qianfangcun profile in the upper reaches of the Hanjiang river valley as the representative material. They are measured using a laser particle analyzer （LS1320） made by Beckman Company, U.S.A. These samples were performed using 6 different pretreatment methods before their grain-size distribution were measured, respectively. The experimental results show that the pretreatrnent methods and steps for the grain size measurement procedures have certainly influenced on results of grainsize distribution. Different samples should be used different retreatment methods and steps. In the process of sample pretreatment, ultrasonic vibration and oscillation time significantly influence the resuits of particle size measurement. Aiming at samples from the upper reaches of the Hanjiang river valley, pretreatment method A（0.8 g sample put into 500 mL beaker, then to pour 10 mL10% H2O2 and 10 mL 10% hydrochloric acid in the beaker, respectively. The beaker is filled with distilled water and static for 72 h, slow pumping to distilled water, putting into 5 mL 0.05 mol/L dispersing agent（（NaPO3）6, then to measure particle size using a laser particle analyzer） is more suitable to weak cementation sediment samples, such as loess, modern topsoil and river sediments et al. Using pretreatment method A could obtain better effect of the particle size measurement because its particles can be sufficiently dispersed. The caking property of paleosol sample in the Hanjiang River valley is very high because of its strong pedogenesis. It is difficult to be completely dispersed particles of paleosol because of closely cemented between particles. There exists great differences in grain-size distribution of the palaeosol sample while it was pretreated by the pretreatment method A, B, C, D, E and F （ Method B： In the method based on A, then ultrasonic vibration with 10 min. Method C： 0.8 g sample was put into 500 mL beaker, then to pour 10 mL10% H202 and 10 mL 10% hydrochloric acid in the beaker, respective- ly. The beaker is filled with distilled water and static for 72 h, slow pumping to distilled water, putting into 5 mL 0.05 mol/L dispersing agent（（NaPO3）6）, at the same time with using ultrasonic vibration 20 min, then to measure particle size using a laser particle analyzer. Method D： The samples were digested with H2O2 and hydrochloric acid, beaker was filled with distilled water and static for 72 h, putting into 10 mL 0.05 mol/L dispersing agent（（NaPO3）6）, then ultrasonic vibration with 20 min. Method E： The samples were digested with H2O2 and hydrochloric acid, stirring 15 min, beaker was filled with distilled water and static for 72 h, putting into 10 mL dispersant, ultrasonic vibration with 20 min. Method F： The samples were digested with H2O2 and hydrochloric acid, stirring 30 min, beaker was filled with distilled water and static for 72 h, plus 10 mL dispersant, ultrasonic vibration with 20 min）, respectively. The experimental results show that differences of the grain-size index such as the average particle size can be several times fluctuation. The pretreatment method C is more suitable for palaeosol samples from the Hanjing river valley. Dispersion effect of the pretreatment method C for palaeosol sample is better than those of other pretreatment method, including method A, B, D, E and F.