Effects of different pretreatment methods on grain-size measurement of the north red weathering crust

Liaodong peninsula is located in the north of Sino-Korean paraplatform of which tectonics is relatively mature, an important part of Asian paraplatform. Due to the Yanshan movement, there developed lots of structures, such as folds and faults. The strata such as Cambrian is well exposed. Its main lithologies are limestone, quartzite, slate and sandstone. The Liaodong peninsula is located in the southern end of northeast China, surrounded by seas on three sides, and between the Yalu river and Liaohe river, mainly hilly and mountainous terrain. It belongs to the temperate continental monsoon climate, mean annual temperature is around 10 ℃, and mean annual rainfall is 550-950 mm. Rainfall is mainly concentrated in July and August.In this paper, the design of pretreatment methods is as follows. First of all, the samples are digested with 30% H2O2 to remove organic matter, and then four methods are used for preprocessing. Of them, the method A is not disposed by hydrochloric acid, methods B, C and D are all decomposed by hydrochloric acid solution to remove the residual carbonate and secondary free oxides in order to eliminate the cementation of debris and mineral particles. HCl of method C is in the boiling conditions of the reaction. HCl of method B is under normal temperature conditions, and method D changes the ultrasonic vibration time.There are different pretreatment methods for the samples to test, the purpose of which is to analyze the influence of various methods on particle size measurement. Combined with the laser diffraction particle size analyzer, it can explore the analysis results of particle size and the reason for the difference to recommend the most optimal pretreatment method, which can facilitate further studying on weathering crust in the region of grain-size analysis. The experimental results show that the pretreatment methods have a certain effect on the particle size measurement results of red weathering crust in northern China, and the different pretreatment methods make the grain size of the samples have about 5% rotates. Considering the stability of the experiment, the error of the parallel tests of the 4 methods reaches up to 6.78%. Under the existing recognized conditions, reproducibility of particle size measurement results is the most basic demand to experiments. In this paper method C is better than others (A, B and D).The results in different pretreatment methods reflect the basic characteristics of the weathering crust in particle size distribution. The method mentioned in the paper is suitable for the weathering crust of north China, the other types and regions should be combined with the actual situations in order to obtain a more ideal test result.