大颗粒黏土矿物对黏土矿物X射线衍射定量分析的影响

The Impact of Large Grain Clay Minerals on X-ray Diffraction Quantitative Analysis of Clay Minerals

现行X射线衍射分析黏土矿物都是提取粒径小于2μm的悬浮溶液检测样品的黏土矿物组合及含量,含量数据有时与其他检测数据相悖。在鄂尔多斯盆地黏土矿物研究中,通过偏光显微镜和扫描电镜发现存在粒径大于2μm的黏土矿物颗粒,特别是高岭石的粒径多为3～10μm,这些大颗粒黏土矿物会造成含量数据不准确。为了证明大颗粒黏土矿物对其含量测量的影响,本文设计了不同粒径标准的提取物对比试验:随机选取267个样品,每个样品分别按照10μm和2μm标准提取两份悬浮溶液制成测试片,采用SY/T5163—2010行业标准中的检测方法得到10μm和2μm提取物的黏土矿物组合及含量。通过对比发现大颗粒黏土矿物对各类黏土矿物的相对含量测量结果有明显影响:10μm提取物中高岭石含量明显增大;伊利石/蒙脱石间层矿物含量显著降低;伊利石含量的变化小且无规律;绿泥石含量整体变化较小,少量样品中绿泥石含量发生了明显的偏离,与大颗粒高岭石的赋存有关。本研究提出应结合地质状况和工作目的审慎选择提取粒径的标准,对SY/T 5163—2010中的黏土矿物提取粒径标准作出修订。

BACKGROUND:Current X-ray Diffraction analysis of clay minerals is used to detect the clay mineral assemblages and contents of suspended solution with a particle size of less than 2μm,but the content data is sometimes inconsistent with other test data.The clay minerals with grain sizes larger than 2μm in the Ordos Basin were observed by Polarizing Microscope and Scanning Electron Microscope(SEM).The kaolinite has grain sizes ranging from 3μm to 10μm,which would result in imprecise content data of clay minerals.OBJECTIVES:To evaluate the influence of large particle clay minerals on the relative content of clay minerals by designing a comparative test of extracts from different particle size.METHODS:267 samples were selected randomly,and each sample was prepared by extracting two suspension solutions according to the standards of 10μm and 2μm,respectively.The clay mineral assemblages and contents of 10μm and 2μm extracts were obtained using the analytical method in the SY/T 5163-2010 industry standard.RESULTS:Through comparison,it is found that large-grained clay minerals have a significant effect on the relative contents of various types of clay minerals.The clay minerals in 10μm extracts have a higher content of kaolinite than the 2μm extracts.Illite/montmorillonite interlayer mineral contents decrease significantly.The change in the illite content is small and irregular.The overall change in chlorite content is small,and the chlorite content in minor samples deviates significantly,which is related to the occurrence of large-particle kaolinite.The standard for extracting grain size should be carefully selected in combination with the geological conditions.CONCLUSIONS:It is proved by this experiment that large particle kaolinite has a significant influence on the relative content of clay minerals.Furthermore,the extraction of particle size standards for clay minerals should be carefully chosen by the actual geological conditions and the purpose of the work.It is also suggested that the industry standard SY/T 5163-2010 should be revised.