同步辐射X射线衍射光谱在地带性土壤粘粒矿物研究中的应用

X射线衍射（XRD）光谱是分析土壤粘粒矿物组成的重要手段，但常规XRD分析存在前处理复杂、耗时较长、光谱分辨率低、扫描不充分等问题。为此，该研究依托北京同步辐射装置（BSRF）的4B9A衍射实验站，以我国东部不同气候带（即温带、亚热带、热带）的7种地带性森林土壤（棕色针叶林、暗棕壤、棕壤、黄棕壤、黄壤、赤红壤和砖红壤）为研究对象，利用同步辐射X射线衍射（SR-XRD）光谱对土壤粘粒矿物组成特征进行分析。结果表明：（1）温带土壤（棕色针叶林、暗棕壤和棕壤）质地以粘壤土为主，而亚热带土壤（黄棕壤、黄壤和赤红壤）分布在粘土和粘壤土的分界线上；从亚热带到热带，土壤质地呈现出粘土→壤土→砂土的变化趋势。（2）土壤硅铝率（Sa）表现为温带土壤（5.22）>热带土壤（4.53）>亚热带土壤（4.49）；同样地，硅铝铁率（Saf）也呈现出温带土壤（4.06）>热带土壤（3.53）>亚热带土壤（3.36）的变化规律。（3）从温带到热带，土壤粘粒矿物中高岭石的含量增加、结晶度提高，而伊利石的含量则逐渐减少；温带土壤以2∶1型粘粒矿物为主，而热带土壤则以1∶1型矿物为主；在SR-XRD光谱中鉴定出了伊蒙混层、长石两种粘粒矿物的存在，而这两种矿物在常规XRD光谱中未被识别。（4）与常规XRD法相比，利用SR-XRD法分析土壤粘粒矿物组成具有以下优势：一是前处理工作量较少，常规XRD法需将粘粒样品制成不同类型的载玻片再进行测定，而SR-XRD法直接测定粘粒样品即可；二是光谱分辨率高，SR-XRD法的分辨率可达到≤100 nm，从而能够检测到更多的衍射峰；三是实验效率提高，SR-XRD法的优化扫描步长可达0.04°，比常规XRD法增加1倍，从而提高了测试效率；四是扫描辨识度增加，SR-XRD法的看光时间可优化为4 min，是常规XRD法的2倍，使得样品的扫描更加充分。

Application of Synchrotron Radiation X-Ray Diffraction Spectroscopy in the Study of Clay Minerals in Zonal Forest Soils

X-ray diffraction(XRD)spectrum is an important method to analyze the clay mineral composition of the soil,but conventional XRD analysis has some problems such as complex preprocessing,long time-consuming,low spectral resolution and insufficient scanning.So based on the 4B9A diffraction experiment station of Beijing Synchrotron Radiation Facility(BSRF),7 zonal forest soils(including brown coniferous forest,dark brown soil,brown soil,yellow brown soil,yellow soil,red soil and red brick soil)in different climate zones(temperate zone,subtropical zone and tropical zone)in the east of China were studied in this study.The characteristics of clay mineral composition in soils were analyzed by using synchrotron radiation X-ray diffraction(SR-XRD)spectra.The results showed that:(1)the texture of temperate soil(i.e.brown coniferous forest,dark brown soil and brown soil)was mainly clay loam,while that of subtropical soil(i.e.yellow brown soil,yellow soil and red soil)was distributed on the boundary line between clay and clay loam;from subtropical to tropical,the texture of soil presented the changing trend of clay loam and sand.(2)Sa of the soil showed the trend of temperate soil(5.22)>tropical soil(4.53)>subtropical soil(4.49);similarly,Saf also showed the trend of temperate soil(4.06)>tropical soil(3.53)>subtropical soil(3.36).(3)From the temperate zone to the tropical zone,the content of kaolinite and crystallinity of clay minerals in the soil increased,while the content of illite decreased gradually.In the temperate zone,the clay minerals were mainly 2∶1 type,while in the tropical zone,the clay minerals were mainly 1∶1 type.The existence of two kinds of clay minerals,i.e.illite mixed layer and feldspar,was identified in the SR-XRD spectrum,while was not identified in the conventional XRD spectrum.(4)Compared with the conventional XRD method,the SR-XRD method had the following advantages in the analysis of soil clay mineral composition:First,the preprocessing work was less,the conventional XRD method needed to determinate clay samples in different types of glass slides,while the SR-XRD method could directly determine clay samples;Second,the optical spectrum resolution was high,and the resolution of SR-XRD method could reach≤100 nm,so more clay could be detected;Third,the optimized scanning step length of SR-XRD method could be 0.04,which was two times as that of conventional XRD method,thus improving the testing efficiency;Four,the scanning identification degree was increased,and the viewing time of SR-XRD method could be optimized to 4 minutes,which was 2 times of that of conventional XRD method,which made the scanning of samples more full.