XRD-Rietveld全谱拟合法定量土壤矿物可行性研究——以四川盆地常见紫色土为例

FEASIBILITY STUDY ON QUANTIFICATION OF SOIL MINERALS BY XRDRIETVELD FULL-SPECTRUM FITTING METHOD-A CASE STUDY FROM COMMON PURPLISH SOIL IN SICHUAN BASIN

土壤的固体骨骼是复杂的晶质-非晶质矿物的多相混合物,其矿物组成与准确定量直接影响土壤的性质、结构及肥力水平的评价,常规基于峰位-强度(d-I/I0)的X射线外标法受限于参比强度值的多选而不能准确的反应矿物真实含量,无定标Rietveld全谱拟合法在定量复杂组成的自然界土壤矿物上依然存在准确性验证的问题。针对上述问题,根据土壤中常见的矿物类型和大致含量,选取结晶良好的高纯单矿物配置4组3~6相固定比例的土壤模拟样品(石英+赤铁矿+高岭石;石英+赤铁矿+高岭石+伊利石;石英+赤铁矿+高岭石+伊利石+方解石;石英+赤铁矿+高岭石+伊利石+方解石+碱性长石),并对K值法、RIR值法和Rietveld全谱拟合法3种方法定量结果进行讨论,选择四川盆地分布广泛的紫色土开展Rietveld全谱拟合法及非晶质成分定量的实际应用。结果表明,4组土壤模拟样品Rietveld法定量结果(绝对偏差范围0.8%~4.8%,均值2.7%)与K值法定量结果(0.6%~8.8%,均值3.1%)显著优于RIR值法定量结果(绝对偏差范围1%~28%,均值11.2%),对于低含量的黏土矿物,Rietveld全谱拟合法(绝对误差范围1.8~3.8,均值2.3)比K值法(绝对误差范围1.4~5.5,均值3.0)反应更加灵敏。紫色土样品Rietveld全谱拟合法定量后换算的元素分布曲线与化学分析(XRF)结果分布曲线相关程度高,其相关性达到99.78%,表明全谱拟合法定量结果能较为真实的反映样品信息。无定标的XRD-Rietveld全谱拟合法定量方法规避了常规分析手段带来的分析误差,能有效的提高定量结果的精度,具有广阔的应用前景。

The solid framework of soil represents a complex mixture of crystalline and amorphous miner-als,whose precise mineral composition and quantification play a crucial roie in evaluating soil properties,structure,and fertility levels.Traditional X-ray external scaling methods based on peak intensity(d-l/I0)are hindered by the need for multiple reference intensity values selection,making it challenging to accu-rately reflect the true mineral content.Similarly,uncalibrated Rietveld full spectrum fitting methods still struggle with accuracy verification in quantifying complex natural soil minerals.In this study,we employ the Rietveld full spectrum fitting method to address these challenges.We select high purity single minerals with excellent crystallization and configure four sets of soil simulation samples with fixed proportions of 3-6 phases(quartz+hematite+kaolinite;quartz+hematite+kaolinite+illite;quartz+hematite+kaolin-ite+illite+calcite;quartz+hematite+kaolinite+illite+calcite+potassium feldspar).We comparatively discuss the quantitative results of the K value method,RIR value method,and Rietveld full spectrum fit-ting method.Furthermore,we conduct practical applications of the Rietveld full spectrum fitting method and quantitative determination of amorphous composition in the purplish soil widely distributed in the Si-chuan Basin.Our results demonstrate that the quantitative results of the Rietveld method(absolute devia-tion range=0.8%-4.8%,mean value=2.7%)and K value method(0.6%-8.8%,mean value=3.1%)outperform those of the RIR value method(absolute deviation range=1%-28%,mean value=11.2%)across the four groups of soil simulation samples.For low-content clay minerals,the Rietveld full spec-trum fitting method(absolute error range=1.8-3.8,mean value=2.3)exhibits greater sensitivity than the K-value method(absolute error range=1.4-5.5,mean value=3.0).The element distribution curve of the purplish soil sample,quantified using the Rietveld full spectrum fitting method,correlates highly with the chemical analysis(XRF)results,with a correlation of 99.78%,indicating that the quantitative results of the full spectrum fitting method can more accurately reflect the sample information.These find-ings highlight the potential of the unmarked XRD-Rietveld full spectrum fitting quantitative method to a-void analytical errors associated with conventional methods and effectively enhance the accuracy of quanti-tative results,thereby offering significant application prospects.