Abstract
Soil minerals study is vital in terms of investigating the major soil forming compounds and to find out the fate of minor and trace elements in soils. It is also essential for the soil-plant interaction purpose. To identify soil mineral phases especially clay minerals, X-ray diffraction (XRD) has been a popular technique. The clay mineralogical information of soils in Bangladesh is limited, especially in Ganges flood plain region (Agro Ecological Zone (AEZ) 12 and 13). Therefore, to overcome this limitation, in this study, we performed XRD analysis of <2 mm fractions soil samples of AEX 12 and 13. However, identifying mineralogical phases by XRD in <2 mm fractions soils is not so straight-forward due to many practical problems. We fully matched only two mineralogical phases in all the soil samples which is quartz and potassium-Aluminum-Silicate. However, the full XRD peaks indicate that more minerals are also present, but due to heterogeneity of soils samples, it is difficult to find other minerals phases by only XRD peak of <2 mm fractions. Therefore, to find more information about mineralogical phases, we performed XRF analysis that provides the elemental composition of minerals phase as oxide. XRF analysis indicated the presence of secondary minerals like illite and chlorite. The presence of high percentage Fe oxide not only indicated the iron mineral phase (goethite and ferrihydrite) but also indicated iron rich high charge smectite minerals (beidellite). The presence of iron rich smectite minerals in the Ganges sediments reported in several previous studies. Thus, we concluded that only XRD in <2 mm fractions of soils is not adequate to identify the mineralogical phases of soil samples. Others analyses like XRF, XRD in <2 μm fractions will be necessary to locate an entire image of soil mineralogical phases.
Highlights
The commonest method for qualitative and quantitative mineral composition determination in soils is the X-Ray Diffraction (XRD)
The cation exchange capacity (CEC) was in a range from 15.4 to 20.7 cmol∙(+)∙kg−1 in all the studied soils and was found to be in the high categories according to the Bangladesh soil standard [18]
To fully understand clay mineral characteristics, clay mineralogy by XRD and chemical composition by X-ray Fluorescence Spectrometry (XRF) were examined in the Lower Ganges River Floodplain and Gnages Tidal Floodplain by collecting soil samples from several locations
Summary
The commonest method for qualitative and quantitative mineral composition determination in soils is the X-Ray Diffraction (XRD). The complexes of minor elements yield broad low-intensity XRD peaks, and these peaks often overlap with high-intensity peaks from silica, thereby making identification and quantitative determination difficult [3]. To overcome these limitations in XRD, researchers often use other techniques like XRF to get more information about soil minerals. X-ray Fluorescence Spectrometry (XRF) is a quick method for determining of the total elemental composition of soil samples. The determination of elements by XRF is providing the semi-quantitative information about soil mineral phases [3]
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