Rapid and quantitative major element analysis method for wet fine-grained sediments using an XRF microscanner

Abstract

Several types of X-ray fluorescence (XRF) core scanners have been developed to fulfill the demands for high-resolution, rapid, chemical analysis of wet sediment cores. However, their application to quantitative analysis has been hampered by the difficulty of evaluating the XRF absorption effect of water in a water film on the sediment surface and interstitial water within the sediments, especially for lighter elements. In this study, we established a non-destructive, rapid, high-resolution, and quantitative chemical analysis method for wet fine-grained sediment samples using an XRF microscanner. Results of our experiments suggest that the degree of XRF absorption by the water film, which develops on the wet sample surface covered with Mylar film, shows a clear positive correlation with the water content of the sediments under the measurement area. A clear positive correlation also exists between the degree of XRF absorption by the interstitial water and the water content of the sediments under the measurement area. We evaluated the XRF absorption by the thin water film using the relationship between the water content and thickness of the thin water film, and the XRF absorption by the interstitial water using its relation with the water content. The water content under the measurement area is estimated from the average transmitted X-ray intensity that is measured on the same measurement area simultaneously with the measurement of XRF intensities. The dry sample equivalent XRF intensities of major elements (Al, Si, K, Ca, Ti, and Fe), which are the XRF intensities of wet samples corrected for the XRF absorption by the thin water film and the interstitial water, show better correlation with the major element concentrations determined by conventional XRF methods. Using this new method, it is possible to measure the average water content and average concentrations of the 6 major elements simultaneously for a square area as small as 0.5 × 0.5 mm on the wet fine-grained sediment within 6 min, which is nearly ten times faster than the conventional XRF method.