Amount of amorphous materials in relationship to arsenic, antimony, and bismuth concentrations in a brown forest soil

The objective of this study was to examine the relationship between the amounts and chemical compositions of total amorphous materials and elements in the soil. Total amorphous materials in a brown forest soil were quantified by an X-ray powder diffraction method, chemical compositions of total amorphous materials were determined by a balance sheet method, and arsenic (As), antimony (Sb), and bismuth (Bi) concentrations in the soil were analyzed. The soil samples were collected in 10-cm increments from the surface to 100 cm depth in central Ibaraki Prefecture, Japan. After separating each sample into fractions by grain size, the amorphous ratio of each fraction was determined. Total amorphous materials decreased from 360 g kg− 1 at 0–10 cm depth to 210 g kg− 1 at 90–100 cm. The chemical compositions of the total amorphous materials were different in different size fractions of soil. Finer fractions had much Fe2O3, and coarser fractions much SiO2. As, Sb, and Bi concentrations were generally higher in the finer fractions but decreased with depth. As, Sb, and Bi were positively correlated with the Fe2O3 component in total amorphous materials. These findings can be explained by the affinity of each element to solid phases.