The association of phosphorus with iron in ferruginous soil concretions

Abstract

Ferruginous concretions from various Australian and German soils and samples of bog iron ore from various European localities were examined by X-ray diffraction and electron microprobe techniques. The association between phosphorus and iron in these samples was looked at from the point of view of differences in iron mineralogy and genesis. When surface area is considered it appears that hematite, goethite and possibly maghemite show phosphorus adsorption levels in the same order of magnitude as those obtained on synthetic preparations of these minerals. In most cases a high phosphorus content is associated with a high iron, but the converse is not true, so that although the iron minerals are definite sinks for the phosphorus in the environment a linear relation cannot be expected due to the variation in time and spatial distribution of these two elements. In the younger European soils the phosphorus/iron ratios are generally higher (average 0.015), reaching values as high as 0.05 in some bog iron ores formed in gleys, whereas in the older Australian soils the average ratio is 0.002.