Element Partitioning in Size‐ and Density‐Fractionated Sewage Sludge and Sludge‐Amended Soil

Abstract Direct characterization of trace‐element‐bearing minerals in solid waste and waste‐affected soils requires the use of mineral preconcentration techniques. This study was conducted to evaluate the effectiveness of a nondestructive physicochemical fractionation technique when applied to Los Angeles sewage sludge and sewage‐sludge‐amended Domino soil (fine‐loamy, mixed, thermic Xerollic Calciorthid). Bulk samples and the physicochemical separates were subjected to analysis for 31 elements using neutron activation. The concentrations of Ca, Ce, Cs, La, Nd, Sb, Sm, and Tb in the sludge exceeded previously reported concentration ranges. The long‐term application of sewage sludge to the Domino soil at agronomic rates resulted in the accumulation of Ba, Ce, Co, Cr, Cu, La, Nd, Ni, Pb, Sm, Sr, and Zn in the zone of incorporation. However, only the concentrations of Cs, La, Sb, and Tb exceeded uncontaminated soil concentration ranges as a result of sludge amendments. For a majority of the elements, the highest concentrations were in the heavy‐density fractions. The fractions with the highest element concentrations accounted for only a minor percentage of the mass of the bulk sample. The bulk of the total element mass was associated with light‐density materials in sewage sludge and the middensity materials in the amended soil. Application of the density‐magnetic separation scheme to sewage sludge was more effective in preconcentrating elements than was application of the size‐density fractionation scheme to amended soil. However, the fractionations performed here may not be sufficient for direct identification of trace solid phases by some direct methods of analysis. Cluster‐dendrogram analysis, using the element concentrations in the various density separates, indicated that the elements could be grouped into four significantly different classes. In general, the results of such analyses can be used, in conjunction with results from direct and other indirect methods of analysis, to infer element associations in the solid phase.