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Trace Elements in Fly Ash and Their Release in Water and Treated Soils¹

ABSTRACT

Fly ash from a coal-fired power plant was separated into various-sized fractions which were then chemically characterized. The fly ash contained higher concentrations of B, Co, Cr, Cd, Mo, Ni, Pb, As, and Se than normally found in soils. Except for Cd, Co, and Pb, trace elements were more concentrated in the < 53-µm than in the > 250-µm fraction. Solubility of trace elements in water increased greatly as the equilibrium pH was lowered.

Three soils, an acid sand, a calcareous loamy sand, and a calcareous silt loam, were amended with five rates of fly ash up to 1.0% by weight and equilibrated at moisture contents of 1/3 bar or saturation for periods ranging up to 29 weeks. Solubility of trace elements in water and DTPA extracts were observed. Application of fly ash increased soil pH; the acid soil exhibited the greatest increase. Except for B, fly ash amendment up to 1.0% did not result in elevated concentration of either water-soluble or DTPA-extractable trace elements. Additions of fly ash to the acid soil decreased DTPA-extractable Fe, Mn, Ni, Co, and Pb. The data demonstrated that the alkalinity of fly ash plays a significant role in regulating the availability of trace elements in the amended soils.

Key Words: coal-fired power plants • heavy metals • environmental pollution • waste material

¹ Contribution from the Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA 92502. This research was supported by Southern California Edison Co. under Contract no. U3294908.

² Postgraduate Research Soil Scientist, Associate Professor and Professor of Soil Science, and Specialist, respectively. Senior author is presently Senior Research Scientist, SCS Engineers, Long Beach, CA 90807.

Received for publication June 12, 1978.