Leachability of Trace Metals from Sandy or Rocky Soils Amended with Coal Fly Ash

Abstract

Application of coal fly ash as a soil amendment for Florida sandy or rocky soils is an alternative to disposal of coal fly ash and also will improve soil physical and chemical properties and increase crop production. However, environmental fate of trace metals in coal fly ash is a major concern. The objective of this experiment was to evaluate movement of trace metals in coal fly ash amended soil columns. Three soils were collected from south Florida to represent Alfisols, Entisols, and Spodosols. Each of three representative soil was packed into separate columns (32.5 cm long and 7.5 cm inner diameter), amended with coal fly ash at rates of 0, 40, 80 Mg ha−1 and leached with 10 pore volumes of water, which is equivalent to 113.8 cm rainfall. Leachates were analyzed for Zn, Cu, Mn, Fe, Cd, Pb, and Ni. There was no detectable Cd in leachate from any of the soil columns. The maximum concentrations of Zn from all three soils with or without coal fly ash amendment were below the Maximum Contamination Level (MCL) for drinking water. High concentrations of Fe, Pb and Mn in leachate were more closely related to the background concentrations of these metals in three soils than to the coal fly ash application. Application of 80 Mg ha−1 coal fly ash to Riviera soil elevated Cu concentration in leachate above MCL. After completion of leaching, soil columns were divided into five sections (5 cm each) and analyzed for total concentrations of selected metals. The results showed that application of coal fly ash increased all of the trace metals measured in soils at top 5 cm or 5–10 cm depth after leaching. Concentrations of Zn, Cu, Mn, and Cd were also elevated in soil depths from 5 to 25 cm of Riviera soils mainly because the soil has very sandy texture and low organic carbon.