Plant Uptake of Trace Elements from Coal Gasification Ashes

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Abstract
Uptake of trace elements in annual ryegrass (L. multiflorum Lam.) grown in mixtures of three gasification ashes and two soils under greenhouse conditions is reported. The gasification ashes selected were those produced in fluidized‐, fixed‐, and entrained‐bed gasification processes. Soils consisted of a surface agricultural soil and a subsurface weathered shale. Plant uptake was evaluated under two management regimes, with and without lime and fertilizer amendments. Six harvests were made over 180 d. Ryegrass yields were highly dependent on application of lime and fertilizer regardless of quantity or type of ash in the soil‐ash mixtures. Yields from unlimed/unfertilized treatments were low because of the limited supply of N, P, and K and phytotoxic levels of Al, Cd, Ni, and Zn. The entrained‐bed ash contained a relative high S concentration (38 g/kg) that oxidized and made the soil‐ash mixtures very acid (pH < 4). Ryegrass grown in unlimed/unfertilized soil‐ash mixtures of this ash contained very high concentrations of Al, B, Cd, Co, Mo, Ni, and Zn (up to 2449, 97, 24, 38, 5, 532, and 1109 mg/kg, respectively). Many of these concentrations were considered to be phytotoxic and/or sufficiently high to be toxic to animals under continuous long‐term grazing conditions. However, applications of the same gasifier ash to soils that were limed and fertilized with N, P, and K produced ryegrass that did not contain phytotoxic levels of any of the trace elements examined or concentrations that would be of concern in the transport of these metals along foodchains to man. Risk was related to soil pH, a factor that can be managed with proper liming and fertilizing practices.