Weathered Fly Ash Research Articles

Long‐term supply and uptake by plants of elements from coal fly ash

Abstract To assess the mineral composition of plants growing in pure fly ash, grasses growing on lysimeters filled with alkaline, neutral, or acid fly ash were sampled several times in a 6‐year period. The samples were analyzed for elements essential for plants and animals as well as non‐essential, but environmentally significant, trace elements. Grasses were also sampled from ash dumps that were 20 and 30 years old. Fly ash is not a proper source of plant macronutrients N, P, and K. Plant growth on the alkaline fly ash can be influenced for some time by the high salinity of that ash. Grasses growing on unweathered fly ash were found to be high in Al, B, Co, Fe, Mo, Ni, Pb, and Se. Concentrations of several elements declined in time but levels of B, Fe, Mo, and Ni were still elevated in grasses on both fly ash dumps. All concentrations, except Al, were lower than toxicity levels for plants as found in literature. In plants growing on fresh fly ash concentrations of Mo, Pb, and Se can exceed the maximum tolerable levels for domestic animals. On weathered fly ashes (ash dumps) the Mo, Pb, and Se concentrations in grasses were below the maximum tolerable levels. Effects on animals by Mo in weathered ash may not be excluded because Mo concentrations can be high enough to induce Cu deficiency. Animals that feed on plants grown on fly ash could suffer from Ca, Mg, Na, and P deficiency.

Edaphological characteristics of unweathered and weathered fly ashes from Gondwana and lignite coal

Naturally weathered and unweathered samples of fly ashes produced from Gondwana and lignite coals were characterized for their edaphological properties. The particle size distribution in these fly ashes varied widely, and the percentage of <0·002 mm size particles governed their water holding capacity. All fly ashes were noncoherent in the dry state and had lower particle density than quartz and mulite. The fly ashes were low in available N, but were sufficient in available P, K, Ca, Mg, S, Cu, Fe, Mn, Zn and B. Among the fly ashes, unweathered lignite fly ash was the richest source of K, Ca, Mg, S and Fe, while weathered lignite fly ash had the highest amounts of Mn, Zn and B. The pH of the fly ashes was closely related to the ratio of exchangeable Ca to exchangeable Al. The fly ashes were high in soluble salt, but were poor in cation exchange capacity. As an amendment to correct soil pH, the fly ashes had a poor buffering capacity. Weathering decreased the total Fe, available S and exchangeable Na percentages, but increased the organic C content of the fly ashes. Invariably, an excess of soluble salts and exchangeable Na could limit plant growth on fly ash dumps. Toxic levels of B and Al existed in only some fly ashes.

Leaching Characteristics of Fly Ash after Four Years of Natural Weathering

AbstractThe natural weathering process of fly ashes was studied in artificial fly ash beds. The ashes were previously classified according to their total alkali content into acid, neutral and alkaline. After 4 years the effects of weathering are minor. The formation of concretions due to local cementation by calcite is observed in alkaline fly ash. Small brown pellets, highly enriched in some heavy metals, are present in the acid fly ash beds. Under natural conditions leaching is mainly confined to the alkaline fly ash. Elements which are leached most are sulphur and some alkalis as well as minor amounts of some trace elements.Shake- and column experiments of the weathered fly ashes with acids of pH 1 and 4, the latter also in combination with complexing agents, were carried out in order to check if the natural leaching process may be accelerated artificially. Strong acids (pH= 1) were most effective, but relatively large quantities of major elements were also leached. Experiments with the weak acids, combined with complexing agents, resulted in leaching percentages which did not significantly differ from experiments without these agents. This indicates that a major part of the elements are present in an immobile form; because of the use of sulphuric acid, it is likely that they are in some cases precipitated as sulphates (e.g. barium, calcium).

Effect of soil application of fly ash on chemical composition and yield of corn (Zea mays L.) and on chemical composition of displaced soil solutions

Field investigations were initiated in 1971 to study the effect of a weathered fly ash sample on yield and nutrient concentration of corn (Zea mays L.) and on composition of displaced soil solutions, and to determine rates of fly ash that could be applied to soils without adversely affecting plant growth. Application of weathered ash at rates ranging from 18 to 288 metric tons/ha did not decrease corn grain yields on either Groseclose silt loam or Woods-town loamy fine sand. Corn grain yields were increased on the Woodstown soil in 1972 where cumulative rates of 216 and 288 metric tons/ha of fly ash were applied, which was attributed in part to increased soil moisture. Plant analysis data indicated that B and Mn concentrations were not increased to toxic levels as had been reported in other investigations with unweathered fly ash. Soil solution data verified that toxic amounts of these elements were not released from the weathered ash sample.