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Trace metal release from a Western Australian coal fly ash

Wood, Ian Burton (1985) Trace metal release from a Western Australian coal fly ash. Honours thesis, Murdoch University.

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Coal fly ash is the major solid residue from coal fired electric power generation. Although composed predominantly of a sparingly soluble aluminosilicate matrix, fly ash also has an appreciable soluble surface layer which is reported in the literature as containing significant concentrations of various toxic trace metals. Fly ash is therefore considered to have the potential to generate leachates with significant environmental impact.

A series of experiments were conducted to determine the leaching characteristics and extent of trace metal release from a Western Australian coal fly ash under static and dynamic conditions. It was found that the leachates generated were particularly acidic (pH values' less than 4) compared to values reported in the literature. This acidity is attributed to the adsorbed sulphur oxides on the ash and the relatively low concentrations of calcium, magnesium and sodium oxides. As expected from the acidic nature of the leachates, the trace metal concentrations observed were relatively high with respect to the levels reported in the literature. The concentrations were generally in the order of several parts per million, often exceeding the accepted Australian water quality criteria for drinking and irrigation waters.

The effectiveness of two alternative approaches to reducing the trace metal concentrations in the leachates were 1nvestigated. Alkalisation of the slurries using sodium hydroxide or lime effectively reduced all trace metals to below their detection limits.

Of these two alkalis, lime proved the most effective under dynamic leaching conditions. Of the three possible ash dam substrates investigated (sand, limestone and clay), limestone proved the most effective - reducing most trace metals to below their detection limits. The performance of the clay layer was surprisingly poor and is partially attributed to the acidic nature of the leachate. The sand layer, as expected had no detectable effect on the leachate.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Environmental and Life Sciences
United Nations SDGs: Goal 12: Responsible Consumption and Production
Notes: A digital copy of this thesis is not available. Your library can request a copy from Murdoch University Library via Document Delivery. A fee applies to this service.
Supervisor(s): Ho, Goen and Mandyczewsky, R.
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