Mining
 
Alternate Management Options for the Control of Acid Materials at Coal Mines in the Bowen Basin Queensland
C Hanahan  University of Queensland, Brisbane
The management of acid mine drainage at coal mines in the Bowen Basin depends on low rainfall to minimise transport of the products of the oxidation of sulphide minerals, primarily pyrite.  Thus, generation of acid mine drainage (AMD) occurs mainly during rain events.  Management involves channeling run-off from rain events into active pits and then either pumping the generated AMD out to evaporation ponds or in some cases pumping into underground shafts no longer in use.  Acid-generating tailings are stored in ponds with water covers.  Alternative management options are proposed here.
 
Red mud, the iron-rich residue from the caustic extraction of alumina from bauxite ore using the Bayer process, is a highly alkaline waste produced in large quantities.  At the Queensland Alumina Ltd. (QAL) refinery in Gladstone, QLD, the 8,000 dry tonnes of residues produced daily are neutralised with seawater, resulting in a reaction pH (1:5) of 8.6 - 8.8.  The author’s PhD project has investigated the abilitites of seawater neutralised red mud to neutralise acidity and trap trace metals associated with acid mine drainage.
 
The study reported here trials the use of seawater neutralised red mud to treat surface waters collected from three sites at two coal mines in the Bowen Basin.  Alternative management options are proposed to treat the AMD from storm events and to treat and enhance rehabilitation of tailings.  A leaky dam lined with red mud for the slow infiltration of collected storm run-off could replace evaporation ponds.  Co-disposal of red mud with dewatered tailings could enhance rehabilitation potential and eliminate the need to maintain water covers.  The reduction in transport costs of the red mud, a waste product with its own management costs, by using the coal trains returning empty to the Bowen Basin coal mines from Gladstone lends an additional cost benefit to these management options.

Brown Coal Derived Pproducts for Ameliorating Soil Acidity
J Issa, A Patti and W Jackson Monash University,  Melbourne
High acidity in soil is directly related to high toxic aluminium levels.  An increase in pH is desirable down to the root zone of crops (>10 cm).  Typical treatments such as lime and gypsum only increase pH near the soil surface unless they are physically incorporated; this is labour and cost intensive, and may also cause soil degradation.
Humic acid derived from brown coal, with added calcium, when applied to the soil surface, can increase pH deeper into the soil profile.  The humates can move down with water percolating the soil.  As they move down, the added calcium bound to the humate’s cation exchange sites (the acidic oxygen functional groups) can exchange with toxic aluminium ions and ions on exchange sites in the soil.  Thus the soil pH is buffered, nutrient transport to plants assisted, and phytotoxic aluminium bound and rendered harmless to plants.
 
Humic material fractions obtained from brown coal can be classified according to their solubility in acid and base.  These fractions differ in their ability to decrease soil acidity.  The ‘humin’ fraction (base-insoluble) has a low acid group content and moves slowly through the soil.  Humic acid (base-soluble, acid-insoluble) and fulvic acid (base and acid-soluble) move more rapidly; fulvic acid has more acidic groups than humic acid, but its lower molecular weight makes it more susceptible to microbial degradation, so that it is destroyed before benefiting the soil.
K Humate is a commercially available source of humate (ex HRL Agriculture Pty Ltd, Australia) derived from brown coal.  It can be obtained by the treatment of brown coal with potassium hydroxide.  Calsulmag is a commercial treated coal fly ash (also ex HRL Agriculture Pty Ltd) which can be used instead of lime due to its high inorganic calcium and magnesium content.  When K humate and Calsulmag are combined in an aqueous mixture, and applied to the surface of an acidic soil, pH is increased (from 3.8 to 4.5) as is exchangeable calcium (30-50%), while exchangeable aluminium is decreased (30-50%), down to a 5 cm depth.
 

Optimisation of Underground Coal Gasification for Improved Performance and Reduced Environmental Impact
A Beath and C Mallett CSIRO Exploration and Mining, Brisbane
Development of improved UCG processes has been performed using two complementary methods.  The first of these is the utilisation of detailed models of the gasification of coal under the conditions experienced in UCG.  The development of these models is discussed and the sensitivity of the models to variables such as temperature, pressure, water ingress and feed gas composition input is analysed.  In the second stage of the optimisation various process arrangements for the surface plant were simulated using a commercial process modelling software package.  The objective was to determine process arrangements that had both high efficiency and minimal emission of greenhouse gases.  The processes were all specifically designed for electricity generation, however the techniques used could also be applied to synthesis gas production.  The preferred process developed allows for separate combustion of hydrogen, with a stream comprised of methane, carbon monoxide and other gases being burnt separately in oxygen, allowing for sequestration of a carbon dioxide rich stream.  Disposal of the carbon dioxide could possibly be in spent underground gasification sites.  As the majority of the gas processing is carried out at high pressures, there is minimal expenditure of energy in recompression of the carbon dioxide for sequestration.
 
 
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