Categories
By-product Loads

Mill Tailings

Mill tailings are, by definition, fine-particle residues of milling operations that are devoid of metal values. Particle-size distribution is one of the essential ways of characterizing tailings. The mining industry distinguishes “sands” and “slimes” as components of residues.

Materials left over after the process of separating the valuable fraction from the uneconomic fraction (gangue) of an ore. Tailings are distinct from overburden. Waste rock or other material that overlies an ore or mineral body.

Mill Tailings
Mill Tailings

Mill Tailings Economics

Losses to tailings is the most important parameter in deciding whether a deposit or milling process is economically viable or not. Early milling operations often did not take adequate steps to make tailings areas environmentally safe after closure. Modern mines, particularly those in jurisdictions with well-developed mining regulations and those operated by responsible mining companies, often include the rehabilitation and proper closure of tailings areas in their costs and activities.

Site selection for tailings disposal has to be based on economic and environmental considerations. Additional, tailings impoundment site has to be close to the mill, for economic reasons and to conform with the following three requirements:

  • Be mineralogically barren
  • Have strong structural geology to bear the weight of the impoundment
  • Have a geomorphology that allows surface waters to bypass the dam or drain through it

Factors influencing the design of tailing impoundment include site characteristics, tailing characteristics, effluent characteristics, mine/mill characteristics

STORAGE AND DISPOSAL

Tailings may be discarded on land, into a watercourse, or in a sizable body of water. In the case of underground mining, at least part of the tailings may have to be pumped back into the mine.

Uses for tailings – backfill excavated space, but usually discarded. If possible, tailings should not be stored underground; it is prudent to dispose of milling tailings on the surface and have them easily available when more efficient extraction processes exist. Storing tailings inactive open-pit mines is obviously impossible. Also, abandoned open-pit quarries far from active mills.

Historically, tailings were disposed of in the most convenient manner, such as in downstream running water or down drains. Because of concerns about these sediments in the water and other issues, tailings ponds came into use. The sustainability challenge in the management of tailings and waste rock is to dispose of the material. Such that it is inert or, if not, stable and contained, to minimize water and energy inputs and the surface footprint of wastes and to move toward finding alternate uses.

SOURCES

Other By-Products

Categories
By-product Uncategorized

ASH IN STEAM LOCOMOTIVES

The ash in steam locomotives is a byproduct from burning pulverized coal in the coal burner. During combustion, mineral impurities in the coal (clay, feldspar, quartz, and shale) fuse in suspension and float out of the combustion chamber with the exhaust gases. As the fused material rises, it cools and solidifies into spherical glassy particles. The ash is then collected from the exhaust gases by electrostatic precipitates or bag filters.

The amount of residue let in the ash pan for operating coal burners is dependent on the quality of coal being burned. Anthracite and high quality bituminous left much less ash than the same quantity of lignite. Also, thee exist the issue of quality with the amount of foreign matter mixed in with the coal – the reason why firemen referred to some grades of coal as “Real Estate”. If a given locomotive was operated rom division point to division point, the ash pan would be emptied at the end of the run. 

ASH IN STEAM LOCOMOTIVES
ASH IN STEAM LOCOMOTIVES

USES AND APPLICATION

Ash can be used as prime material in many cement-based products. Such as poured concrete, concrete block, and brick. One of the most common uses of ash is in Portland cement concrete pavement or PCC pavement. Road construction projects using PCC can use a great deal of concrete, and substituting ash provides significant economic benefits. Ash has also been used as embankment and mine fill.

Uses of coal ash include:

  • Concrete production, as a substitute material for Portland cement, sand.
  • Fly-ash pellets which can replace normal aggregate in concrete mixture.
  • Embankments and other structural fills (usually for road construction)
  • Grout and Flowable fill production
  • Waste stabilization and solidification
  • Cement clinker production – (as a substitute material for clay)
  • Mine reclamation
  • Stabilization of soft soils
  • Road subbase construction
  • As aggregate substitute material (e.g. for brick production)
  • Mineral filler in asphaltic concrete
  • Agricultural uses: soil amendment, fertilizer, cattle feeders, soil stabilization in stock feed yards, and agricultural stakes
  • Loose application on rivers to melt ice
  • Loose application on roads and parking lots for ice control

DISPOSAL AND ENVIRONMENTAL CONCERNS

Ash is produced when coal is burned. The environmental laws require power companies and steam locomotives to trap and properly dispose of it. Disposal presents a challenge because of the sheer amount of coal ash produced by steam locomotives and coal-fired power plants, and also because the heavy metals in coal make ash a potentially dangerous substance.

Coal is a material that’s full of harmful substances, and there are still some questions about whether heavy metals would be able to leach from concrete made with coal ash. Concerns have also been raised over whether using fly ash would expose builders to lawsuits and exempt them from insurance coverage.

In the past, fly ash produced from coal combustion was simply entrained in flue gases and dispersed into the atmosphere. This created environmental and health concerns that prompted laws that have reduced fly ash emissions to less than 1% of ash produced. Worldwide, more than 65% of fly ash produced from coal power stations is disposed of in landfills and ash ponds.

Ash that is stored or deposited outdoors can eventually leach toxic compounds into underground water aquifers. For this reason, much of the current debate around fly ash disposal revolves around creating specially lined landfills that prevent the chemical compounds from being leached into the ground water and local ecosystems.

SOURCES

Ash is made from Coke and Coal