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The Final Word on Fines

Posted By Therese Dunphy On September 1, 2009 @ 10:32 am In Articles,Carved In Stone,Departments | No Comments

by Bill [1] Langer [1]

My wife, Pam, reads, critiques, and has veto power over every Carved in Stone article sent to Aggregates Manager. She said the topic of fines is stupefying and hinted that future articles on the subject might end up in the recycling bin.

Because this is my last chance, I have included a list of potential markets for fines. Of course, each use requires fines of specific physical and chemical properties, and not all fines can be marketed for all listed uses.

If you can’t market all your fines, you might want to limit their production. The amount of fines generated during aggregate production is, in part, a function of the mineral composition and texture of the rock. Less energy is generally used to separate individual mineral particles than to break them apart. All other things being equal, blasting and crushing a coarse-grained rock will generate fewer fines than a fine-grained rock.

Similarly, softer minerals break down more easily than harder minerals, and processing rocks with low abrasion resistance produces more fines than rocks with high abrasion resistance. The shape of the fine particles is also influenced by mineralogy. Processing a rock with a high content of flaky or elongated minerals will tend to produce more flaky-shaped fines than processing a rock with equigranular minerals.

Blasting also affects the production of fines. Increasing explosive energy produces smaller feedstock for the primary crusher, resulting in increased productivity and reduced costs for crushing. However, too much fragmentation can generate an excess of fines. Blasting commonly is optimized according to handling and crusher requirements, but could include a marketing strategy for all the products generated, even the fines.

During processing, multiple stages of crushing and screening are commonly used to maintain a relatively low reduction ratio (ratio of particle-size of feed material to particle-size of crusher product), which is more efficient and results in fewer fines being generated at each stage. However, using many stages with low reduction ratios may cumulatively produce more fines than a process using fewer stages with higher reduction ratios.

The generation of fines also depends on the type of crushers and feed rates being used. Impact crushers generally produce more fines (perhaps as much as 25 to 30 percent) than compressive crushers (jaw and cone crushers). Feed rates resulting in rock-on-rock interaction in an impact crusher commonly generate more fines than rock-on-metal interaction. But keep in mind, rock-on-metal interactions cause high wear of crusher components and create different particle shapes than rock-on-rock interactions.

Storage of fines affects the final use. Fines have a very large surface area in relation to the particle size, and the increased surface area sometimes facilitates weathering and chemical alterations to stockpiled material. Fines stored in stockpiles are exposed to the air and may weather differently than those stored in settling ponds. Fines stored in settling ponds are also more difficult to handle and ship than fines that are stored dry. The good news is that, in some situations, fines can be dredged from settling ponds and dried in specially constructed drainage cells, thus allowing them to compete for markets commonly thought only available to dry-stored fines.

I think this stuff is fascinating, but if I bored you with this story about fines, you have my wife to thank. She allowed it — this time.

Author’s Note: Thanks to Terry Lee, of Florida Environmental Dredging, for information on dredging fines from settling ponds.

 

Uses of fines from  A to Z

Acid mine drainage abatement

Aglime

Anti-skid bituminous concrete abrasive

Base/sub-base

Baseball fields

Concrete block

Desulfurization of power plant flue gas

Filler for fertilizer, paper, paint, plastics

Flowable fill

Golf courses

Granules for roofing shingles

Horse stalls and cattle lots

Ice control for highways

Insulation

Landfill cover

Low-cost masonry products

Manufactured aggregates

Masonry sand

Pipe bedding

Portland cement

Pond and pool liners

Poultry grit

Precast pipes

Quarry and pit reclamation and backfill

Railroad and light rail track sub-ballast

Septic systems

Sterile growing medium

Top soil and compost amendment

Unfired earth bricks

Wetlands restoration

Zoo exhibit substrate


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[1] Bill: mailto:blanger@usgs.gov

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