Comminution
{{short description|Reduction of solid materials to a smaller average particle size}}
Image:Geevor waterwheel stamps.jpg (left side of image, next to water wheel) used in 19th century Cornwall for communition of tin ore]]
Comminution is the reduction of solid materials from one average particle size to a smaller average particle size, by crushing, grinding, cutting, vibrating, or other processes.{{cite book |doi=10.1002/14356007.b02_05 |chapter=Size Reduction |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2000 |last1=Bernotat |first1=Siegfried |last2=Schönert |first2=Klaus |isbn=978-3-527-30385-4 }} Comminution is related to pulverization and grinding. All use mechanical devices, and many types of mills have been invented. Concomitant with size reduction, comminution increases the surface area of the solid.
For example, a pulverizer mill is used to pulverize coal for combustion in the steam-generating furnaces of coal power plants. A cement mill produces finely ground ingredients for portland cement.{{cite book |doi=10.1002/14356007.a05_489.pub2 |chapter=Cement |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2008 |last1=Sprung |first1=Siegbert |isbn=978-3-527-30385-4 }} A hammer mill is used on farms for grinding grain and chaff for animal feed. A demolition pulverizer is an attachment for an excavator to break up large pieces of concrete. Comminution is important in mineral processing, where rocks are broken into small particles to help liberate the ore from gangue.{{cite journal |doi=10.1016/s1002-0721(17)60971-2 |title=A Review on the Cracking, Baking and Leaching Processes of Rare Earth Element Concentrates |date=2017 |last1=Sadri |first1=Farzaneh |last2=Nazari |first2=Amir Mohammad |last3=Ghahreman |first3=Ahmad |journal=Journal of Rare Earths |volume=35 |issue=8 |pages=739–752 |bibcode=2017JREar..35..739S }} Comminution or grinding is also important in ceramics, electronics, and battery research.{{cite journal |doi=10.1039/c2cs35256g |title=Nanostructured Sulfur Cathodes |date=2013 |last1=Yang |first1=Yuan |last2=Zheng |first2=Guangyuan |last3=Cui |first3=Yi |journal=Chemical Society Reviews |volume=42 |issue=7 |pages=3018–3032 |pmid=23325336 }} Mechanical pulping is a traditional way for paper making from wood. The mastication of food involves comminution. From the perspective of chemical engineering, comminution is a unit operation.
In geology, comminution refers to a natural process during faulting in the upper part of the Earth's crust.{{cite journal|last=Sibson|first=R.H.|year=1986|title=Earthquakes and rock deformation in crustal fault zones|journal=Annual Review of Earth and Planetary Sciences|volume=14|page=156|doi=10.1146/annurev.ea.14.050186.001053|url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?db_key=AST&bibcode=1986AREPS..14..149S&letter=0&classic=YES&defaultprint=YES&whole_paper=YES&page=149&epage=149&send=Send+PDF&filetype=.pdf|accessdate=2 July 2011|bibcode=1986AREPS..14..149S}}
Energy requirements
The comminution of solid materials consumes energy.{{cite book|last1=Kanda|first1=Yoshiteru|last2=Kotake|first2=Naoya|section=Chapter 12: Comminution Energy and Evaluation in Fine Grinding|editor1-last=Salman|editor1-first=Agba D.|editor2-last=Hounslow|editor2-first=Michael J.|title=Handbook of Powder Technology, Volume 12: Particle breakage|publisher=Elsevier|year=2007|pages=529–551|isbn=9780080553467|url=https://books.google.com/books?id=sPk0OhP_brIC&q=comminution&pg=PA530|access-date=August 20, 2010}} Approximately 65% of the power for the production of cement is consumed in comminution.{{cite journal |doi=10.1016/0032-5910(91)80109-V |title=The effect of grinding aids on the fine grinding of limestone, quartz and Portland cement clinker |date=1991 |last1=Sohoni |first1=S. |last2=Sridhar |first2=R. |last3=Mandal |first3=G. |journal=Powder Technology |volume=67 |issue=3 |pages=277–286 }}
The comminution energy can be estimated by:
- Rittinger's law, which assumes that the energy consumed is proportional to the newly generated surface area;{{Citation |last1=Jankovic |first1=A. |last2=Dundar |first2=H. |last3=Mehta |first3=R. |date=March 2010 |title=Relationships between comminution energy and product size for a magnetite ore |journal=Journal of the Southern African Institute of Mining and Metallurgy |volume=110 |pages=141–146 |url=http://www.metso.com/miningandconstruction/mct_service.nsf/WebWID/WTB-120106-22576-209D0/$File/021.pdf |postscript=. |access-date=2015-06-16 |archive-url=https://web.archive.org/web/20130306164447/http://metso.com/miningandconstruction/mct_service.nsf/WebWID/WTB-120106-22576-209D0/$File/021.pdf |archive-date=2013-03-06 |url-status=dead }}
- Kick's law, which related the energy to the sizes of the feed particles and the product particles;Kick, F.M. Das Gesetz der proportionalen Widerstände und seine anwendung felix. Leipzig, Germany. 1885.
- Bond's law, which assumes that the total work useful in breakage is inversely proportional to the square root of the diameter of the product particles, [implying] theoretically that the work input varies as the length of the new cracks made in breakage.Bond, Fred C. (1975) It Happened to Me, Ch. 130. Amazon.com. Retrieved May 29, 2011.Bond, F.C. The third theory of comminution.Trans. AIME, vol. 193, 1952.
pp. 484–494.
- Holmes's law, which modifies Bond's law by substituting the square root with an exponent that depends on the material.
Three forces are typically used to effect the comminution of particles: impact, shear, and compression.
Methods
Image:FlCell.PNG cell used to process ores after communition. A mixture of ore and water called pulp [1] enters the cell from a conditioner, and flows to the bottom of the cell. Air [2] or nitrogen is passed down a vertical impeller where shearing forces break the air stream into small bubbles. The mineral concentrate froth is collected from the top of the cell [3], while the pulp [4] flows to another cell.]]
File:Cmp prinzip.jpg, a kind of grinding.Mahadevaiyer Krishnan, Jakub W. Nalaskowsk, and Lee M. Cook, "Chemical Mechanical Planarization: Slurry Chemistry, Materials, and Mechanisms" Chem. Rev., 2010, vol. 110, pp 178–204. {{doi|10.1021/cr900170z}}]]
There are several methods of comminution. Comminution of solid materials requires various types of crushers and mills depending on the feed properties such as hardness at various size ranges and application requirements such as throughput and maintenance. The most common machines for the comminution of coarse feed material (primary crushers) are the jaw crusher (1m > P80 > 100 mm), cone crusher (P80 > 20 mm) and hammer crusher. Primary crusher products in intermediate feed particle size ranges (100mm > P80 > 20mm) can be ground in autogenous (AG) or semi-autogenous (SAG) mills depending on feed properties and application requirements. For comminution of finer particle size ranges (20mm > P80 > 30 μm) machines like the ball mill, vertical roller mill, hammer mill, roller press or high compression roller mill, vibration mill, jet mill and others are used. For yet finer grind sizes (sometimes referred to as "ultrafine grinding"), specialist mills such as the IsaMill are used.
Trituration, for instance, is comminution (or substance breakdown) by rubbing. Furthermore, methods of trituration include levigation, which is the trituration of a powder with a non-solvent liquid, and pulverization by intervention, which is trituration with a solvent that can be easily removed after the substance has been broken down.
See also
- {{annotated link|Mill (grinding)}}
- {{annotated link|Particle size distribution}}
- {{annotated link|Crusher}}
- Electromagnetic vortex intensifier with ferromagnetic particles - Special equipment for ultrafine grinding
- Burr mill
External links
- [https://web.archive.org/web/20110421040839/http://www.rollermill.net/ore-mill/roller-coal-mills.html Roller Coal Mills], via Internet Archive
- {{cite book|last=Gupty|first=Chiranjib Kumar|title=Chemical Metallurgy|publisher=Wiley-VCH Verlag|year=2003|page=130|isbn=9783527605255|url=https://books.google.com/books?id=2PAarkWieIQC&q=comminution&pg=PA130|access-date=August 22, 2010}}
References
{{Reflist}}
{{Extractive metallurgy}}
Category:Mechanical engineering