# Does coal float in water? **URL:** \ **Category:** Factual Questions\ **Created:** [November 13, 2007, 11:46pm UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307 "2007-11-13T23:46:38Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![Mr.Excellent](https://avatars.discourse-cdn.com/v4/letter/m/f19dbf/32.png) [@Mr.Excellent](https://boards.straightdope.com/u/Mr.Excellent)\ **Post date:** [November 13, 2007, 11:46pm UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/1 "2007-11-13T23:46:38Z")
Does coal float in water? I’ve got a bet on this with my housemate. Because I’m a dork. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [November 13, 2007, 11:48pm UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/2 "2007-11-13T23:48:48Z")
Yes, clean coal floats. If it’s “dirty” with other minerals, it may sink. ---
**Author:** ![Santo\_Rugger](https://avatars.discourse-cdn.com/v4/letter/s/e95f7d/32.png) [@Santo\_Rugger](https://boards.straightdope.com/u/Santo_Rugger)\ **Post date:** [November 14, 2007, 12:00am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/3 "2007-11-14T00:00:14Z")
In Albuquerque, one of the main east-west thoroughfares on the east side are two one-way streets, Lead and Coal. I remember which one goes which way by remembering that lead sinks (down, towards downtown), and coal floats (up, towards the mountains). ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [November 14, 2007, 12:03am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/4 "2007-11-14T00:03:14Z")
[This site](http://www.uky.edu/KGS/coal/estimatingTons.htm) says that coal has a higher density than water (and thus would not float): > [@](#): > > Anthracite: specific gravity = 1.47 > Bituminous: specific gravity = 1.32 > Subbituminous: specific gravity = 1.30 > Lignite: specific gravity = 1.29 ---
**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\ **Post date:** [November 14, 2007, 1:00am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/5 "2007-11-14T01:00:52Z")
I have a large (about 4 pounds) chunk of coal in my garage, I’ll be right back. . . . . . . . . . . . . I’m back. The chunk of coal I have sunk. It didn’t sink like a rock though, it took it’s time reaching the bottom of the bucket. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [November 14, 2007, 1:01am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/6 "2007-11-14T01:01:46Z")
Sicne we have a nay-sayer, I bring cite from the US Department of Energy: > [@US DOE](#): > > Typically, in one washing process, the coal chunks are fed into a large water-filled tank. The coal floats to the surface while the sulfur impurities sink. (From [Education](http://www.fossil.energy.gov/education/energylessons/coal/coal_cct2.html)) ---
**Author:** ![Bytegeist](https://avatars.discourse-cdn.com/v4/letter/b/9dc877/32.png) [@Bytegeist](https://boards.straightdope.com/u/Bytegeist)\ **Post date:** [November 14, 2007, 1:10am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/7 "2007-11-14T01:10:44Z")
So, logically . . . _why do witches burn?_ ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [November 14, 2007, 1:11am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/8 "2007-11-14T01:11:30Z")
[QUOTE=gotpasswords] Sicne we have a nay-sayer, I bring cite from the US Department of Energy: [/QUOTE] Yes, but the cite given by **Xema** gives added information: > [@](#): > > There are several types of density separation processes in preparation plants but the most common involves floating crushed coal in a fluid. The fluid’s density is adjusted for the density (specific gravity) of the coal being processed. **Materials such as powdered magnetite or diesel fuel are added to water to increase the water’s specific gravity (relative density) to just more than the specific gravity of the crushed coal**. If the fluid’s specific gravity is greater than the coal and less than the mineral impurities, the coal floats and the impurities sink. In modern preparation plants the additives can be added and removed throughout the preparation process for the specific gravity of the coals being processed. The floating coal is removed, rinsed with water to remove the additives in the fluid, and dried. Bolding added. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 14, 2007, 1:12am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/9 "2007-11-14T01:12:29Z")
[QUOTE=gotpasswords] Sicne we have a nay-sayer, I bring cite from the US Department of Energy: (From [Education](http://www.fossil.energy.gov/education/energylessons/coal/coal_cct2.html)) [/QUOTE] I can’t help thinking that what they really meant to say was that the pyrite impurities sink right to the bottom and the coal pieces form a layer above that (but not actually floating on the surface of the water). Coal usually sinks, but it doesn’t sink like a rock- an effect exploited by the locals in Easington Colliery in the North of England (where my mother was born and grew up) - and no doubt the locals of other places with a similar setup - there was an elevated railway that ran from the pit head works, across the cliff tops and out to sea - a constant stream of wheeled buckets would trundle out to the end, tip their contents (coal slag) into the sea, turn around and return on another track. the whole lot would sink, but the coal would eventually get washed up on the shore - not because it floated, but because it was lighter than the beach rocks, so it would form a layer on the seabed - on top of the stones. The locals would collect the free coal in sacks on the sea shore, to save money. ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [November 14, 2007, 1:54am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/10 "2007-11-14T01:54:19Z")
[QUOTE=gotpasswords] Sicne we have a nay-sayer, I bring cite from the US Department of Energy: (From [Education](http://www.fossil.energy.gov/education/energylessons/coal/coal_cct2.html)) [/QUOTE] Well, given that I’m probably the only person on the SDMB **who has actually worked at a coal wash plant** , I’ll have to join the naysayers. Coal is cleaned in a bath that typically uses pulverized magnetite to separate it out. Sometimes successive baths are used with varying densities, and sometimes with water or air jigs assisting. Coal fines _will_ float on water, but that is a surface tension effect, not a density effect. Pyrites and rock are quite heavy, relatively, and sink out very easily\*. However, the pyrites and rock are trapped within the coal, and that’s why you have to crush it. It quickly becomes a trade-off - the more you crush the coal the more effort you expend and the more difficult it becomes to handle and dry - but you clean it more. Coal wash plants play an enormous number of “what-if” games to try to optimize the crush/wash process. I have honestly spent weeks working on those what-if scenarios for one plant. I’ve also seen innumerable water-filled hellholes at coal power plants where the coal was lying in a layer at the bottom, with a mixture of oily/volatile scum and fines on the top. I have never, not from anthracite to lignite, seen coal float in ordinary water. Given how varied coal is, however, it’s entirely possible that something odd, like a cannel coal or a very peaty Lignite B, may have a specific gravity less than 1. So I won’t say “all” coal sinks, but “almost all.” There are many other cleaning processes which are used, and the magnetite process is one of the filthiest and most terrible ones to work at. - There is a caveat, but no one here really wants to hear me talk any more to explain it. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 14, 2007, 1:58am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/11 "2007-11-14T01:58:22Z")
[QUOTE=Una Persson] - There is a caveat, but no one here really wants to hear me talk any more to explain it. [/QUOTE] I do! ---
**Author:** ![Una\_Persson](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/una_persson/32/346_2.png) [@Una\_Persson](https://boards.straightdope.com/u/Una_Persson)\ **Post date:** [November 14, 2007, 2:14am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/12 "2007-11-14T02:14:54Z")
[QUOTE=Mangetout] I do! [/QUOTE] With some coals, such as Wyoming Powder River Basin sub-bituminous coals (also Indonesian coals, for another common example), the sulfur and ash are somewhat finely dispersed and sometimes called “organically bound.” Cleaning them is of very limited value, and often only removes the loose rock, soil, clays, etc. associated with the mining process, rather than intrinsic pyrites and ash/rock found in Eastern US bituminous coals. Therefore, in some coals the pyrites and rock don’t sink out very easily at all, and from a cost-benefit analysis it’s very hard to justify. I have many chunks of pyrite from coal, as well as many piece of coal with pyrites gleaming from within their dark matrix (note that in the industry, it’s unfortunately not uncommon for people to call anything rejected by a mill as “pyrites”, which hearkens back to a time when pyrites were much more common). The largest pieces of true pyrite I ever found were at a Florida power plant, where it was coming out of the pulverizers in buckets. They are quite heavy and pure, and of the 500+ coal units I’ve visited, I’ve never seen the like. I also have a small collection of other objects that were separated from coal during the cleaning process, such as broken mining parts, interesting rocks, and a large lump of copper which I’ve never been able to identify, and which is a great conversation piece. Things I have seen but not collected include boots, shovels, clothing, tires, and animals. Things I know of but have not seen include human bodies. ---
**Author:** ![Joey\_P](https://avatars.discourse-cdn.com/v4/letter/j/919ad9/32.png) [@Joey\_P](https://boards.straightdope.com/u/Joey_P)\ **Post date:** [November 14, 2007, 4:23am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/13 "2007-11-14T04:23:03Z")
[QUOTE=Bytegeist] So, logically . . . _why do witches burn?_ [/QUOTE] Because rocks float…Well, very small rocks. I got better ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [November 14, 2007, 8:21am UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/14 "2007-11-14T08:21:42Z")
[QUOTE=Una Persson] With some coals, such as Wyoming Powder River Basin sub-bituminous coals (also Indonesian coals, for another common example), the sulfur and ash are somewhat finely dispersed and sometimes called “organically bound.” Cleaning them is of very limited value, and often only removes the loose rock, soil, clays, etc. associated with the mining process, rather than intrinsic pyrites and ash/rock found in Eastern US bituminous coals. Therefore, in some coals the pyrites and rock don’t sink out very easily at all, and from a cost-benefit analysis it’s very hard to justify. I have many chunks of pyrite from coal, as well as many piece of coal with pyrites gleaming from within their dark matrix (note that in the industry, it’s unfortunately not uncommon for people to call anything rejected by a mill as “pyrites”, which hearkens back to a time when pyrites were much more common). The largest pieces of true pyrite I ever found were at a Florida power plant, where it was coming out of the pulverizers in buckets. They are quite heavy and pure, and of the 500+ coal units I’ve visited, I’ve never seen the like. I also have a small collection of other objects that were separated from coal during the cleaning process, such as broken mining parts, interesting rocks, and a large lump of copper which I’ve never been able to identify, and which is a great conversation piece. Things I have seen but not collected include boots, shovels, clothing, tires, and animals. Things I know of but have not seen include human bodies. [/QUOTE] Thanks - that was quite interesting. I’d love to see a photo gallery of your found items, if you should ever create one. ---
**Author:** ![gotpasswords](https://avatars.discourse-cdn.com/v4/letter/g/c57346/32.png) [@gotpasswords](https://boards.straightdope.com/u/gotpasswords)\ **Post date:** [November 15, 2007, 4:29pm UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/15 "2007-11-15T16:29:06Z")
[QUOTE=Q.E.D.] Yes, but the cite given by **Xema** gives added information. [/QUOTE] I am willing to believe that the US Government left out some key information. :dubious: I’m also endlessly amazed at the variety of professions represented here. I knew **Una Persson** has been involved with power plants, but didn’t realize they’d been washing the coal as well. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [November 15, 2007, 5:41pm UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/16 "2007-11-15T17:41:23Z")
> [@](#): > > I knew Una Persson has been involved with power plants, but didn’t realize they’d been washing the coal as well. She’s done everything with coal. I wouldn’t be surprised if she one day announced that she supervised the deposition of dead megaferns to form the stuff, millions of years ago. ---
**Author:** ![brewha](https://avatars.discourse-cdn.com/v4/letter/b/91b2a8/32.png) [@brewha](https://boards.straightdope.com/u/brewha)\ **Post date:** [November 15, 2007, 5:57pm UTC](https://boards.straightdope.com/t/does-coal-float-in-water/426307/17 "2007-11-15T17:57:41Z")
Let’s see I can recall correctly churches green gravy cider lead apples bread (very small) rocks a DUCK! Nope no charcoal. I got nothin.