Science Questions

Can we re-use the ash from burning waste?

Sun, 4th Mar 2012

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Andrew Reitemeyer, Facebook asked:

Waste is often burnt to produce energy. Could we use the ash from that and reclaim useful trace elements?


Yes.  There are two types of ash that come from thermal treatment – one is known as incinerated bottom ash and that's the majority of it which is the clinker that drops out of the bottom of the furnace if you like.  That can be safely recycled and used as good quality aggregate and that happens already.  They take the metals out, any metals that are left in it, and again those various metals are recycled.  The bottom ash itself is used as aggregate for road building, for block making, et cetera.  

The interesting bit and where the science bit comes in, I guess, is the other type of ash - known as air pollution control residue - which is where you've injected lime and carbon, and things, to remove any pollutants.

Increasingly, we’re looking to re-use that particular type of ash in the manufacture of gypsum or the replacement of gypsum for gypsum board and such like.  So, science is being applied to look at new ways of recycling that because everything about both thermal treatment and energy recovery as well as the rest of the waste and recycling industry these days is all about getting the most resource efficiency that we can out of all the materials we use as a society.


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Hopefully the recycled sheet rock doesn't have fumes.

Another type of ash would be waste from burning wood in your fireplace, which can be used to fertilize your garden if it is clean. CliffordK, Tue, 6th Mar 2012

As plasterboard is now banned from landfill (acidified gypsum evolves hydrogen sulphide) and the volumes of desulphogypsum from cleaning flue gasses from coal fired power stations, the volume of virgin gypsum mined in the UK has decreased drastically.  (although for a long time much of the gypsum used in the UK was opencasted at Los Lesares (near Almeria) in SE Spain - europes largest gytpsum quarry)

It is also generally easier to extract materials from waste before it is burnt - often using conventional and eddy current magnets to remove ferrous and non ferrous metals rather than procesing ash - which (as noted) is commonly used as secondary aggregate.

Simialrly a lot of process slag from contemporary and historic iron/ steel processing is used as aggregate in a variety of (specialist) applications or as "Ag Slag" a soil improver (due to high lime content)

Mazurka, Fri, 9th Mar 2012

i heard that due to prior nukebomb testings, the ash may have cesium? or whatever radioactives CZARCAR, Sat, 10th Mar 2012

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