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Removing heavy metals from biomass after biobsorbtion?

 
Maja Gustavsson
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Hello! I have absolutely no clue where to place this post but, does anyone here have experience with biobsorbtion of heavy metals? (For those unfamiliar with the term, biobsorbtion is the removal of heavy metals from soils and waters by using plants that absorb them.) I wonder if this is something that would be possible to do on a small, homestead scale?

Since I will soon have access to a bit of land near the baltic sea, one of my priorities is going to be supporting the fishing waters there. Lots of seaweed will be planted, as sadly this place is pretty much dead thanks to human activity. One idea I have been toying with is using species of seaweed that will absorb copper and cadmium from the sea bottom, to then be removed for the process to be repeated. (I like to think of it as a buffer against the possibilities of toxin buildup in my soils, since I will be growing food nearby. Plus the facts that I'm going to be fishing there..)

That is, of course, the easy part... the difficult part is knowing what to do with the metal-ridden seaweed! I tried looking up this, but I just want to grow stuff, not get a degree in chemistry, unless I know I can actually do this at home somehow Does anyone have experience with disposing of this kind of biomass? What do I do with it? CAN I do anything with it, that would separate the metals from the biomass, without advanced chemistry knowledge or expensive equipment?
 
John Elliott
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Maja Gustavsson wrote:
That is, of course, the easy part... the difficult part is knowing what to do with the metal-ridden seaweed!


Dig a deep hole. Believe me, I do have the chemistry degree, and what you learn in getting that degree is "how deep do you dig the hole?" If you dig a shallow hole and there is significant movement of groundwater, those metals can reappear where you don't want them.

If you burn your biomass first, then many of the metals will become metal oxides, which can be good, as a lot of these metal oxides are significantly less labile in the environment. It might take some acidic leaching to get the oxide into a soluble form.

There are some hard rock mines that have filled up with acidic water and are now leaching unwanted metals into the biosphere. In this case, even though the hole that the miners dug was deep, it wasn't deep enough.

My recommendation? Collect up all the biomass, dry it out and burn it, and then use the ash as filler in concrete projects. Once your cadmium and copper are encased in concrete, they will be much less of a problem for you.
 
Maja Gustavsson
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John Elliott wrote:
My recommendation? Collect up all the biomass, dry it out and burn it, and then use the ash as filler in concrete projects. Once your cadmium and copper are encased in concrete, they will be much less of a problem for you.


Now, THIS is actually a really good idea.. plus, it gives me an excellent excuse to do concrete stuff! Thanks a bunch, John, I'll absolutely keep this in mind. I was a bit worried that the best thing to do would involve some fancy expensive equipment (it would be worth it, but more difficult), but this is something I can actually do at home without much of an investment. Perfect.
 
Ian Rule
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Oxidation! Brilliant! Im falling head over heals for these forums - hard not to love having every natural science degree 'on loan'.
Nice brains!
 
William Clark
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I can appreciate your concern for heavy metals, so I did a bit of research for you I searched Google for "use of biomass ash in concrete" and got a few useful results. in one study done in Sri Lanka found that wood ash could be used to replace sand in cement blocks. they found that if 15% of the sand was replaced with ash that the blocks performed as well as regular blocks structurally.

Also, when you burn the dried sea weed make sure to NOT do it in an open burn pile, have some kind of furnace/stove with some baffles in it to collect the fly ash. At least in coal fired furnaces some of the worst metals are in the fly ash.

hmmm a bit more research indicates that most of the cadmium will be in the fly ash. ... this is the article that I found that bit in "infohouse.p2ric.org/ref/35/34190.pdf" it is a direct PDF download. I searched Google for this "distribution of cadmium in fly ash and bottom ash in biomass fired" to find that one, it also seems that willow will adsorb a large amount of Cadmium... who knew
 
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