[Terrapreta] Charcoal is hydrophobic

[Gerald Van Koeverden]

Hans,

When I got a load of biochar (particle size <2 mm.) from a pyrolysis  
plant, I was told it was hydrophobic.  I took some and put it on top  
of some water in a dish, and it floated.  However, if one shakes up  
the mixture and let it sit for a while, it sinks and stays on the  
bottom.  Thus, under saturated conditions, it absorbs water.   
Apparently, it has a bulk density of 0.25, but because of its  
porosity, the actual carbon structures have a density of approx. 1.5.

Perhaps it is only hydrophobic under unsaturated conditions?

In this way this is like soil.  Have you ever seen the water movement  
demonstration with two distinct layers of soil? If a layer of sand  
overlays one of clay, and water is added to the top, water won't be  
absorbed by the clay until the top layer of sand is completely  
saturated.

Gerrit

On 3-Nov-07, at 8:59 AM, Brian Hans wrote:

> All the reseach i have read says it holds water.
>
> So have I, yet there is it. Im not saying I am sure one way or  
> another... Im just offering some concepts here that dont add up. I  
> wonder if someone specifically has examined this like the turf ppl  
> did for humic?
>
> Let me add some more reasons I question the status quo;
>
> Activated carbon is hydrophobic. ' Due to the mainly hydrophobic  
> surface properties, activated carbon adsorbs preferably organic  
> substances and other non-polar compounds from the gaseous and  
> liquid phase '.
>
> If humic is hydrophobic and activated carbon is hydrophobic, Im  
> curious why I should think charcoal (TP) is hydrophobic?
>
> Another comment would be this... If I were to add a whole bunch of  
> oil to my soil, I wouldnt expect that oil to hold water. Remember  
> the saying 'oil and water dont mix'.
>
> Just to see what would happen, thismorning after I wrote the  
> initial thread I threw a bunch of horticultural grade charcoal into  
> a glass of water... Its still floating almost 2 hrs later.
>
> If something has a high CEC rate, how can it also be hydrophilic?
>
> I can show you research on the Australian Equivalent of Leoardite  
> (zeolite) which contradicts this research.
>
> Great. Lets see it. I'll wait...
>
> Regardless, zeolite is not charcoal or humic acid, but a non-carbon  
> mineral.
>
> Certainly the results of adding charcoal/humic to the soil could  
> have some other effect to the soil to add hydrophilicy in other  
> ways (like maybe more biota). But the stuff itself, is hydrophobic.
>
> Brian Hans
>
>
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