Re: Biochar versus Activated Carbon #activatedcarbon


Hugh McLaughlin
 

Rick,

The term "activate" is a term of art with respect to "activated carbon". Because virtually nothing is defined in the biochar world, anything and everything "activates" biochar, since it seems any change qualifies. CP demonstrated that filing after filing. The levels of vacuum used in their technology had minimal impact beyond fooling the naive at the USPTO.

Regards,

Hugh



On Wednesday, May 6, 2020, 9:27:49 PM EDT, Rick Wilson via groups.io <rick012@...> wrote:


Hugh, that may be one of the best ways to activate biochar.  As it cools, the gases inside the biochar will contract, pulling in liquid in and overcoming any hydrophobicity that may exist.   Add some acidic acid, and you neutralize the pH. Rick

On Monday, May 4, 2020, 08:17:01 AM PDT, Hugh McLaughlin via groups.io <wastemin1@...> wrote:


All,

If you boil biochar in a sealed mason jar, let it cool and repeat, it sinks (see the Baseline Biochar Metrics for the delineated method). The skeleton has a density of 1.5 to 1.75, with crystalline graphite at 2.26 (theoretical). The real world falls short due to defects and voids.

- Hugh

On Sunday, May 3, 2020, 8:06:07 PM EDT, Rick Wilson via groups.io <rick012@...> wrote:


What you have to remember is that biochar is mostly an air ball after it is produced.  Full of air.  Nothing can get in very far. 
Carbon is more dense than water, so biochar should sink in water, it does not. 

In principle, incipient wetting should pull water into the pores of bicochar.  Most of the time, the pores contain hydrocarbons which are hydrophobic. So wetting only occurs after long periods in the soil. or through artificial “activation"
This is why Cool Planet’s activation process used vacuum to force infiltration into the pores (with acidic acid).

If you think you can inoculate biochar with microbes that survive in the soil, no that does does not work. Extremely difficult to change the soil microbiome, foreign microbes just get eaten up by the natural microbiome. 

Can you use microbes to facilitate overcoming the hydrophobicity of the biochar, so that its inner pores become wet?  “Activation” Yes you can. And the process probably reduces the pH of the char which can help nutrient availability. 

Rick

On May 3, 2020, at 4:52 PM, Nando Breiter <nando@...> wrote:

Stephan,

If I'm not mistaken, I saw some indication in one of your papers that microbial life was only detected near the surface of char particles. Is that not the case?

Nikolaus discussed this with me on several occasions. Pores may run through the entire particle, but microbial populations will only survive where there is access to nutrients, aerobic microbes also need oxygen. I know that I read one paper that specifically measured the depth to which bacteria were detected in char pores - on the order of perhaps 100 microns - but I lost track of it and have not been able to find it again. 



On Mon, May 4, 2020 at 12:18 AM Stephen Joseph <joey.stephen@...> wrote:
Dear Nando

what is the reference that shows this.  Most wood and bamboo biochar have pores going all the way through their structure

Research has shown that soil microbiological life survives to a depth of some 50 to at most 100 microns.

Just to be clear there are many different ways activated carbon is made and some activated carbon has a high degree of functionality (COOH and OH groups) through post processing.

Regards
Stephen

On Mon, May 4, 2020 at 7:38 AM Nando Breiter <nando@...> wrote:
Ron,

CEC declines with rising pyrolysis intensity. The fundamental reason is that as pyrolysis intensity increases, increasing amounts of hydrogen and oxygen are driven out of the char. Cation exchange capacity depends on COOH and OH functional groups on the surfaces of any decomposed organic carbon, whether the decomposition process is biological or thermal. 

As you know, activated carbon is usually made at elevated pyrolysis temperatures and residence times, which drives a significant amount of oxygen and hydrogen out of the char as gases. At temperatures between 300° C and about 550° C, carbon monoxide is the predominant gas, so that is the temperature range in which oxygen is outgassed. Above 550° hydrogen becomes the predominant gas produced during pyrolysis with increasingly less CO as the temperature rises. Research generally shows CEC falling towards zero at pyrolysis temps between 600° and 650° C. 

I've spelled this out on our Rationale page here: http://biochar.info/?p=en.rationale and on our Biochar Preparation page here: http://biochar.info/?p=en.biochar_preparation

Cation exchange capacity is a surface phenomenon. Adsorbed minerals must be released to the soil solution for plants to access them, hence the exchange part of the term is important to keep in mind. Activated carbon, or char produced at higher temps, might adsorb / absorb minerals into its pore structure or surfaces via other mechanisms than the negatively charged COOH and OH functional groups that plant life evolved with, but particularly deeper in a pore, those minerals will tend to stay put, if for no other reason than pores tend to become clogged over time.

Research has shown that soil microbiological life survives to a depth of some 50 to at most 100 microns in a char pore, in that range, roughly the width of a human hair. The reason is that microbiota must have access to freely circulating soil solution, or they will die out from lack of dissolved organic matter to feed on. If soil solution was continually pumped via some mechanism in and out of char pores, we would expect to see microbiological life surviving deeper in those pores, but from the research papers I've read, some of which are referenced above, this is not the case.

We might postulate from this bit of information that CEC will generally only function efficiently and freely to a similar pore depth, 50 to 100 microns. While it may be true that a root hair or hyphae might wander into a char pore from time to time, the remaining interior surface area is most likely underutilized in terms of cation exchange capacity unless the char particle size is reduced to micron scale, which as you know is the size that predominates in terra preta soils. 




CarbonZero Sagl
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Switzerland

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On Sun, May 3, 2020 at 3:44 AM Brian Lewis <strongbold@...> wrote:
Nice little article Hugh. Very readable. Recently i was trying to explain the difference between biochar and charcoal to a group and realised that one important and obvious difference was that biochar is best when quenched on completion (whereas it would be self-defeating to quench charcoal).

Cheers 
Brian Lewis 
Maccy Biochar 



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--
Nando Breiter
http://biochar.info
CarbonZero Sagl
Astano, Switzerland





--
Nando Breiter
http://biochar.info
CarbonZero Sagl
Astano, Switzerland

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