'Hydrophilic or Hydrophobic?' - that is the question!

Slow anoxic cooled char made in a Kon Tiki kiln at Albrechshohe

As discussed on the website this is a very important question and I have been trawling around looking for ways of telling and then what to do about it. We want hydrophilic biochar to put into the soil. If the char is quenched with water when it is still very hot and reactive with oxygen, immediately after pyrolysis is complete - then the resulting biochar will tend towards hydrophilic. Note the cautious scientific language. If the char is allowed to cool in an anoxic atmosphere immediately after pyrolysis then it will tend towards hydrophobic.

Incidentally the easiest way to test whether charcoal is one or the other is to add water. If it floats it's phobic if it sinks it's philic.

Talking to Dr James Joyce this morning on Skype from Australia, I learned that hydrophobic char has a strongly positively and -negatively charged surface. Whilst hydrophilic char has a weakly charged positive and negative surface. 

Water holding capacity experiments

Water holding capacity experiments

The surface chemistry is complex and James said that applying gentle heat and slight acidity (usually not necessary) can help weaken the surface charge, making it hydrophilic! Tidily pom. Apparently clay particles in soil behave in much the same way.

If we take our char dust and soak it in 60 deg C water for two hours. This should do the trick and then we can soak again in a fertiliser mixture to charge it, adding EM (effective microbes)which would be denatured if heated to 60 deg C, at this stage.

Voila William and over to you.

dfg 15.00 11.02.16