I am trying to test my biochars (charred biomass residues) in ammonia absorption tests. The more acidic biochars (hydrochars) work better, they have a lower pH than the high temperature chars. Assuming i want to acidify my biochars with e.g. H2SO4, what is an optimum acid quantity to achieve maximum NH3 absorption?
As pH and temperature increase the losses from ammonia volatilization also increases. Ammonia volatilization is especially an issue at pH superior to 7.5. Under pH 7.0 ammonia volatilization is minimal. Higher pyrolysis temperature causes the biochar to be come increasingly alkaline. Using a low temperature of pyrolysis much of alkalinity of the char can be avoided. Another approach would be adding product like sulfur to lower the biochar pH reaction. The lower pH biochar could be used for alkaline soils where acidity would be more favorable. In acid soils the use of alkaline biochar work to help modify soil pH with beneficial effects. Some of the best results with biochars have been in acid weathered oxisols and ultisols.
To answer this cannot be anwered without knowing the flux of ammonia.
But what is the benefit of acidifying the biochar anyway? Ammonia can easily be scrubbed by the acid itself. So why use the acid to acidify the biochar if it can be done directly?
It is about valorising the biochar, upgrading agro residues to valuable products, and converting the spent biochar to a N- containing fertilizer
Yes I agree with prof. Yan also chemisorption has to be considered in that case as a mechanism :)
To neutralize the alkaline nature of biochar one of your options is to lower the char temperature which can result neutral char at about 350 C. For the stimulation of a material with nitrogen capacity if you continue to go with alkaline product Nitrogen as Ammonium Sulfate would have significant ability to provide pH lowering. In areas which are predominantly alkaline in their soil reaction that would be effective providing lower pH Nitrogen and Sulfur.
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