New approaches to measuring biochar density and porosity

It is clear that the density and porosity of biochar will impact its mobility in the environment, its interaction with the soil hydrologic cycle, and its suitability as an ecological niche for soil microorganisms. However, the wide range of biochar pore sizes complicates biochar porosity characteriz...

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Bibliographic Details
Published in:	Biomass & bioenergy Vol. 66; pp. 176 - 185
Main Authors:	Brewer, Catherine E., Chuang, Victoria J., Masiello, Caroline A., Gonnermann, Helge, Gao, Xiaodong, Dugan, Brandon, Driver, Laura E., Panzacchi, Pietro, Zygourakis, Kyriacos, Davies, Christian A.
Format:	Journal Article
Language:	English
Published:	Kidlington Elsevier Ltd 01-07-2014 Elsevier
Subjects:	Agronomy. Soil science and plant productions Biochar Biological and medical sciences Chemistry Colloidal state and disperse state Envelope density Exact sciences and technology Fundamental and applied biological sciences. Psychology Gas sorption analysis General and physical chemistry Mercury porosimetry Physical properties Physics, chemistry, biochemistry and biology of agricultural and forest soils Pore volume Porous materials Skeletal density Soil science Structure, texture, density, mechanical behavior. Heat and gas exchanges Mercury porosimetry Skeletal density Pore volume Envelope density Biochar Gas sorption analysis Density Characterization Carbonization Sorption Gases Pore size Surface properties Environment Porosity Surface area Physicochemical properties
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Summary:	It is clear that the density and porosity of biochar will impact its mobility in the environment, its interaction with the soil hydrologic cycle, and its suitability as an ecological niche for soil microorganisms. However, the wide range of biochar pore sizes complicates biochar porosity characterization, making it challenging to find methods appropriate to connect the fundamental physical properties of density and porosity to environmental outcomes. Here, we report the use of two fast, simple density measurement techniques to characterize biochar density and porosity. We measured biochar skeletal density by helium pycnometry and envelope density by displacement of a dry granular suspension. We found that biochar skeletal density ranged from 1.34 g cm−3 to 1.96 g cm−3, and increased with pyrolysis temperature. Biochar envelope density ranged from 0.25 g cm−3 to 0.60 g cm−3, and was higher for wood biochars than grass biochars—a difference we attribute to plant cell structures preserved during pyrolysis. We compared the pore volumes measured by pycnometry with those measured by nitrogen gas sorption and mercury porosimetry. We show that biochar pore volumes measured by pycnometry are comparable to the values obtained by mercury porosimetry, the current benchmark method. We also show that the majority of biochar pore volume is in macropores, and thus, is not measured by gas sorption analysis. These fast, simple techniques can now be used to study the relationship between biochar's physical properties and its environmental behaviors. [Display omitted] •Biochar's density and porosity relate to its environmental interactions and transport.•Biochar porosity is difficult to characterize due the wide range of pore sizes.•We measured biochar porosity by combining skeletal and envelope density measurements.•Biochar skeletal density increases with pyrolysis temperature.•Biochar envelope density and porosity vary primarily with biomass feedstock.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23
ISSN:	0961-9534 1873-2909
DOI:	10.1016/j.biombioe.2014.03.059