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Determination of carbonate-C in biochars

Wang, Tao LU ; Camps-Arbestain, Marta; Hedley, Mike; Singh, Bhupinder Pal; Calvelo-Pereira, Roberto and Wang, Congying (2014) In Soil Research 52(5). p.495-504
Abstract
Although carbonate-carbon (C), an integral part of biochar-C, contributes to the liming properties of that material, it also interferes with the estimation of the stable organic C fraction in biochars. In this study, four methods were compared in order to quantify the carbonate-C in biochars: two direct (a titrimetric procedure and thermogravimetric analysis, TGA), and two indirect (acid treatment with separation by filtration and acid fumigation). The titrimetric method showed a high recovery of added carbonate-C (average 98.8%, range 1.5-38 mg), and the standard deviations of carbonate-C for all biochars tested were <0.1% when 1 g of sample was used. The acid treatment with a filtration step overestimated the carbonate-C content (on... (More)
Although carbonate-carbon (C), an integral part of biochar-C, contributes to the liming properties of that material, it also interferes with the estimation of the stable organic C fraction in biochars. In this study, four methods were compared in order to quantify the carbonate-C in biochars: two direct (a titrimetric procedure and thermogravimetric analysis, TGA), and two indirect (acid treatment with separation by filtration and acid fumigation). The titrimetric method showed a high recovery of added carbonate-C (average 98.8%, range 1.5-38 mg), and the standard deviations of carbonate-C for all biochars tested were <0.1% when 1 g of sample was used. The acid treatment with a filtration step overestimated the carbonate-C content (on average by a 4-fold increment) due to the loss of dissolved or fine particulate organic C during filtration. The acid fumigation method was suitable for biochars containing high amount of carbonate-C (>0.3% wt) and when the isotopic signature of organic C in biochars is to be determined. The TGA method (either in N-2 or a dry air atmosphere) was reliable when calcite was the main carbonate form in biochars, but was inadequate for samples containing a considerable amount of whewellite and certain carbonate-bearing minerals (e. g. magnesite) that decompose at <600 degrees C. Because more than half of the biochar samples investigated in the literature and in this study (58% of the 117 samples) contained <0.4% carbonate-C (and 38% of these contained no detectable carbonate-C), low-cost screening methods were developed to identify the biochars needed for carbonate-C analysis. For this purpose, two methods were proposed: (i) a manometric test; and (ii) a ratio between predicted fixed C : total C (FC/TC) and measured FC/TC, where predicted FC/TC was estimated using the following relationship: (FC/TC) = -0.1081(H/C)(2) - 0.1794(H/C) + 1.0097, as derived from values obtained in the literature. A decision tree, including two steps (a screening step and a titrimetric procedure) could be used to determine accurately the carbonate-C in biochars. (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Soil Research
volume
52
issue
5
pages
495 - 504
publisher
CSIRO Publishing
external identifiers
  • scopus:84903396668
ISSN
1838-675X
DOI
10.1071/SR13177
language
English
LU publication?
yes
id
62d48365-fb92-4624-baeb-a36fb05c433d (old id 8034176)
date added to LUP
2015-10-02 14:58:34
date last changed
2017-08-06 03:23:24
@article{62d48365-fb92-4624-baeb-a36fb05c433d,
  abstract     = {Although carbonate-carbon (C), an integral part of biochar-C, contributes to the liming properties of that material, it also interferes with the estimation of the stable organic C fraction in biochars. In this study, four methods were compared in order to quantify the carbonate-C in biochars: two direct (a titrimetric procedure and thermogravimetric analysis, TGA), and two indirect (acid treatment with separation by filtration and acid fumigation). The titrimetric method showed a high recovery of added carbonate-C (average 98.8%, range 1.5-38 mg), and the standard deviations of carbonate-C for all biochars tested were &lt;0.1% when 1 g of sample was used. The acid treatment with a filtration step overestimated the carbonate-C content (on average by a 4-fold increment) due to the loss of dissolved or fine particulate organic C during filtration. The acid fumigation method was suitable for biochars containing high amount of carbonate-C (&gt;0.3% wt) and when the isotopic signature of organic C in biochars is to be determined. The TGA method (either in N-2 or a dry air atmosphere) was reliable when calcite was the main carbonate form in biochars, but was inadequate for samples containing a considerable amount of whewellite and certain carbonate-bearing minerals (e. g. magnesite) that decompose at &lt;600 degrees C. Because more than half of the biochar samples investigated in the literature and in this study (58% of the 117 samples) contained &lt;0.4% carbonate-C (and 38% of these contained no detectable carbonate-C), low-cost screening methods were developed to identify the biochars needed for carbonate-C analysis. For this purpose, two methods were proposed: (i) a manometric test; and (ii) a ratio between predicted fixed C : total C (FC/TC) and measured FC/TC, where predicted FC/TC was estimated using the following relationship: (FC/TC) = -0.1081(H/C)(2) - 0.1794(H/C) + 1.0097, as derived from values obtained in the literature. A decision tree, including two steps (a screening step and a titrimetric procedure) could be used to determine accurately the carbonate-C in biochars.},
  author       = {Wang, Tao and Camps-Arbestain, Marta and Hedley, Mike and Singh, Bhupinder Pal and Calvelo-Pereira, Roberto and Wang, Congying},
  issn         = {1838-675X},
  language     = {eng},
  number       = {5},
  pages        = {495--504},
  publisher    = {CSIRO Publishing},
  series       = {Soil Research},
  title        = {Determination of carbonate-C in biochars},
  url          = {http://dx.doi.org/10.1071/SR13177},
  volume       = {52},
  year         = {2014},
}