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. 2018 Apr 18;190(5):294.
doi: 10.1007/s10661-018-6681-8.

A case study: what is leached from mallee biochars as a function of pH?

Caroline Lievens  1 , Daniel Mourant  2 , Xun Hu  2 , Yi Wang  2 , Liping Wu  2 , Angelina Rossiter  2 , Richard Gunawan  2 , Min He  2 , Chun-Zhu Li  2
Affiliations

A case study: what is leached from mallee biochars as a function of pH?

Caroline Lievens et al. Environ Monit Assess. .

Abstract

Biochar is widely considered as a soil amendment. This study aims to investigate the leaching of macronutrients (K, Mg and Ca) and organics from biochars produced from mallee biomass (wood, leaf, bark) in a fluidised-bed pyrolyser at 500 °C. Biochars were soaked in solutions of varying pH values and shaken for a pre-set period of time ranging from 1 h to 4 weeks. The initial pH values of the leaching solutions used (3.4, 5.5, 7 and 8.5) covered the pH range of the soils in the Wheatbelt region of Western Australia (WA). For these bark, leaf and wood biochars, we can conclude that the biochars have a liming capacity for the acid soils of the WA Wheatbelt, depending on the feedstock. The maximum leachabilities and leaching kinetics of the macronutrients K, Mg and Ca depend on the pH of the solution in which biochar was soaked. Apparently, Ca, K and Mg in biomass are converted into different species upon pyrolysis, and the biomass species are critical for the extent of the leachability of macronutrients. Further, the chemical form of each nutrient retained in the biochars will dictate the kinetics as a function of soil pH. This study's GC/MS analysis of solvent extraction of the biochars showed potential toxicity due to the leaching of light organic compounds when biochars are added to soils. Furthermore, this study also showed the influence of pH on the leaching of large aromatic organics from the biochars. Apart from the pH of leaching solution, the influence of the biomass feedstock on the leaching kinetics of large aromatic organics from biochars was demonstrated. These leached aromatic organics were characterised by UV-fluorescence spectroscopy.

Keywords: Biochar; GC-MS; ICP-OES; Leaching; Macronutrients; Mallee; UV-fluorescence; pH.

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Figures

Fig. 1
Fig. 1
Changes in the pH of leachates as a function of leaching time during the leaching of biochars from the pyrolysis of wood, leaves and bark. The trend lines in all figures have simply connected the datum points and do not represent any model calculations
Fig. 2
Fig. 2
Leaching kinetics of K, Ca, Mg (mg/kg char) from 500 °C biochars at different initial pH values
Fig. 3
Fig. 3
UV fluorescence spectra of bark, leaf and wood (500 °C) biochar of the leaching solutions as a function of leaching time and initial pH value as indicated
See this image and copyright information in PMC

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