Abstract:
Digestion of biomass derived carbonaceous materials such as biochar (BC) can be challenging due to their
high chemical recalcitrance and vast variations in composition. Reports on the development of specific
sample digestion methods for such materials remain inadequate and thus require considerable attention.
Nine different carbonaceous materials; slow-pyrolyzed tea-waste and king coconut BC produced at
300 C, 500 C and 700 C, sludge waste BC produced at 700 C, wet fast-pyrolyzed Douglas-Fir BC and
steam activated coconut shell BC have been tested to evaluate a relatively fast and convenient openvessel
digestion method using seven digestion reagents including nitric acid (NA), fuming nitric acid
(FNA), sulfuric acid (SA), NA/SA, FNA/SA, NA/H2O2 and SA/H2O2 mixtures. From the tested digestion reagents,
SA/H2O2 mixture dissolved low temperature produced BC (LTBC) within 2 h with occasional
shaking and no external heating. Except peroxide mixtures, the other reagents were used to evaluate
microwave digestion (MWD) efficiency. Nitric acid mixture was capable of only completely digesting
LTBC in the MWD procedure whereas FNA, NA/SA and FNA/SA mixtures resulted in the successful
dissolution of all tested carbonaceous materials. Amongst them, FNA provided the least matrix effect in
the quantification of the four metals tested using flame atomic absorption spectrophotometry. Tested
recoveries for FNA were satisfactory as well. It was concluded that FNA is a preferable reagent for microwave
digestion of BC.
