Cellulose and Charcoal: oxidation chemistry and combustion
Traditionally, chemical decontamination of charcoal has been limited to simple acid, base, acid (ABA) methods, which yield variable results depending on environmental conditions and diagenetic processes. The use of chemical (wet) oxidation with a variety of reagents has been shown to significantly enhance the removal of organic contamination. Similarly, oxidation chemistry applied to wood has yielded superior results, particularly when pure cellulose is isolated, and there is much discussion on the relative merits of fixed-high-temperature versus 2 or 3-stage stepped-combustion of the oxidised products.
Dizzy Gillespie's research in these fields has mainly employed the chlorine-containing oxidation reagents hypochlorite, chlorite and chlorate on both wood and charcoal, which are being compared with oxidations using dichromate and peroxide pursued by other researchers. Recent applications, partly funded by AINSE grants 09/035 and 10/143, of a simple hypochlorite-chlorite oxidation protocol to wood samples known to be beyond radiocarbon range (buried kauri logs, New Zealand, woody fragments from the gut contents of a Diprotodon from Lake Callabonna, South Australia, and from Lake Xere Wapo, New Caledonia) have produced 14C background results on cellulose. Since cellulose is a polymeric organic compound, it will combust almost completely in oxygen at temperatures above ~330°C, so stepped-combustion is counterproductive.
Left: Woody fragments from the gut contents of an extinct Diprotodon found at Lake Callabonna, South Australia. Upper 2 bits untreated, lower 2 bleached with hypochlorite. Right: Subfossil kauri wood from New Zealand, shown before and after hypochlorite-chlorite oxidation (photos: Dizzy).
- Keith Fifield and Stewart Fallon, AMS radiocarbon, ANU
- The AMS radiocarbon team at ANSTO, Sydney
- Janelle Stevenson and Geoff Hope, Archaeology & Natural History, ANU
- Rod Wells, Biological Sciences, Flinders University
- Gillespie, R. (1990). On the use of oxidation for AMS sample pretreatment. Nuclear Instruments & Methods B52, 345-347.
- Gillespie, R. (1997). Burnt and Unburnt Carbon: Dating charcoal and burnt bone from the Willandra Lakes, Australia. Radiocarbon 39(3), 239-250
- Gillespie, R., Fifield, L.K., Levchenko, V., Wells, R. (2008). New 14C ages on cellulose from Diprotodon gut contents: explorations in oxidation chemistry and combustion. Radiocarbon 50, 75-81.
- Stevenson, J., Gillespie, R., Hope, G., Jacobsen, G., Fallon, S., Levchenko, V. (no date) The archaic and puzzling record of Lake Xere Wapo, New Caledonia. In: Altered Ecologies: fire, climate and human influence on terrestrial landscapes, Haberle, S., Stevenson, J., Prebble, M. (eds), Terra Australis 32, 381-393.