Journal of Analytical and Applied Pyrolysis 108 (2014) 26–34 Contents lists available at ScienceDirect Journal of Analytical and Applied Pyrolysis journa l h om epage: ww w.elsevier.com/locate/jaap Characterization of an enriched biochar Chee H. Chia a,∗ , Bhupinder Pal Singh b , Stephen Joseph a , Ellen R. Graber c , Paul Munroe a a School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia b NSW Department of Primary Industries, Elizabeth Macarthur Agricultural Institute, Woodbridge Road, Menangle, NSW 2568, Australia c Institute of Soil, Water and Environmental Sciences, The Volcani Center, Agricultural Research Organization, POB 6, Bet Dagan 50250, Israel a r t i c l e i n f o Article history: Received 5 September 2013 Accepted 29 May 2014 Available online 5 June 2014 Keywords: Biochar Characterization Stability Microstructure a b s t r a c t Carbonized materials are responsible for maintaining a high level of fertility and soil organic matter in soils such as the Amazonian Dark Earths, also known as Terra Preta. It is hypothesized that an enriched biochar, which will have long term stability similar to Terra Preta, can be synthesized by mixing biochars with manures, minerals and clays and heating the mixture at low temperatures. This treatment will promote bonding between the mineral and the organic phases, which may occur naturally after several years of aging in soil. This paper describes the characterization of an enriched biochar by a range of analytical methods. Examination of the enriched biochar showed that it has high concentrations of exchangeable cations, available phosphorus and high acid neutralizing capacity. Structural analysis of the enriched biochar reveals a microstructure that suggests that bonding has indeed occurred between the biochar and mineral phases. Using natural 13 C abundance and a two-pool exponential model, the half-life of enriched biochar-C was estimated to be 104 years in a clayey soil. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Biochar is a carbon-rich solid material produced by heating biomass in an oxygen-limited environment. It may be added to soils where, potentially, it can act as a means to sequester carbon (C) and to maintain or improve soil and agronomic functions [1,2]. Biochar can form a highly stable pool of C, promote plant growth and potentially mitigate greenhouse gas emissions from soil [3–5]. Research has shown that carbonized materials are responsible for maintaining a high level of soil organic matter (SOM) in ancient soils such as Amazonian Dark Earths (ADE), which is likely due to its high stability in soil [6]. Recent studies using 11 different types of biochars (Eucalyptus saligna wood and leaves, papermill sludge, poultry litter, cow manure, etc.) pyrolyzed at 2 different temper- atures has shown that the estimated mean residence time (MRT) of C in biochars varied between 90 and 1600 years [7]. However, even though it is apparent that application of biochars to soil will increase SOM over a long period of time, little is known about the reactions that takes place between biochars and soil. Cheng and Lehmann [8] showed an increase in oxygenated func- tional groups, acidity and negative charge at the surface of oak biochar particles aged for 12 months in a controlled aerobic incu- bation experiment. These findings are supported by results from ∗ Corresponding author. Tel.: +61 2 9385 4435; fax: +61 2 9385 6400. E-mail address: c.chia@unsw.edu.au (C.H. Chia). Joseph et al. [9], who examined aged biochar particles extracted from field trials, and reported an increase in negative surface charge and oxygenated functional groups as compared with freshly pro- duced biochar particles. It has been suggested that changes in the surface properties of biochars may promote the aggregation of organo-mineral complexes at biochar surfaces [9]. This is supported by research into ADE, where it was deduced that slow oxidation at the edges of the aromatic backbone of black C-generated carboxylic groups, resulted in increased cation exchange capacity (CEC) and the formation of organo-mineral complexes [10]. Studies of the structure and chemistry of ADE have revealed that these soils are composed of micro-aggregates that may have been formed by the interaction of thermally treated organic mat- ter, charcoal and ash from fires, residual fired clay, and fragments of bones [11–13]. Liang et al. [14] found that ADE has a higher water holding capacity (WHC), higher CEC and higher fertility com- pared to adjacent soils. Chia et al. [15] demonstrated, through analytical electron microscopy, that ADE particles consisted of a mixture of black C (possibly arising from the breakdown of biochar), clays and other minerals, including titanium dioxide, manganese oxides, iron hydroxides, calcium phosphate and calcium carbon- ate. Dünisch et al. [16] showed that by mixing charcoal with ashes or by impregnating wood residues with nutrients such as N, P, and K, slow-release N- and K-fertilizers can be produced. It was hypothesized that an organo-mineral complex that may have simi- lar properties to ADE could be produced by mixing manures/sludge, woody materials, clays, and other minerals, and heating these at http://dx.doi.org/10.1016/j.jaap.2014.05.021 0165-2370/© 2014 Elsevier B.V. All rights reserved.