Surface Complexation Theoretical Descriptions of the Sorption of Organic-Acid Munition Constituents on Variably Charged Surfaces: Preliminary Findings.

As highly soluble organic acids, many next-generation munitions offer greater flexibility in creating more concentrated explosive formulations. Depending on the system acidity (pH) relative to the solute acid dissociation constant (pK_a), these organic acid munition constituents (OAMC) may exhibit charged solute species whose sorption on natural solids may be described (and predicted) using well-developed surface complexation theory – something not feasible with conventional munition constituents (MC). We hypothesize that OAMC sorption is described using surface complexation mechanisms. Here, we discuss preliminary batch sorption tests (where system pH is unbuffered preliminary evidence) from ongoing laboratory studies where the sorption of three OAMCs of interest are: 3-nitro-1,2,4-triazole-5-one (NTO), 4,6-bis-nitroamino-1,3,5-triazole-2-one (DNAM), and 3,4-dinitro-pyarzole (DNP). Sorbents tested represent different mineral and organic domains common in soil but exhibiting variably charged surface behavior, including compost-extracted humic acid, Fe-, Mn-, and Al-oxide solids, and acid-washed kaolinite mineral. The appearance of a sorption edge with respect to pH will provide evidence that surface complexation mechanisms are important to predicting the sorption behavior of the OAMCs. Here, we describe follow-on work designed to characterize the charge profile of the sorbents as well as quantify the inherent sorption constant for OAMC sorption.