Ammonium nitrate solution (ANSOL), the wastewater produced from the manufacturing of nitramine munitions, represents a recoverable and potentially economically viable resource if its hazardous components could be removed, particularly the nitramine compounds Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), trace metals such as chromium, and residual alkylamines. To meet the need for improved, cost-effective purification strategies for ANSOL, the project team is developing flow-through electrochemical reactors that generate reductants and oxidants in situ for nitramine transformation and iron-based reactors that provide reactive iron complexes or surfaces for chromium removal. The reactor units uses low power and is capable of sustained, long-term operation without chemical additives. The objective of this project is to adapt the team's current electrochemical and adsorption technologies into a three-stage treatment system that specifically addresses the challenges to purifying ANSOL.
The central hypothesis for this work is that electrochemical and adsorption technologies can selectively remove nitramine compounds and chromium from ANSOL to create a purified, salable product. A three-stage process for purifying ANSOL without removing ammonium or nitrate is envisioned: (i) an electrochemically-induced degradation of organic munitions compounds in a plug flow reactor that provides cathodic reduction surfaces, adsorbed atomic hydrogen reductants, and hydroxyl radicals; (ii) a separate electrochemical (or passive) plug flow reactor featuring reactive forms of iron for removal of trace chromium; and (iii) a granular activated carbon-based adsorption plug flow reactor for alkylamine removal. Laboratory experiments with bench-scale reactors will be conducted to optimize reactive material performance and operating conditions. For the optimized treatment system, a process model and a sustainability model will be created for use as a system design tool and a scaling feasibility assessment.
This work will support the strategies to convert ANSOL wastewater to a valuable resource. The technological development will result in a three-stage purification system with demonstrated sustained treatment effectiveness at the bench scale and a multicomponent model tool for scale-up. The technology will generate a variety of nonspecific reductants and oxidants that are applicable to any nitramine compound. Reactive iron surfaces will be generated and evaluated specifically for chromium removal, but these surfaces will also have applicability to other trace metal contaminants. Reaction conditions will be created using inert and cost-effective materials (stainless steel, activated carbon, iron metal) under low electric power. Cathode and anode materials and their operating conditions will be optimized to ensure removal of hazardous organics and chromium at various flow rates. The optimized treatment system will be operable within high ionic strength wastewaters and not require chemical reagent addition. Kinetic models will be created from experimental data and used to simulate and predict unit operation performance within a system-wide process model that will provide a basis for field-scale treatment system design including life cycle assessment. This project will also serve the scientific community by providing insight to nitramine and chromium transformation processes.