| Military ordnance production facilities generate explosive-laden wastewater streams, referred as pinkwater, which must be treated prior to their discharge off the plant facility limits. Among the energetic compounds present in pinkwater, RDX, TNT, and HMX are major compounds and have particular environmental concerns since they are toxic and persistent in the environment. The currently applied technology for treating the energetic compounds in pinkwater is activated carbon adsorption. However, the adsorption is a non-destructive technology, which could create future liability issues. Furthermore, treatment of pinkwater with activated carbon is expensive because the exhausted carbon has to be regenerated or dispose to the special landfills. This study evaluated the utilization of zero-valent iron (ZVI) as a potential reducing agent for the treatment of pinkwater in order to reduce treatment time, and operational costs. ZVI treatment can be used as a first treatment step to transform RDX, TNT, and HMX into reduced organic compounds which are easily biodegradable.; The effectiveness of ZVI as a reducing agent was evaluated under neutral and acidic conditions. Experimental results show that ZVI is effective in reducing RDX, TNT, and HMX in aqueous solutions. The reduction of the energetic compounds proceed very fast under acidic conditions, but slowly at neutral pH. The reduction of HMX was found to be the rate-limiting step. The effect of the acid used (CH3COOH, H2SO4, and HCl) to adjust the initial pH of the reaction medium on the reduction of RDX, TNT, and HMX by ZVI was evaluated. Acetic acid yielded the highest reduction rates. The reduction by-products of RDX under acidic condition were examined. Nitrous oxide, nitrite, and three nitroso derivatives---MNX (hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine), DNX (hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine), and TNX (hexahydro-1,3,5-trinitroso-1,3,5-triazine)---were identified and quantified. The nitroso compounds (MNX, DNX, and TNX) were found to undergo further reduction by ZVI. The reduction of RDX, TNT, and HMX is modeled using a pseudo first order kinetics and a site-saturation kinetics model.; Keywords - energetic compounds, RDX, TNT, HMX, pinkwater, zero valent iron, reduction, kinetics, reaction by-products. |
