Aquifer soil cation substitution and adsorption of TNT, RDX, and HMX

The production of 2,4,6-trinitrotoluene (TNT), 1, 3,5-trinitro-1,3,5-hexahydrotriazine (RDX), and octahydro-1,3,57-tetranitro-1,3,5,7-tetrazocine (HMX) has resulted in significant contamination of soil and groundwater at ammunition plants. The development of remediation and risk management strategies requires an understanding of the environmental fate and transport processes affecting TNT, RDX, and HMX The transformation and soil sorption are key process descriptors that must be quantified to effectively evaluate the environmental fate of these contaminants in aquifer soils and groundwater. The objective of this laboratory study was to determine the effects of changing composition of simulated groundwater on TNT, RDX, and HMX adsorption in low carbon aquifer soils. Batch shake tests using homo-ionic aquifer soils and clay minerals were used to determine the effects of cation composition on sorption. Results of batch shake tests showed that simulated groundwater cation composition substantially affected the sorption of TNT in aquifer soils. Saturation of the cation exchange sites with K+ and NH4+ resulted in increased TNT sorption to the aquifer soils by up to 9780%. TNT adsorption by biionic K+:Ca++, aquifer soil increased until 40% saturation of the exchange sites was attained. Past this point, pronounced increases in adsorption were not observed until 100% saturation with K+ was reached. Changing the cation substitution on aquifer soils by saturation with either K+ or NH4+ did not consistently increase the adsorption of RDX and HMX. TNT shows great potential for treatment using cation substitution, while this is not the case for nitramines.