Theme: 01. Remediation Technology Innovations

Topic Area: 01f. Emerging Remediation Technologies

Formatted Title:

Adsorptive Removal of Munitions Compounds from Aqueous Solutions via Graphene Nanoplatelets

Background/Objectives:

Treatment technologies for waters contaminated with insensitive munition (IM) compounds are being investigated to enhance performance, efficiency, and sustainability, as the current state of the science in this field is limited. Based on properties inherent to each munitions constituent, treatment technologies capable of removing mixtures of IM, in addition to legacy munitions, are potentially scarce or inefficient. Thus, treatment trains or mixed treatment systems that may require large footprints or be infeasible for environmental applications are often considered. However, graphene, a nanotechnology composed of two-dimensional carbon in a lattice-like structure, has shown promise as an adsorptive technology capable of removing organic compounds with high capacities from aqueous solutions. This attribute provides an opportunity to develop strategies for managing munitions constituents individually and collectively using this singular technology. Thus, graphene was investigated to assess its efficacy as a treatment technology for aqueous IM and legacy munitions.

Approach/Activities:

Bench-scale studies were conducted with the following IM compounds: 2,4-dinitroanisole (DNAN), nitroguanidine (NQ), and nitrotriazolone (NTO); 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-s-triazine (RDX) were also investigated as traditional munitions for comparison. Graphene nanoplatelets were evaluated against these compounds individually to determine adsorption capacities and kinetics for each system. Various grades of graphene were used to determine trends among the properties of the materials. Aqueous solutions were also adjusted to gauge impacts of environmental influences on performance. Additionally, desorption techniques were evaluated to determine potential reuse applicability of the nanotechnology and further evaluate process sustainability. Granular activated carbon (GAC) was also analyzed as a comparative technology.

Results/Lessons Learned:

These evaluations showed significant adsorption of each munition investigated. However, DNAN and TNT were removed in the highest quantities at each phase of the study. Furthermore, each compound followed either a Langmuir or Freundlich isotherm model. Additionally, each munition constituent exhibited relatively rapid adsorption kinetics – following a pseudo-second order model – at any graphene concentration assessed. Studies involving pH and ionic strength showed that NTO was the only constituent impacted by either environmental characteristic. However, graphene exhibited a greater tendency to flocculate as ionic strength was increased. Analysis of thermodynamics via temperature adjustment indicated that physisorption was the dominant mechanism for adsorptive removal for each IM. Furthermore, adsorption capacity was greatly dependent on dry surface area of the graphene. Desorption studies showed that high pH caused near total removal of NTO from the graphene surface. Additionally, DNAN was transformed at high pH to 2,4-dinitrophenol (2,4-DNP), which was released into solution from graphene Each munitions constituent was desorbed from the graphene in the presence of an organic solvent. Following successful desorption, graphene exhibited an increased capacity for reuse as an adsorbent against munitions compounds relative to control graphene samples that were not effectively regenerated. These results suggest the use of graphene as a sustainable technology for treatment of munitions-laden waters.

Florence Sanchez

Affiliation

Refine Results

Adsorptive Removal of Munitions Compounds from Aqueous Solutions via Graphene Nanoplatelets