Thomas W. Robison

Preconcentration of low levels of americium and plutonium from waste waters by synthetic water-soluble metal-binding polymers with ultrafiltration

A preconcentration approach to assist in the measurement of low levels of americium and plutonium in waste waters has been developed based on the concept of using water-soluble metal-binding polymers in combination with ultrafiltration. The method has been optimized to give over 90% recovery and accountability from actual waste water.

PREPARATION OF WATER-SOLUBLE POLYMERS MODIFIED WITH SULFUR DONORS FOR RECOVERY OF HEAVY METALS

Polyethylenimine (PEI) was modified with ligands containing sulfur donors to give soluble polymers for binding toxic metal ions. Reaction of purified PEI with mercaptosuccinic anhydride, ethylene sulfide, or methylthiocyanate gave PEI-MSA (25% functionalization), PEI-ET (100% functionalization), and PEI-TU (25% functionalization), respectively. Purification of the polymers was accomplished by diafiltration. The capacities for toxic metal ions (Hg, Cd, and Pb) and transition metal ions (Cu and Ni) were measured for each of the polymers. PEI-ET and PEI-TU showed high affinity for the softer metal ions, Hg and Cd, with loading capacities substantially higher than those for the base polymer PEI. Both polymers had high capacities for Cu. Release of the metal ions from the polymers was accomplished by lowering pH; however, small amounts of metal remained bound to the polymers at pH 1. Competition studies showed that PEI-TU and PEI-ET bound Hg and Cu more strongly than Cd and Pb.

The Removal of Pu(IV) from Aqueous Solution Using 2,3‐Dihydroxyterephthalamide‐Functionalized PEI with Polymer Filtration

Abstract Polymer filtration (PF) uses a size‐exclusion ultrafiltration membrane to retain higher molecular weight species while allowing the passage of smaller species through the membrane. Metal‐ion separations from aqueous streams are accomplished with PF by using water‐soluble chelating‐polymers (WSCP), which are appropriately sized polymers that have covalently attached metal‐binding ligands. In this study, a new WSCP was prepared by modifying polyethylenimine (PEI) through an amide linkage to attach 2,3‐dihydroxyterephthalamide (TAM) groups that have high binding constants for high valent metal cations. The TAM ligand contains a dimethylethylenediamine side chain that was found to maintain polymer solubility throughout the working pH and ionic strength ranges studied. The new WSCP (designated PDT) showed selectivity for Pu(IV) over Am(III). For example, at pH 4.5, the distribution coefficient (D) was 1.6 × 103 for Am(III) (14% bound) and 1.3 × 106 for Pu(IV) (99.3% bound). The Pu(IV) D increased as a function of pH, and the highest D was 4.8 × 106 at pH 11.4, corresponding to 99.8% bound. Varying the PDT concentration from 0.1% to 0.001% had little effect on Pu(IV) D values. The high formation constant of the Pu(IV)‐PDT complex appears to promote the oxidation of Pu(III) to Pu(IV), even in the presence of a high concentration of reductant, 0.25‐M hydroxylamine nitrate (HAN). The same high formation constant allows the TAM‐containing polymer to compete with plutonium polymer formation, as plutonium absorbed on the walls of a glass vessel dissolved after contacting it with PDT for 2 days.

Solution Behavior of Modified Polyethylenimine (PEI) Polymers by Light Scattering Investigations

The eight average molecular weights, as well as other characteristics such as the second virial coefficients and root-mean-square (RMS) radii of gyration of poly (ethyleneimine) (PEI) and various derivatives, have been determined in solution light scattering studies. The solution dynamics of PEI and carboxylated and phosphorylated derivatives were studied a pH of 3.3, 7.0 and 10.0. Measurements were made in freshly distilled and de-ionized water as well as in 0.1 M, 1 M and 5-M solutions of sodium chloride in water. Molecular weights were calculated from Berry plots. The purified polymer, PEI-1, gave a molecular weight of 39,600 g/mol., while the same polymer, which was not purified, PEI-2, has MW of 43,100 g/mol.

Chelating water-soluble polymers for waste minimization

Within the DOE complex and in industry there is a tremendous need for advanced metal ion recovery and waste minimization techniques. This project sought to employ capabilities for ligand-design and separations chemistry in which one can develop and evaluate water- soluble chelating polymers for recovering actinides and toxic metals from various process streams. Focus of this work was (1) to develop and select a set of water-soluble polymers suitable for a selected waste stream and (2) demonstrate this technology in 2 areas: removal of (a) actinides and toxic RCRA metals from waste water and (b) recovery of Cu and other precious metals from industrial process streams including from solid catalysts and aqueous waste streams. The R&D was done in 4 phases for each of the 2 target areas: polymer synthesis for scaleup, equipment assembly, process demonstration at a DOE or industrial site, and advanced ligand/polymer synthesis. The TA- 50 site at Los Alamos was thought to be appropriate due to logistics and to its being representative of similar problems throughout the DOE complex.

Robust membrane systems for actinide separations

Our objective in this project is to develop very stable thin membrane structures containing ionic recognition sites that facilitate the selective transport of target metal ions, especially the actinides.

Removal of Pu-238 from aqueous process streams using a polymer filtration process

A glovebox facility is under construction at Los Alamos that will recover a significant quantity of the impure Pu-238 that exists in scrap and residues from past production operations. The general flowsheet consists of milling, acid dissolution, ion exchange, precipitation, calcination, oxygen isotope exchange, and waste treatment operations. As part of the waste treatment operations we are using polymer filtration to remove Pu-238 to meet facility discharge limits. Polymer filtration (PF) technology uses water-soluble polymers prepared with selective receptor sites to sequester metal ions, organic molecules, and other species from dilute aqueous solutions. The water-soluble polymers have a sufficiently large molecular size that they can be separated and concentrated using ultrafiltration (UF) methods. Water and small, unbound components of the solution pass freely through the UF membrane while the polymer concentrates in the retentate. The permeate stream is “cleaned” of the components bound to the polym...