The use of columns of the zeolite clinoptilolite in the remediation of aqueous nuclear waste streams.

Mud Hills clinoptilolite has been used in an effluent treatment plant (SIXEP) at the Sellafield nuclear reprocessing site. This material has been used to remove 134/137Cs and 90Sr successfully from effluents for 3 decades. Samples of the zeolite have been tested in column experiments to determine their ability to remove radioactive Cs+ and Sr2+ ions under increasing concentrations of competing ions, Ca2+, Mg2+, Na+ and K+. These ions caused increased elution of Cs+ and Sr2+. Ca2+, Mg2+ and K+ were more effective competitors than Na+. For Na+, it was found that if concentration was reduced, then column performance recovered rapidly.

Separation of lanthanum, hafnium, barium and radiotracers yttrium-88 and barium-133 using crystalline zirconium phosphate and phosphonate compounds as prospective materials for a Ra-223 radioisotope generator.

Crystalline hybrid organic/inorganic ion exchangers based on zirconium phosphate and phosphonate compounds were evaluated for application in radium-223 generator for radiopharmaceutical applications. Various compositions were synthesized and the selectivity of these materials was determined for inactive lanthanum, hafnium and barium, and radiotracers yttrium-88 and barium-133. The hybrid materials show very efficient lanthanum/barium separation; the response for zirconium phosphate was even better. A small-scale column loaded with pelletized zirconium phosphate compound demonstrated excellent retention of (88)Y and release of (133)Ba.

The effect of carbon type on arsenic and trichloroethylene removal capabilities of iron (hydr)oxide nanoparticle-impregnated granulated activated carbons.

This study investigates the impact of the type of virgin granular activated carbon (GAC) media used to synthesize iron (hydr)oxide nanoparticle-impregnated granular activated carbon (Fe-GAC) on its properties and its ability to remove arsenate and organic trichloroethylene (TCE) from water. Two Fe-GAC media were synthesized via a permanganate/ferrous ion synthesis method using bituminous and lignite-based virgin GAC. Data obtained from an array of characterization techniques (pore size distribution, surface charge, etc.) in correlation with batch equilibrium tests, and continuous flow modeling suggested that GAC type and pore size distribution control the iron (nanoparticle) contents, Fe-GAC synthesis mechanisms, and contaminant removal performances. Pore surface diffusion model calculations predicted that lignite Fe-GAC could remove ∼6.3 L g(-1) dry media and ∼4 L g(-1) dry media of water contaminated with 30 µg L(-1) TCE and arsenic, respectively. In contrast, the bituminous Fe-GAC could remove only ∼0.2 L/g dry media for TCE and ∼2.8 L/g dry media for As of the same contaminated water. The results show that arsenic removal capability is increased while TCE removal is decreased as a result of Fe nanoparticle impregnation. This tradeoff is related to several factors, of which changes in surface properties and pore size distributions appeared to be the most dominant.

Simultaneous removal of perchlorate and arsenate by ion-exchange media modified with nanostructured iron (hydr)oxide.

Hybrid ion-exchange (HIX) media for simultaneous removal of arsenate and perchlorate were prepared by impregnation of non-crystalline iron (hydr)oxide nanoparticles onto strong base ion-exchange (IX) resins using two different chemical treatment techniques. In situ precipitation of Fe(III) (M treatment) resulted in the formation of sphere-like clusters of nanomaterials with diameters of approximately 5nm, while KMnO4/Fe(II) treatments yielded rod-like nanomaterials with diameters of 10-50nm inside the pores of the media. The iron content of most HIX media was >10% of dry weight. The HIX media prepared via the M treatment method consistently exhibited greater arsenate adsorption capacity. The fitted Freundlich adsorption intensity parameters (q=K x C(E)(1/n)) for arsenate (1/n<0.6) indicated favorable adsorption trends. The K values ranged between 2.5 and 34.7mgAs/gdry resin and were generally higher for the M treated media in comparison to the permanganate treated media. The separation factors for perchlorate over chloride (alpha(Cl-)(ClO4-)) for the HIX media were lower than its untreated counterparts. The HIX prepared via the M treatment, had higher alpha(Cl-)(ClO4-) than the HIX obtained by the KMnO(4)/Fe(II) treatments suggesting that permanganate may adversely impact the ion-exchange base media. Short bed adsorber (SBA) tests demonstrated that the mass transport kinetics for both ions are adequately rapid to permit simultaneous removal using HIX media in a fixed bed reactor.

Effect of silica and pH on arsenic uptake by resin/iron oxide hybrid media.

The recently imposed maximum contaminant level (MCL) of 10microg/L for arsenic has necessitated many water providers to implement efficient treatment systems to reduce the arsenic content in potable water supplies across the United States. A popular, cost-effective solution is to adsorb the arsenic onto hydrous iron oxide-based granular media. Hybrid media, consisting of hydrous iron oxides impregnated into a polymeric substrate in order to improve mechanical stability, have also been developed. The effective operational bed life of these adsorptive media is strongly dependent on the chemistry of the water being treated. High levels of silica combined with pH values greater than 8 have been shown to have a detrimental effect on the arsenic removal efficiency of all adsorptive media. Batch arsenate (arsenic(V)) adsorption experiments were performed to evaluate the effect of pH and silica on the static arsenic capacity of two iron oxide-based hybrid media, ArsenX(np) (a commercially available media) and npRio (a developmental media). From the data obtained, it was evident that the presence of increased levels of silica enhanced the detrimental effect of elevated pH on arsenic capacity, being most noticeable at pH 8 and above. In a solution containing 30ppm of SiO(2), a decrease in arsenic capacity as high as 71.8% was observed when the pH was increased from 7 to 9. Reducing the pH of the water prior to treatment may therefore be an economic option for improving media performance in drinking waters containing high concentrations of silica.

Magnetic property studies of manganese-phosphate complexes.

Phosphoric acid forms two distinct coordination compounds with manganese salts in aqueous media, a two-dimensional layered structure, [Mn(HPO4).(H2O)3], 1, under ambient conditions, and a three-dimensional synthetic mineral, [Mn5(mu-OH2)2(HPO4)2(PO4)2(H2O)2], 2, under hydrothermal procedures, at 120 degrees C. In compound 1, the oxygen atom of the doubly deprotonated phosphoric acid interconnects the metal centers to form a layered structure. The neutral hydrophilic layers of 1 are separated by 5.5 A and may potentially intercalate hydrophilic organic guest molecules. The metal centers in 2 are octahedral and bridged by PO4(3-), HPO4(2-), and OH2 groups to form a complex three-dimensional network. XPS analysis on 1 and 2 confirms that manganese exists in the +2 oxidation state. Compound 2 is a poor ion exchanger, but some improvement is observed on partial dehydration. The magnetic properties of both 1 and 2 were studied in detail to examine the amplitude of the magnetic interactions through phosphate ligand bridges. While 1 reveals dominant antiferromagnetic interactions between the spin carriers, a complete investigation of the magnetic properties of 2 revealed its true nature to be a glassy magnet.