Sorption of uranium compounds by zirconium-silica nanosorbents

Abstract

Bitemplate (solubilization) synthesis was used to obtain new mesoporous zirconium-silica nanosorbents that can be successfully used to recover uranium compounds from sulfate and carbonate solutions.Studies concerned with sorption methods for recovery of uranium compounds from aqueous solutions, seawater, and wastewater pay primary attention to synthesis of new, or modifi cation of already known, sorbents in order to raise their sorption capacity for uranium, improve their selectivity, and elucidate the sorption mechanism in relation to the pH of the medium and forms in which the sorbate is present in solution.The following sorbents have been used: natural minerals (quartz, muscovite, labradonite [1], pozzolan [2]); zeolites [3], including organozeolites [4] produced by treatment of clinoptilolite-containing tuffs with polyhexamethylene guanidine; sorbents based on wood and lignin [5] with high content of phosphorus; polymers: polymeric chelate sorbents [6]; biopolymer chitosan [7]; Al, Si, Ti oxides, sulfi des, and phosphates, including hydrogels based on the SiO 2 -TiO 2 formulation (in hydrogen form) [8]; crystalline TiO 2 modifi ed with amorphous aqueous SiO 2 [9], titanium phosphates and phosphosilicates [10]; ion-exchange resins: phosphoric acid resins and sulfocation-exchange resins [11]; anionexchange resins: macroporous [12], low-basic [13], high-basic [14], and resins of gel and porous structure [15]; activated carbons: oxidized [16] and modifi ed with arsenazo reagents [17].The wide assortment of sorbents enables their choice for recovery of uranium compounds from aqueous media of various compositions. At the same time, there hardly is any evidence about purposeful synthesis of sorbents with prescribed pore sizes that would match the size of molecules or ions of uranium compounds being sorbed. However, the number of studies in this area has noticeably increased recently (2007)(2008)(2009)(2010) [18][19][20][21][22].The goal of our study was to fi nd whether recovery of uranium(VI) compounds from aqueous solutions by sorption with zirconium-silica nanosorbents is possible and can be effi cient. EXPERIMENTALZirconium-silica nanosorbents were synthesized by bitemplate (solubilization) method from inexpensive reagent: sodium silicate, zirconyl chloride, and industrial fraction of a surfactant [23,24]. Freshly synthesized starting samples were subjected to hydrothermal (980°C) and thermal (600°C) treatments. The specifi c surface of the samples (Table 1) was determined from the argon sorption by the BET method [25] (sample nos. 1-10) and from isotherms of low-temperature sorption-desorption of nitrogen (Fig. 1, sample nos. 1 and 9), measured with Quantachrome NovaWin2 instrument. The pore size distribution was found from the desorption isotherms by using the BJH model.As objects of study served sulfate and carbonate solutions of uranium(VI), which contained 2 × 10 -4 mol (50 mg) of the metal per liter. The concentration of

Kinetics of sorption of uranium(VI) compounds with zirconium-silica nanosorbents

“…When the mass fraction of ZrO 2 in the sorbent samples increased, the pore diameter of the sorbents increased, while the specific surface area accordingly decreased ( Table 1). The range of pH corresponding to the isoelectric state of the sorbent surface was 3.0-3.5 [5].…”

“…The solutions were prepared from reagent grade UO 2 (CH 3 COO) 2 [4]. Experiments on the kinetics of sorption of uranium compounds from carbonate and sulfate solutions were performed at initial and experimentally established [5] optimum pH values, namely, pH 4 (starting carbonate solutions) and 7 (sulfate solutions). In the starting car bonate solutions with pH 4, uranium(VI) was in the form of a mixture of UO (91%) and UO 2 OH + (9%) cations; in sulfate solutions with pH 7, as a mixture of UO 2 OH + (13.7%) and UO 2 (OH) 2 (86.3%) [4].…”

Formation of Zirconium Hydrophosphate Nanoparticles and Their Effect on Sorption of Uranyl Cations

“…If the composite is based on inert polymer [ 16 ], its sorption capacity is insignificant. Some types of composites are suitable only for anion removal [ 32 , 33 ].…”