Chromatographic separation of platinum group metals from simulated high level liquid waste using macroporous silica-based adsorbents.
To separate platinum group metals (PGMs) from high level liquid waste, three novel macroporous silica-based adsorbents, namely, (Crea+Dodec)/SiO2-P, (Crea+TOA)/SiO2-P and (MOTDGA+TOA)/SiO2-P, were synthesized by introducing extractants Crea (N',N'-di-n-hexyl-thiodiglycolamide), TOA (Tri-n-octylamine), MOTDGA (N,N'-dimethyl-N,N'-di-n-octyl-thiodiglycolamide) along with theirs modifier, Dodec (n-dodecyl alcohol), into 50μm diameter SiO2-P particles by impregnation. Chromatographic separation of PGMs from simulated high level liquid waste was investigated by column method. It was found that 100% of Pd(II) and Re(VII) could be eluted out from simulate HLLW in 3.0M HNO3 solution using three adsorbents. For Ru(III) and Rh(III), high temperature has distinct effect on the adsorption rate and a further study for Ru(III) and Rh(III) is necessary to separate them from HLLW completely. In all six column experiments, a relatively satisfactory chromatographic separation operating for PGMs from simulated HLLW was obtained using (Crea+TOA)/SiO2-P adsorbent packed column at 323K.
Recovery of palladium by silica/polymer-based 2,6-bis(5,6,7,8-tetrahydro-5,8,9,9-tetramethyl-5,8-methano-1,2,4-benzotriazin-3-yl)pyridine adsorbents from high level liquid waste
ABSTRACT The adsorption properties of a porous silica-based adsorbent 2,6-bis(5,6,7,8-tetrahydro-5,8,9,9-tetramethyl-5,8-methano-1,2,4-benzotriazin-3-yl)pyridine (Me2-CA-BTP/SiO2-P) towards Pd(II) were investigated. The adsorption ability of Me2-CA-BTP/SiO2-P towards Pd(II) increased dramatically with the increase of HNO3 concentration and showed a saturated uptake of Pd(II) after the HNO3 concentration reached 3 mol/dm3. It was found that nitrate ion would participate in the adsorption reaction. Palladium adsorption kinetic and isotherm were in accordance with the pseudo-second-order rate law and Langmuir isotherm adsorption model, respectively. Thiourea could effectively elute the adsorbed palladium from Me2-CA-BTP/SiO2-P. Adsorption studies with high level liquid waste elements showed a high selectivity towards Pd(II) over other fission product elements in ≥3 mol/dm3 HNO3 solution. The stability of Me2-CA-BTP/SiO2-P against HNO3 was satisfied for the reason of the adsorption performance keeping for Pd(II) after a long-time contact with HNO3 solution. The adsorbent performed good γ-irradiation stability in dry state and low concentrations of HNO3. The presence of HNO3 enhanced the radiolysis and the adsorbent still reserved a presentable adsorption amount after γ-irradiation in 3 mol/dm3 HNO3.
The history and development of the dental surveyor--Part III.
The dental surveyor is an indispensable instrument capable of performing a number of prosthodontic procedures. Surprisingly, the technique of surveying casts as part of the treatment planning procedure did not emerge until early in the twentieth century. This article reviews the origins and early use of the dental surveyor. It includes features common to all surveyors as well as the principal uses of these instruments.