Marek Majdan

Equilibrium study of selected divalent d-electron metals adsorption on A-type zeolite

The objective of the presented study was to investigate the adsorption of Cu, Co, Mn, Zn, Cd and Mn on A-type zeolite. The isotherms for adsorption of metals from their nitrates were registered. The following adsorption constants K of metals were found: 162,890, 124,260, 69,025, 16,035, 10,254, and 151 [M(-1)] for Cu, Co, Mn, Zn, Cd, and Ni, respectively, for the concentration range 10(-4)-10(-3) M. On the other hand, the investigation of pH influence on the distribution constants of metals showed that the adsorption of metals proceeds essentially through an ion-exchange process, surface hydrolysis, and surface complexation. The supplementary results from DRIFT, scanning electron microscopy, and X-ray diffraction methods confirmed the presumption about the possible connection between the electronic structure of divalent ions and their adsorption behavior, showing that ions with d5 and d10 configurations such as Mn2+, Zn2+, Cd2+, with much weaker hydrolytic properties than Cu2+ and Ni2+, strongly interact with the zeolite framework and therefore their affinity to the zeolite phase is much stronger when compared with that of the Ni2+ ion, but at the same time not as strong as the affinity of the Cu2+ ion, the latter forming a new phase during the interaction with zeolite framework. For Zn2+, during inspection of the correlation between the proton concentration H/Al and zinc concentration Zn/Al on the zeolite surface, the formation of the surface complex [triple bond]S-OZn(OH) was proposed. A correlation between the heterogeneity of proton concentrations H/Al on Me-zeolite surfaces and the hydrolysis constants pKh of Me2+ ions was found.

Uranium sorption on bentonite modified by octadecyltrimethylammonium bromide.

The sorption of U(VI) on octadecyltrimethyl-bentonite was investigated at the pH values of the aqueous phase ranging from 3 to 10 and the concentrations of U(VI): 0.1-1 mmol/dm(3). The concentrations of alkylammonium cation in bentonite were increased from 21% to 150% of CEC (cation exchange capacity). It was determined that the sorption of U(VI) on modified bentonite, i.e. the distribution constant -K(d) decreases with the percent of mineral modification until it attains a minimum at 76% of CEC and then increases again. The effective sorption of U(VI) was found to be in the pH range: 6-10 for the modified bentonite and was explained as the consequence of U(VI) anionic hydroxy complexes sorption. Both FT-IR and XRD spectra of the modified bentonite were analyzed and provided arguments for the existence of surfactant cations in the form of monolayer and bilayer in the interlamellar space of bentonite. In turn the luminescence spectra of bentonite suspensions, i.e. their character at different values of pH, proved the existence of hydroxide-like planar polymeric U(VI) species in the bentonite phase at pH 9.

Silica with immobilized phosphinic acid-derivative for uranium extraction

A novel adsorbent benzoimidazol-2-yl-phenylphosphinic acid/aminosilica adsorbent (BImPhP(O)(OH)/SiO2NH2) was prepared by carbonyldiimidazole-mediated coupling of aminosilica with 1-carboxymethylbenzoimidazol-2-yl-phenylphosphinic acid. It was obtained through direct phosphorylation of 1-cyanomethylbenzoimidazole by phenylphosphonic dichloride followed by basic hydrolysis of the nitrile. The obtained sorbent was well characterized by physicochemical methods, such as differential scanning calorimetry-mass spectrometry (DSC-MS), surface area and pore distribution analysis (ASAP), scanning electron microscopy (SEM), X-ray photoelectron (XPS) and Fourier transform infrared (FTIR) spectroscopies. The adsorption behavior of the sorbent and initial silica gel as well as aminosilica gel with respect to uranium(VI) from the aqueous media has been studied under varying operating conditions of pH, concentration of uranium(VI), contact time, and desorption in different media. The synthesized material was found to show an increase in adsorption activity with respect to uranyl ions in comparison with the initial compounds. In particular, the highest adsorption capacity for the obtained modified silica was found at the neutral pH, where one gram of the adsorbent can extract 176mg of uranium. Under the same conditions the aminosilica extracts 166mg/g, and the silica - 144mg/g of uranium. In the acidic medium, which is common for uranium nuclear wastes, the synthesized adsorbent extracts 27mg/g, the aminosilica - 16mg/g, and the silica - 14mg/g of uranium. It was found that 15% of uranium ions leached from the prepared material in acidic solutions, while 4% of uranium can be removed in a phosphate solution.

Unexpected difference in phenol sorption on PTMA- and BTMA-bentonite

The comparison of phenol sorption on phenyltrimethylammonium (PTMA)- and benzyltrimethylammonium (BTMA)-bentonite shows a clear difference as far as phenol sorption isotherms are concerned. For PTMA-bentonite the sorption isotherm is of a straight-line character which results from simple partitioning of phenol between the aqueous and organic phases sorbed on the bentonite surface. For BTMA-bentonite the isotherm has a convex shape, characteristic of physicochemical sorption. For the first time a three-parametric model, including the dissociation constant of phenol pK(a), distribution constant of phenol Kd(phen) and phenolate anion Kd(phen)(-) between the aqueous phase and the bentonite phases is used for the evaluation of phenol sorption on organoclays with pH change. The model shows that the values of Kd(phen) are higher than those of Kd(phen)(-) for all investigated initial phenol concentrations. The inspection of the FTIR spectrum of BTMA-bentonite loaded with phenol in the regions 1300-1600 and 1620-1680 cm(-1) shows the features of pi-pi electron interaction between the benzene rings of phenol and the BTMA cation together with the phenol-water hydrogen bond strengthened by this interaction.

Adsorption of light lanthanides on the zeolite A surface

Abstract Adsorption studies of light lanthanides on the powdered zeolite type A are presented. It results from the mathematical description of the adsorption isotherms and from complementary scanning electron microscopy (SEM) studies of the adsorbent surface, that heterogeneity of the A type zeolite is most pronounced in the case of lanthanum and cerium, which fact correlates very well with the ability of these lanthanides to hydroxide complexes formation. It was found from the observation of the distribution constants Kd of lanthanides on pH values of the aqueous phase, that lanthanide adsorption proceeds through ion-exchange pathway up to pH 4.9, 4.8, 5.2, 4.0, 4.5 for La, Ce, Pr, Nd and Sm, respectively. For higher pH values surface hydrolysis with evolution of LnpZe3p(OH)q−q seems to be dominant component in the overall adsorption process. The separation of Nd from La, Ce and Pr via adsorption process is recommended.

The separation factors of the lanthanides in the Ln(NO3)3-NH4NO3-TBP system. Effects of change in activity coefficients

Abstract The change in the molar activity coefficients of the lanthanide nitrates is determined from the extraction data in the Ln(NO 3 ) 3 -NH 4 NO 3 -TBP system. It is concluded that at high NO 3 concentrations (6–10 M ) higher lanthanide nitrato complexes Ln (NO 3 ) n 3− n are formed to a remarkable extent, which results in the sudden increase in the activity coefficients in the Sm-Er range. The improvement in the separation factors of the light lanthanides with the NO 3 − concentration increase is observed for TBP, which is in contrast to the Aliquat 336 + TBP system.

Scanning electron microscopy and DRIFT study of metal-loaded Y zeolites

Abstract The chemical composition of the ‘surface’ of metal-loaded Y zeolites was investigated by SEM technique. The negative correlation between proton C H/Al and metal C Me/Al local concentrations for Mn, Cu and Zn, resulting from the interaction (ion exchange) of metal ions Me 2+ with ‘surface’ hydroxide bridges ≡Al–OH–Si≡ was found. In turn the positive correlation of C H/Al vs. C Me/Al for Cd was explained as stabilization of CdZe 2 and Cd(OH)Ze complexes in the zeolite structure through the formation of hydrogen bonds with hydroxide bridges. The supplementary Diffusive Reflectance Infrared Study of metal-loaded zeolite showed the sensitivity of framework vibration band T–O–T for Me 2+ ions interaction with negative oxygens of zeolite framework. In connection with this finding two groups of ions were recognized: Mn 2+ , Cd 2+ , Zn 2+ with strong interaction and consequent shift of T–O–T band toward lower frequencies and Co 2+ , Ni 2+ , Cu 2+ ions group with weak interaction with the zeolite framework with consequent position of T–O–T at higher frequencies.

Correlation in the lanthanide series

SummaryThe correlations lgK vs. lgK′,V vs.V′ (K - stability constant of the complex,V - unit cell volume of compound) within the lanthanide tetrads were reviewed. Ligands with -C = N-group were found to show a positive deviation from the lgK vs. lgK′ plot.ZusammenfassungEs wurden die Korrelationen lgK gegen lgK′ undV gegenV′ (wobeiK die Stabilitätskonstante des Komplexes ist undV das Einheitszellenvolumen) innerhalb der Lanthanidentetraden untersucht. Bei Liganden mit -C = N-Gruppen wurde eine positive Abweichung von von der lgK - lgK′-Geraden festgestellt.

The influence of different salting-out agents on the extraction of Ce, Eu, Gd, Tb using tri-n-butyl phosphate

The extraction enthalpies ΔHo of Ce, Eu, Gd, Tb nitrates usingTBP in the presence of different salting-out agents in aqueous phase were determined. It was established that the extraction process is the most exothermic in the case of LiNO3.ZusammenfassungEs wurden die Extraktionsenthalpien ΔHo von Ce-, Eu-, Gd- und Tb-Nitrat unter Verwendung vonTBP in Gegenwart verschiedener Aussalzmittel in wäßriger Phase bestimmt. Es wurde festgestellt, daß der Extraktionsprozeß im Fall von LiNO3 am meisten exotherm verläuft.

Some remarks on the periodical change of the stability constants of the lanthanide complexes

The correlations between the values of the lgK (K = stability constant of the lanthanide complex) and the reciprocal of the ionic radius 1/r or the sum of the ionization potentials Σ13I for the lanthanide ions were reviewed for different ligands. A straight-line relationship (lgK′ − lgK)/lgK′ vs. (1/r′ − 1/r)/(1/r′) or vs. (Σ13I′ − Σ13I)/Σ13I′ was found within the tetrads La-Nd, Gd-Ho, and Er-Lu.ZusammenfassungEs wurde eine Übersicht der Korrelationen zwischen den Werten von logK (K = Stabilitätskonstante der Lanthanidenkomplexe) und den reziproken Ionenradien 1/r oder der Summe der Ionisierungspotentiale Σ13I für die Lanthanidenionen für verschiedene Liganden gegeben. Dabei wurde eine lineare Korrelation für (lgK′ − lgK)/lgK′ gegen (1/r′ − 1/r)/(1/r) oder gegen (Σ13I′ − Σ13I)/Σ1/3I′ innerhalb der Tetraden La-Nd, Gd-Ho und Er-Lu aufgefunden.