Comparison of single and sequential extraction procedures for the study of rare earth elements remobilisation in different types of soils

With the continual increase in the utilisation of rare earth elements (REE) for industrial and agricultural purposes, research into the environmental and biogeochemical behaviour of REE had attracted much interest in recent times. This study principally describes the distribution of REE in four different types of soils like lateritic soil (S-1), in situ natural soil (S-2), soil contaminated by mining activity (S-3) and accidentally polluted soil (S-4) utilizing the optimised BCR sequential extraction procedure and partial extractions with various types of single extractants such as unbuffered salt solutions 0.1 M NaNO₃, 0.01 M CaCl₂, 1 M NH₄NO₃; complexing agents 0.005 M DTPA and 0.05 M EDTA; acid solutions 0.43 M CH₃COOH and 1 M HCl. Comparison of the sum of the four BCR fractions, which included an aqua regia attack on the residue, with the pseudo-total aqua regia digest values to assess the accuracy of the BCR partioning approach has been undertaken. Partial extraction results with several single extractants have also been reported for all the REE elements including yttrium which have been analysed by the optimised BCR procedure. Results obtained after 24 h extraction with each of the single extractant have also been discussed. The extraction with 1 M HCl during 24 h yielded similar quantities of REE as those released under the combined steps of 1, 2 and 3 of the BCR sequential extraction for all the four different type of soil samples indicating that this reagent can be used successfully to estimate the total extractable contents of REE in various types of soil samples.     

Spectrophotometric study of some Mn(II) ternary complexes and their analytical applications

Abstract  

New ternary complexes of Mn(II) with py, bipy, and terpy as primary ligand (L₁) and 2′,4′,5′,7′-tetraiodofluorescein (I₄FlCOOH) as secondary ligand (L₂) were prepared. The stoichiometry for these complexes was found to be Mn(II):L₁:L₂ = 1:2:1, and the complex formula proposed is [Mn(L₁)₂(I₄FlCOO)]⁺. The effect of substituent groups of L₂ and the nitrogen atoms of L₁ on complex formation with Mn(II) was studied. Moreover, the interference of some cations and anions in the determination of Mn(II) by this method was investigated and the interferences of Cu(II) and Fe(III) with Mn(II) in their corresponding alloys were considered. A simple, rapid, and sensitive spectrophotometric method for determination of Mn(II) in its salts and Mn in its alloys is suggested.     

A new approach to determine soil microbial biomass by calorimetry

A method to determine soil microbial biomass (SMB) by isothermal calorimetry is reported. Soil samples ranging in pH from 6.2 to 9.4 and different textures were used to develop the method. Soil at 60% of its field capacity humidity was amended with a previously determined amount of glucose as to give the maximal response of CO₂ evolution. Then, an aliquot was weighed in the calorimeter ampoule and specific thermal power (p)–time (t) curves were obtained at 25 °C. After 1–2 h, a vial containing a 0.5 M NaOH solution was introduced to determine the specific thermal power due to CO₂ evolution, pCO₂ during 1–2 h. Then, the vial was removed and the experiment continued for 1–2 h. Specific thermal power due to CO₂ evolution was converted to rate (CO₂-C/mm³ g⁻¹ h⁻¹) by using the heat of reaction of CO₂ with NaOH and the molar volume. This value was further converted into SMB/μg g⁻¹ by using a conversion factor of 32.4. A guide to perform the calculations is given. Values of log SMB were linearly related with values of log p giving a similar relation to a previously reported where SMB was determined by conventional methods.     

The sorption of Eu(III) on calcareous soil: effects of pH,ionic strength,temperature, foreign ions and humic acid

The sorption of Eu(III) on calcareous soil as a function of pH, humic acid (HA), temperature and foreign ions was investigated under ambient conditions. Eu(III) sorption on soil was strongly pH dependent in the observed pH range. The effect of ionic strength was significant at pH < 7, and not obvious at pH > 8. The type of salt cation used had no visible influence on Eu(III) uptake on soil, however at low pH values, the influence of anions was following the order: Cl⁻ ≈ NO₃ ⁻ > ClO₄ ⁻. In the presence of HA, the sorption edge obviously shifted about two pH units to the lower pH, whilst in range of pH 6–7, the sorption of Eu(III) decreased with increasing pH because a considerable amount of Eu(III) was present as humate complexes in aqueous phase, then increased again at pH > 11. The results indicated that the sorption of Eu(III) on soil mainly formed outer-sphere complexes and/or ion exchange below pH ~7; whereas inner-sphere complexes and precipitation of Eu(OH)₃(s) may play main role above pH ~8.     

Synthesis, Characterization and Relaxation Properties of Four Non-ion Transition Metal Manganese(II), Cobalt(II), Nickel(II) and Copper (II) Complexes with Derivatives from Diethylene Triamine Pentaacetic Acid and Isoniazid

A novel ligand (H₂L), diethylenetriamine-N,N′,N′′-triacetylisoniazide N,N′′-bisacetic acid, and its four non-ion transition metal complexes, ML · nH₂O (M = Mn, n = 4; M = Co, Ni, n = 2; M = Cu, n = 1), have been synthesized and characterized on the basis of elemental analysis, molar conductivity, ¹H-NMR, FAB-MS, TG-DTA analysis and IR spectrum. In addition, relaxivity (R₁) of the complexes was determined, the relaxivity of MnL, CoL, NiL, CuL as well as Gd(DTPA)²⁻ used as a control are 6.94, 2.79, 2.52, 1.59 and 4.34 l mmol⁻¹ s⁻¹, respectively. The relaxivity of MnL is larger than that of Gd(DTPA)²⁻. The results show that the complex of MnL may be a potential MRI contrast agent.     

Preparation and thermal behaviour of divalent transition metal complexes of pyromellitic acid with hydrazine

Hydrazine forms two different types of complexes with divalent metal ions and pyromellitic acid (H₄pml) in aqueous medium: (i) hydrazinium complexes of formulae, (N₂H₅)₂M(pml)·xH₂O, where x = 3 for M=Ni and x = 4 for M=Co or Zn, and (N₂H₅)₂Mn(H₂pml)₂, at pH 4.5, (ii) neutral hydrazine complexes with formulae, M₂(pml)(N₂H₄) _n ·xH₂O where M=Co or Ni when n = 4 and x = 5 or 4 and M=Zn or Cd when n = 2, and x = 4 or 3 at pH 7, and M(H₂pml)(N₂H₄)·xH₂O where x = 4; M=Cu and x = 0; M=Hg, at pH 3, 7.5, respectively. All the complexes are insoluble in water, alcohol and ether. The N–N stretching frequency (990–1,007 cm⁻¹ for coordinated hydrazinium ion and 956–985 cm⁻¹ for bridged neutral hydrazine) indicates the nature of hydrazine present in the complexes. Simultaneously TG-DTA analysis indicates that hydrazinium complexes undergo dehydration and dehydrazination in a single step endothermally in the range of 289–300 °C whereas neutral hydrazine complexes undergo endothermic dehydration (~100 °C) followed by exothermic dehydrazination in the temperature range, 253–332 °C. The anhydrous metal carboxylates further decompose exothermally to leave the respective metal oxides or metal carbonates except zinc, which gives its oxalate as the end product. X-ray powder patterns indicate that even the complexes with the same formulation possess no isomorphism.     

Olefin epoxidation with H2O2 in the presence of Mn(II) dicarboxylate coordination polymer catalysts

Abstract  

The Mn(II) dicarboxylate coordination polymers [Mn(μ-terephthalate)(H₂O)₂] _n , [Mn(μ-oxalate)(H₂O)₂] _n , and [Mn(μ-d-(−)-tartrate)] _n were prepared in water and characterized by FT-IR spectroscopy and CHN analysis. Particles of the terephthalate catalyst were also synthesized, by reaction of terephthalic acid and MnCl₂·4H₂O by a sonochemical method. The catalytic potential of these coordination polymers as slow-release sources of catalytically active Mn species was tested in the oxidation of cyclooctene to its epoxide in acetonitrile, using hydrogen peroxide as oxygen source. For the terephthalate species the catalytic activity was found to increase with increasing dielectric constant and dipole moment of the solvent (being highest in acetonitrile), with reaction temperature to a maximum at 60 °C, and with an imidazole co-catalyst (highest activity found for a imidazole-to-catalyst molar ratio of 20:1). Good activity with more than 64% conversion in 24 h was obtained for epoxidation of cyclooctene and cyclohexene, whereas low yields only were obtained from aryl-substituted olefins. Some exo versus endo regioselectivity was found for norbornene.     

Extraction studies of uranium into a third-phase of thorium nitrate employing tributyl phosphate and <Emphasis Type="Italic">N,N</Emphasis>-dihexyl octanamide as extractants in different diluents

Extraction behavior of 1 × 10⁻²–0.1 M U(VI) from aqueous phases containing 0.86 M Th(IV) at 4 M HNO₃ in 1.1 M tributyl phosphate (TBP) and 1.1 M N,N-dihexyl octanamide (DHOA) solutions in different diluents viz. n-dodecane, 10% 1-octanol + n-dodecane, and decahydronaphthalene (decalin) was studied. Third-phase formation was observed in both the extractants using n-dodecane as diluent. There was a gradual decrease in Th(IV) concentration in the third-phase (heavy organic phase, HOP) with increased aqueous U(VI) concentration [0.71 M (no U(VI))–0.61 M (0.1 M U(VI)) for TBP; 0.27 M (no U(VI))–0.22 M (0.1 M U(VI)) for DHOA]. The HOP volume in case of DHOA was ~2.2 times of that of TBP. Uranium concentration in HOP increased with its initial concentration in the aqueous phase [from 1.8 × 10⁻² M (0.01 M U(VI))–0.162 M (0.1 M U(VI)) for TBP; from 1.4 × 10⁻² M (0.01 M U(VI))–0.14 M (0.1 M U(VI)) for DHOA] suggesting that Th(IV) was being replaced by U(VI). An empirical correlation was developed for predicting the concentrations of uranium and thorium in HOP for both the extractants. No third-phase appeared during the extraction of uranium and thorium from the aqueous phases employing 10% 1-octanol + n-dodecane, or decalin as diluents, and therefore, were better choices as diluent for alleviating the third-phase formation during the reprocessing of spent thorium based fuels, and for the recovery of thorium from high-level waste solutions.     

Synthesis,structures, photoluminescence,and theoretical investigations on two new Zn(II)/Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands

Abstract  

Two new neutral mononuclear Zn(II) and Mn(II) complexes with pyridine-2-amidoxine and carboxylate ligands, [Zn(paH)₂(OAc)₂]·2CH₃OH (paH = pyridine-2-amidoxine, HOAc = acetic acid) (1), and [Mn(paH)₂(OAc)₂]·C₂H₅OH·2H₂O (2), have been prepared and characterized structurally by X-ray crystallography. 1 and free paH exhibit photoluminescence at room temperature in solid state, which is rare so fare for metal complexes with oxime-based ligand. The emissions of 1 and free paH arise from the metal-perturbed paH-based π → π* ligand-to-ligand charge transfer transition (LLCT) and π → π* charge transfer transition in nature, respectively, in terms of the density functional theory level calculations and molecular orbital analyses.     

Synergic effect of triphenylphosphine oxide (TPPO) on the extraction of Hg(II), Se(IV), Co(II) and Mn(II) with fluorinated pyrazolone (HPMTFP)

Extraction of Hg(II), Se(IV), Mn(II) and Co(II) has been carried out with 1-phenyl-3-methyl-4-trifluoroacetyl-2-pyrazolin-5-one (HPMTFP) and triphenylphosphine oxide (TPPO) into chloroform from pH 1–10. Quantitative extraction of Hg(II), Mn(II) and Co(II) at pH 4 with equimolar 0.05M (PMTFP+TPPO) in chloroform was observed. Se(IV) remains unextracted at this pH range. The stoichiometric composition of the extracted complexes M(PMTFP)₂·nH₂O (M=Mn, Hg), M(PMTFP)₂·2TPPO (M=Mn and Co) and Co(PMTFP)₂·TPPO·H₂O at less than 0.1M TPPO has been established. The formation constantsK _m,0 andK _m,n and stability constants _m,n have been computed. The analytical method developed was applied to the IAEA standard reference material (SRM) potato fluor V-4 for the determination of these elements using NAA technique.     

Pseudocapacitive behaviors of nanostructured manganese dioxide/carbon nanotubes composite electrodes in mild aqueous electrolytes: effects of electrolytes and current collectors

Nanostructured MnO₂/carbon nanotubes composite electrode material was prepared using the liquid-phase deposition reaction starting with potassium permanganate (KMnO₄) and manganese acetate (Mn(Ac)₂·4H₂O) as the reactants and carbon nanotubes (CNTs) as the substrates. The structure and morphology of the material was characterized by X-ray diffraction, infrared spectroscopy, and transmission electron microscope techniques. The electrochemical properties of the nano-MnO₂/CNTs composite electrode in 1 M LiAc and 1 M MgSO₄ solutions and in 1 M RAc (R = Li, Na, and K)–1 M MgSO₄ mixed solutions, respectively, were studied. Experimental results demonstrated that the specific capacitance and rate discharge ability of the nano-MnO₂/CNTs composite electrode in 1 M LiAc–1 M MgSO₄ mixed solution is superior to that in 1 M LiAc or 1 M MgSO₄ solution. For the 1 M RAc (R = Li, Na, and K)–1 M MgSO₄ mixed electrolytes, the specific capacitance of the composite electrode was found to be in the following order: LiAc > NaAc > KAc.     

Comparative evaluation of two substituted diglycolamide extractants for ‘actinide partitioning’

Extraction behaviour of actinides, lanthanides, fission products and structural elements has been studied with the two diglycolamide extractants, namely N,N,N′,N′-tetra-2-ethylhexyl diglycolamide (T2EHDGA) and N,N,N′,N′-tetraoctyl diglycolamide (TODGA). The acid extraction studies suggested that T2EHDGA (K_H: 1.8) is less basic as compared to its linear homologue, TODGA (K_H: 4.1). The distribution ratio of Am(III) by 0.1 M diglycolamides followed the order: TODGA > T2EHDGA. The number of ligand molecules present in the stoichiometry of the extracted species of Am(III) was found to be three and four for T2EHDGA and TODGA, respectively. Thermodynamics studies suggested that the extraction of Am(III) by both the extractants is exothermic in nature. The radiolytic stability of TODGA and T2EHDGA solutions in n-dodecane has been investigated. Due to lower distribution ratio of Am by T2EHDGA, 0.2 M of its solution has been used as compared to 0.1 M solution of TODGA. The distribution behaviour of various metal ions, viz. Am, Nd, Fe, Mo, Cr, Sr and Cs has been studied from nitric acid as well as from simulated high level waste solution.     

Spectroscopic and DFT studies of photoactivatable Mn(I) tricarbonyl complexes

A combined experimental study and density functional theory calculations of fac‐[MnBr (CO)₃L] complexes (L = 2‐(2′‐pyridyl)benzimidazole ligand, furnished with either morpholine (L^morph) or phthalimido (L^phth) side‐chain) were performed using different spectral and analytical tools. The synthesized complexes released carbon monoxide upon the exposure to LED source light at 468 nm. Illumination of fac‐[MnBr (CO)₃L] (10 μM) in the myoglobin solution (Mb) produced about 25 μM MbCO. The plateau of the CO release process is attained within 25 min. With the aid of time‐dependent density functional theory calculations, the observed lowest energy absorption transition at ~ 400 nm has a ground‐state composed of d (Mn)/π (pyridyl) and excited‐state of ligand π*‐orbitals forming MLCT/π‐π^*. Natural population analyses of fac‐[MnBr (CO)₃L] were carried out to get information about the strength of Mn–CO bonds, electronic arrangment and natural charge of manganese ion.     

Novel Mn(III) heterochelates: synthesis,thermal, spectroscopic,and coordination aspects

This article describes the synthesis, structural features, and thermal studies of novel Mn(III) heterochelates of the type [Mn(SB _n )(L)(H₂O)]·xH₂O [H₂SB _n  = Nicotinic acid [1-(3-methyl-5-oxo-1-phenyl-4,5 dihydro-1H-pyrazol-4yl)-acylidene]-hydrazide where acyl = acetyl (H₂SB₁); benzoyl (H₂SB₂); propionyl (H₂SB₃); buteryl (H₂SB₄); phenyl acetyl (H₂SB₅); and HL = 5-Chloro-7-iodo-8-hydroxyquinoline (clioquinol)]. The heterochelates have been characterized on the basis of elemental analyses, magnetic susceptibility measurements, cyclic voltammetric studies, (FTIR and electronic) spectra, and thermal studies. The FAB mass spectrum of [Mn(SB₁)(L)H₂O]·3H₂O has been carried out. The cyclic voltammetric studies reveal that quasi-reversible reduction process of Mn(III)/Mn(II) coupled system suggesting that the ligands readily destabilize higher oxidation states of metal ion. Kinetic parameters such as order of reaction (n) and the energy of activation (Ea) were calculated using Freeman–Carroll method. The pre-exponential factor (A), the activation entropy (S*), the activation enthalpy (H*), and the free energy of activation (G*) were calculated using Horowitz–Metzger equations.     

Magnetostructural examination of Mn(III) complexes [Mn(cyclam)X2]+ with strong axial ligands

Three novel Mn(III) cyclam complexes, [Mn(cyclam)(NCBH₃)₂](CF₃SO₃), [Mn(cyclam)(NCBPh₃)₂](CF₃SO₃), and [Mn(cyclam)(NCSe)₂](CF₃SO₃) · H₂O, have been synthesized. These complexes are in the high-spin state between 4 and 350 K, and show large zero-field splittings. The crystal structure of [Mn(cyclam)(NCBH₃)₂](CF₃SO₃) was determined where the axial elongation of Mn–N bonds is found to be the largest among the homologue complexes. Ligand field in the [Mn(cyclam)X₂]⁺ complex series was examined by angular-overlap model calculation.     

Sorption behavior of Am<Superscript>3+</Superscript> on suspended pyrite

Sorption behavior of ²⁴¹Am (~10⁻⁹ M) on naturally occurring mineral pyrite (particle size: ≤70 μm) has been studied under varying conditions of pH (2–11), and ionic strength (0.01–1.0 M (NaClO₄)). The effects of humic acid (2 mg/L), other complexing anions (1 × 10⁻⁴ M CO₃ ²⁻, SO₄ ²⁻, C₂O₄ ²⁻ and PO₄ ³⁻), di- and trivalent metal ions (1 × 10⁻³ M Mg²⁺, Ca²⁺ and Nd³⁺) on sorption behavior of Am³⁺ at a fixed ionic strength (I = 0.10 M (NaClO₄)) have been studied. The sorption of ²⁴¹Am on pyrite increased with pH from 2.8 (84%) to 8.1 (97%). The sorption of ²⁴¹Am decreased with ionic strength at low pH values (2 ≤ pH ≤ 4), but was insensitive in the pH range of 4–10, suggesting the formation of outer-sphere complexes on pyrite surface at lower pH, and inner-sphere complexes at higher pH values. The sorption of ²⁴¹Am increased in the presence of (i) humic acid (5 < pH < 7.5), and (ii) C₂O₄ ²⁻ (2 < pH < 3). By contrast, other complexing anions such as (carbonate, phosphate, and sulphate) showed negligible influence on ²⁴¹Am sorption. The presence of Mg²⁺, Ca²⁺ ions showed marginal effect on the sorption profile of ²⁴¹Am; while the presence of Nd³⁺ ion suppressed its sorption significantly under the conditions of present study. The sorption of ²⁴¹Am on pyrite decreased with increased temperature indicating an exothermic process.     

Determination of bioavailable iron in noncontaminated Slovak soils by flame atomic absorption spectrometry

A method for the extraction of bioavailable iron from soils from various parts of Slovakia using a buffered diethylenetriaminepentaacetic acid (DTPA) solution was utilized. The extractant consists of 0.005 mol dm⁻³ DTPA, 0.1 mol dm⁻³ CaCl₂, and 0.1 mol dm⁻³ triethanolamine with pH of 7.3. DTPA was selected as the chelating agent because it can effectively extract micronutrient metal, iron. Distribution of iron in the horizons of various types of soils with respect to bioavailable iron was evaluated. The bioavailable iron in the extracts was determined by flame atomic absorption spectrometry. The calibration standards were prepared in the same surroundings as the extracts. Comparing to the average of 2.7–3.7 % total iron contents in Slovak soils, the available amounts of iron represent in average only very small amounts, approximately 0.3 % in comparison to total amounts.     

Lithium extraction/insertion process on cubic Li-Mn-O precursors with different Li/Mn ratio and morphology

The cubic phase LiMn₂O₄ precursors are prepared by high-temperature calcinations (1003 K) of LiOH⋅H₂O and MnO₂ mixture with Li/Mn molar ratio = 0.55. The Li₄Mn₅O₁₂ precursors are synthesized via low-temperature solid-phase reaction (673 K) of LiNO₃ and MnO₂ mixture with Li/Mn molar ratio = 1.0. The ion-sieves counterparts (named SMO-H and SMO-L, respectively) are obtained by the acid treatment of Li-Mn-O precursors. The structure, chemical stability, morphology, ion-exchange property and mechanism of Li-Mn-O precursors and MnO₂ ion-sieve were systematically examined via X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), Infrared Spectroscopy (IR), X-ray photoelectron spectroscopy (XPS) and lithium ion selective adsorption measurements. The result shows the more compact Mn-O lattice makes the Li₄Mn₅O₁₂ spinel more stable after the Li⁺ is extracted. The results of IR and XPS show adsorption process of SMO-H exists ion-exchange between the Li⁺ and protons, and redox reaction, but only exists ion-exchange between the Li⁺ and protons in SMO-L. Agglomeration is well-improved by low calcination temperature and the morphology of the Li₄Mn₅O₁₂ precursor and final MnO₂ ion-sieve are effectively controlled within low-dimensional structure. The maximum pH titration capacity of SMO-L for Li⁺ is 6.76 mmol⋅g⁻¹, but only 3.47 mmol⋅g⁻¹ for SMO-H. The ion-sieve obtained from Li₄Mn₅O₁₂ precursor is promising in the lithium extraction from brine or seawater.     

Density functional computation of 55Mn NMR parameters

Gradient-corrected (GGA) and hybrid variants of density functional theory are used to compute geometries and ⁵⁵Mn chemical shifts of MnO₄ ⁻, Mn(CO)₆ ⁺, Mn₂(CO)₁₀, Mn(CO)₅ X [X=H, Cl, C(O)Me], Mn(CO)₅ ⁻, Mn(NO)₃(CO), and Mn(C₅H₅)L _x [L _x =(CO)₃, C₆H₆, C₇H₈]. For this set of compounds, substituent effects on δ(⁵⁵Mn) are significantly underestimated with the pure GGA functional BPW91 and are well described with hybrid functionals such as mPW1PW91 and, in particular, B3LYP. The computed data provide evidence for solvent and counterion effects on δ(⁵⁵Mn) of MnO₄ ⁻ and Mn(CO)₆ ⁺, respectively. The latter, in the presence of Cl⁻, may be described as highly fluxional Mn(CO)₅C(O)Cl. Electric field gradients computed with the B3LYP functional can be used for a qualitative rationalization of observed trends in ⁵⁵Mn NMR line widths. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s002140020338x Received: 17 January 2002 / Accepted: 13 March 2002 / Published online: 3 June 2002     

A family of ferrocene-rich Mn7, Mn8 and Mn13 clusters

The use of ferrocene-1,1′-dicarboxylic acid (fdcH₂) in Mn cluster chemistry has led to a family of ferrocene-rich Mn₇, Mn₈ and Mn₁₃ clusters. The complexes are all mixed-valence. Solid-state DC and AC magnetic susceptibility studies have established the Mn₇, Mn₈ and Mn₁₃ complexes to possess S = 2, 5 and 9/2 ground states, respectively.