Calculation Of Species Distribution Research Articles

Arsenic triggered nano-sized uranyl arsenate precipitation on the surface of Kocuria rosea

Arsenic (As) and uranium (U) frequently occur together naturally and, in consequence, transform into cocontaminants at sites of uranium mining and processing, yet the simultaneous interaction process of arsenic and uranium has not been well documented. In the present contribution, the influence of arsenate on the removal and reduction of uranyl by the indigenous microorganism Kocuria rosea was characterized using batch experiments combined with species distribution calculation, SEM–EDS, FTIR, XRD and XPS. The results showed that the coexistence of arsenic plays an active role in Kocuria rosea growth and the removal of uranium under neutral and slightly acidic conditions. U-As complex species of UO2HAsO4 (aq) had a positive effect on uranium removal, while Kocuria rosea cells appeared to have a large specific surface area serving as attachment sites. Furthermore, a large number of nano-sized flaky precipitates, constituted by uranium and arsenic, attached to the surface of Kocuria rosea cells at pH 5 through P=O, COO−, and C=O groups in phospholipids, polysaccharides, and proteins. The biological reduction of U(VI) and As(V) took place in a successive way, and the formation of a chadwickite-like uranyl arsenate precipitate further inhibited U(VI) reduction. The results will help to design more effective bioremediation strategies for arsenic-uranium cocontamination.

Study on the influence and mechanism of polyferric sulfate on COD removal and reuse of scheelite flotation wastewater

This study investigated an efficient method for removal COD of scheelite flotation wastewater (SFW) with polyferric sulfate (PFS) and the reuse of the treated water into the flotation system. The mechanism of COD removal was studied by scanning electronmicroscopy coupled with energy-dispersive X-ray spectroscopy, X-ray diffraction, Fourier transforminfrared spectroscopy, species distribution calculation and kinetics. Results showed that 66.85 % COD removal was achieved with PFS treatment under the optimum conditions (Contact time: 30 min, PFS dose: 1.5 g/L, and initial solution pH: 8). The COD of SFW was reduced from 207.36 mg/L to 68.75 mg/L and the COD removal capacity could reach 92.41 mg/g. The treated SFW could be reused in scheelite-flotation system without affecting index of scheelite. In addition, amorphous ferric hydroxide (Fe(OH)3(s)) was formed during Fe(III) hydrolysis, and it could reacted with oleate to the formation of iron carboxylate, resulting the removal of COD in SFW. The kinetic analysis of PFS treatment process showed that the removal of COD obeyed the pseudo-second-order kinetic model, and the main rate-limiting step of the adsorption of amorphous Fe(OH)3(s) was chemisorption.

Removal of suspended solids from weathered tungsten-ore beneficiation wastewater by electroneutralization and chemical precipitation

The direct reuse of weathered tungsten-ore beneficiation wastewater (WTBW) in tungsten-flotation system seriously deteriorates the flotation index of tungsten because of its high content of suspended solids (SS). In the present study, an innovative technology using calcium chloride (CaCl2) to remove SS from WTBW was established based on the theory of electroneutralization and chemical precipitation. A series of laboratory tests was performed to determine the optimal conditions for SS removal from WTBW. Species-distribution calculation, zeta potential, X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy were used to analyze the underlying mechanism. Results showed that the content of SS in WTBW decreased from 25.16×103 mg/L to 22.56 mg/L after CaCl2 treatment. A concentrate with tungsten grade and recovery of 1.93% and 74.81%, respectively, was obtained by reusing the treated wastewater in the tungsten-flotation system. Compared with untreated wastewater, the tungsten grade and recovery of concentrate increased by 0.45% and 12.20%, respectively. Moreover, the Ca2+ supplied by CaCl2 can neutralize the negative charge on SS surface and further react with CO32– and SiO32– in solution to form CaCO3(S) and CaSiO3(S), which explained why CaCl2 can promote the aggregation and sedimentation of SS.

Dimeric and Trimeric Uranyl(VI)-Citrate Complexes in Aqueous Solution.

This research addresses a subject discussed controversially for almost 70 years. The interactions between the uranyl(VI) ion, U(VI), and citric acid, H3Cit, were examined using a multi-method approach comprising nuclear magnetic resonance (NMR), ultraviolet-visible (UV-vis), attenuated total reflectance Fourier-transform infrared (ATR FT-IR), and extended X-ray absorption fine-structure (EXAFS) spectroscopies as well as density functional theory (DFT) calculations. Combining 17O NMR spectroscopy and DFT calculation provided an unambiguous decision on complex configurations, evidencing for the first time that the dimeric complex, (UO2)2(HCit-H)22-, exists as two diastereomers with the syn-isomer in aqueous solution strongly favored over the anti-isomer. Both isomers interconvert mutually with exchange rates of ∼30 s-1 at -6 °C and ∼249 s-1 at 60 °C in acidic solution corresponding to an activation barrier of about 24 kJ mol-1. Upon increasing the pH value, ternary dimeric mono- and bis-hydroxo as well as trimeric complexes form, that is, (UO2)2(HCit-H)2(OH)3-, (UO2)2(HCit-H)2(OH)24-, (UO2)3(O)(Cit-H)38-, and (UO2)3(O)(OH)(Cit-H)25-, respectively. Stability constants were determined for all dimeric and trimeric species, with log β° = -(8.6 ± 0.2) for the 3:3 species being unprecedented. Additionally, in the 6:6 sandwich complex, formed from two units of 3:3 species, the 17O NMR resonance of the trinuclear uranyl(VI) core bridging μ3-O is shown for the first time. Species distribution calculations suggest that the characterized polynuclear U(VI)-citrate species do not significantly increase uranium(VI) mobility in the environment. Furthermore, we revise the misconceptions in the aqueous U(VI)-citric acid solution chemistry, that is, structures proposed and repeatedly taken up, and outline generalized isostructural considerations to provide a basis for future U(VI) complexation studies.

Effects of metal ions on the flotation separation of spodumene from feldspar and quartz

The effects of Ca(II), Mg(II), Cu(II), and Fe(III) on the flotation separation of spodumene from feldspar and quartz were investigated by single-mineral and artificial-mixed-ore flotation experiments using α-bromododecanoic acid (α-BDDA) as a collector. At pH≈7, Ca(II), Mg(II), and Cu(II) selectively improved the flotation of spodumene, which facilitated the separation of spodumene. Although Fe(III) exhibited strong activation ability, its selectivity toward spodumene was low, which impaired the separation of spodumene. Moreover, the sequence of addition of metal ions had an impact on the separation of spodumene. When Ca(II) and Mg(II) were used as activators in the artificial-mixed-ore flotation experiments, concentrates with recoveries of 75.6% and 76.3% and Li2O grades of 5.8% and 5.2% were obtained, respectively. Adsorption and activation mechanisms of metal ions were analyzed by adsorption amount measurements, Fourier transform infrared spectroscopy, species distribution calculation, and frontier orbital theory calculation. Results indicated that the amount of α-BDDA adsorbed on spodumene was higher than those adsorbed on feldspar and quartz when Ca(II), Mg(II), and Cu(II) were employed as activators, which led to a higher recovery of spodumene. When the pH was approximately 7, Ca(II), Mg(II), Fe(III), and Cu(II) were mainly present as Ca2+, Mg2+, Fe(OH)3 and Fe(OH)2+, and Cu(OH)2, Cu2+, and Cu(OH)+, respectively. The results of frontier orbital theory calculations demonstrated that α-BBBA, Ca2+, and Mg2+ easily adsorbed on spodumene than on feldspar and quartz. Therefore, Ca(II) and Mg(II) facilitated the separation of spodumene. However, Fe(OH)2+ preferentially reacted with spodumene, whereas Fe(OH)3 preferably reacted with feldspar and quartz, which caused low selectivity of Fe(III) toward spodumene. Similarly, Cu2+ and Cu(OH)+ easily adsorbed on spodumene, whereas Cu(OH)2 preferentially adsorbed on feldspar and quartz. Thus, the selectivity of Cu(II) toward spodumene was inferior compared to those of Ca(II) and Mg(II).

Preparation of PbI2 Microflakes by pH-Controlled Double-Jet Precipitation

Introduction: Pure PbI2 crystal particles with a flaky shape were prepared by a pH-constant double-jet precipitation process, which has the significant advantages of easy operation and scaling-up. It was found that a pH below 5.0 of the mixing solution is the appropriate range for the formation of pure PbI2 phase, while at a pH above 5.0, the PbIOH phase would appear immediately and decrease its solubility in DMF (dimethylformamide) for the preparation of a high-quality film of perovskite solar cells. Materials and Methods: Various instruments, including XRD, FTIR, SEM/EDS were used to characterize the precipitated particles obtained under different experimental conditions, and the effect of various parameters, including pH, concentration of the lead ions, feeding rate, and the characteristics of the surfactants on the particle was investigated systematically. Thermodynamic calculation of species distribution in the solution systems of Pb2+-I-- H2O, Pb2+-I--Cit-H2O and Pb2+-I--EDTA-H2O were carried out to identify the indispensable role of pH on the formation of highly pure lead iodide crystals. The crystallization of PbI2 was regarded as the basis of the formation of flake-like products, which was also strongly dependent on the pH value of the solution. Results: It was found that at a low concentration of the PbI2 precursor, such as with very dilute lead ions or with a very slow feeding rate, the XRD reflection peaks at 12.67°, 38.67° and 52.39° will dominate, while the peaks at 25.91°, 34.27°, and 39.51° will become dominant in the case of high concentration. The lead iodide particles were tested by mixing them in DMF, and it was found that the samples precipitated at a pH of 2 and 4 could dissolve and form a homogeneous solution easily, while the sample produced at a pH of 6 would form a turbid suspension, and could not dissolve completely to obtain a clear solution. Conclusion: The results presented in this work provide detailed and significant information about the synthesis of highly pure PbI2 which may be applied in the fabrication of perovskite solar cells.

Efficient removal of Cu(II) and citrate complexes by combined permanent magnetic resin and its mechanistic insights

Owing to the enormous threat from anthropogenic contamination in water resources, the effective control of heavy-metal pollution has become increasingly important. In this study, the combination of permanent magnetic anion exchange resin (MAER) and magnetic cation exchange resin (MCER) was employed to efficient removal of Cu(II) and citrate acid (CA). The removal mechanisms were systematically investigated by batch adsorption experiments, and also certificated by species distribution calculation, kinetic tests and solid-phase characterizations. The presence of CA markedly inhibited the adsorption of Cu(II) onto MCER, while the co-existing Cu(II) was beneficial for CA uptake onto MAER. With the increase of Cu(II) concentrations, the adsorption amount of CA onto MAER gradually increased and reached a plateau, with promotion rates ranging of 24.4%–47.9%. For combined magnetic resins treatment, as the MAER dosage increased from 0 to 1.50 g/L, the removal efficiencies of CA and Cu(II) were enhanced from 1.1% and 33.2% to 98.8% and 99.1%, respectively. The anionic [Cu-CA] complexes (mainly CuL− and a small fraction of Cu2L22−) in bi-solutes system possessed higher affinity than free-CA species towards MAER, resulting in a mutual enhancement of Cu(II) and CA uptake. Both decomplexing-adsorption of Cu(II) from neutral Cu species (CuHL0) by MCER and direct complex-adsorption of anionic complex species (CuL− and Cu2L22−) by MAER were proposed as the mechanisms for synergetic removal of CA and Cu(II) in combined processes. Furthermore, nanoscale Cu powders were recovered from the desorption liquid by chemical reduction. The combined magnetic resins exhibited superior reusability over five repeated cycles, indicating their great potential in treatment of complexing heavy metal-organic acid wastewaters.

Equilibrium, Kinetic and Structural Properties of Gallium(III) and Some Divalent Metal Complexes Formed with the New DATAm and DATA5m Ligands.

The development of 68 Ge/68 Ga generators has made the positron-emitting 68 Ga isotope widely accessible and raised interest in new chelate complexes of Ga3+ . The hexadentate 1,4-di(acetate)-6-methyl[amino(methyl)acetate]perhydro-1,4-diazepane (DATAm ) ligand and its bifunctional analogue, 1,4-di(acetate)-6-pentanoic acid[amino(methyl)acetate]perhydro-1,4-diazepane (DATA5m ), rapidly form complexes with 68 Ga in high radiochemical yield. The stability constants of DATAm and DATA5m complexes formed with Ga3+ , Zn2+ , Cu2+ , Mn2+ and Ca2+ have been determined by using pH potentiometry, spectrophotometry (Cu2+ ) and 1 H and 71 Ga NMR spectroscopy (Ga3+ ). The stability constants of Ga(DATAm ) and Ga(DATA5m ) complexes are slightly higher than those of Ga(AAZTA). The species distribution calculations indicated the predominance of Ga(L)OH mixed-hydroxo complexes at physiological pH. The 1 H and 71 Ga NMR spectroscopy studies provided information about the coordinated functional groups of ligands and on the kinetics of exchange between the Ga(L) and Ga(L)OH complexes. The transmetalation reactions between the Ga(L) complexes and Cu2+ citrate (6<pH<8.5) occur through both spontaneous and OH- -assisted dissociation of the Ga(L)OH species. At pH 7.4 and 25 °C, the half-lives of the dissociation of Ga(DATAm ), Ga(DATA5m ) and Ga(AAZTA) were 11, 44 and 24 h, respectively. Similar half-lives have been obtained for the ligand-exchange reactions between the Ga(L)OH complexes and transferrin. The equilibrium and kinetic data indicate that the Ga(DATA5m ) complex is a good 68 Ga-based radiodiagnostic candidate.

Structure of Aqueous Lithium Tetraborate Solution

The structure of aqueous lithium tetraborate solutions was investigated by species distribution calculation and synchrotron X-ray scattering. It shows that the dominant species in supersaturated solution at 298.15 K is B4O5(OH) 4 2− and the minor species are B3O3(OH) 5 2− , B3O3(OH) 4 − and B(OH)3. The ‘intramolecular’ structural parameters of B4O5(OH) 4 2− , such as bond length and coordination number, were gives out using density function theory calculation. X-ray scattering study shows that the distance Li–O(H2O)I of [Li(H2O)4]+ is about 0.1983 nm with the coordination number(CN) 4 in tetrahedral configuration. The B–O(H2O) distance in hydrated anion B4O5(OH)4(OH2) 8 2− is 0.3662 nm with the CN 12. The Li+–B distance is about 0.3364 nm with a coordination number ~1.0. The temperature effect on solution structure was also discussed.

Structure of aqueous potassium pentaborate solution

The structure of aqueous potassium pentaborate solution has been confirmed by species distribution calculation, synchrotron X-ray scattering, density function theory calculation. The kinds of species and the transformation relationship were investigated by species distribution calculation. The radial distribution function and the structure parameters were given out by synchrotron X-ray scattering experiment. The hydration distance of K–O(H2O) is ∼0.294nm with a average hydration number of 8.0. The B–O(H2O) distance in hydrated anion [B3O3(OH)4(H2O)n]− were determined to be ∼0.37nm with the hydration number of 4–5. The structure and interaction energy of the first hydration sphere of [K(H2O)n]+ and [B3O3(OH)4(H2O)n]− were also studied by density functional theory calculation.

Structure of aqueous potassium metaborate solution

The structure of aqueous potassium metaborate solutions has been confirmed by X-ray scattering, Raman spectra and species distribution calculation. The optimized structure of B(OH)4− was obtained by density functional theory calculation. The hydration distance and hydration number of K+ in aqueous potassium metaborate solution were given by X-ray scattering. The B–O(H2O) distance in hydrated anion B(OH)4− were determined to be 0.37nm with the hydration number of 2.3 per hydroxyl(–OH). The K–B distance of the contact ions KB(OH)40 was measured to be 0.34nm.

Solvent extraction of rhodium chloride from aqueous solutions and its separation from palladium and platinum

The extraction of Rh chlorocomplexes with trioctylamine (TOA) or with Aliquat 336 (diluted with toluene) and its subsequent separation from Pd and Pt was studied. Species distribution calculations showed that the predominant species of Rh–Cl present in 1 M HCl is Rh(H 2O)Cl 5 2−. Spectrophotometric measurements of Rh–chloride in the organic phase showed that Rh(H 2O)Cl 5 2− is being extracted and slowly converted into a dimer, Rh 2Cl 9 3−. Stripping is carried out with concentrated HCl. It is difficult to separate Rh chlorides from Pd and Pt by solvent extraction, and a gel-chromatographic method is therefore proposed in order to solve this problem.

Experimental determination of the complexation of strontium and cesium with acetate in high-temperature aqueous solutions

Radionuclides are present in contaminated surfacial waters, but their behavior in the presence of natural organic acids is poorly known. Dissociation constants for the strontium acetate (SrCH3COO+) and cesium acetate (CsCH3COO0) ion pair were determined by potentiometry at temperatures from 25 to 175°C at the saturation pressure of water. Logarithms of measured dissociation constants (log K) decrease with increasing temperature, showing that Sr and Cs complexing increases as temperature rises. Log K for SrCH3COO+ decreases from −1.38 at 25°C to −2.10 at 175°C, whereas log K for CsCH3COO0 decreases from 0.00 at 25°C to −0.85 at 175°C. Species distribution calculations performed by means of the experimentally determined dissociation constants in this study suggest that acetate complexes do not dominate either aqueous Sr or Cs speciation in most natural fluids; Cs acetate complexes likely never account for more than a few percent of the total Cs in solution. Although Sr-acetate complexing is more important, it may only dominate in extreme conditions.

The Influence of Mucus on Copper Speciation in the Gill Microenvironment of Carp (Cyprinus carpio)

pH and mucus (as total organic carbon) in the gill microenvironment of carp, Cyprinus carpio, exposed to various concentrations of total copper were measured in an exposure experiment using Playle's apparatus. The activities of free copper ions in both inspired and expired waters were determined using a copper ion selective electrode. A trial-and-error procedure of coupling species distribution calculations (MINEQA2) with single-site complexation modeling (mucus–copper) was proposed for computation of both copper speciation and complexation capacity of gill mucus for copper in an interactive loop. The method was demonstrated to be valid in calculating the metal speciation in this study. It was found that pH and alkalinity in the gill microenvironment were slightly higher than in the surrounding water of pH 6.7. The rates of excretion of CO2, HCO−3, and mucus at the gills increased, either linearly or nonlinearly with increases in the total copper concentration in the surrounding water. The conditional complexation stability constant of the mucus was calculated as log k=5.32, while the complexation stability equivalent concentration of the mucus was derived as 0.95 mmolCu/mgC. As a consequence of changes in pH and alkalinity, in conjunction with occurrence of mucus, copper speciation in the gill microenvironment is significantly different from that in the surrounding water, with 3–20% of the copper complexed by the gill mucus. The sequence of species domination also shifted from CuCO03, Cu2+, CuHCO+3, and Cu(OH)02 in the surrounding water to CuCO03, Cu2+, Cu(OH)02, CuHCO+3, and mucus–Cu in the gill microenvironment.

Solvent Extraction of Gallium With D2EHPA From Acidic Sulphate Solutions—Equilibria and Complexation

Gallium is extracted with di-2-ethyl hexyl phosphoric acid (D2EHPA) from acidic solutions (pH > 0.4–0.5) by a cation exchange mechanism predominantly as GaR3·HR; the stoichiometry of the reaction has been determined and the apparent equilibrium constant (for I = 0.5) is found to be 0.757 mol l−1. The presence of sulphates in the aqueous solution has a significant negative effect on gallium equilibrium distribution. Using the available literature data on mass-stability constants of gallium complexes present in such solutions, a program for calculation of species distribution has been developed. Its predictions are used in interpreting the experimental results for the effect of sulphates on gallium extraction. Résumé Le Gallium est extrait de solutions acides (pH > 0.4–0.5) au moyen de l'acide di-2-ethyl hexy phosphorique (D2EHPA) et principalement par un mécanisme d'échange cationique du type GaR3·HR; la stoichiométric de la réaction a été déterminée et la constante apparente d'équilibre (pour I = 0.5) est évaluée à 0.757 mol l−1. La présence de sulfates en solution aqueuse a un effet négatif significatif sur la distribution d'équilibre du Gallium. À partir de données existantes dans la littérature sur les constantes de stabilité massique des complexes de Gallium présents dans de telles solutions, un programme a été élaboré afin de calculer la distribution des espéces. Les prédictions sont utilisées pour interpréter les résultants expérimentaux des effets des sulfates sur l'extraction du Gallium.

Polymerization reactions in hydrolyzed iron(III) solutions

The hydrolysis and polymerization of iron(III) have been investigated, using the potentiometric titration method, at 25°C in 1 M NaClO 4, KNO 3, KCl and in 1 M NaNO 3 in the presence of sulfate. Species distributions in solution at the end of the equilibrium region (the onset of polymerization reactions) were calculated using the equilibrium speciation models which had been determined for the present work. Assuming that the composition of the polymers is [Fe(OH) 3− j X j/ k ] n where X k− is the anion present in solution, the species distribution calculations show that the values of j in both 1 M KNO 3 and 1 M NaClO 4 medium are 0.0, and 0.5 in 1 M KCl, and 0.6 in 1 M NaNO 3 in the presence of sulfate. These j values are constant over a range of total iron(III) concentration of 0.0002 to 0.020 M. This suggests that Cl − and SO 4 2− are incorporated in the structure of the polymers. The change of n ̃ values (average number of OH − bound per total Fe(III)) from 0.49–1.14 in the solution to 2.37–3.01 in the polymer phase caused the generation of proton during the polymerization process which was manifested as the observed pH relaxation.

Characterization of uranium(VI) in seawater1

The physicochemical characterization of uranium(VI) in seawater is described on the basis of species distribution calculations and experiments using polarography and spectrophotometry in artificial seawater at elevated uranium concentrations. Various dissolved uranium(VI) species are identified under different conditions of pH and carbonate concentration. Below pH 4, the hydrated uranyl ion is present in the “free” state (forming “labile” complexes). Above pH 4, a stepwise coordination of uranyl by the carbonate ion occurs. The monocarbonate complex is formed in the pH range 4–5, the bicarbonate uranyl complex between 5 and 6. Above pH 8, uranium is present predominately as the tricarbonate and to a smaller extent as a trihydroxide complex. There is satisfactory agreement between our experiments and the theoretically computed distribution of uranium(VI) in seawater based on published stability constants.The experiments done at higher concentrations are justified by theoretical distributions showing that there is no great difference in species distribution between the uranium at concentrations of 10−4 and 10−8 mol dm−3.