Diffusion Coefficients Of Pb Research Articles

Zero-carbon inertization processes of hazardous mine tailings: Mineral physicochemical properties, transformation mechanism, and long-term stability

Hazardous mine tailings (HMTs) dam failures can cause devastation to the ecology environment, people's lives and property, which require expensive and complicated remediation engineering systematacially. A cheap and sustainable inertization disposal is proposed for de-risking HMTs without any carbon emissions, stabilizing hazardous heavy metal cations within safety minerals and also sequestering CO2 in the process, simultaneously. Herein, lead-zinc tailings as target HMTs were inertized by using waste rice husk ashes (RHAs) and carbide slag (CS) with a certain ratio, and lead-zinc tailings hardened pastes (LZTHPs) were investigated based on the experimental performance, analytical characteristics, and simulation diffusion methods, to deeply unveil the minerals transformation mechanisms and long-term stability from the cation perspectives. Results revealed that LZTHPs’ compressive strength ranged from 1.04–4.73 MPa and leaching toxicity concentrations of Pb, Zn, Cr, and Cd reached 0.03 mg/L, 1.78 mg/L, 0.01 mg/L, and 0.01 mg/L, respectively. C-S-H gels (Type I and II), cation hydroxides and CO2 mineralization carbonates were the hydrates in LZTHPs. Pb (86%), Zn (78%), Cr (76%), and Cd (65%) were immobilized as residual state, and CO2 mineralization capacity was 0.16 kg/kg. The diffusion coefficient of Pb, Zn, Cr, and Cd below 4.48 × 10−10 cm2/s, 1.39 × 10−10 cm2/s, 4.72 × 10−10 cm2/s, and 0.30 × 10−12 cm2/s, which would be sufficient in most scenarios to adequately stabilize tailings. Diffusion control is the leaching mechanism of cations. After 100 years of simulation diffusion, the diffusion areas of Pb, Zn, Cr, and Cd are 1.33 × 10−3∼1.49 cm2, 2.47 × 10−4∼0.48 cm2, 2.47–8.61 × 10−4 cm2, and 1.49 cm2, respectively, and the environmental impact of LZTHPs was negligible. This study provides promising solutions for alleviating hazardous tailings dangerous, achieving sustainable development with zero-carbon emission, implying the concept of eliminating waste by waste, synchronously.

Interfacial corrosion behavior between O atoms and alloy elements at iron-liquid LBE interface by first-principles molecular dynamics

The interfacial corrosion behavior between LBE adding O atoms and Fe substrate surface containing alloy elements (Cr, Ni, Al, Si) has been studied by first-principles molecular dynamics simulations. Theoretical calculations show that the O atoms in liquid LBE could form the protective oxide layer with the alloy elements (Cr, Al, Si) on the Fe substrate surface at the iron-liquid LBE interface, in which slows down the corrosion process. The estimated mean effective potential energy path suggests that breaking the OSi bond requires the highest energy barrier of 0.61 eV among the doped elements. Besides, the diffusion coefficient shows that Si atom has the lowest value of 0.277 × 10−5 cm2/s, which indicated that adding doped-Si atoms can effectively slow down the corrosion process of the steel. In addition, the diffusion coefficient of Pb, Bi and O atoms in this work is much lower compared with the previous work, indicating that the oxide layer formed at the iron-liquid LBE interface can effectively improve the corrosion resistance of the steel. In a word, this work is instructive for a deeper understanding of corrosion mechanism and provides valuable information for the performance evaluation and material design of the steel under reactor conditions.

Electrochemical extraction of lead from urea−1-ethyl-3-methylimidazolium fluoride system containing PbO at 353 K

Abstract To electrochemically extract Pb from PbO at room temperature, a new electrolyte, urea−1-ethyl-3- methylimidazolium fluoride (urea−[EMIM]F), was synthesized to dissolve PbO. Afterwards, the electrochemical behavior of Pb in this electrolyte was studied. The density, viscosity and conductivity of this electrolyte were investigated before electroextraction. The electrochemical behavior of Pb in the urea−[EMIM]F system was recorded via cyclic voltammograms, chronoamperometry and potentiostatic electrolysis. The results illustrate that Pb can be electrochemically extracted from PbO in this system at room temperature and that Pb reduction involves a quasireversible process and follows a one-step and two-electron transfer process. The reduction of Pb proceeds with a three-dimensional (3D) progressive model. With an increase in temperature, the onset potentials for Pb reduction shift anodically. The diffusion coefficient of Pb(II) is determined to be 6.88×10−10 cm2/s at 353 K. Additionally, spherical Pb particles are obtained after electrodeposition in the urea−[EMIM]F system via potentiostatic electrolysis.

Eco-friendly and facile electrochemical synthesis of sub-micrometer lead powders in deep eutectic solvents using galena as a raw material

The sub-micrometer lead powders were electrodeposited on a mild steel (MS) substrate in PbS-containing (10–50 mM) choline chloride–urea deep eutectic solvent (ChCl–urea DES) at 353 K and 2.5 V. The electrochemical behaviors of the Pb(II)/Pb on MS and glass carbon electrodes were determined by cyclic voltammetry and chronoamperometry measurement. It indicates that the reduction of Pb(II) is a quasi-reversible process. The increase in PbS concentration effectively promotes the EPb(II)/Pb shift in positive direction which can facilitate the reduction of Pb(II). The initial nucleation stage of metallic lead on MS electrode is a three-dimensional instantaneous nucleation for diffusion control and the diffusion coefficient of Pb(II) at 353 K is about 2.40 × 10−7 cm2/s. The three-dimensional sub-micrometer lead particles are agglomerated together and composed of many overlapped lead flakes about 150–200 nm. Moreover, the XRD results reveal that metallic lead can be deposited with a face-centered-cubic structure and the strongest peak intensity is (111) plane. This finding provides a theoretical guidance for the one-step preparation of sub-micrometer lead powders using galena concentrate as raw material by an eco-friendly and facile electrochemical approach in close neutral electrolyte, which can efficiently shorten the production flow and realize the integration of metallurgy and material processes.

An evaluation of stabilised/solidified contaminated model soil using PC-based and MgO-based binders under semi-dynamic leaching conditions.

The leaching performance of stabilised/solidified contaminated model soil was studied to investigate the benefit of stabilisation/solidification treatment using novel binders over conventional binders. Different combinations of Portland cement (PC), ground granulated blast-furnace slag (GGBS), pulverised fly ash (PFA), and magnesia (MgO) were used and grouped into PC-based and MgO-based binders. A semi-dynamic leaching test was used, where the cumulative releases of Zn, Cu, Ni, Pb, Ca, and Mg were measured and the effective diffusion coefficients (De) and the leachability indices (LX) were calculated. The effects of different binders and water/cement ratios (w/c) on the migration of different metals after treatment were also discussed. The results showed that w/c ratio has a significant impact on the cumulative leachability of heavy metals. The diffusion coefficients of Pb and Zn are higher than those of Cu and Ni. In addition, mixes (w/c at 0.5:1) showed better performance in immobilising heavy metals than mixes (w/c at 1:1), especially in the case of Cu, Ni, and Pb.

Electrodeposition of Pb from PbO in urea and 1-butyl-3-methylimidazolium chloride deep eutectic solutions

In this work, urea and 1-butyl-3-methylimidazolium chloride (urea-BMIC) deep eutectic solutions were used as electrolytes for electrodeposition of lead from lead oxide. The electrochemical behavior of Pb (II) ions was investigated by cyclic voltammetry, chronopotentiometry, and chronoamperometry techniques at 353–373K. Cyclic voltammograms and chronopotentiograms indicate that the reduction of Pb (II) ions to Pb is a diffusion-controlled quasi-reversible process and it proceeds via one step two-electron transfer process at −0.38V (vs. Ag). The diffusion coefficient of Pb (II) ions increases from 3.22×10−8cm2s−1 to 1.49×10−7cm2s−1 as temperature increases from 353K to 373K. The activation energy for diffusion is determined to be 83.93kJmol−1. In addition, results from chronoamperometry show that lead deposition involves in a three-dimensional instantaneous nucleation and diffusion-controlled growth. On the other hand, the electrodeposit on a Cu substrate was pure Pb as confirmed by X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS). Scanning electron microscopy (SEM) image indicated that a uniform, dense, and non-dendritic coating with grain size of 3μm in diameter was prepared by potentiostatic electrolysis at −0.4V (vs. Ag). The optimized current efficiency (96.17%) and energy consumption (0.11kWhkg−1) was obtained by potentiostatic electrolysis at −0.4V (vs. Ag) and 373K from urea-BMIC deep eutectic solutions containing 0.072moldm−3 PbO.

Ab Initio Molecular Dynamics Studies of Pb m Sb n (m + n ≤ 9) Alloy Clusters

Structure, stability, and dynamics of Pb m Sb n (m + n ≤ 9) clusters were investigated using ab initio molecular dynamics. Size dependence of binding energies, the second-order energy difference of clusters, dissociation energy, HOMO-LUMO gaps, Mayer bond order, and the diffusion coefficient of Pb m Sb n clusters were discussed. Results suggest that Pb3Sb2, Pb4Sb2, and Pb5Sb4 (n = 2 or 4) clusters have higher stability than other clusters, which is consistent with previous findings. In case of Pb-Sb alloy, the dynamics results show that Pb4Sb2 (Pb-22.71 wt pct Sb) can exist in gas phase at 1073 K (800 °C), which reasonably explains the azeotropic phenomenon, and the calculated values are in agreement with the experimental results (Pb-22 wt pct Sb).

Size evolution of ion beam synthesized Pb nanoparticles in Al.

The size evolution of Pb nanoparticles (NPs) synthesized by ion implantation in an epitaxial Al film has been experimentally investigated. The average radius R of Pb NPs was determined as a function of implantation fluence f. The R(f) data were analyzed using various growth models. Our observations suggest that the size evolution of Pb NPs is controlled by the diffusion-limited growth kinetics (R2∝f). With increasing implantation current density, the diffusion coefficient of Pb atoms in Al is evident to be enhanced. By a comparative analysis of the R(f) data, values of the diffusion coefficient of Pb in Al were obtained.

Electrodeposition of Lead from 1-butyl-1-methylpyrrolidinium Bis(trifluoromethylsulfonyl)amide Ionic Liquid

The electrochemical behavior of lead (Pb) was investigated in an amide-type ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA), containing Pb(TFSA)2. The cathodic and anodic currents corresponding to electrodeposition and stripping of Pb, respectively, were observed by cyclic voltammetry. The formal potential of Pb(II)/Pb couple was found to be −0.68 V vs. Ag/Ag(I), which is more negative by 0.11 V than that of Sn(II)/Sn couple. The diffusion coefficient of Pb(II) at 25°C was 0.8 × 10−7 cm2 s−1, which was close to those of divalent metal species in BMPTFSA. The local change of the viscosity and density of the ionic liquid near the electrode surface during electrodeposition and stripping of Pb was confirmed by electrochemical quartz crystal microbalance. The nucleation process and the morphology of electrodeposited Pb were found to be dependent on the deposition potential, probably due to accumulation of BMP+ at the surface of the negatively polarized electrode.

Clarified sludge (basic oxygen furnace sludge) – an adsorbent for removal of Pb(II) from aqueous solutions – kinetics, thermodynamics and desorption studies

The basic oxygen furnace waste generated in steel plant has been used as a low cost adsorbent for the removal of Pb(II) from aqueous solution. The effect of pH, adsorbent dosage, initial metal ion concentration, contact time and temperature on adsorption process was studied in batch experiments. Results of the equilibrium experiments showed that the solution pH was the key factor affecting the adsorption characteristics. Optimum pH for the adsorption was found to be 5 with corresponding adsorbent dosage level of 5 g/L. The equilibrium was achieved within 1 h of contact time. Kinetics data were best described by pseudo second order model. The effective particle diffusion coefficient of Pb(II) is the order of 10 −10 m 2/s. The maximum uptake was 92.5 mg/g. The adsorption data can be well fitted by Freundlich isotherm. The result of the equilibrium studies showed that the solution pH was the key factor affecting the adsorption. External mass transfer analysis was also carried out for the adsorption process. The thermodynamic studies indicated that the adsorption is spontaneous and endothermic. The sorption energy (10.1745 kJ/mol) calculated from Dubinin–Radushkevich isotherm indicated that the adsorption process is chemical in nature. Desorption studies were carried out using dilute mineral acids to elucidate the mechanism of adsorption. Application studies were carried out considering the economic viewpoint of wastewater treatment plant operations.

Diffusion coefficients of metals and metal complexes in hydrogels used in diffusive gradients in thin films

Diffusion coefficients of metal ions and metal–ligand complexes in hydrogels were measured at ionic strengths of 0.1–100 mmol L −1 using a diffusion cell. The three different types of hydrogel were all based on polyacrylamide and have been commonly used in the technique of diffusive gradients in thin films (DGT), where accurate diffusion coefficients are essential for the assessment of the concentrations of labile metal in solution. There was little difference in the diffusion coefficients of either Cu and Cd measured in gels with thicknesses of 0.4, 0.8 and 1.6 mm, showing that any diffusion boundary layer in solution was negligibly small. The diffusion coefficients of Pb, Ni, Cu and Cd in simple inorganic solutions was independent of ionic strength (1–100 mmol L −1), except at very low ionic strengths (0.1 mmol L −1) where the value of D was 50% lower. This observation is consistent with the gel having a positive charge that creates a Donnan partitioning of cations at the gel surface. Diffusion coefficient of Pb complexes decreased with increasing size of the ligand, in the order of diglycolic acid (DGA), nitrilotriacetic acid (NTA), fulvic acid and humic acid. In freshwaters the contribution of fulvic acid species to measured DGT mass should be considered. No significant difference was found between the rate of diffusion of Cu and Cd through the mostly commonly used gel and the filter membrane at the face of the DGT device. Diffusion coefficients obtained using a gel with small pore size (restricted gel) plus filter membrane were higher than those obtained using the restricted gel alone. It may be necessary to modify the standard DGT equation for restricted gel deployments, to take into account the difference in diffusion between the gel and the filter membrane.

Diffusion coefficients of Pb in AgPb determined by surface segregation studies

Due to experimental issues, atomic transport kinetics in nanostructures is still rarely quantitatively investigated despite its significant importance for the design of nanostructure fabrication processes and the prediction of nanoobject structure and physical property ageing. Atomic diffusion in nanostructures is expected to be mainly mediated via atomic transport in interfaces. However, in order to fully understand atomic transport in nanostructures, it is necessary to develop experimental methods allowing for the measurement of diffusion coefficients in nanovolumes, in interfaces, and in interface intersections. To date, this type of measurement has been essentially performed in nanocrystalline materials, giving access to diffusion measurements in nanocrystals corresponding to the nanograins, in grain boundaries corresponding to the interfaces between disoriented crystals of same nature, and in triple junctions corresponding to the grain boundary intersections. This chapter presents the current methods and techniques reported in the literature that have been used for such a type of measurement. Some of the original observations concerning atomic transport in nanocrystalline materials are also presented and discussed.

Study of Pb(II) in various H 2O-H 2SO 4 mixtures by differential pulse polarography: solubility of lead sulphate, diffusion coefficient of Pb(II) and half-wave potential of Pb(Hg)/Pb(II)

A study of some properties of Pb(II) in solutions of sulphuric acid was carried out by means of differential pulse polarography. The range of concentrations of acid extended from 0.6 to 70 weight % of H 2SO 4 (0.06-11.5 M). Determination of the solubility of lead sulphate was found to be in good agreement with NBS's results in the range of H 2SO 4 concentrations they studied. With increasing concentration in H 2SO 4, the diffusion coefficient was found to decrease more than expected from the Stokes-Einstein equation, while the standard potential of Pb/Pb(II) related to she was found to increase. This led to a more important self-discharge of the negative electrode of the lead-acid battery.

Leaching mechanism of PbOSiO 2 glasses in acid solution

The leaching mechanism of xPbO(100- x)SiO 2 glasses ( x=35, 40, 50, 55, 60 mol%) in a nitric acid has been investigated by solution analysis and surface analysis. It was observed that the removal of Pb depended on PbO content in a complicated way. For short periods of leaching, the removal of Pb increases gradually with the PbO content up to 50 mol% and remains at a nearly constant value at more than 50 mol%. For longer periods, it increases gradually with the PbO content in all concentration regions. This result is well explained by the combination of two types of mechanisms. One is the selective leaching of Pb and the other is the dissolution of the glass surface or the leached layer with residual Pb. The selective leaching of Pb is considered to be controlled by the interdiffusion of Pb 2+ and H + ions. The diffusion coefficients of Pb 2+ and H + ions were determined by a numerical analysis from the Pb in-depth profiles in the leached layer.

Metastable precipitation kinetics in NaCl:Pb 2+ crystals at room temperature

The RT precipitation kinetics have been studied for the metastable phase in NaCl:Pb 2+ crystals by precise density measurements. The results obtained seem to be unaccountable in terms of the diffusion-controlled growth of constant or increasing number of particles. The observed process is concluded to be a coalescence (Ostwald ripening). At the late stage the experimental data fit the t − 1 3 law for solute depletion predicted by the asymptotic coalescence theory of Lifshitz and Slezov. A diffusion coefficient of Pb 2+ in the NaCl lattice and the particle size have been estimated by using the theory.

PbTe-Pb1−xSnxTe superlattices prepared by a hot wall technique

The PbTe-Pb0.8Sn0.2Te superlattices were made by the hot wall technique on BaF2 substrates. Two superlattices with the period thickness of 100 and 200 Å were analyzed by sputtering-Auger electron spectroscopy and good results were obtained. The interdiffusions of Pb and Sn across the junction were also investigated and the diffusion coefficients of Pb and Sn at 300 °C were found to be 1.8 and 2.9×10−17 cm2/sec, respectively.

Rapid ion-exchange techniques for radiochemical separations

The short-lived nuclear isomers, Pb 207 m (0·8 sec) and Ir 191 m (4·9 sec) have been identified and characterized after rapid anion-exchange separation from their long-lived parents, Bi 207 (8 years) and Os 191 (16 days). Diffusion of daughter activities from the resin to solution phase is sufficiently rapid to permit satisfactory separation from the parent activities. In the strong base anion exchanger used, the diffusion coefficient of tracer Pb(II) was found to be 7·8 × 10 −8 cm 2/sec at 25°C. The yield of the Pb 207 m separation, as calculated from diffusion theory and the measured diffusion coefficient of Pb(II), is in fair agreement with that observed. Results are discussed in regard to general applicability of the ion-exchange technique for rapid separations.

Preparation and Properties of Lead Telluride

Single crystals of lead telluride, , have been prepared and their resistivity and Hall coefficients determined. Both n‐ and p‐type lead telluride have been produced, but they were not of high resistivity. Charge carrier concentration in every case has been . Hall mobility of n‐ and p‐type carriers was found to be about 2240 and 860 cm2/volt‐sec, respectively.Material of p‐type was converted to n‐type by allowing lead to diffuse into the crystal at 500°C. The value of the diffusion coefficient of Pb in at this temperature is estimated to lie between .