Pb Phase Research Articles

Large‐Area Lead Monolayers under Cover: Intercalation, Doping, and Phase Transformation

Intercalation is a promising approach for tailoring the electronic structure of epitaxial graphene on SiC. It enables the formation of otherwise unstable 2D phases of elements and allows the investigation of the interplay between the 2D materials and the substrate. Detailed studies have been conducted on the Pb intercalation process, as well as the structure and electronic properties of the 2D Pb layer using low‐energy electron microscopy and photoelectron spectroscopy. The low‐energy bands of Pb show good agreement with density‐functional theory calculations. A uniform Pb intercalation layer with (1 × 1) periodicity with respect to the SiC substrate is found. The quasifreestanding graphene is effectively screened from the doping influence of the substrate, leading to charge neutrality. Instead, the 2D Pb layer compensates for the spontaneous polarization of the substrate, allowing for the doping of a metal layer under cover. A phase transformation from the (1 × 1) intercalation phase into a bubble phase with quasi‐tenfold periodicity with respect to graphene occurs if the system is provided with sufficient energy. These results experimentally quantify the interaction between the 2D Pb layer, the substrate, and the graphene layer, demonstrating a first step toward controlling the diversity of 2D Pb phases.

Bifocal lenses with adjustable intensities enabled by bilayer liquid crystal structures.

In this paper, we propose bifocal lenses based on bilayer structures composed of a liquid crystal (LC) cell and LC polymer, and the relative intensity of two foci can be adjusted arbitrarily through applying an external voltage. Two LC layers have different light modulation functions: when circularly polarized light passes through the first layer, part of the outgoing light is converted with PB phase modulation and another part is not converted; followed by the second layer, PB modulation of these two parts would be simultaneously realized but with opposite signs; thus the transmitted left- and right-handed circularly polarized (LCP and RCP) light can be independently controlled. As proof-of-concept examples, longitudinal and transverse bifocal lenses are designed to split an incident LCP light into two convergent beams with orthogonal helicity, and the position of the two foci can be flexibly arranged. Benefitting from the electrically controlled polarization conversion efficiency (PCE) of the LC cell, the relative intensity of the two foci can be adjusted arbitrarily. Experimental results agree well with theoretical calculations. Besides, a broadband polarization and an edge imaging system based on the proposed bifocal LC lenses have also been demonstrated. This paper presents a simple method to design a functional multilayer LC device and the proposed bifocal lenses may have potentials in the optical interconnection, biological imaging, and optical computing.

High-reliability Sn37Pb/Sn58Bi composite solder joints by solid-liquid low-temperature soldering

As the feature sizes of integrated circuits approach their physical limits, 3D packaging has emerged as a crucial technology for enhancing integration and extending Moore's Law. To meet the future requirements for low-temperature solder and interconnect processes in aerospace 3D packaging, this study combined Sn37Pb solder balls with Sn58Bi solder paste to prepare uniform composite solder joints under reflow conditions of 180°C for 10 minutes (CS-180–10) and 190°C for 1 minute (CS-190–1). The Bi atoms dissolved in the Pb phase strengthened the composite solder and made the crystal structure more ordered and predictable. The composite solder joints formed under both process conditions exhibited shear strengths higher than those of Sn37Pb solder joints prepared at 220°C for 1 minute, both before and after aging at 100°C. The fracture mode of the composite solder joints transitioned from ductile to mixed ductile-brittle with aging. Additionally, the composite solder demonstrated better creep resistance than SnPb solder at all tested strain rates in nanoindentation tests. Compared to CS-180–10, the lower heat input CS-190–1 featured finer Pb phases and Pb grains, better wettability, and better thermal stability. CS-190–1 showed only a 5.9 % decrease in shear strength after 42 days of aging at 100°C. This study offers a new solution for low-temperature, high-reliability interconnections in future aerospace integrated circuit 3D packaging.

Non-Destructive Analysis of Pb-Acid Battery Positive Plates, Based on Neutron Tomography

Lead-acid batteries (LABs) are one of the first rechargeable batteries. Historically used for backup power during the early public electricity network, LABs now hold a global market share of approximately 50%, mainly in automotive applications and energy reserves for telecommunication and data networks. Their low energy density and high surge current make them suitable for high-current, in-time applications. The LAB electrochemical cell consists of PbO2 as the positive electrode, metallic Pb as the negative electrode, and H2SO4 as the electrolyte.The composition of the positive electrode active material (PAM) involves mixtures of α- and β-PbO2 and an amorphous gel phase of Pb(IV) oxy-hydroxides, determining the PAM's functional properties. The hydrated Pb(IV) oxy-hydroxide is the electrochemically active phase, conducting ions but not electrons. The mechanical consistency of the PAM relies on α-PbO2, acting as a structural binder, while β-PbO2 provides electronic conductivity. LAB performance is influenced by the proportions of α and β crystalline zones. Jointly, α - and β -PbO2 act as a Pb(IV) reservoir for reduction, occurring through the gel phase during discharge. Together, α- and β-PbO2 function as a reservoir for Pb(IV) reduction, a process that takes place through the gel phase during discharge in lead-acid batteries (LABs). These two crystalline phases, α- and β-PbO2, reform from the gel phase during charging, and their proportions depend on the specifics of the charging process and the material state. Consequently, the relative amounts and distribution of α and β crystalline zones play a crucial role in influencing the overall performance of LABs.In the present investigation, we propose, for the first time, an ex situ NT investigation of intact PPs, endeavouring to assess the internal structure of the PAM (pore formation) and spine/PAM decohesion of real battery electrodes – fabricated with two alternative metallurgical methods (punching P and gravity casting G) – subjected to harsh electrochemical testing conditions, representative of recharge abuse. Our study is complemented by X-ray radiography - aimed at pinpointing spine and PAM cracking – and cross-sectional SEM imaging aimed at disclosing details with spine/PAM interface: grid shape variation, corrosion depth, mode and mechanism, corrosion layer nature and thickness.The synergic effect of these measurments enable a complete understanding and tracking of the PPs degradation mechanism : (i) NT offered a 3D quantitative and qualitative assessment of PAM porosity ,spine/PAM decohesions, and highly attenuating regions. Aging led to pore growth, with G electrodes displaying more extensive cracking. Variations in porosity distribution between P and G electrodes is observed. Hydrogenated gel distribution differed between electrode types and with aging. (ii) XR provided a non-destructive grid-scale overview. P electrodes exhibited limited defects, while G electrodes showed extensive spine issues. Corrosion progression differed from local SEM observations (iii) in which corrosion is explored at the spine/PAM interface, revealing no clear correlation between current density and corrosion. Representative micrographs for P and G electrodes were shared.The combination of these technique enable a complete characterization of positive plate degradation,.The methodical use of NT holds the potential to establish a comprehensive morpho chemical knowledge base for comprehending the manufacturing and aging processes of lead-acid battery electrodes directly visualization of the 3D arrangement of the hydrogen-containing electroactive amorphous phase, is a crucial metric for assessing the state of health (SOH) that is typically challenging to access experimentally This approach, coupled with in operando capabilities, relies on the quantitative examination of functionally significant features and their changes throughout the aging process. Figure 1

Two types of cubic components coexisting in the paraelectric phase of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 revealed by synchrotron radiation X-ray diffraction

The crystal structures of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3 (PMN) have been investigated using synchrotron radiation X-ray powder diffraction. Two different types of cubic components coexist in the paraelectric phase at 600 K. The first is Cubic-I, in which the Pb ion is isotropically off-centered from the corner of the perovskite-type unit cell. The other, Cubic-II, has the Pb ion preferentially off-centered in the <111> directions from the corner. The volume fractions of Cubic-I and Cubic-II are approximately 83% and 17%, respectively. Previous studies have shown that only approximately 20% of PMN transitions to a rhombohedral structure at 100 K. This observation suggests a close relationship between Cubic-II and the rhombohedral structure at low temperatures. The intrinsic structural inhomogeneity observed in the paraelectric phase, such as variations in the disordering behavior of Pb ions, is potentially linked to the relaxor characteristics of PMN.

Suppression of vortex electromagnetic wave divergence by modulating the wave front dislocation line

Abstract When the beam is transmitted in the atmosphere, under the influence of atmospheric turbulence, the beam will occur energy attenuation, wavefront distortion and other phenomena, which will seriously affect the transmission and reception of information. Based on the PB phase principle enhances the focusing capability of the auto-focusing Airy Gaussian vortex beam by regulating the wavefront error curvature of the vortex beam, and then enhances the resistance of the beam against atmospheric turbulence. The results reveal the curvature of the wavefront error curve and the peak intensity of the light field of the beam can be changed by changing the beam polarization state parameters n and m in the focal plane. The auto-focusing Airy Gaussian vortex beam with the polarization state parameters m=1, n=4 increases the peak magnitude of the light field intensity in the focal plane of the auto-focusing Airy Gaussian vortex beam with the polarization state parameters m=0, n=0 to 1.99 times. Demonstrate that geometric phase tuning the auto-focusing Airy Gaussian vortex beams can enhance resistance to atmospheric turbulence. Furthermore, this paper extends this method to the field of millimeter wave. Under the transmission distance of 1km, the peak intensity of the initial vortex electromagnetic wave after the geometric phase adjustment is increased to 3.33 times, and the receiving radius of the target surface is reduced to 0.24 of the initial vortex electromagnetic wave. It shows that geometric phase-regulated vortex electromagnetic wave can suppress vortex electromagnetic wave divergence and have potential applications in wireless communication.

Microscopic damage in eutectic SnPb alloy: First-principles calculations and experiments

This study aims to comprehensively elucidate the microscopic origins of damage in eutectic SnPb alloy through atomic-scale investigations, a crucial endeavor for enhancing the alloy’s properties and furthering the development of Pb-free solders. First-principles calculations based on density functional theory (DFT) were employed to examine the mechanical constants and defect formation energies of the Pb phase, the β-Sn phase, and potential Sn/Pb eutectic phases in the SnPb alloy. The Voigt-Reuss-Hill approximation was utilized to derive the mechanical parameters of the elastically stable structure in SnPb alloy, facilitating the prediction of its mechanical properties. The defect formation energy calculations revealed a higher difficulty in forming vacancy defects in the β-Sn phase compared to the Pb phase. This discrepancy can be attributed to the stronger interactions between Sn atoms, resulting in the formation of more stable Sn-Sn bonds, thereby impeding vacancy generation in the β-Sn phase. Furthermore, the Pb phase exhibited a tendency for Sn atoms to occupy octahedral interstitial sites, whereas in the β-Sn phase, Pb atoms tended to displace neighboring Sn atoms along the [110] orientation into adjacent interstitial sites and occupy their lattice positions. Experimental observations complemented these calculation findings, demonstrating significant Sn element presence, up to 27.22 at%, in the Pb-rich phase, with notable microvoid damage primarily concentrated within this region. This observation aligns with the conclusions drawn from first-principles calculations and unveils the microscopic origins of damage in eutectic SnPb alloys.

Microstructure and properties of multi-layer laser cladding Cu-10Pb-10Sn anti-friction coating

The preliminary experimental results show that the laser cladding technology can produce a well-formed single-layer lead bronze cladding layer with a thickness of 250 μm. The ideal process parameters of the single-layer laser cladding test were selected to study the multi-layer cladding, and the microstructure and properties of the multi-layer cladding were evaluated. The results show that, the multi-layer cladding is composed of α-Cu, Cu41Sn11, Cu5.6 Sn, Pb, and SnO2 phases. There are fine equiaxed crystals at the top of the cladding layer while columnar crystals growing perpendicular to the fusion line at the bottom. The maximum hardness of cladding layer is 248.2 HV near the bottom fusion line. The wear mechanism of multi-layer cladding layer combines abrasive wear and adhesive wear, with wear weight loss and average friction coefficient of 0.0025 g and 0.1161, respectively. The average shear strength between the substrate and the cladding layer is 129 MPa, the shear fracture mode is ductile fracture. Compared with single-layer cladding, the anti-friction performance of multi-layer cladding is significantly improved.

Efficient Removal of Pb(II) Ion Using Tio2/Zno/Sio2 Nanocomposite from Aqueous Solutions Via Adsorption-Photocatalysis Process

This research aims to investigate the usage of a TiO2/ZnO/SiO2 (TZS) composite prepared via a 24-h hydrothermal process at 180° C to remove Pb(II) through adsorption-photocatalysis. Pb(II) exposure has known health risks, making this study significant. The research explores the impact of pH, the nanocomposite quantity, and contact time in the process. Adsorption-photocatalysis was carried out in the dark for 60 min, followed by irradiation with a 160-watt mercury lamp. The adsorption process of Pb(II) ion removal adhered to the pseudo-second-order model regarding kinetics, while the adsorption isotherm corresponded to the Freundlich isotherm. Additionally, the assessment of photocatalysis kinetics showed that the removal of Pb(II) ions followed a pseudo-first-order model, resulting in a 99.58% elimination of Pb(II) ions. Post-adsorption-photocatalytic treatment, a yellowish precipitate was observed. The XRD pattern result of the yellowish precipitate confirmed the presence of PbO as the formed Pb phase. The study concludes that the TiO2/ZnO/SiO2 nanocomposite as adsorbent-photocatalyst is a highly effective, efficient, and promising method to remove Pb(II) contamination from aqueous solutions.

Lead Speciation, Bioaccessibility, and Sources for a Contaminated Subset of House Dust and Soils Collected from Similar United States Residences.

Residential lead (Pb) exposure is of critical concern to families globally as Pb promotes severe neurological effects in children, especially those less than 5 years old, and no blood lead level is deemed safe by the US Center for Disease Control. House dust and soils are commonly thought to be important sources of Pb exposure. Probing the relationship between house dust and soil Pb is critical to understanding residential exposure, as Pb bioavailability is highly influenced by Pb sources and/or species. We investigated paired house dust and soil collected from homes built before 1978 to determine Pb speciation, source, and bioaccessibility with the primary goal of assessing chemical factors driving Pb exposure in residential media. House dust was predominately found to contain (hydro)cerussite (i.e., Pb (hydroxy)carbonate) phases commonly used in Pb-based paint that, in-turn, promoted elevated bioaccessibility (>60%). Pb X-ray absorption spectroscopy, μ-XRF mapping, and Pb isotope ratio analysis for house dust and soils support house dust Pb as chemically unique compared to exterior soils, although paint Pb is expected to be a major source for both. Soil pedogenesis and increased protection from environmental conditions (e.g., weathering) in households is expected to greatly impact Pb phase differences between house dust and soils, subsequently dictating differences in Pb exposure.

Fabrication of MAX‐Phase Composites by Novel Combustion Synthesis and Spontaneous Metal Melt Infiltration: Structure and Tribological Behaviors

In this work, a new scheme is developed and experimentally tested for fabricating family of MAX–metal composites. This scheme combines the combustion synthesis (CS) process to obtain a porous MAX‐phase skeleton and process of metal melt infiltration spontaneously, which is then used to fabricate Ti3SiC2–TiC–Sn and Ti3SiC2–TiC–(Sn–Pb) composites. The resultant composite samples have an uneven density along the length, which steadily decrease from the point of contact of the sample with the molten tin to the opposite edge. Existence of Ti3SiC2, TiC, Sn, and (Sn and Pb) phases in the composite samples is confirmed using X‐ray diffraction and energy‐dispersive spectroscopy analyses. Comparative tribological characterizations are performed on fabricated Ti3SiC2–TiC–Sn and Ti3SiC2–TiC–(Sn–Pb) composite samples. Herein, these results are compared against standalone Sn and Sn–Pb samples as baseline and reveal major differences in friction and wear mechanisms due to addition of select MAX phases via novel CS process. As a whole, in the present study, a novel synthesis process is established to fabricate MAX‐phase composites and its enhanced tribological behavior and wear mechanisms which can have plethora of applications ranging from aerospace, automotive to biomedical sectors, are validated.

Mechanism of corrosion behavior between Pb-rich phase and Cu-rich structure of high Sn–Pb bronze alloy in neutral salt spray environment

The corrosion behavior and corrosion mechanism of the Pb-rich phase and Cu-rich structure of the Sn–Pb bronze alloy in a high-chloride and high-humidity environment were studied. The phase composition of the bronze alloy was analyzed by observing the metallographic and EPMA element distribution, the potential of the microstructure was characterized by SKPFM. The corrosion products and morphology results after electrochemical and neutral salt spray tests were analyzed. The results showed that the matrix structure of bronze material was composed of Pb-rich phase and Cu-rich structure (α(I) phase and (δ+α(II)) eutectoid). During the corrosion process, the rich Pb phase preferentially corroded as the anode and diffused towards the surroundings, while the rich Cu structure served as the cathode. In the rich-Cu structure, compared with δ, the α phase was used as the anode. The corrosion products on the alloy surface mainly included Cu2O, PbCO3, and Cu2(OH)3Cl. As the corrosion gradually deepened along the depth of α phase, the galvanic couple effect between α phase and δ phase and the “oxygen concentration cell” effect gradually increased.

Application of aqueous extracts of &lt;i&gt;Alternanthera brasiliana, Chromolaena odorata&lt;/i&gt; and &lt;i&gt;Tridax procumbens&lt;/i&gt; plants in remediating lead contaminated soils

Soil washing is an effective method of removing lead from contaminated soils. However, great limitations abound in the choice of washing solution that is ecologically sustainable for agricultural soils. In this study, applications of plant soluble extracts in remediating of Pb contaminated soils for ecological sustainability were carried out. Batch laboratory experiments were done using aqueous extracts of Alternanthera brasiliana, Chromolaena odorata, Tridax procumbens and water as control at varying soil-pulp-densities (SPD) of 3, 6, 9, 12, 15%, and washing time of 1, 3, 6, 12 h. For contaminated soil, percentage removal efficiency followed the order: Alternanthera brasiliana (38.1±0.28%) &gt; Chromolaena odorata (21.8±0.12%) &gt; Tridax procumbens (21.3±0.18%). The most appropriate ratio for contaminated soil was 3% SPD at 12 h washing time. Removal efficiency was found to be substantially depended on geochemical phase of Pb (exchangeable-4.04%) in contaminated soil and washing solution pH (5.68). Lead removal efficiency was observed to increased proportionally with increasing washing time, but decreased with increasing SPD. Spike soil with high exchangeable Pb-78.9% recorded significant Pb removal of 63.4±0.24% with Alternanthera brasiliana, 47.8±0.22% with Chromolaena odorata, 38.3±0.38% with Tridax procumbens and 52.0±0.26% with water. Analysis of variance at p=0.05 indicated a significant difference inpercentage Pb removal efficiency across all the four washing solutions. However, the statistical T-test indicated no significant difference at p=0.05 in percentage Pb removal efficiency between both soils. Also, moderately positive correlations were observed between contaminated and spiked soils for Alternanthera brasiliana (0.676), Chromolaena odorata (0.570) and Tridax procumbens (0.517) while negative correlation observed for water (0.485) which served as the control. The three plant extracts exhibited good potential characteristics as washing solutions for the treatment of Pb contaminated soils. Chemical modifications are recommended to enhance and improve their efficiencies when considering the geochemical phase of Pb in soil.

Quantum criticality at cryogenic melting of polar bubble lattices

Quantum fluctuations (QFs) caused by zero-point phonon vibrations (ZPPVs) are known to prevent the occurrence of polar phases in bulk incipient ferroelectrics down to 0 K. On the other hand, little is known about the effects of QFs on the recently discovered topological patterns in ferroelectric nanostructures. Here, by using an atomistic effective Hamiltonian within classical Monte Carlo (CMC) and path integral quantum Monte Carlo (PI-QMC), we unveil how QFs affect the topology of several dipolar phases in ultrathin Pb(Zr0.4Ti0.6)O3 (PZT) films. In particular, our PI-QMC simulations show that the ZPPVs do not suppress polar patterns but rather stabilize the labyrinth, bimeron and bubble phases within a wider range of bias field magnitudes. Moreover, we reveal that quantum fluctuations induce a quantum critical point (QCP) separating a hexagonal bubble lattice from a liquid-like state characterized by spontaneous motion, creation and annihilation of polar bubbles at cryogenic temperatures. Finally, we show that the discovered quantum melting is associated with anomalous physical response, as, e.g., demonstrated by a negative longitudinal piezoelectric coefficient.

Metallurgical pathways of lead leaching from brass

Leaded (Pb) brass components used in water pipeworks are prone to lead leaching following soldering or brazing during installation. Synchrotron radiation X-ray imaging shows that in the initial state of potable-water grade brass samples, Pb exists mainly as isolated or linked-together particles from sub-micron to several microns large. On heating to the usual soldering temperature of ~200 °C, the Pb contents surface rapidly via diffusion pathways involving an interpenetrating Pb–brass structure with orientation relationship (11bar{1})α-brass//(220)Pb; [011]α-brass//[bar{1}13]Pb. On heating to the usual brazing temperature of 700 °C, the Pb particles melt and expand in volume, with the Pb content forced into the brass lattice preferentially along {101}α-brass planes, forming Pb phase of low sphericity or even large sheets. On immersion in water, the surfaced Pb particles are oxidized to form PbO needles along the normal direction of {bar{2}bar{2}2}PbO planes, which are then easily washed away to cause Pb leaching.

Degeneracy in Intercalated Pb Phases under Buffer-Layer Graphene on SiC(0001) and Diffuse Moiré Spots in Surface Diffraction.

First-principles density functional theory (DFT) is used to analyze the stability of Pb intercalated phases under buffer layer graphene on SiC(0001) as a function of the supercell size, Pb coverage, and degree of Pb ordering. By comparing the chemical potentials of such two-dimensional Pb structures, we find that there is a family of structurally distinct thermodynamically preferred Pb subsurface configurations with minute stability differences. These differences are comparable to the thermal energies at about 450 °C, where the Pb intercalated phases are grown. High-resolution surface-diffraction experiments using Spot Profile Analysis Low-Energy Electron Diffraction (SPA-LEED) confirm this high degree of degeneracy of the Pb intercalated phases from broad, low-intensity moiré spots observed exclusively from intercalated Pb. The low intensity of the moiré spots implies the coexistence of structurally different subsurface Pb phases.

Advancing broadband light structuring through single-size nanostructured all-dielectric meta-devices

Traditional optical components and most artificially engineered structures (metamaterials) used for light manipulation are usually designed for narrow bandwidth and limited functionalities. Furthermore, bulkiness and inefficiency limit their application for integrated devices. Metasurfaces, the ultracompact counterpart of bulky metamaterials, exhibit an unprecedented ability to manipulate incident electromagnetic waves at a micron scale. Metasurfaces have emerged as promising candidates for light structuring and its potential applications, ranging from high-capacity data communication to particle manipulation. Despite significant advancement in metasurfaces, realizing high-performance metadevices exhibiting a broadband light manipulation capability is still challenging due to the material's intrinsic nature and lack of a more straightforward design methodology. Here, we demonstrated a broadband single-cell driven all-dielectric metadevice platform to realize high-performance phase modulation for light structuring over the broad visible spectrum475−650nm. The building block consists of an intelligently optimized nanoantenna made of unique zinc sulfide material that employs the PB phase to realize single-layered broadband metadevices for structured light generation, ensuring a decent average transmission efficiency ηavg=79.9% over the intended band. To prove the concept, we designed numerous metadevices for structured light generation and numerically investigated each under the illumination of selected visible wavelengths. We envisioned that the presented work could accelerate real-life applications such as high-resolution color imaging, optical communication and sensing, quantum information processing, and micromanipulation.

Photo- and Thermal-Induced Ion Migration and Phase Separation in Mn-Doped Two-Dimensional PEA2PbX4 Perovskite.

Ion migration and phase separation in perovskite materials have negatively affected the solid-state lighting and display. Studying photo- and thermal-induced degradation is considered as a promising approach to understanding the luminescence mechanism and promoting practical applications. Herein, the Mn-doped two-dimensional PEA2PbX4 (X = Cl, Br, I) microcrystals with changing halogen composition were synthesized by an acid-assisted post-processing strategy. Then, photo- and thermal-induced degradation was studied by using steady-state and time-resolved photoluminescence (PL) spectroscopy. The band edge exciton PL peak of Mn-doped 2D PEA2PbX4 microcrystals was adjusted from 397 to 500 nm. The reduced Mn PL lifetime (1.37 to 0.21 ms) was monitored under ion exchange from Cl to Br to I. The degradation mechanism could be divided into two cases: (i) The halide ion migration in Mn-doped 2D perovskite under continuous illumination was revealed, suggesting that the migration of Cl ions was more accessible than that of Br and I. (ii) The PL redshift and lifetime reduction were observed after annealing at 420 K, which means that thermally induced aggregation of Mn ions resulted in the formation of Mn2+-Mn2+ dimers. In addition, the experimental results indicated that the induced B-site phase separation at high temperature annealing made the mixed perovskite phase of Pb and Mn ultimately transform into pure PEA2PbBr4 and PEA2MnBr4.

Geochemical fractionation and potential release behaviour of heavy metals in lead‒zinc smelting soils

The lack of understanding of heavy metal speciation and solubility control mechanisms in smelting soils limits the effective pollution control. In this study smelting soils were investigated by an advanced mineralogical analysis (AMICS), leaching tests and thermodynamic modelling. The aims were to identify the partitioning and release behaviour of Pb, Zn, Cd and As. The integration of multiple techniques was necessary and displayed coherent results. In addition to the residual fraction, Pb and Zn were predominantly associated with reducible fractions, and As primarily existed as the crystalline iron oxide-bound fractions. AMICS quantitative analysis further confirmed that Fe oxyhydroxides were the common dominant phase for As, Cd, Pb and Zn. In addition, a metal arsenate (paulmooreite) was an important mineral host for Pb and As. The pH-stat leaching indicted that the release of Pb, Zn and Cd increased towards low pH values while release of As increased towards high pH values. The separate leaching schemes were associated with the geochemical behaviour under the control of minerals and were confirmed by thermodynamic modelling. PHREEQC calculations suggested that the formation of arsenate minerals (schultenite, mimetite and koritnigite) and the binding to Fe oxyhydroxides synchronously controlled the release of Pb, Zn, Cd and As. Our results emphasized the governing role of Fe oxyhydroxides and secondary insoluble minerals in natural attenuation of heavy metals, which provides a novelty strategy for the stabilization of multi-metals in smelting sites.

The effects of iron-rich ultramafic pegmatite on the composition and mineralogy of the UG2 chromitite: a case study in the western Bushveld Complex, South Africa

Discordant iron-rich ultramafic pegmatites (IRUPs) intersect the UG2 chromitite at many places in the Bushveld Complex. The effects of IRUP interactions on the UG2 ore mineralogy and PGE grade are assessed at the Thaba mine, north-west Bushveld, based on a borehole profile through the UG2 layer and detailed analysis of mineral textures and compositional variations across the UG2-IRUP contacts using micro-XRF element mapping. The UG2-IRUP interaction operated at different scales and probably by different mechanisms. At the local scale (< 10 cm), a thin layer of Fe–Ti–Cr spinel and ilmenite formed on the IRUP side of the contact with UG2, whereas the UG2 chromitite developed grain coarsening, loss of interstitial silicates, and chemical gradients in Cr, Al, Fe, and Ti that extend a few centimeters from the contact into the seam. These local effects are attributed to the intrusion of IRUP melt into the solidified UG2 layer, followed by re-equilibration of the oxide minerals across the contact during cooling. On a larger scale, changes in the ore and gangue mineral assemblages in UG2 took place throughout the entire meter-thick main seam. Compared with regional UG2 compositions, chromite has higher TiO2 and lower Mg#, and there is an anomalously low abundance of interstitial plagioclase. The IRUP-affected UG2 shows relatively abundant secondary hydrous silicates, replacement of PGE sulfides by PGE alloys and PGE-As–Sb–Bi–Te–Pb phases, and formation of secondary Ni–Cu–Fe sulfides after pentlandite and chalcopyrite. These large-scale effects are attributed to hydrothermal fluids derived from IRUP melts. The IRUP bodies at the Thaba mine caused redistribution of PGE within the UG2 layer but did not significantly reduce the overall grade. However, significant changes in the ore mineral assemblage and an increased abundance of secondary silicates can reduce the efficiency of PGE recovery.