Vacuum Separation Research Articles

Separation and purification of Ag and Se via vacuum thermal decomposition-volatilization of Ag2Se

In this study, theoretical and experimental investigations of the green separation and purification of Ag and Se from Ag2Se are conducted under vacuum. The vacuum separation theory calculation results indicate that the vapor pressure of Se is significantly higher than those of Ag and Ag2Se. Furthermore, the separation coefficient of the Se-Ag binary system is in the range of 104–105, and the Se content in the vapor phase exceeds 99.99 wt%. In contrast, the theoretical calculation results of vacuum thermal decomposition show that Ag2Se decomposes to Se2 (g) and Ag (l) at 1326.74 and 1488.21 K when the pressures are 1 and 10 Pa, respectively. The vacuum separation and purification experiments demonstrate that the purity of Se in the volatiles reaches 97.22 wt% at 1523 K, 50 Pa, and 480 min, and the main phase is the pure Se phase. Moreover, the purity of Ag in the residue reaches 91.88 wt%, and the main phase is the pure Ag phase. The vacuum thermal decomposition-volatilization proposed in this study can achieve environmentally friendly, short separation and purification of Ag and Se in Ag2Se.

Activity Calculation and Vacuum Separation Theoretical Research concerning Ag–Cu, Ag–Sb and Cu–Sb Binary Alloys

The Ag–Cu–Sb system is a key component of lead anode slime and boasts an exceptionally high economic recovery value. In this work, six models, including the Molecular Interaction Volume Model (MIVM), Modified Molecular Interaction Volume Model (M-MIVM), Wilson equation, Miedema model, Regular Solution Model (RSE) and Sub-Regular Solution Model (SRSE), are used to calculate the predicted values of the activity and its deviations with experimental data for binary alloys in the Ag–Cu–Sb system for the first time. The result reveals that the overall means of the average relative deviation and average standard deviation of the M-MIVM are 0.01501 and 3.97278%, respectively, which are about two to six times smaller than those of the other five models, indicating the stability and reliability of the M-MIVM. In the meantime, the predicted data of the Cu–Ag binary alloy at 1423 K, Sb–Ag binary alloy at 1250 K and Sb–Cu binary alloy at 1375 K calculated from the M-MIVM are more reliable and pass the Herington test. Then, the separation coefficient–composition (β–x), temperature–composition (T–x–y) and pressure–composition (P–x–y) of the Cu–Ag, Sb–Ag and Sb–Cu binary alloys are plotted based on the M-MIVM and vacuum theories, showing that the Cu–Ag binary alloy is relatively difficult to separate and that high temperatures or high copper contents are detrimental to obtaining high-purity silver. Meanwhile, theoretical data of the T–x–y diagram are consistent with the available experimental data. These results can guide vacuum separation experiments and industrial production concerning Ag–Cu, Ag–Sb and Cu–Sb binary alloys.

Vacuum evaporation and condensation thermodynamics and evaporation kinetics of pure silver

A comprehensive analysis of the characteristics of vacuum evaporation and condensation of pure silver is crucial for advancing vacuum separation and purification technology for crude silver. This study analyzes the vacuum evaporation and condensation thermodynamics and evaporation kinetics of pure silver. The results reveal a substantial increase in the saturated vapor pressure and theoretical maximum evaporation rate of pure silver with increasing temperature. When the temperature is in the range of 1373 ∼ 1773 K and the pressure is in the range of 0.1 ∼ 10 Pa, the average molecular free path is between 0.514 ∼ 66.415 cm. Moreover, the mean molecular free path of silver increases with increasing temperature and decreasing pressure. Besides, the silver triple point occurs at a temperature of 1234.78 K and a pressure of 0.343 Pa. The average evaporation rate of pure silver demonstrates a linear relationship with temperature, and the relationship with pressure conforms to the Logistic model. Notably, the vacuum evaporation of pure silver is a first-order reaction. Furthermore, in this study, the kinetic equation of vacuum evaporation of pure silver is established. In the temperature range of 1473–1673 K, the gas phase mass transfer is the rate-controlling step rather than the mass transfer in the gas phase boundary layer. As the temperature increases, the rate-controlling step gradually changes into gas relative flow mass transfer and gas-liquid interface evaporation mass transfer.

Clean and sustainable elimination of arsenic–aluminum slag from smelted crude tin via vacuum volatilization – Fractional condensation

In high–tech industries, Sn is an indispensable strategic metal. However, the pyrometallurgical refining process of crude Sn is marred by the production of a substantial amount of hazardous solid waste, primarily As–Al slag, which poses a direct threat to the ecological safety of production areas. To address this problem, this study developed a novel process for that eliminates As–Al slag from a source of crude Sn by employing a vacuum volatilization – fractional condensation process, which was validated by theoretical calculations and laboratory experiments. Theoretically, at system pressures in the 1–10 Pa, the initial volatilization temperatures of Sn, Sb, and As vary significantly. However, the formation of intermetallic compounds can induce the volatilization of Sn. Experimentally, the condensation temperature for Sb was predominantly between 603 K and 810 K, and that for As was between 331.7 K and 484.7 K, which are significantly different ranges. Under optimal experimental conditions, the separation rate of Sb in the Sn–Sb alloy was 93.92%, and the resultant Sn product contained 0.0143% Sb. During the volatilization of the Sn–As alloy, the presence of Sn4As3 compounds impeded the volatilization of As; hoewver, the As content in the Sn product was 0.0053%. In the directional condensation of the As–Sb alloy, the condensation temperatures for As and Sb were similar to those of the pure metals, yielding As and Sb products with purities of 99.99% and 99.95%, respectively. Industrial production trials treating HACT via a continuous vacuum separation – intermittent vacuum separation process achieved direct recovery rates of 72.99% for Sn and 71.15% for Sb, with a total energy consumption as low as 1086 kWh/t. Similarly, the treatment of LACT via a multi–stage continuous vacuum separation process yielded residues that satisfied production standards at a treatment cost of 1187 RMB/t. This entire process requiresno additives, and substantially mitigates the generation of As–Al slag at the source.

Oxidation transformation and vacuum separation for direct preparation of antimony trioxide products from lead anode slime

Antimony, a crucial metal resource, plays a significant role in various important fields. This study developed an environmentally and efficient technology for the preparation of antimony oxide, which consists of oxidative transformation and vacuum separation of lead anode slime (LAS). The chemical environment in which each substance is subjected to changes, causing the substances containing Sb and As to both be oxidatively transformed into Sb2O3 and As2O3 in the oxidation section. In a further vacuum ambiance, As2O3 and Sb2O3 are volatilized into the gas phase, respectively. analysis results confirm that the antimony trioxide product isolated and prepared was a high-quality nanoscale cubic crystalline Sb2O3 powder. The novel method effectively combines the oxidation and volatilization properties of each Sb-containing and As-containing materials, enabling the efficient recovery of valuable Sb metal resource from LAS while ensuring safe and sustainable avoidance of arsenic contamination. Most importantly, the whole process generates no waste that could harm the environment. Overall, these findings provide a convenient and eco-friendly approach for extracting valuable metals from secondary resources containing antimony.

Introducing the embedded random phase approximation: H2 dissociative adsorption on Cu(111) as an exemplar

The random phase approximation (RPA) as a means of treating electron correlation recently has been shown to outperform standard density functional theory (DFT) approximations in a variety of cases. However, the computational cost of the RPA is substantially more than DFT, especially when aiming to study extended surfaces. Properly accounting for sufficient surface ensemble size, Brillouin zone sampling, and vacuum separation of periodic images in standard periodic-planewave-based DFT code raises the cost to achieve converged results. Here, we show that sub-system embedding schemes enable use of the RPA for modeling heterogeneous reactions at reduced computational cost. We explore two different embedded RPA (emb-RPA) approaches, periodic emb-RPA and cluster emb-RPA. We use the (experimentally and theoretically) well-studied H2 dissociative adsorption on Cu(111) as our exemplar, and first perform full periodic RPA calculations as a benchmark. The full RPA results match well the semi-empirical barrier fit to experimental observables and others derived from high-level computations, e.g., from recent embedded n-electron valence second order perturbation theory [Zhao et al., J. Chem. Theory Comput. 16(11), 7078–7088 (2020)] and quantum Monte Carlo [Doblhoff-Dier et al., J. Chem. Theory Comput. 13(7), 3208–3219 (2017)] simulations. Among the two emb-RPA approaches tested, the cluster emb-RPA accurately reproduces the energy profile (maximum error of 50 meV along the reaction pathway) while reducing the computational cost by approximately two orders of magnitude. We therefore expect that the embedded cluster approach will enable wider RPA implementation in heterogeneous catalysis.

A multi-stage volatilization and condensation process for green and efficient recovery of valuable metals from High-Sb crude Sn

Circulation of Sb in an Sn refining system strongly affects the production process. In this study, an innovative multi-stage vacuum separation process was developed and successfully applied on an industrial scale. Our results indicate that Sn–Sb alloys can be completely separated by vacuum evaporation. In this study, we used single-factor experiments to investigate the effects of distillation temperature and time on several factors, such as the Sn content in the residue, Sb content in the volatile matter, separation rate, and direct recovery rate of Sb from high-Sb crude Sn. The purity of the obtained Sn and Sb products was above 99%, and the recovery rate of the metal was above 99% under the optimal distillation conditions of 1673 K and 150 min. In addition, we suggest that Sn volatilization occurs due to the presence of SbSn intermetallic compounds. A two-stage vacuum-separation process for high-Sb crude Sn was developed for industrial production. Continuous production data showed that the direct yields of Sn and Sb were 72.99% and 71.15%, respectively. The total power consumption of this process was as low as 1086 kWh/t, which is better than the corresponding parameters of other treatment processes.

Separation of mixture of Sb2S3-PbS, Sb2S3-FeS, PbS-FeS by vacuum distillation

To provide technical guidance for the vacuum distillation and separation of sulfide in lead-antimony-iron sulfide ore, the vacuum distillation and separation of pure antimony-lead sulfide, antimony-iron sulfide, and lead-iron sulfide was carried out. The PbS–Sb2S3 mixed separation experiment under 5 Pa shows that to obtain high purity antimony sulfide volatiles, the distillation temperature must be lower than 650 °C, and to obtain high purity lead sulfide in the residue, the distillation temperature should be higher than 750 °C, and beyond 80 min to promote the evaporation of antimony sulfide to the gas phase completely. The PbS–FeS mixed separation experiment under 5 Pa shows that to achieve the separation of lead and iron sulfide, the distillation temperature must be higher than 900 °C. Theoretical calculation shows that antimony sulfide may be decomposed at 700 °C under 5 Pa. Therefore, 650 °C is the most suitable temperature. Neither lead nor ferrous sulfide undergo decomposition reactions under 5 Pa in this study.

Theoretical calculation and experimental investigation on vacuum gasification separation of Ag-Cu-Au ternary alloy

In this study, an innovative method for vacuum gasification separation of Ag-Cu-Au alloy was proposed. The saturated vapor pressure of each component is calculated theoretically, and the activities of Au-Cu and Ag-Cu-Au alloys are calculated by molecular interaction volume model (MIVM). The results show that the activities of Au-Cu alloy calculated by MIVM is accurate and reliable. Based on activity prediction, the separation coefficients of Au-Cu alloy were calculated. The results show that the separation coefficients of Au-Cu alloy are between 0.0037 ∼ 0.6626 in the temperature range of 1337–1773 K. Subsequently, the vapor-liquid equilibrium composition and vapor-liquid equilibrium phase diagram of Au-Cu and Ag-Cu-Au alloys were calculated, and the vapor-liquid equilibrium measurement experiments of Ag-Cu-Au alloy were carried out. The results show that vacuum gasification is challenging to realize the separation of Au-Cu alloy. During the vacuum gasification separation process of Ag-Cu-Au alloy, silver volatilizes into the vapor phase. When the pressure is 10 Pa and the mole fractions of silver, copper and gold in the liquid phase are 0.2, 0.1 and 0.7, respectively, the equilibrium temperature is 1545.5 K, and the mole fractions of silver, copper and gold in the vapor phase are 0.994, 0.002 and 0.004 respectively. The corresponding experimentally determined mole fractions of silver, copper, and gold in the vapor phase were 0.9666, 0.0333, and 5.89 × 10−5, respectively. In addition, the distribution and occurrence state of each element in the vacuum separation process of Ag-Cu-Au alloy were determined by EPMA.

Clean and efficient separation process for high-antimony crude tin

Antimony circulates in a tin refining system, which strongly affects the production process. In this study, continuous vacuum separation and discontinuous vacuum separation processes were developed for high-antimony crude tin (HACT). During the industrial treatment of 60 t of HACT, product I of crude Sn and Sn–Sb alloy I were obtained by continuous vacuum separation at a temperature of 1473 K and pressure of 20–100 Pa. Then, Sn–Sb alloy I produced crude Sb and Sn–Sb alloy II via intermittent vacuum separation at 1273 K and 20–150 Pa. Finally, Sn–Sb alloy II was subjected to intermittent vacuum separation without adding any reagents, which generated no waste gas or water. The direct yields of Sn and Sb were 72.99% and 71.15%, respectively, while the total power consumption of the described process was as low as 1086 kWh/t, which were superior to the corresponding parameters of other treatment processes. This paper reports a novel clean and efficient HACT industrial treatment method with an open Sb circuit from the Sn refining system.

Near-field radiative heat transfer between irregularly shaped dielectric particles modeled with the discrete system Green's function method

Near-field radiative heat transfer (NFRHT) between irregularly shaped dielectric particles made of SiO2 and morphology characterized by Gaussian random spheres is studied. Particles are modeled using the discrete system Green's function (DSGF) approach, which is a volume integral numerical method based on fluctuational electrodynamics. This method is applicable to finite, three-dimensional objects, and all system interactions are defined independent of thermal excitation by a generalized system Green's function. The DSGF method is deemed suitable to model NFRHT between irregularly shaped particles after verification against the analytical solution for chains of two and three SiO2 spheres. The NFRHT results reveal that geometric irregularity in particles leads to a reduction of the total conductance from that of comparable perfect spheres at vacuum separation distances smaller than the particle size, a regime in which NFRHT is a surface phenomenon. At vacuum separation distances larger than the particle size, NFRHT becomes a volumetric process, and the total conductance between irregularly shaped particles converges to that of comparable perfect spheres. Spectral analysis reveals, however, that particle irregularity leads to damping and broadening of resonances at all separation distances, thereby highlighting the importance of the DSGF method for spectral engineering in the near field. The reduced spectral coherence when particle size is larger than the vacuum separation distance is attributed to coupling of surface phonon-polaritons within the randomly generated, distorted particle features. For particle size smaller than the vacuum separation distance, resonance broadening and damping is linked with the multiple localized surface phonon modes supported by the composite spherical harmonic morphologies of the Gaussian random spheres.

Investigation on the occurrence state and distribution behavior of elements in the separation and purification of crude silver by vacuum volatilization - Fractional condensation

In this paper, an innovative idea of vacuum separation and purification of crude silver is proposed, and theoretical calculations and kilogram-scale experimental studies are carried out. The theoretical calculation results show that the order of saturated vapor pressure and theoretical maximum volatilization rate of each element in crude silver is Se > Te > Sb > Bi > Pb > Ag > Cu > Au. In the temperature range of 1373–1773 K, the separation coefficient and vapor-liquid equilibrium composition of Ag-Au and Ag-Cu alloys were calculated. The experimental results show that the crude silver is mainly composed of Ag-Au and Ag-Cu-Se-Te phases. Under the optimal experimental conditions, the total volatilization rate of crude silver after primary vacuum separation and purification was 90.36%, and the distribution rates of gold and silver in the residue were 98.26% and 1.10%, respectively. The secondary vacuum separation and purification of the first and second order condenser volatile from the primary vacuum separation and purification were carried out, and gold was enriched 149 and 128 times in the residue, respectively, and the main phases of the volatiles were Ag, Ag2Se and Ag2Te, of residue were Au-Sb phase, Au-Cu phase and Au-Ag-Cu phase.

Theoretical calculation and experimental study on the separation mechanism of PbS-Sb2S3

Jamesonite (Pb4FeSb6S14) is a complex antimony sulfide mineral and an important raw material for the extraction of lead and antimony. Under vacuum conditions, the internal interaction mechanism of PbS and Sb2S3 during thermal decomposition is unclear and difficult to separate. In order to explore the interaction mechanism between PbS and Sb2S3, the thermodynamic data of Pb-S and Sb-S systems were firstly calculated by thermodynamic calculation method, PbS and Sb2S3 cluster substances that may exist in the gas phase were obtained under the given temperature conditions. On this basis, ab initio molecular dynamics was used to calculate the mean square displacement and diffusion coefficient of PbS and Sb2S3 gas phase clusters. The vacuum distillation experiments of lead sulfide and antimony trisulfide confirmed the volatilization and diffusion of PbS and Sb2S3, and verified the theoretical calculation results. According to the experiment, the volatilization temperature of Sb2S3 is much lower than that of PbS. The theoretical calculation results are consistent with the experimental results, which indicates that the calculation of the diffusion properties of PbS and Sb2S3 gas phase clusters by molecular dynamics simulation is reliable. This is also an effective and simple method to predict whether the mixed melt of PbS and Sb2S3 can be separated, which provides theoretical guidance for the vacuum separation of PbS and Sb2S3.

Theoretical research on vacuum separation of Au−Ag alloy

To provide an accurate prediction of the product component dependence of temperature and pressure in vacuum distillation and give convenient and efficient guidance for the designing of the process parameters of industrial production, according to the molecular interaction volume model (MIVM), the separation coefficient (β) and vapor−liquid equilibrium composition of Au−Ag alloy at different temperatures are calculated. Combined with the vapor−liquid equilibrium (VLE) theory, the VLE phase diagrams, including the temperature−composition (T−x) and pressure−composition (p−x) diagrams of Au−Ag alloy in vacuum distillation are plotted. The triple points and condensation temperatures of gold and silver vapors are calculated as well. The results show that the β decreases and the contents of gold in vapor phase increase with the distillation temperature increasing. Low pressures have positive effect on the separation of Ag and Au. The difference between the condensation temperatures of gold and silver is about 450 K in the pressure range of 1−10 Pa.

Enhancing removal of hydrogen from granular polysilicon by innovating vacuum separation model and method for SoG-Si

Silane process of granular polysilicon has become a promising method for the preparation of polysilicon due to its continuous low temperature, simple process and low energy consumption. However, granular silicon contains more hydrogen than conventional columnar silicon, which can result in the deterioration of single crystal furnace thermal field life and rod stability by the “hydrogen jump” in the process of Czochralski method. Hydrogen removal has become an important problem to be solved in the industry development. Thus, we propose a hydrogen separation model suitable for silicon system based on vacuum experiment and thermodynamic calculation, which can provide a theoretical basis for the research and development of silicon dehydrogenation method. The predicted removal rate of hydrogen at different temperatures and vacuum pressures is in good agreement with the experimental results, reflecting the reasonability of the model. The results show that the hydrogen removal rate increases with the increasing of temperature and the decreasing of pressure, where temperature plays a leading role in the removal of hydrogen in silicon. At less than one atmosphere, the increase in dehydrogenation rate by 1 °C ranges from 0.01% to 0.25% in the temperature range from 1450 to 1800°CAt temperatures below 1800°Cthe maximum dehydrogenation rate is less than 0.001% for each 1pa reduction in pressure from one atmospheric pressure to 1000pa. According to the model calculation results, a hydrogen removal method is designed by using the vacuum electromagnetic induction. The deep removal of trace hydrogen in silicon has been realized, hydrogen in silicon drops rapidly from around 20 ppm to less than 5 ppm.

Application of modified molecular interaction volume model for phase equilibrium of PbS–Sb2S3 system in vacuum distillation

In this paper, the modified molecular interaction volume model (M-MIVM) was used to calculate the activities of components of the PbS–Sb2S3 binary matte system. On this basis, the vapor-liquid equilibrium (VLE) data of the PbS–Sb2S3 system were calculated by M-MIVM in combination with the theory of vacuum metallurgy and VLE. Additionally, the VLE experiment of the PbS–Sb2S3 binary matte system was conducted to correctly interpret the results of the model. The calculated results of the VLE of the model were consistent with the experimental values, and the VLE calculation of the PbS–Sb2S3 binary matte system by M-MIVM was reliable. This is an effective and convenient method to predict the relationship between product components with temperature and pressure in vacuum distillation of PbS and Sb2S3 mixed melts, providing theoretical guidance for vacuum separation and purification of PbS and Sb2S3.

Reduction of Volatile Impurities in Zinc Chloride Melt with Metallic Iron and Its Effect on Vacuum Separation Behavior

Reduction of Volatile Impurities in Zinc Chloride Melt with Metallic Iron and Its Effect on Vacuum Separation Behavior

Amino acids adsorption onto the (111) surface of cubic zirconia: a density functional theory study

The adsorption of six amino acids onto (111) surface of cubic ZrO2 was theoretically investigated using density functional theory (DFT). DFT calculations with D3 dispersion correction were carried out with the PBE exchange–correlation functional. Mechanism, molecular adsorption structures, and energies were calculated. The (111) surface of cubic ZrO2 was modeled using a slab with 9 atomic layers (81 atoms). The slab thickness was 7.3 A, and a vacuum separation of 12 A was used with periodic boundary conditions. The results showed that the order of the molecular adsorption energies is ASP > HYP > GLY > ALA > LYS > PRO. Furthermore, adsorption of amino acids on the zirconia surface showed complete hydrogen transfer from GLY, ALA, HYP, and ASP to the surface. For LYS and PRO, hydrogen transfer does not occur. Topological analysis of the electron localization function (ELF) was applied to study the nature of the molecule-surface interactions. It was found that the dissociation of molecules and strong chemical bonds of adsorbed atoms to surface oxygen atoms play an important role in the adsorption mechanism.

Arsenic Removal and Recovery of Germanium and Tungsten in Toxic Coal Fly Ash from Lignite by Vacuum Distillation with a Sulfurizing Reagent.

Every year, billions of tons of lignite are burnt to generate electricity, meanwhile generating large amounts of coal fly ash (CFA) that is regarded as an industrial waste. During lignite combustion, arsenic and scarce metals are simultaneously volatilized in the form of oxide into CFA. This study proposed an effective vacuum distillation method to remove As and recover Ge and W from CFA. The feasibility of separating As and recycling Ge and W from CFA was verified by the theoretical analysis. The experimental result indicated that the removal ratio of As was 96 ± 1% and the contents of Ge and W reached 0.75 ± 0.023 and 0.24 ± 0.016 wt % in the residue, which were enriched 17.2 and 1.2 times, respectively, at a temperature of 550 °C, with 50 wt % sulfurizing agent added under pressure of 1 Pa and 240 min of heating. For the condensed product, chemical species As2S3 and As4S4 were detected by X-ray photoelectron spectroscopy analysis. For Ge and W in the residue, GeOx (x < 2), GeS, WOx (x < 3), and WS2 were the main chemical species. The potential mechanism involved in the release of arsenic from CFA, vacuum sulfurization, evaporation, and condensation was proposed. The kinetic analysis indicated that the apparent activation energy (Eα) was 31.24 kJ mol-1. Those results encourage further exploration of vacuum separation technology to environmentally friendly recycle CFA.

Sustainable chemical reaction-free vacuum separation process to extract selenium from high-value-added hazardous selenium sludge

High-value-added hazardous selenium sludge extracted from copper anode slime may cause serious selenium contamination and potential threats to human health if improperly treated. In this study, a sustainable chemical reaction-free vacuum separation process was used to extract selenium and recycle valuable metals from selenium sludge. The process comprises low-pressure dehydration and Se extraction by vacuum distillation. The laboratory-scale results indicate that 90.76% of selenium was extracted from volatiles at a purity of 98.68% under the optimum distillation conditions of 693 K, 90 min and 30–50 Pa. Ag and Au were enriched to 28004 g/t and 1226 g/t in residues from 2560 g/t and 112 g/t, respectively, in raw materials, representing increases of 10.4 and 10.25 times. On this basis, a low-pressure melting-vacuum distillation process and equipment with an annual selenium sludge disposal capacity of 500 metric tons were developed for industrial production. The continuous production data show that the purity of the extracted selenium always exceeded 98.0%, the direct yield ratio of selenium exceeded 96.5%, and the consumption was only 1150 kW h electricity per ton of selenium ingot output. Additionally, Ag and Au were enriched by over 11 times in the residue. The discharged water evaporated, and residues were returned to the comprehensive copper anode slime treatment process for the further valuable metal extraction. Compared with chemical processes, the proposed technology consumes fewer resources and reduces the environmental impacts, resulting in better economic and sustainability assessment results. The proposed process meets the demand for cleaner production within the selenium metallurgical industry.