Joint utilization and harmless elimination of aluminum dross and refined magnesium slag to simultaneously recover metallic aluminum and fusing agent.

Refined magnesium slag and aluminum dross are two typical hazardous solid wastes that contain significant amounts of leachable fusing agent and aluminum droplets encapsulated by dense oxidized films, respectively. This study creatively proposes a safe and green method for the joint utilization of these two wastes. The interfacial reaction behavior revealed that the dense oxidized films of the aluminum droplets were significantly broken by the erosive action of the fusing agent, providing the necessary conditions for the movement of aluminum droplets. Consequently, the aluminum droplets successfully broke free from the oxidized films and separated together with the fusing agent from the dross under the force of supergravity. The recovery ratios of metallic aluminum and fusing agent reached 98.95 % and 98.13 %, while the aluminum and fusing agent contents in the tailings were reduced to 0.82 wt% and 3.71 wt%. The study also discusses the leaching characteristic of the tailings and the scalability for industrial applications of this method in detail. This study not only achieves valuable resource recovery but also reduces the leaching risk and alleviates the land occupation and ecosystem pressure caused by industrial wastes. The tailings can be harmlessly utilized in related fields through subsequent scientific treatment.

Effect of Enhanced Gravity on the Microstructure and Mechanical Properties of Al0.9CoCrFeNi High-Entropy Alloy.

The influence of enhanced gravity on the microstructure and mechanical properties of the Al0.9CoCrFeNi high-entropy alloy, which was solidified under normal gravity (acceleration 1 g) and enhanced gravity (acceleration 140 g, acceleration 210 g, and acceleration 360 g) conditions is reported in this paper. Its solidification under enhanced gravity fields resulted in refinement of the columnar nondendritic grain structure and an increase in the area fraction of the body-centered cubic (BCC) structure phases. The mass transfer strengthened by enhanced gravity promoted element diffusion and enrichment, which caused changes in the composition and microstructure that, in turn, affected the mechanical properties of the alloy. The compressive strength and plasticity of the sample solidified at acceleration 360 g were equal to 2845 MPa and 36.4%, respectively, which are the highest values reported to date for Al0.9CoCrFeNi alloy.

Preparation of steel slag porous sound-absorbing material using coal powder as pore former.

The aim of the study was to prepare a porous sound-absorbing material using steel slag and fly ash as the main raw material, with coal powder and sodium silicate used as a pore former and binder respectively. The influence of the experimental conditions such as the ratio of fly ash, sintering temperature, sintering time, and porosity regulation on the performance of the porous sound-absorbing material was investigated. The results showed that the specimens prepared by this method had high sound absorption performance and good mechanical properties, and the noise reduction coefficient and compressive strength could reach 0.50 and 6.5MPa, respectively. The compressive strength increased when the dosage of fly ash and sintering temperature were raised. The noise reduction coefficient decreased with increasing ratio of fly ash and reducing pore former, and first increased and then decreased with the increase of sintering temperature and time. The optimum preparation conditions for the porous sound-absorbing material were a proportion of fly ash of 50% (wt.%), percentage of coal powder of 30% (wt.%), sintering temperature of 1130°C, and sintering time of 6.0hr, which were determined by analyzing the properties of the sound-absorbing material.

Preparation and Compression Behavior of High Porosity, Microporous Open-Cell Al Foam Using Supergravity Infiltration Method.

By employing a method that combines a NaCl compacting template and supergravity infiltration, open-cell aluminum (Al) foam with varying porosities was prepared. The Al foam fabricated has a pore size of 400 µm and porosity ranging from 0.72 to 0.88. The experimental results indicate that, with an increase in compaction pressure during the NaCl compacting process, the porosity of the foam Al increases and the struts become finer. As the gravity coefficient increases, the density and integrity of the foam Al also increase. Due to the effectiveness of supergravity in overcoming the infiltration resistance between the NaCl preform and molten Al, the supergravity infiltration method holds promise as a practical new technique for fabricating high-porosity open-cell Al foam.

A green method to clean copper slag and rapidly recover copper resources via reduction-sulfurizing smelting and super-gravity separation at low temperature.

Massive copper slag containing heavy metals is produced in copper making and 0.5 - 8.0 wt% Cu is lost into it, deserving to be recovered. In this study, the waste coke and gypsum were employed to clean the copper slag, the lost copper was reduction-sulfurized and enriched to the matte droplets. However, the free-settling of matte droplets under normal gravity needed a higher temperature of 1350 â„ƒ. On this basis, the matte droplets were efficiently separated from the cleaned slag via super-gravity at a low temperature of 1200 â„ƒ within 3 min, the recovery ratio of Cu was up to 99.56%, and the grade of Cu in the matte phase and cleaned slag was 85.84 wt% and 0.08 wt%, respectively. Moreover, the migration, distribution and leaching behavior of heavy metal elements (Pb, Zn, Ni, etc.,) were performed and analyzed, and the treatment and utilization of volatilized vapors and tailings were also discussed. This study proposed a green method to clean the copper slag and simultaneously recover copper resources via reduction-sulfurizing smelting and super-gravity separation at a low temperature, providing scientific guidance and application prospects for the synergistic treatment of hot copper slag with waste coke and gypsum.

Basic properties of sintering dust from iron and steel plant and potassium recovery.

With the production of crude steel, China produces several million tons of sintering dusts which contain a great deal of valuable metals such as, K, Na, Zn, Pb. If discharged directly without adequate treatment, these elements can lead to adverse effects on the environment. Therefore, it is very necessary to determine how to separate these elements from the dust before discharge. Several physical and chemical detection methods were used to study the basic properties of sintering dust. At the same time, preliminary experiments on the recovery of the potassium resources from the sintering dust were carried out. The mean particle size of the electrostatic precipitator (ESP) dust determined by a laser granulometer was 41.468 microm. Multi-point BET and single-point BET analysis showed that the surface area of the ESP dust was 2.697 m2/g. XRD measurements detected the following phases in the ESP dust: Fe2O3, Fe3O4, KCl and NaCl, and Fe2O3, Fe3O4 and SiO2 in the water-washed dust. SEM-EDS results proved that in the ESP dust, K mostly existed in the form of KCl particles without being coated. Leaching experiments showed that the KCl in the ESP dust could be separated and recovered by water leaching and fractional crystallization. Through the recovery experiments, the yield of K-Na vaporized crystalline salt was 18.56%, in which the mass fractions of KCl, NaCl, CaSO4 and K2SO4 were about 61.03%, 13.58%, 14.03% and 9.97%, respectively. This process is technically viable and considerable in economic benefit. There was almost no secondary pollution produced in the whole recovery process.

Effect of Supergravity Field on the Microstructure and Mechanical Properties of Highly Conductive Cu Alloys.

In consideration of the characteristics of supergravity to strengthen solidification structures, the effect of the supergravity field (SGF) on the grain refinement and mechanical properties of Cu-0.5Sn alloys was investigated in this paper. Firstly, it was experimentally verified that the addition of Sn could effectively refine the grain. Subsequently, the variations in grain size, tensile strength, and plasticity of the Cu-0.5Sn alloy were compared in normal and SGF conditions. The results revealed that the tensile strength and plasticity of the alloy increased with the increase in gravity coefficient. The ultimate tensile strength of the Cu-0.5Sn alloy in a normal gravity field was 145.2 MPa, while it was 160.2, 165.3, 167.9, and 182.0 MPa in an SGF with G = 100, 300, 500, and 1000, respectively, and there was almost no effect on conductivity. Finally, it was clarified that the mechanism of grain refinement by SGF was that the intense convection caused the fracture of the dendrites to become new nucleating particles. The increased viscosity under SGF hindered the diffusion of atoms in the melt and slowed down the movement of atoms toward the nucleus, leading to a decrease in grain size.

A novel electrocoagulation process with centrifugal electrodes for wastewater treatment: Electrochemical behavior of anode and kinetics of heavy metal removal.

Anodic passivation is a key problem to impair the efficiency of in the electrocoagulation (EC) process. Process intensification of EC has attracted increasingly greater attention. In this work, a novel centrifugal electrode reactor was designed and applied in EC process to enhance the treatment of simulated heavy metal wastewater using aluminum anode. Results showed that the removal efficiency of heavy metals was significantly improved by the centrifugal electrodes, compared with the stationary electrodes. Electrochemical behavior of centrifugal electrodes was analyzed by an improved rotating disk electrode system. Anodic polarization behavior of aluminium showed a typical characteristic of dissolution in centrifugal electrodes, rather than passivation in static condition. Anode dissolution was controlled by the diffusion of Cl- ion that was enhanced by centrifugal electrodes. Thus, anode passivation was reduced. In addition, the kinetics analysis indicated that the removal of heavy metals in EC by centrifugal electrodes conformed to Variable-Order-Kinetic (VOK) model based on the Langmuir adsorption.

Microstructure and Mechanical Properties of Ni-20Cr-Eu2O3 Composites Prepared by Vacuum Hot Pressing.

Ni-20Cr-Eu2O3 composites were designed as new control rod materials and were synthesized from Ni, Cr, and Eu2O3 mixture powders via ball milling and vacuum hot pressing. During ball milling, Eu2O3 was fined, nano-crystallized, amorphized, and then dissolved into matrix. The effect of Eu2O3 content on the microstructure and mechanics was researched, and the corresponding mechanism was discussed. The relative densities, grain sizes, and microhardness increased when Eu2O3 content increased. According to the TEM observations, Eu2O3 particles showed a semi-coherent relationship with the matrix. The results of mechanical property testing showed that the ultimate tensile strength, yield strength, and elongation decreased with the Eu2O3 content increased. The maximum ultimate tensile strength, yield strength, and elongation were 741 MPa, 662 MPa, and 4%, respectively, with a 5 wt.% Eu2O3 addition. The experimental strengths were well matched with the theoretical values calculated by the strengthening mechanisms indicating that this method was highly effective for predicting the mechanical properties of Ni-20Cr-Eu2O3 composites.

Recovery of aluminum-zinc alloy from 55%Al-Zn dross by supergravity separation.

As a by-product of hot-dip 55%Al-Zn coating processing, the dross contains high levels of Al and Zn. However, no cost-effective recycling methods have been reported to date. Therefore, this work aims at developing a novel method for Al-Zn alloy recovery from an industrial 55%Al-Zn dross using supergravity separation. The separation efficiency was analyzed as a function of separation time and temperature as well as the gravity coefficient (G). Al-Zn alloy was recovered at G values above 70. Separation at higher temperatures benefited the recovery of Al-Zn alloy but decreased the removal rate of Fe impurities due to the increased Fe solubility. With the optimal conditions at 590 °C and G > 500, over 86 wt. % of Al-Zn alloy, containing only 0.4 wt. % of Fe, was recovered. According to the FactSage software calculation, the solubility of Fe increases from 0.06 to 1.11 wt. % when the temperature rises from 550 to 650 °C. This is consistent with the experimental results. The purified alloy could then be further used in the hot-dip 55%Al-Zn bath for production. This study demonstrates the feasibility of supergravity separation as a promising process efficient for recovering Al-Zn alloy from 55%Al-Zn dross.

Hydrogen Permeation Behavior of Zirconium Nitride Film on Zirconium Hydride.

Hydrogen permeation barrier plays an important role in reducing hydrogen loss from zirconium hydride matrix when used as neutron moderator. Here, a composite nitride film was prepared on zirconium hydride by in situ reaction method in nitrogen atmosphere. The phase structure, morphology, element distribution, and valence states of the composite film were investigated by XRD, SEM, AES, and XPS analysis. It was found that the composite nitride film was continuous and dense with about 1.6 µm thickness; the major phase of the film was ZrN, with coexistence of ZrO2, ZrO, and ZrN0.36H0.8; and Zr-C, Zr-O, Zr-N, O-H, and N-H bonds were detected in the film. The existence of ZrN0.36H0.8 phase and the bonds of O-H and N-H revealed that the nitrogen and oxygen in the film could capture hydrogen from the zirconium hydride matrix. The hydrogen permeation performance of nitride film was compared with oxide film by permeation reduction factor (PRF), vacuum thermal dehydrogenation (VTD), and hydrogen permeation rate (HPR) methods, and the results showed that the hydrogen permeation barrier effects of nitride film were better than that of oxide film. The zirconium nitride film would be a potential candidate for hydrogen permeation barrier on the surface of zirconium hydride.

Mechanisms of Growth and Hydrogen Permeation of Zirconium Nitride Film on Zirconium Hydride.

Nitride film as a hydrogen permeation barrier on zirconium hydride has seldom been studied. In this work, the zirconium nitride films were prepared on zirconium hydride in an atmosphere of N2 and N2 + H2 at 500~800 °C, with a holding time of 5 h and 20 h, and the mechanisms of film growth and hydrogen permeation were analyzed. The results showed that the film growth was mostly influenced by the temperature, followed by the reaction atmosphere and the holding time. The hydrogen could increase the nitrogen diffusivity during the formation of zirconium nitride films. The in situ nitriding conditions were optimized as 800 °C, N2 + H2 atmosphere, and 5~20 h. The chemical composition of ZrN-based films was mainly comprised of Zr and N, with a minor content of O. In addition, the film exhibited a major phase of ZrN, accompanied by the coexistence of ZrO2, ZrO, ZrN(NH2), and ZrN0.36H0.8, as well as O-H and N-H bonds based on the XPS analysis. The as-prepared ZrN base films in the present study exhibited superior hydrogen permeation resistance to other ZrO2 films previously reported. The hydrogen permeation resistance of the films could be attributed to the following mechanisms, including the chemical capture of hydrogen by the above-mentioned compounds and bonds; the physical barrier of continuous and dense film incurred from the volume effect of different compounds based on Pilling-Bedworth model and the different nitrogen diffusion coefficients at different temperatures.

Effect of Phase Composition on Leaching Behavior and Mechanical Properties of Ceramics from Ferrochrome Slag and Tundish Slag.

Ferrochrome slag (FS) and tundish slag (TS) are two typical slags containing high contents of Cr2O3 (3.88 wt.%) and MnO (18.69 wt.%), respectively. In this study, batches of ceramics were prepared from FS and TS, and their Cr/Mn leaching behaviors, mechanical properties and microstructures were investigated. Results showed that ceramics with 80 wt.% FS or 85 wt.% TS had acceptable properties. By controlling its composition and sintering temperature, pyroxene or spinel phases could become the main crystalline phases of the fired ceramics containing either of the two slags. For both slag series, pyroxene phases contributed to higher bending strengths, whereas spinel phases led to lower Cr/Mn leaching rates. Both ceramic containing 20 wt.% FS and ceramic containing 85 wt.% TS had the main crystals of pyroxene phases and possessed the highest bending strengths (FS20: 114.52 MPa and TS85: 124.61 MPa). However, both ceramic containing 80 wt.% FS and ceramic containing 25 wt.% TS with main crystals from the spinel phases had the lowest Cr/Mn leaching rates (FS80: Cr 0.05% and TS25: Mn 0.43%). Therefore, optimum designs for the compositions of ceramics from different slags were achieved by changing the proportions of pyroxene and spinel phases to obtain a balance between the high strengths of materials and the stable retention of heavy metal ions. This study provides an important basis for long-term research on the large-scale reuse of heavy metal-containing slags in the ceramic industry.

Electrochemical behavior of aluminium anode in super-gravity field and its application in copper removal from wastewater by electrocoagulation.

Anodic passivation is a key problem to reduce the efficiency of electrocoagulation (EC) process. Super-gravity technology was introduced into EC process to enhance the treatment of heavy metal wastewater using pure aluminum electrode. The results showed that the removal ratio of Cu increased, and the cell voltage decreased with the increase of gravity coefficient, suggesting a promoting effect of super-gravity field on electrocoagulation process. Electrochemical behavior of aluminium anode in super-gravity field was analyzed by potentiodynamic polarization, cyclic voltammetry and electrochemical impedance spectroscopy. It was found that anodic polarization behavior of aluminium showed a typical characteristic of dissolution in super-gravity, rather than passivation in normal gravity. The type of anode dissolution changed from pitting corrosion to uniform corrosion in super-gravity field. The outer oxidized film of anode was thinning, and more Al3+ ions were released by anode dissolution, which was attributed to the super-gravity enhancement of the mass transfer process of Cl- ions. In addition, X-ray diffraction and Fourier transform infrared spectroscopy indicated that the flocs generated in super-gravity field had amorphous and looser Al-O framework structure. As a result, the efficiency of EC process was improved by super-gravity.

Novel and efficient purification of scrap Al-Mg alloys using supergravity technology.

Supergravity technology is an efficient method for the separation of trace elements from Al-Mg alloys made of their scraps. This study investigated the enrichment and separation behavior of impurities from Al-Mg alloy using supergravity technology under various conditions. After supergravity enrichment, nonmetallic inclusions and precipitated intermetallic compounds were concentrated at the bottom of the samples, and the enrichment degree positively correlated with the gravity coefficient. High-purity Al-Mg alloys was obtained with efficient impurity removal from the alloy melt of the scraps by filtration in supergravity fields. Improving the gravity coefficient benefited the recoveries of the Al and Mg but had little influence on the purity of the obtained Al-Mg alloy. Although the recoveries of the Al and Mg increased slightly with increasing the separation temperature, the removal rates of the metallic impurities were relatively low at elevated temperatures. At the temperature of 500 °C, gravity coefficient of 600, and separation time of 1 min, 91.6% and 90.1% of Al and Mg were recovered, respectively. Their corresponding mass fractions in the filtered Al-Mg alloy were 99.2 wt%. An amplified experimental centrifugal separation apparatus was also designed for purifying the alloys on an engineering scale. The results indicate that supergravity technology is feasible on an industrial scale and that it can be potentially employed as a separation and purification process.

Purification of metallurgical-grade silicon combining Sn-Si solvent refining with gas pressure filtration.

In this study, the purification of metallurgical-grade silicon using a combination of solvent refining and gas pressure filtration was investigated in the Sn-Si alloy. After the solvent refining process, the silicon was separated from the solvent by gas pressure filtration. The effects of pressure differentials (p), separation temperatures (T), and silicon contents in the alloy (ω (a)) on the separation efficiency were evaluated. The filtration result was improved with a higher pressure differential. The separation temperature had little effect on the separation efficiency, whereas a higher silicon content in the alloy led to a decrease of the separation efficiency. The final purification result after separation was examined, and a better separation contributed to the removal of impurity. The optimal result for separation was obtained at p = 0.30 MPa, T = 250 °C, and ω (a) = 20 wt%, and 93.6% of tin was separated into the filtrate, while almost all the silicon was recovered and formed the separated silicon with a silicon content of 80.0 wt%. At the same time, most impurities were eliminated and 94.9% of B was removed after refining the sample twice.

Separation of metals from metal-rich particles of crushed waste printed circuit boards by low-pressure filtration.

In recent years, recovery of metals from electronic waste (e-waste) within China has become increasingly important due to potential supply risk of strategic raw material and environmental concerns. Printed circuit boards (PCBs) contain lots of valuable metals together with plenty of hazardous materials, which are considered both an attractive secondary resource and an environmental contaminant. Pressure filtration is an effective and environmentally friendly method for separating and recycling comminuted PCBs. Present work is focused on the recovery of metals from PCBs by low-pressure filtration separation. A two-stage separation process was adopted to selectively recover Pb-Sn and Cu alloys at different temperatures. The results showed that the temperature and pressure had great influence on the recovery of metals in the separation process. After the two-stage separation process, the total recoveries of Pb, Sn, Cu and Zn were 79.96%, 89.91%, 88.80% and 68.57% respectively, when the temperature is 1350 °C and the pressure is 0.30 MPa. This is a high-efficiency, short-flow, clean-production, and environmental-friendliness that can improve the recovery of metals and realize the reuse of waste resources.

A green method of respectively recovering rare earths (Ce, La, Pr, Nd) from rare-earth tailings under super-gravity.

A green method was proposed for respectively recovering rare earths (REEs) under super-gravity from rare-earth tailings which are massively stockpiled in the Bayan Obo tailings dams. Firstly, the REEs (Ce, La, Pr, Nd) were discovered to be precipitated as the rare earth oxyfluoride, rare earth ferrate and britholite phases respectively at various temperature ranges of 1773-1673 K, 1673-1473 K and 1473-1373 K. However, the Re-rich phases were intimately intertwined with each other in the normal-gravity. Consequently, respective recovery of REEs (Ce, La, Pr, Nd) at their corresponding precipitation temperatures was conducted under the super-gravity. 98.38% of (Ce) were firstly enriched into the rare earth oxyfluoride and separated from the tailings as driven by the super-gravity, 97.70% of (La) were enriched into the rare earth ferrate and separated subsequently, and the residual REEs were precipitated further into britholite. Accordingly, high-purity of rare earth oxyfluoride, rare earth ferrate and britholite phases were attained respectively, achieving the green and efficient recovery of REEs (Ce, La, Pr, Nd) from the tailings with no additives, no hazardous wastes and no secondary pollution.

Manufacturing of open-cell aluminum foams via infiltration casting in super-gravity fields and mechanical properties.

Replicated open-cell aluminum foams were produced by infiltration casting in super-gravity fields. Infiltration of preforms packed by NaCl particles with different sizes was conducted to demonstrate the technical feasibility of this method. The relative densities between 0.25 and 0.34 of the aluminum foams were obtained by varying the NaCl particle size of the preform from 600 to 200 µm. Increasing the gravity coefficient (G) increased the centrifugal pressure (P c) and correspondingly improved the relative densities and structural integrity of the resulting foams. As P c increased, the aluminum foam exhibited a transition from a structure of smooth struts to a relatively complex structure where many protrusions extended inside the pores from the surface of the struts. Also, the specific relationship between the minimum centrifugal pressures necessary to produce self-standing aluminum foams and the NaCl particle size of the preform was established. The minimum centrifugal pressures of 32, 49 and 83 kPa were required for aluminum foams with pore sizes of 600, 400 and 200 µm, respectively. Preliminary results show that super-gravity infiltration is promising to be a practical manufacture process for replicated open-cell aluminum foams.

Concentration of precious metals from waste printed circuit boards using supergravity separation.

Printed circuit boards (PCBs) comprise valuable metals, precious metals, and hazardous materials. Thus, they are considered both attractive secondary sources of metals and environmental pollutants. This study is based on the selective separation of Pb-Sn, Sn-Cu, and Cu-Zn alloys, where supergravity separation was used to concentrate precious metals (i.e., Ag, Au, and Pd) from PCBs in Cu-Zn alloy and final residue. The temperature and gravity coefficient were found to have great influence on the concentration of precious metals in said alloy and residue. At the optimized temperature of 1300 °C, gravity coefficient of 1000, and separation time of 5 min, the Ag, Au, and Pd contents in the Cu-Zn alloy increased by 1.65, 2.05, and 1.54 times, respectively, compared to their concentrations in the original PCBs, while those in the final residue increased by 0.63, 1.02, and 2.62 times, respectively. By combining an appropriate hydrometallurgical process with the present supergravity separation and concentration of precious metals, this clean and efficient process provides a new pathway to recycle valuable metals and prevent environmental pollution by PCBs.