As an environmentally hazardous waste, electric arc furnace (EAF) dust had a potential to provide a wider resource of potassium if recycled due to high potassium content. In this study, the chemical and mineralogical characteristics of the EAF dust, especially the existing state of potassium, were analyzed. The results showed that the dust consisted dominantly of manganese oxides (Mn3O4, MnO, MnO2) and manganese silicate (MnSiO3). The K element existed in the dust was in the form of potassium permanganate (K2Mn4O8, insoluble) and potassium sulfate/sulfite (soluble). Then the soluble potassium salts in the dust were recovered by water leaching and crystallization. The recovery ratio of K reached 88.2%, and the products K2SO4 and KCl with the K2O content of 65.25% were obtained. During leaching, the Mn3+ and Mn4+ components were reduced to Mn2+ by sulfide (S2−) or sulfite (SO32−), and the S2− and SO32− components were oxidized to SO42−. The leaching kinetics was studied by the specific electrical conductivity method. The apparent activation energy was 7.76±0.65 kJ/mol, suggesting that the rate controlling step of leaching process was the diffusion of K+ through the diffusion layer.
A 3D model applying temperature- and carbon concentration- dependent material properties was developed to describe the scrap melting behavior and carbon di
Recently, the recovery and utilization of rare earth elements (REEs) from secondary resources have become increasingly important with the rapid consumption
The aim is exploring a new MgO heterogeneous deposition coating method to increase the coating amount, and investigating its sticking prevention effect on the fluidized bed reduction of iron ore. The pure Fe2O3 or iron ore particles were coated with Mg(OH)2 using the heterogeneous deposition coating method. In order to restrain the homogeneous nucleation and promote the heterogeneous nucleation during precipitation, the NH4Cl–NH3·H2O pH buffer solution was employed to adjust the OH− concentration. The actual MgO coating amount on the particle surface has been improved to 3.8 wt%, and the sticking problem of Hualian iron ore during fluidized reduction can be avoided with the MgO coating amount of 0.91 wt%. This coating method achieved a satisfactory uniformity of the coating film, and there was nearly no uncoated part on the coated particle surface. The combination strength between the coating layer and particles' surface with different coating methods was investigated via a blowing system, and it was concluded that the solution and heterogeneous deposition coating methods could achieve a higher coating strength than the dry or slurry coating methods.
Bayan Obo tailings is unique polymetallic resource associated with iron, niobium (Nb) and rare earths (REEs). However, conventional extraction processes are not economically viable for Nb and REEs due to their low-grade nature. To overcome this challenge, a new approach was employed in this study. The Fe-Nb-RE associated tailings were first reduced and iron-slag was separated at low temperatures under super gravity. This process transformed Nb and REEs into a Nb/REEs-rich phase in the primary enriched slag, which was then separated from the slag by super gravity to obtain a high-grade enriched sample. The end result was a sample with Nb2O5 and RE2O3 mass fractions of up to 24.98 wt% and 30.01 wt%, respectively. This process successfully concentrated Nb and REEs from associated elemental impurities and gangue minerals in the Fe-Nb-RE associated ultra-low-grade tailings, making extraction easier, optimizing subsequent leaching/dissolution, and reducing the number of steps and material flows required in the downstream hydrometallurgical extraction.
Magnesium salt slag is generated during the refining of crude magnesium and usually contains a large amount of soluble chloride salts, which will cause serious environmental problems. In this study, a new method was proposed for sustainable recovery and reutilization of molten salt from magnesium salt slag via supergravity separation. The phase transformation of molten salt with temperature was studied. The molten salt was in a fully molten state at 800–750 °C, while the NaCl precipitated at 750–700 °C, meantime combined with MgCl2 and tightly encapsulated the fine MgO particles. Therefore, recovery of molten salt was conducted at 800 °C enhanced by supergravity separation, where the molten salt and MgO-rich particles were efficiently recovered within 5 min with high recovery rates of 98.9 % and 99.5 %, respectively. Moreover, the recovered molten salt removed 98.6 % of oxide inclusions in the crude magnesium refining process. Meanwhile, the fine MgO-rich particles with w(MgO)=76.3 % and 1–10 µm was recovered from the magnesium salt slag, where the leaching amount of Cl- was decreased to 0.586 g/L, which was below the Chinese standard for chlorine ion content in solid wastes. Therefore, this manuscript provided a novel process for recovering molten salt from magnesium salt slag without additives and secondary pollution, meanwhile reducing the generation of solid waste and hazards.
The stickiness of bed material was highly relevant to agglomeration/defluidization in fluidized-bed reduction of iron ore. In this paper, a quantitative model was developed to associate solid surface viscosity (particle adhesion) of a granular group with particle size distribution (PSD) function. The calculation was focused on the sintering behavior of particles with different sizes. This model explained theoretically the dependence of particle adhesion on PSD parameters and thus can be used as a reference to select the particle composition of bed materials for fluidization reduction of iron ore.
Based on the precipitation experiment results of titanium bearing molten slag during cooling liquation, perovskite (CaTiO3) was the first precipitated phase, and 1593–1563 K was the advantageous precipitation temperature of perovskite from the molten simulated slag with a basicity of 1.30. So if perovskite could be separated from the slag melt at this temperature range, at which perovskite becomes a solid state while other minerals form into the molten slag, it would be beneficial for the solid-liquid separation between them. Hence, selective separation experiments of perovskite from titanium bearing slag melt with a basicity of 1.30 at 1578 K by super gravity were carried out in this study, and the results confirmed that it was an effective method. In this process, the molten slag moved along the super gravity direction and went through the filter and then concentrated as the slag phase in the bottom crucible, in which it was practically impossible to find any perovskite grains. In contrast, all the perovskite grains were intercepted by the filter and concentrated as the perovskite phase on the filter, which appeared as the typical dendrite structure. Consequently, after super gravity separation with gravity coefficient of G = 660 to G = 840 at 1578 K for 10 minutes, the mass fraction of TiO2 in the perovskite phase was up to 46.36 wt%, whereas that of the slag phase was only 8.77 wt%. In this case, the recovery ratio of Ti in the perovskite phase was up to 78.17%.
TiC ceramics, a kind of ultra-high temperature ceramics, are primarily prepared by the synthesized TiC powders from high purity metallic titanium or titania. In this work, a novel method for sustainable utilization of hot Ti-bearing blast furnace slag to prepare TiC ceramics was developed. Firstly, the Ti was efficiently transformed into the TiC in hot Ti-bearing blast furnace slag through carbothermal reduction. The high-purity TiC powders were fully recovered from molten carbonized Ti-bearing slag through supergravity separation, where the mass fraction and recovery ratio of Ti in TiC powders were up to 77.89 wt.% and 95.58 %. The TiC ceramics with a relative density of 98.23 % were prepared from the recovered TiC powders via spark plasma sintering method, which possess the favourable mechanical properties including Vickers hardness (Hv) of 23.3 ± 0.4 GPa, fracture toughness (K IC) of 3.96 ± 0.24 MPa m1/2 and flexural strength of 371.9 ± 15.4 MPa.
An innovative approach of super gravity was proposed to separate fine Al2O3 inclusions from liquid steel in this study. To investigate the removal behavior
The anosovite was effectively separated from the modified titanium (Ti)-bearing slag melt in a reducing atmosphere by supergravity. The slag melt went thro
Bayer red mud is a kind of solid waste generated during the production of alumina, which is hazardous to environment due to the high alkalinity caused by soluble sodium. Therefore, a green method for solidification and recovery of soluble sodium from red mud through stepwise separation via super-gravity was developed in this research. Firstly, the Na was completely enriched into the Na-rich slag through the separation of FeAl 2 O 4 phase from the red mud via super-gravity. Subsequently, the Na was solidified and recovered further as NaAlSiO 4 from the Na-rich slag via super-gravity separation at its single crystallization temperature of 1423-1323 K. Accordingly, the soluble sodium was recovered stepwise into Na-rich slag and then to the stable phase (NaAlSiO 4 ) from red mud with a high recovery ratio of 78.14%. Moreover, the low leaching ratio of Na + in NaAlSiO 4 confirmed that the soluble sodium in red mud was efficiently solidified and recovered friendly to the environment.
Bayer red mud, a solid waste that is generated during the production of alumina, is classified as an industrial solid waste because of the high alkalinity
Due to the oolitic structure of the high phosphorus iron ore and the closely wrapping of apatite and hematite phases, an approach using jet mill was utiliz
At present, the utilization of vanadium slag suffers from underutilization of Ti resources and the generation of large quantities of toxic tailings. Therefore, there is an urgent need for a green and sustainable process to achieve the recovery of V and Ti from vanadium slag. In this study, the crystallization mechanism of V and Ti in vanadium slag with basicity and temperature was revealed. The results indicated that V in vanadium slag with a basicity of 1.6 was enriched primarily to Fe2VO4 at 1500-1400 °C, whereas Ti was mainly crystallized into CaTiO3 at 1400-1200 °C. On this basis, above 90.22 % of V and 87.89 % of Ti were firstly recovered into Fe2VO4 and Ti-enriched slag via super-gravity at 1400 °C, respectively. After that, over 81.04 % of Ti was further recovered into CaTiO3 from the Ti-enriched slag via super-gravity at 1200 °C. Following two separations, the high-purity Fe2VO4 with up to 40.56 wt% V2O3 and CaTiO3 with up to 54.42 wt% TiO2 were obtained, which could be used for the preparation of FeV alloy and Ti pigments. The tailings with a FeO content exceeding 39.93 wt% could be further used to recover Fe. This method simultaneously extracts V and Ti resources from vanadium slag, avoids the generation of toxic tailings at source, and can combine with the current V metallurgy process, realizing the comprehensive utilization of vanadium slag in a green and sustainable way.
The significant increase in global consumption of rare earth elements (REEs) has attracted more attention to the separation of REEs from complex rare-earth systems. Bayan Obo ore is the world’s largest rare-earth deposit, where REEs are mainly transfered to RE-concentrate which contains various species of REEs (mainly includes lanthanide: Ce, La, Pr, and Nd). This study reported a new finding and technology for selective separation of different REEs from Bayan Obo RE-concentrate system. The basic data on phase transformation of different REEs in CaO-SiO 2 -CaF 2 -P 2 O 5 -Fe 3 O 4 -RE 2 O 3 systems were reported, and firstly found that different REEs of Ce, La, Pr and Nd could be selectively enriched into cerium oxide, lanthanum ferrate, praseodymium apatite and neodymium apatite, respectively. A novel technology of separating RE-phases via super gravity was proposed, various high-purity RE-phases containing different REEs were separated and characterized, and the crystal information missing in the current database were supplemented.
