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Calcification roasting–acid leaching of high-chromium vanadium slag (HCVS) was conducted to elucidate the roasting and leaching behaviors of vanadium and chromium. The effects of the purity of CaO, molar ratio between CaO and V2O5 ( n (CaO)/ n (V 2 O 5 )), roasting temperature, holding time, and the heating rate used in the oxidation–calcification processes were investigated. The roasting process and mechanism were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetry–differential scanning calorimetry (TG–DSC). The results show that most of vanadium reacted with CaO to generate calcium vanadates and transferred into the leaching liquid, whereas almost all of the chromium remained in the leaching residue in the form of (Fe 0.6 Cr 0.4 ) 2 O 3 . Variation trends of the vanadium and chromium leaching ratios were always opposite because of the competitive reactions of oxidation and calcification between vanadium and chromium with CaO. Moreover, CaO was more likely to combine with vanadium, as further confirmed by thermodynamic analysis. When the HCVS with CaO added in an n (CaO)/ n (V 2 O 5 ) ratio of 0.5 was roasted in an air atmosphere at a heating rate of 10°C/min from room temperature to 950°C and maintained at this temperature for 60 min, the leaching ratios of vanadium and chromium reached 91.14% and 0.49%, respectively; thus, efficient extraction of vanadium from HCVS was achieved and the leaching residue could be used as a new raw material for the extraction of chromium. Furthermore, the oxidation and calcification reactions of the spinel phases occurred at 592 and 630°C for n (CaO)/ n (V 2 O 5 ) ratios of 0.5 and 5, respectively.

Previously, we found that the inward diffusion of oxygen from the atmosphere to the interior of vanadium slag (V-slag) has a significant influence on the roasting reaction and may possibly be the dominant mechanism of this reaction. However, the existing reaction mechanism does not reflect the role of oxygen in calcification roasting. In view of this, the proposed study aims to verify the influence of oxygen using the diffusion couple technology, and propose the reaction equations involving oxygen describing the calcium vanadate formation from the surface to the interior of V-slag. The V-slag/CaO diffusion couples were prepared by vacuum hot-pressing, and diffusion experiments were performed under different oxygen partial pressures at a temperature of 1083 K. First, the surfaces in contact with the atmosphere (S(xz)) during roasting were analyzed by electron probe microanalysis (EPMA), Fourier transform-infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD). Then, the diffusion couple was cut along a direction perpendicular to the V-slag/CaO interface and S(xz). The interior surface (S(xy)) was also analyzed by EPMA, FT-IR, and XRD. At S(xz), new phases were clearly observed in the vicinity of V-slag/CaO interface and characterized mainly as CaV2O6, Ca2V2O7, and Ca3V2O8. Moreover, the diffusion thickness of those new phases increased with the oxygen partial pressure. At S(xy), although relatively weak diffraction peaks and absorption bands of CaV2O6, Ca2V2O7, and Ca3V2O8 were detected, no distinct new phases were observed near the V-slag/CaO interface. Considering that the diffusion capacities of Ca and V at S(xz) and S(xy) cannot be evaluated based on the diffusion thickness, the use of interdiffusion coefficient was proposed to quantify the difference among the diffusion capacities. The average interdiffusion coefficients of Ca and V at S(xz) calculated as 1.02 × 10−8 and 0.91 × 10−8 cm2 s−1, respectively, were practically a hundred times these at S(xy). Following the conclusion that the calcium vanadate formation was governed by the inward oxygen diffusion, new reaction equations for describing the formation mechanism of calcium vanadate in calcification roasting were proposed. These equations, derived from the vacancy mechanism, express that the hoses and calcium vanadate are generated by Ca2+, V2O5, and O2.

Cr has a disadvantage in competing with V for CaO during calcification roasting of V-Cr slag. However, there are almost no quantitative indicators that can directly describe the competing relationships. In previous studies, V-Cr slag/CaO and V2O5/CaO systems were studied using the diffusion couple technique. This article, as a supplement, aims to present the diffusion characteristics of Cr2O3/CaO system and proposes the use of diffusion energy to quantify the competition with V2O5/CaO system. The Cr2O3/CaO diffusion couple was prepared by the hot-pressing method and annealed in a vacuum furnace at 1173 K to 1573 K for 30 to 120 minutes. The Cr2O3/CaO interfaces under different annealing conditions were analyzed through electron probe microanalysis, X-ray diffraction, and Fourier transform infrared spectroscopy. The analysis results showed that CaCr2O4 was the main intermediate in the vicinity of the Cr2O3/CaO interface at 1273 K to 1573 K. The formation of CaCr2O4 was very slight (compared with V) at 1173 K, which verified that Cr was indeed at a disadvantage (compared with V) for occupying CaO during roasting. The diffusion thickness of CaCr2O4 was linearly dependent on the square root of the roasting time, indicating that the solid-solid reaction between Cr2O3 and CaO was governed by the diffusion process. Based on the vacancy mechanism, new equations that involve the diffused Ca2+ (or Cr3+), undiffused Cr2O3 (or CaO), and undiffused O2− of the Cr-rich layer (or Ca-rich layer) are proposed to describe the formation of CaCr2O4. The interdiffusion coefficients at 1273 K, 1373 K, 1473 K, and 1573 K were determined to be 6.04 × 10−10, 8.4 × 10−10, 1.09 × 10−9, and 1.72 × 10−9 cm2 s−1, respectively. The calculated diffusion activity energy of Cr2O3/CaO system (56.53 ± 2.27 kJ mol−1) was only one-fifth of that of V2O5/CaO system.

The goal for current orthopedic implant research is to design implants that have not only good biocompatibility but also antibacterial properties. TiO2 nanotubes (NTs) were fabricated on the titanium surface through electrochemical anodization, which added new properties, such as enhanced biocompatibility and potential utility as drug nanoreservoirs. The aim of the present study was to investigate the antibacterial properties and biocompatibility of NTs loaded with vancomycin (NT-V), both in vitro and in vivo. Staphylococcus aureus was used to study the antibacterial properties of the NT-V. There were three study groups: the commercially pure titanium (Cp-Ti) group, the NT group (nonloaded vancomycin), and the NT-V group. We compared NT-V biocompatibility and antibacterial efficacy with those of the NT and Cp-Ti groups. Compared with Cp-Ti, NT-V showed good antibacterial effect both in vitro and in vivo. Although the NTs reduced the surface bacterial adhesion in vitro, implant infection still developed in in vivo studies. Furthermore, the results also revealed that both NTs and NT-V showed good biocompatibility. Therefore, the NTs loaded with antibiotic might be potentially used for future orthopedic implants.

The effects of basicity and temperature on the reduction process of Hongge high-chromium vanadium-titanium magnetite (HCVTM) sinter were investigated in this work. The main characterization methods of X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscope (SEM), and metallographic microscope were employed in this study. In this work, the reduction of HCVTM sinter with different temperature and basicity were experimented. The Fe, FeO, and TiO in reductive samples increase with increasing basicity and temperatures. The increase of basicity and temperature is favorable to the reduction of HCVTM sinter. The Fe phase has out-migration tendency to the surface of sinter while the perovskite and silicate phases have in-migration tendency to the inside of sinter. The reduction degradation index (RDI) decreases while the reduction index (RI) increases with increasing basicity. The RI increases from 67.14% to 82.09% with increasing temperature from 1073 K to 1373 K.

The effect of microwave treatment on the grinding and dissociation characteristics of vanadium titano-magnetite (VTM) ore were investigated using scanning electron microscopy (SEM), nitrogen absorption measurements, particle size distribution measurements, X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopic analysis, and magnetic separation. SEM analysis showed that microfractures appeared in the microwave-treated VTM, which is attributed to the microwaves’ selective heating characteristic and the differential expansion between minerals and gangues. Nitrogen absorption showed that the microfractures were more pronounced when the microwave heating time was increased. Particle size distribution analysis showed that microwave treatment could improve the grindability of the VTM, thus increasing the weight percent of the fine-ground product. The increase in grindability was more significant with prolonged heating time. Moreover, the particle size distribution of the fine-ground product changed only slightly after the microwave treatment. XRD analysis showed that the crystallinity of the microwave-treated VTM increased with increasing microwave heating time. The magnetic separation tests revealed that the separation efficiency increased as a result of the intergranular fractures generated by microwave treatment. The Fe grade of the magnetic fraction of microwave-treated VTM was 1.72% higher than that of the raw ore. We concluded that the microwave treatment was beneficial, especially for the mineral processing characteristics.

The effect of sinter with different MgO contents on the softening-melting behavior of mixed burden made from chro- mium-bearing vanadium-titanium magnetite was investigated. The results show that with increasing MgO content in the sinter, the softening interval and melting interval increased and the location of the cohesive zone shifted downward slightly and became moderately thicker. The softening-melting characteristic value was less pronounced when the MgO content in the sinter was 2.98wt%-3.40wt%. Increasing MgO content in the sinter reduced the content and recovery of V and Cr in the dripped iron. In addition, greater MgO contents in the sinter resulted in the generation of greater amounts of high-melting-point components, which adversely affected the permeability of the mixed burden. When the softening-melting behavior of the mixed burden and the recovery of valuable elements were taken into account, proper MgO con- tents in the sinter and slag ranged from 2.98wt% to 3.40wt% and from 11.46wt% to 12.72wt%, respectively, for the smelting of burden made from chromium-bearing vanadium-titanium magnetite in a blast furnace.

The sea sand vanadium titanomagnetite has coarse particles, small specific surface area, and great difficulty in agglomeration process. It is difficult for ironmaking enterprises to use it as an ironmaking raw material in large quantities. In this paper, the different methods were adopted to optimize the pellet performance indexes of sea sand vanadium titanomagnetite in order to increase the usage of SSO. The effects of adding ordinary iron ore powder, vanadia-titania fine powder and ball milling pretreatment of SSO on the preparation process of pellet were studied, and the performance indexes of pellet were analyzed. The results showed that the proportion of unground SSO in pellets was up to 40%. The experimental results provided some reference methods to improve the dosage of SSO.

The oxidation induration and reduction swelling behavior of chromium-bearing vanadium titanomagnetite pellets (CVTP) with Cr 2 O 3 addition were studied, and the reduction swelling index (RSI) and compressive strength (CS) of the reduced CVTP with simulated coke oven gas (COG) injection were investigated. The results showed that the CS of the CVTP decreases and the porosity of the CVTP increases with increasing amount of Cr 2 O 3 added. The Cr 2 O 3 mainly exists in the form of (Cr, Fe) 2 O 3 solid solution in the CVTP and as Fe-Cr in the reduced CVTP. The CS of the reduced CVTP increases and the RSI of the reduced CVTP decreases with increasing amount of Cr 2 O 3 added. The limited aggregation and diffusion of metallic iron contribute to the formation of dense lamellar crystals, which leads to the slight decrease for reduction swelling behavior of reduced CVTP. This work provides a theoretical and technical basis for the utilization of CVTP and other Cr-bearing ores such as chromite with COG recycling technology.

Reduction of chromium-bearing vanadium–titanium sinter（CVTS） was studied under simulated conditions of a blast furnace, and thermodynamics and kinetics were theoretically analyzed. Reduction kinetics of CVTS at different temperatures was evaluated using a shrinking unreacted core model. The microstructure, mineral phase, and variation of the sinter during reduction were observed by X-ray diffraction, scanning electron microscopy, and metallographic microscopy. Results indicate that porosity of CVTS increased with temperature. Meanwhile, the reduction degree of the sinter improved with the reduction rate. Reduction of the sinter was controlled by a chemical reaction at the initial stage and inner diffusion at the final stage. Activation energies measured 29.22–99.69 k J/mol. Phase transformations in CVTS reduction are as follows： Fe_2O_3→Fe_3O_4→FeO→Fe; Fe_2TiO_5→Fe_2TiO_4→FeTiO_3; FeO·V_2O_3→V_2O_3; FeO·Cr_2O_3→Cr_2O_3.