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Magnesium vanadates are important chemical products for luminescent materials and energy storage and also important intermediate substances during vanadium extraction, whose solubility behavior is, however, ambiguous and controversial. In this work, three common magnesium vanadates, namely, magnesium ortho-, pyro-, and metavanadate, were synthesized by a solid–solid synthesis method with MgO and V2O5 as raw materials. In optimum synthesis conditions, the obtained pure magnesium vanadates are confirmed using x-ray diffraction analysis. Then, their solubilities in water and in acidic solution in the pH range of 0–7.0 were systematically investigated at different temperatures. Results show that magnesium vanadates are readily soluble in acidic solution but are only slightly soluble in water, while in both cases magnesium metavanadate has higher solubility than orthovanadate and pyrovanadate. This work provides the fundamental data to improve understanding of the vanadium extraction mechanism and the performance control of magnesium vanadate materials.

The fusion of the leaching and purification processes was realized by directly using microemulsion as the leaching agent. The bis-(2-ethyhexyl) phosphoric acid (DEHPA)/n-heptane/NaOH microemulsion system was established to directly leach vanadates from sodium-roasted vanadium slag. The effect of the leaching agent on the leaching efficiency was investigated, in addition to the molar ratio of H2O/NaDEHP (W), DEHPA concentration, solid/liquid ratio, stirring time, and leaching temperature. In optimal situations, the vanadium leaching efficiency reaches 79.57%. The X-ray diffraction characterization of the leaching residue and the Raman spectrum of the microemulsion before and after leaching demonstrate the successful entry of vanadates from the sodium-roasted vanadium slag into the microemulsion. The proposed method successfully realizes the leaching and purification of vanadates in one step, thereby greatly reducing production costs and environmental pollution. It also offers a new way to achieve the green recovery of valuable metals from solid resources.

Based on two considerations of making full use of the residual heat of vanadium slag and exploring a novel green vanadium extraction process, this article employs vanadium slag with high MgO content as raw material, blowing oxygen into the molten vanadium slag and using the residual heat of the vanadium slag to carry out high-temperature roasting experiments. XRD and SEM/EDS were used to characterize the phase evolution and morphology of vanadium slag with high MgO content during oxidation. The results show that at a high temperature of 1723 K, the trivalent vanadium in vanadium slag can be partly transformed into acid-soluble pentavalent vanadium. Titanium-bearing spinel was oxidized into a large amount of strip pseudobrookite Fe2TiO5. After oxidation, vanadium existed in the form of the solid solution of magnesium pyrovanadate (Mg, Mn, Ca)2V2O7. The leaching rate of roasted vanadium slag with high MgO content is significantly higher than that of industrial vanadium slag. With the increase of oxygen blowing time from 10 to 30 minutes, the leaching rate of roasted vanadium slag with high MgO content increases from 23.19 to 53.69 pct.

This article investigated the saturated solubility of MgO in converter vanadium slag and its influencing factors. The experimental results of MgO dissolution equilibrium are consistent with the theoretical calculation results. The results show that in MgO saturated vanadium slag, MgO mainly exists in MgV2O4 and MgSiO3. The increase of V2O3 content or the decrease of the FeO/SiO2 ratio is beneficial to increasing the saturated solubility of MgO in the FeO-SiO2-V2O3 slag system. The saturated solubility of MgO in vanadium slag increases from 7.5 to 8.0 wt.% when the temperature increases from 1633 to 1753 K. In addition, the solubility of MgO also increases with the increase of TiO2 and Al2O3 content and decreases with the increase of MnO content.

Vanadium(V) valence analysis is of great significance to the vanadium recovery and environmental safety of the vanadium extraction industry. The stability constants and stereo structures of complexes between EDTA and vanadium ions with various valences are only roughly estimated, which hinders the development of vanadium valence analysis. This work investigates in detail the complexation behavior of V(IV) and V(V), the most common valences in aqueous solution, with EDTA. The stability constants of [VO(EDTA)]2− and [VO2(EDTA)]3− complexes are determined to be 107.03±0.14 and 105.47±0.25 at pH 6, respectively. First-principles calculations reveal that the stereo structure of the [VO(EDTA)]2− complex is comprised of three 5-membered rings while that of the [VO2(EDTA)]3− complex is comprised of one 8-membered ring, which calls for the reconsideration of V–EDTA structures assumed commonly. This work has corrected the assumed stability constants and stereo structures of V–EDTA complexes and provided the essential knowledge to develop vanadium valence analysis in the vanadium industry.

An effective and environment-friendly method based on one-step sodium hydroxide roasting was proposed to extract vanadium and chromium from vanadium-chromium slag. In optimal conditions (roasting temperature 800 °C and NaOH addition dosage 30%), vanadium spinel was converted into NaVO3 while chromium spinel was converted into Na2CrO4 and CaCrO4. Leaching efficiencies of vanadium and chromium reached 94.87% and 80.51%, respectively. During sodium roasting, Na also reacted with Si, Fe, Ti and Al to produce sodium salts of high melting points, which inhibits sintering of reaction mixture and facilitates the formation of vanadates and chromates. The leaching residues consist mainly of Fe2O3, which can be recycled to converter as flux of slagging materials to achieve resource recycling and zero-discharge of solid wastes. This work has provides a simple green way to extract vanadium and chromium from vanadium-chromium slag, which puts forward the green comprehensive utilization of vanadium-titanium magnetite ores with high chromium contents.

To increase vanadium recovery, it is critical to understand the intrinsic phase evolution during vanadium slag roasting. This work proposes the novel concept of `atomic atmosphere' to effectively evaluate and recognize the microscopic state of the vanadium atom in vanadium slag before and after roasting. Atomic atmosphere includes the chemical state, chemical environment and spatial environment of the atom, and provides a universal way to explore the microscopic phase evolution mechanism during the metal-extraction process from minerals.

A novel strategy for comprehensive utilization of vanadium slag with high-content chromium is proposed in the present study. This approach involves two steps: vanadium slag is first treated by the ...

In China, the wastewater produced after vanadate precipitation (AVP wastewater) from industrial vanadium extraction contains toxic V(V) and carcinogenic Cr(VI). When considering environmental protection and wastewater use, V(V) and Cr(VI) must be extracted and separated from the hazardous AVP wastewater. However, separating V(V) and Cr(VI) is difficult because of their highly similar physicochemical properties. Herein, we propose a novel anion exchange method based on the in situ selectively reductive desorption of Cr(VI) to separate and extract V(V) and Cr(VI) using a weak organic reductant (ethanol) to selectively reduce Cr(VI) anions and transform them into Cr3+ cations, while maintaining V(V) in a H2V10O284- anion form. We indicate that the efficient separation of Cr(VI) from V(V) can be attributed to selective Cr(VI) anion reduction via ethanol. We applied this anion exchange method to separate and recover Cr(VI) and V(V) in AVP wastewater with a Cr(VI) recovery of 95.59% and a V(V) recovery of 94.54%. The final Cr2O3 and V2O5 products had a purity of 98.03% and 96.82%, respectively. This study provides novel insights into the simultaneous separation and extraction of analog transition metals and a comprehensive method to use hazardous wastewater.

The high-chromium vanadium slag is treated by magnesium roasting-acid leaching to obtain Cr-containing tailings, which are not the solid waste but important valuable resources for various fields. In order to extract Cr from these tailings, sodium carbonate as annexing agent mixed tailings was roasted and then leached by water. There are several factors that were investigated including roasting temperature, roasting time, the molar ratio of Na/(V+Cr), leaching time, leaching temperature, and the ratio of L/S. The Cr-containing tailings before and after roasting and the residue after leaching were characterized by XRD. It is indicated that Cr in tailings was all entered into leaching solution due to residue not found Cr-containing phase. Under the optimal conditions, the maximum leaching rate of Cr was 92.49%.

Based on two considerations of making full use of the residual heat of V-slag and exploring a novel green V extraction process, this paper employs MgO as the roasting additive, blows oxygen into the molten V-slag, and uses the residual heat of the V-slag for pre-roasting at high temperature. The influence of MgO on the phase structure of V-slags during oxidation has been investigated by XRD and SEM/EDS. The result shows that MgO as the roasting additive can convert V-slag at a high temperature of 1723 K. With the increase of blowing time of oxygen, the trivalent V in the spinel phase gradually disperses in the silicate matrix and then concentrates in the form of magnesium vanadate solid solution (Mg, Mn, Ca)2V2O7. Furthermore, with the increase of MgO content, the peak intensity of the Mg2V2O7 diffraction peak increases significantly. When the MgO content in V-slag increases from 4.01 to 12.74 wt%, the extraction efficiency increases from 18.99 to 64.07%.

Vanadium slag is composed of many complex phases with various kinds of elements, occurrence forms, and chemical forms. At present, sodium roasting–water leaching can effectively extract vanadium; this technique has been widely used in industrial production, but the current researches to evolution law of the V-concentrating phase in V-slag during the roasting process focus on the macro-level, not directly on micro-level and especially at interface reaction process. Consequently, the microstructure, phase compositions, mineralogical morphology, and elements distribution on the surface of vanadium slag during the roasting process were investigated by various surface analysis techniques. It is essential to truly understand and control the sodium roasting–water extraction process, so the atomic evolution law can be of a great significance to optimize operating conditions in order to raise vanadium recovery rate.

The widely applied methods to extract vanadium are sodium roasting and calcified roasting. However, these roasting methods have difficulties in recycling of wastewater and efficient utilization of leaching residue, which contains high concentration of sodium or calcium sulfate, due to the variety of roasting additives radically. Therefore, a novelty extraction medium by roasting with MgO and leaching with sulfuric acid was introduced in this study. The oxidation and roasting mechanism were systematically studied, providing a theoretical basis for industrial extraction of vanadium. The result shows that under the optimum conditions, the roasting temperature of 900 °C, the Mg/V molar ratio of 0.6, and the roasting time of 1.5 h, the leaching efficiency of vanadium is above 90%. In the processes, vanadium spinel is converted into Mg2V2O7 and Mn2V2O7.

Vanadium (V) and chromium (Cr) co-exist in the whole process of V extraction from the vanadium titano-magnetite ore in China. It remains a challenge to remove trace V(V) from Cr(VI) in a simple way. Based on facile pretreatment of transforming Cr(VI) selectively, a novel method to remove V(V) from Cr(VI) by anion exchange resin Dex-V has been established. The influence of operation parameters including pH, contact time and temperature on adsorption ratio has been investigated. The Langmuir model and Henry model were successfully applied to describe the adsorption behavior of V by the Dex-V resin. It is shown that V is adsorbed chemically in monolayer and the Dex-V resin presents a homogeneous nature. Kinetics of V adsorption was analyzed with the pseudo-second order model, the Richenberg model and the Weber–Morris model. Results show that the rate of V adsorption is controlled by film diffusion in initial 70 min and the intra-particle diffusion contributes to the rate-controlling after 70 min. The proposed method was applied to remove V from real waste water and the removal ratio as high as 96% was obtained, with Cr recovery of 95%, which validates the effectiveness and efficiency of the novel method. This work has thus provided new insights into separation and recovery of analog metals in aqueous.

This paper investigated the non-isothermal crystallization kinetics of the spinel crystals in vanadium slags containing high CaO content. Experiments were performed in combination with theoretical calculation to address this issue, and statistical analyses based on the Crystal Size Distribution theory. The results indicate that low cooling rate and high CaO content benefit the growth of spinel crystals. The growth mechanism is revealed to be controlled by interface reactions and diffusion at the cooling rates of 5 K/min and 15 K/min, respectively. However, at higher temperatures (>1673 K), the growth of spinel crystals is controlled by nucleation. While the temperature is decreased to 1523 K at the cooling rate of 5 K/min, the mean diameter of spinel crystals could reach 36.44 μm. Experimental results combining with theoretical reveal that low cooling rate benefits spinels growth, especially for the interval of 1523 K–1200 K.

In this paper, a series of nitriding experiments were carried out to investigate the phase evolution and element migration in the nitriding process. The results show that it undergoes a low temperature reducing stage firstly. High valent vanadium oxides are reduced to V2O3 between room temperature and 770 °C. In Ar atmosphere, V2O3 reacts with C to form VC in the temperature interval of 770 °C∼1080 °C. In N2 atmosphere, V2O3 reacts directly with N2 and C to form VN in the interval of 670 °C∼1050 °C. During 1050 °C∼1270 °C, part of the VN obtained in the previous reaction stage will react with C to form VC. High temperature is beneficial to the removal of impurity element sulfur. The volatilization of alkali metal elements in the pellet mainly occurs between 670 °C and 1270 °C. However, there are about 20% of sodium and potassium remain in the nitriding product. The volatile alkali metal vapor would react with other gases at the furnace cover to form a white sediment and deposits on the cover. The sediment mainly consists of Na2CO3, K2CO3, Na2SO4, K2SO4, KCl, etc.

Because of the interference from phosphorus, it is practically challenging to efficiently recover vanadium from vanadium slag with high phosphorus contents (VS-HPC). We propose to separate vanadium and phosphorus in aqueous medium via microemulsion extraction, which enables the recovery of vanadium from the leach solution obtained by conventional calcification roasting and acid leaching process of VS-HPC. The influences of various factors on the separation of vanadium and phosphorus have been investigated. Under the most suitable conditions, the extraction efficiency of vanadium can reach as high as 99.9% while that of phosphorus has been impressively lowered to 5.5%. After establishing the microemulsion-based separation method of vanadium and phosphorus, the vanadium element in VS-HPC was extracted to leach solution. The extraction and recovery of vanadium and phosphorus has further enabled, the production of V2O5 with a high purity of 99.7%; the high purity has made the products much more economically appealing than the commonly manufactured V2O5 with a purity of 98.0%. This work has provided new pathways of promoting sustainability in the non-ferrous metal resource utilization.

Present methods of vanadium extraction from vanadium slag suffer from serious environmental pollution due to the large production of solid waste and wastewater. This study proposes a cleaner method of magnesiation roasting–acid leaching, where magnesium oxide is considered to be a recyclable roasting additive. The maximum extraction efficiency achieved in case of vanadium is 95.56%, and the obtained vanadium pentoxide has a high purity of 99.07%. The magnesium in the leaching liquor is recovered as MgO with purity of 99.21%, and recovery rate of 90.13%, which is recycled as the roasting additive. Furthermore, manganese, ammonium sulfate, and water are recovered and recycled from the wastewater, while the ammonia produced during vanadate calcination is recycled. The resulted leaching residues are recyclable by burning in a blast furnace to recover their iron content for reuse. Herein, the recycling and reuse of all the wastewater and leaching residues result in zero discharge, significant cleanliness, and high resource utilization. This work has opened a new pathway of establishing significantly cleaner production process for environmental sustainability via design and incorporation of inner recycling of wastes into the process in which these wastes are produced.

Separation of V(V) and Cr(VI) in aqua is intensively demanded in consideration of full resource utilization and environmental safety of vanadium extraction industry, which is however a challenge due to their highly similar chemical properties. In this work, chromium transformation is firstly conducted to convert Cr(VI) anions into Cr(III) cations that are differentiable from V(V) anions. Then, the microemulsion system of Aliquat 336/isoamyl alcohol/n-heptane/NaCl is utilized to selectively extract V(V) anions by method of microemulsion extraction and leave Cr(III) cations in the raffinate, leading to the separation of V and Cr. In optimal conditions of microemulsion extraction, the extraction efficiency of V is as high as 98.45% while that of Cr is only 4.44%, confirming the efficient separation of V and Cr in aqua. Extracted V is retrieved back to aqueous solution by stripping V-loaded microemulsion and simultaneously concentrated by 4 times with total recovery of 97.91%; Cr(III) left in the raffinate is environmentally safe and ready for direct precipitation recovery. The achieved separation of V(V) and Cr(VI) is thus not only efficient, but also beneficial to their subsequent recovery. This work has demonstrated a powerful separation method for V(V) and Cr(VI) with high separation capacity, efficiency and speed, which lays the essential foundation for the recovery and comprehensive utilization of V and Cr resources in vanadium metallurgy industry.

It has been most widely used to extract vanadium and chromium by sodium roasting–water extraction. However, the current researches about this evolution law only stay at the macro-level. Therefore, it is especially important to study the mechanism of oxidation and sodium consumption in the process of sodium roasting. In this study, sodium hydroxide was used as a sodium additive for roasting experiments. The oxidation and sodiumation processes were systematically studied, providing a theoretical basis for industrial extraction of vanadium and chromium. The results show that the oxidation and sodiumation temperature range of V3+ and Cr3+ is from 425.8 to 882.8 °C. The roasting temperature of 800 °C is the optimum conditions. Under this condition, vanadium spinel is converted into NaVO3, while chromium spinel is converted into Na2CrO4 and CaCrO4.

Vanadium slag is the main raw material to produce vanadium product. The mainstream approach that has been used to extract vanadium from vanadium slag is roasting–leaching. The above leaching solution through precipitation of ammonium polyvanadate (APV), APV-precipitated wastewater was produced. APV-precipitated wastewater contains a certain concentration of vanadium, which needs to require further treatment. In this research, we put forward an efficient method for the extraction of V(V) in aqueous solution using an Aliquat 336/isoamyl alcohol/n-heptane/NaCl microemulsion system. Suitable conditions of extracting vanadium in aqueous solution were studied, including surfactant concentration, the volume ratio of aqueous phase to microemulsion, as well as contacting time. And the extraction mechanism on the microemulsion system has been researched. Extraction of V(V) in APV-precipitated wastewater by microemulsion system also has been investigated; the extraction ratio of V can reach to 99.74%.

Calcification roasting is a clean way to extract vanadium from the vanadium slag. But the subsequent sulfuric acid leaching brings the impurity of phosphorous into the leach liquor of vanadium and thus inhibits the precipitation of vanadates for vanadium recovery. In this paper, a novel selective leaching method using ammonium carbonate ((NH 4 ) 2 CO 3 ) has been proposed for the extraction of vanadium in the calcification-roasted vanadium slag. The (NH 4 ) 2 CO 3 leaching can dissolve calcium vanadates with high selectivity while maintaining other impurities including phosphorous in the solid residue. Ammonium vanadate can be precipitated directly by cooling down without pH adjustment or ammonium salt addition, which makes the (NH 4 ) 2 CO 3 leaching cost-effective. The waste water after precipitation can be recycled back to the leaching circuit, showing the friendliness of (NH 4 ) 2 CO 3 leaching method to the environment. With (NH 4 ) 2 CO 3 leaching, 96.0% of vanadium can be dissolved while the corresponding leaching efficiency of phosphorous is 9.2% using the most suitable condition of solid/liquid ratio 1:20, particle size 45–74 μm, leaching temperature 80 °C, (NH 4 ) 2 CO 3 concentration 600 g/L and leaching time 70 min. This work has laid the foundation for the industrial application of ammonium carbonate leaching and provided new insights into selective leaching of valuable elements in complex minerals.

A novel environment-friendly method based on stepwise roasting has been proposed to extract vanadium and chromium separately from vanadium slag with high chromium content (V–Cr slag), which consists of two stages of sodium roasting–water leaching. Fractional sodium roasting–water leaching is firstly conducted to extract vanadium from the V–Cr slag and 87.9% of vanadium is extracted in optimal conditions. Leaching residue of the fractional roasting stage is then roasted secondarily to extract chromium and 96.4% of chromium is extracted from the leaching residue in optimal conditions. Overall extractions of vanadium and chromium are 98.9% and 96.6%, respectively. Evolution mechanisms of V-bearing and Cr-bearing phases were elucidated by XRD, TG–DSC and SEM-EDS. It is elucidated that V(III) existing as V-spinels in the V–Cr slag is oxidized to water-soluble NaVO3 while Cr(III) remains in the form of Cr-spinels or R2O3 phase (R: Cr, Fe) during the fractional roasting; in secondary roasting, Cr(III) existing as Cr-spinels and R2O3 phase in the leaching residue of fractional roasting stage is oxidized to water-soluble Na2CrO4. Vanadium and chromium have thus been extracted separately and thoroughly at the extraction procedure by controlling the roasting extent of V–Cr slag via the proposed stepwise roasting method. The established method provides new insights for comprehensive utilization of complex minerals containing multiple valuable elements.

The extraction of vanadium from vanadium-containing APV-precipitated wastewater by W/O microemulsion system was studied. In the N263/n-heptane/isoamyl alcohol/NaCl microemulsion system, N263 played double functions of cationic surfactant and extractant to form microemulsion in n-heptane, and isoamyl alcohol was added in the microemulsion as a cosurfactant. The extraction of vanadium by W/O microemulsion systems effectively accelerated the extraction and improved the extractatability because of the enormous increase in the micro-interfacial surface area. Due to ion association with extractant, vanadium was extracted into the microemulsion phase. The influence of different parameters on the extraction ratio (E%) were investigated, including the volume ratio of aqueous phase to microemulsion, surfactant concentration, pH value of the feed solutions, cosurfactant concentration, extraction time as well as temperature. In optimum conditions, the extraction ratio (E%) can reach 97.2%.

After precipitation of ammonium vanadates from vanadium-containing leaching liquor, vanadium (V(V)) and chromium (Cr(VI)) exist in the waste water in form of vanadate ions and chromate ions. In order to efficiently extract and recover V(V) and Cr(VI) from waste water, an environment-friendly method based on anion exchange was investigated in batch tests using macroporous weak base resin Dex-V. The adsorption conditions optimizes in detail, including the effect of pH, initial metal concentration, resin volume, contact time and temperature. The ion-exchange adsorption process for both V(V) and Cr(VI) showed maximum capacity at pH 3.0 for an initial concentration of 100 mg L−1, and reached equilibrium after about 40 min of contact at 298 K. The maximum adsorption ratio under the optimum conditions for V(V) and Cr(VI) was 98.98 and 99.87%, respectively. Result shows that the established method is a promising alternative for simultaneous extraction of vanadium and chromium.

Vanadium (V) metallurgy industry produces significant amount of ammonium polyvanadate (APV) wastewater containing V(V) and Cr(VI), thereby polluting the ecological environment and adversely affecting human health and wasting natural resources. Herein, an efficient method for separating V and chromium (Cr) from APV wastewater is proposed based on an artful pretreatment of the selective transformation of Cr(VI) using microemulsion extraction to realize harmless treatment of the wastewater and recycling of V and Cr resources. The influence of various factors on the V and Cr extraction efficiencies has been investigated, including the extractant concentration, aqueous phase-to-microemulsion volume ratio, contact time, and temperature. Furthermore, the principle of Cr transformation and microemulsion extraction and stripping has been illustrated and the recyclability of the microemulsion has been evaluated. Under optimum conditions, 96.29 % of V(V) and 95.56 % of Cr(VI) were separately recovered from the AVP wastewater, confirming the efficient separation and recovery of V and Cr. This study highlights a new approach for the separate recovery of V(V) and Cr(VI) from hazardous wastewater and provides new insights into the simultaneous detoxification and resource utilization of industrial hazardous wastes.

Calcification roasting followed by acid leaching was an effective and environment-friendly way to extract vanadium from vanadium slag. Kinetics study of leaching calcification roasted vanadium slag with sulfuric acid was critical to increase vanadium extraction. Maximum leaching ratio of 93% was obtained in optimal condition of 15% sulfuric acid as leaching agent with particle size smaller than 75 μm at 55 °C. It was found that there were two distinct stages in leaching process and kinetics of both stages followed shrinking core model. Arrhenius Ea of stage one (initial 10 min) and stage two (10–50 min) were estimated to be 5.72 kJ/mol and 14.16 kJ/mol, respectively. Results showed that leaching rate of stage one was controlled by solid product layer diffusion while that of stage two was controlled by both solid product layer diffusion and chemical reaction though chemical reaction only contributed to a little extent. All results and conclusions had guiding significance to industrial production of V2O5 from vanadium slag.

We develop a novel approach to recover chromium and iron from hazardous vanadium extraction tailings containing high chromium concentrations by synergistic carbothermal reduction of the mixture of chromite and the vanadium extraction tailings. Experiments show that the recoveries of chromium and iron reach 97.81% and 96.82%, respectively, and decrease with increasing mass ratio of chromite and high chromium type vanadium extraction tailings. The recoveries of chromium and iron are higher when graphite powder is used as reductant. The contents of impurity elements C, Si, S and P fluctuate within a small range and satisfy the requirements of national standards. The addition of CaO can greatly reduce the sulfur content in the high carbon ferrochromium product. 98.34% Cr (VI) and 100% V in the tailings were converted during the reduction process. It is demonstrated that carbothermal reduction could efficiently detoxify Cr(VI) in vanadium extraction tailings containing high chromium concentrations.

An effective way to decrease the dephosphorization burden in the current vanadium extraction-steelmaking process is slagging with CaO in vanadium extraction step. The phase composition of vanadium slag with different basicity and the regularities distribution of elements have been investigated by X-ray diffraction analysis and scanning electron microscopy combining with energy disperse X-ray spectrometry, respectively. The results indicate that V mainly concentrates in the spinel phases; Ca and P are rich in the silicate phases. Fe2SiO4 transform to CaFeSiO4, while the basicity of vanadium slag is 1.3. With further increase of basicity, 2CaO·SiO2 could form in the silicate phases. Moreover, the phosphorus-containing phase will transform from Ca3(PO4)2 to Ca3(PO4)2-nCa2SiO4. With the increase of P2O5 content, the crystallization rate of spinels decrease obviously. Furthermore, the peak temperature for crystallization of spinels decrease 5 K with the P2O5 content increasing 1 wt%.

Vanadium doped, nitrogen doped, and vanadium and nitrogen co-doped SrTiO3 powders with size of 20-30 nm in diameter were prepared by high energy milling method respectively. It was found that compared with those of pure SrTiO3, the photocatalytic activities of these three doped SrTiO3 samples for decomposing NO under visible light (λ>400 nm) and near ultraviolet light (λ>290 nm) irradiation were improved, and the co-doped sample exhibited the highest photocatalytic activity. 43.2% NO could be eliminated under the irradiation of light with wavelength larger than 400nm, about 3 times higher than that by pure SrTiO3. The photocatalytic activity of this sample near ultraviolet range is about 1.7 times higher than that of pure SrTiO3. The high visible light photocatalytic activity of this substance may be due to the high visible light absorption and large specific surface area.

Adding CaO into the vanadium extraction converter is an effective way to decrease the dephosphorization burden in subsequent steelmaking process. The crystallisation process of spinel is one of the most decisive factors in the subsequent extraction. The theoretical calculation results show that the temperature of the peak total crystallization rate will decrease 5K with basicity increasing 0.1. The relation between cooling conditions and grain size of spinels is also discussed. It is found that low cooling rate and high basicity benefit spinel crystal growth. And the non-isothermal crystallization kinetics results indicated that the restriction factors of spinel growth is that solid crystals accept new components from liquid-solid interfacial. While the sample was cooled down to 1250°C(1523K) at cooling rate of 5K/min, the crystal growth is consistent with Ostwald coarsening grew up law, and controlled by diffusion of particle.

Viscosities of FeO-SiO2-V2O3-CaO-P2O5 slags have been measured at the temperature range of 1673 K to 1773 K (1400 °C to 1500 °C). This investigated system represents the major components of basic vanadium slag that is an important intermediate product of a novel vanadium extracting process, in which removal of phosphorus and extraction of vanadium can be achieved from the vanadium-containing hot metal simultaneously. It was found that higher CaO/SiO2 ratio resulted in lower viscosity in the composition range of interest. Also, the viscosities increase with the increasing P2O5 concentration. The varying viscosities can be attributed to the modification in complexity and polymerization of the slag network. The variation of apparent activation energies are in tune with the viscosity measurements. The results of this work revealed the effect of CaO/SiO2 and P2O5 on the viscous properties of FeO-SiO2-V2O3-CaO-P2O5 slags and therefore provide the theoretical foundation for the control of the coupling de-P and V-extraction process.

Traditional, calcium compounds cannot be used in vanadium extraction processing due to the limitation of sodium roasting technology, which results in unsatisfied dephosphorization for vanadium-containing hot metal in converter and thus increasing the dephosphorization burden for subsequent steelmaking. The calcium roasting technology is an alternative for vanadium extraction and allows adding lime into vanadium slag in converter. In the present study, vanadium was leached by soda from roasted vanadium slag with high calcium content. Effects of roasting temperature and time, leaching temperature, Na2CO3 concentration andliquid to solid ratio on vanadium leaching rate were studied.

To improve extraction of vanadium from vanadium slag, a better understanding of the structure and physicochemical properties relation of FeO-SiO2-V2O3 system is very important. In this study, the structural and transport properties of the FeO-SiO2-V2O3 system were investigated by means of molecular dynamics simulation with the molar fraction of V2O3 varying from 0 to 20% at a fixed FeO/SiO2 ratio of 1.5. It was found that with the addition of V2O3, Si remains tetrahedral coordination while the coordination number of V increased gradually from 4.56 to 5.06. The fraction of Q4 (tetrahedron with 4 bridging oxygen (BO)) decrease while non-bridging oxygen (NBO) increase suggesting that depolymerization of the network, and the variation of the self-diffusion coefficients of different ions also agree with the structural findings. Thus, V2O3 is regarded a basic-like oxide which acts as network modifier and then decreases the viscosity of the FeO-SiO2-V2O3 system.

Extracting vanadium from vanadium containing hot metal by LD process has been proven an effective solution for the utilization of vanadium-titanium magnetite ore, but the systematic analyses of vanadium extraction rate and mechanism by basic slag are seldom reported. In this study, mathematical model of vanadium transfer from metal to slag was formulated and the rates of vanadium extraction of hot metal with basic slag were investigated. The results indicated that the apparent vanadium extraction rate constant, k p , were in the range of 1.33∼9.07×10–4g/(cm3·s). And the rate constant was increased with the increase of final slag basicity, reaction temperature and stirring gas flow. The apparent of mass transfer parameter decreases significantly from 0.13 cm3/ s to 0 cm3/ s in 20min, and the data changed as negative due to the decrease of slag oxidation and recovery of vanadium from slag to metal.

In the process of precipitating ammonium polyvanadate (APV) to produce vanadium pentoxide in Pan-steel in China, rest waste water usually contains about 24~333mg/L V(V), 2~100g/L Cr(VI),20~500mg/L Si(IV) and 20~100g/L Na2SO4. In order to recover valuable and also toxic metal ions contained in the waste water, effective extraction method of using anion exchange resin was realized to extract Vanadium selectively, leading to effective separation between vanadium and chromium. To ensure vanadium was absorbed by the resin, V(V) and Cr(VI) were reduced to V(IV) and Cr(III) by NaHSO3, respectively, and then V(IV) was oxidized by H2O2 to V(V) anions. Effects of temperature, solution pH, concentration of ions and absorbing time on vanadium absorption rate were investigated. Chromium was precipitated from rest solution while vanadium was eluted from resin by NaOH solution and then precipitated. Results showed that vanadium recovery of 73% could be obtained in optimized condition. The resin could be regenerated by 3% hydrochloric acid, which indicated the recyclability of the resin and thus low cost of this established method.