Calcification Roasting Research Articles

Preparation of calcium aluminate and spinel by hydrolysis and calcination from secondary aluminum dross

AbstractThe direct extraction of alumina from secondary aluminum dross (SAD), which is a dangerous solid waste, is difficult. Moreover, this process easily produces a large amount of solid waste residue, which is not easily utilized. In this paper, a new green process was developed to prepare calcium aluminate and Mg‐Al spinel from SAD by hydrolysis–calcification roasting. The effects of calcium oxide (CaO) content, sintering temperature, and holding time on the properties of calcium aluminate were investigated by single‐factor experiments. The phase transformation mechanism of calcium aluminate was studied by thermodynamic analysis, X‐ray diffraction analysis, X‐ray fluorescence spectroscopy, and scanning electron microscopy. Under the optimal conditions (Ca/Al molar ratio of 0.8, sintering temperature of 1300°C, and holding time of 2 h), the main calcium aluminate phases are CaAl2O4 and Ca2Al2SiO7, the soluble alumina content of the calcium aluminate sample is 49.71 wt.%, and the main phases of the acid‐insoluble residue are Mg‐Al spinel and a very small amount of CaTiO3. The Ca/Al ratio is the key factor affecting the calcium aluminate phase—with increasing Ca/Al ratio, the calcium aluminate phase is transformed from CaAl4O7 to CaAl2O4 and eventually to Ca12Al14O33, and the Si‐containing phase changes from Ca2Al2SiO7 to CaSiO4.

Novel Process to Prepare a Vanadium Electrolyte from a Calcification Roasting–Acid Leaching Solution of Vanadium Slag

Novel Process to Prepare a Vanadium Electrolyte from a Calcification Roasting–Acid Leaching Solution of Vanadium Slag

Removal of Sodium from Vanadium Tailings by Calcification Roasting in Reducing Atmosphere.

Vanadium tailings from vanadium extraction by a sodium roasting process are solid waste and cannot be used in sintering and ironmaking due to their high sodium content. In this paper, a calcification and reduction roasting process was proposed to remove sodium from vanadium tailings. The effects of Ca(OH)2 addition, reduction temperature, and roasting time on the sodium removal behavior and compression strength of pellets were studied. The addition of Ca(OH)2 and the reduction of iron oxides promoted the sodium-containing phases to transform to be simpler, which could enhance sodium removal. The sodium removal rate was up to 93.47% and the compression strength of the reduced products was 4497 N/P, and the metallized ratio of the product was higher than 70% under the optimal conditions: roasting at 1200 °C for 2 h with the Ca(OH)2 addition of 35%. The treated product after removing sodium can be recycled in the ironmaking process in a steel company.

Kinetics Study on the Leaching of Copper from Calcification Roasting Copper Refining Slag Using Waste Acid

Kinetics Study on the Leaching of Copper from Calcification Roasting Copper Refining Slag Using Waste Acid

Investigation on separation principle of vanadium and chromium among Fe2VO4-CaO-FeCr2O4 system: Simplify and simulate calcification roasting process of vanadium-chromium slag

The competitive reaction of vanadium and chromium with calcium additives, along with the formation mechanism of calcium vanadate and calcium chromate are the central issue to the efficient separation and extraction of vanadium and chromium from vanadium-chromium slag (V-Cr slag) by calcification roasting. In this study, Fe2VO4 and FeCr2O4 were synthesized to simulate the vanadium chromium spinel in V-Cr slag; then, the reaction mechanism of Fe2VO4-CaO-FeCr2O4 powder system was studied by XRD, SEM and leaching experiments. Results showed that calcium vanadate and calcium chromate are generated after roasting Fe2VO4-CaO system and FeCr2O4-CaO system individually. In Fe2VO4-CaO-FeCr2O4 system, as n(CaO)/n(V2O3) is 2, vanadium exists in the form of Ca2V2O7 while almost all Cr2O3 from the decomposition of FeCr2O4 reacts with Fe2O3 to continuously form solid solution with more FeCr2O4 adding. After leaching, the addition of FeCr2O4 has no obvious effect on the leaching ratio of vanadium, and the leaching ratio of chromium decrease with FeCr2O4 adding. Consequently, 94.03% of vanadium and 0.15% of chromium are leached with n(CaO)/n(V2O3)/n(Cr2O3) of 2/1/1.03 at 900 °C. When n(CaO)/n(V2O3) is 4, Fe2VO4 is oxidized and calcified gradually to form Ca2V2O7 and Ca3V2O8 with increasing roasting temperature. A small amount of CaCrO4 is generated owing to the calcification of chromium, and most chromium still exists in the form of solid solution. The reaction result of Cr2O3 and Fe2O3 is the superposition of solid solution reactions with different degrees. Increasing the roasting temperature can significantly reduce the chromium leaching ratio. All above would provide a theoretical support for the calcification roasting process from V-Cr slag.

Research on the Removal of Sodium from Vanadium Tailings by Calcification Roasting and NaOH Leaching

Vanadium tailings are a common solid waste in the vanadium industry. As they are rich in Fe, vanadium tailings could be a potential raw material for the blast furnace. However, the presence of approximately 4% Na2O in vanadium tailings is a major impediment to its return to the blast furnace. A novel method for removing sodium from vanadium tailings by calcification roasting and subsequent NaOH leaching was proposed in this work. The method demonstrated that calcification roasting of vanadium tailings can not only volatilize a part of sodium but also facilitate the dissolution of sodium during the subsequent NaOH leaching process. The thermodynamic analysis and behaviors of vanadium tailings during calcification roasting were systematically investigated. The transformation of sodium-containing phases in vanadium tailings during calcification roasting was studied. Further, the promoting effect of calcification roasting on sodium leaching by NaOH was clarified. The total removal efficiency of sodium was 80.37% under optimal conditions, and the residue obtained after sodium removal can be used as a raw material in the blast furnace process for in-plant recycling.

Effect of chromium content on the phase composition, crystallization and components extraction of vanadium slag

The existence of chromium in vanadium slag is generally considered to affect its phase composition, micromorphology, and further vanadium extraction by calcification roasting process. In this work, remelting and crystallization were used to prepare vanadium slag with different Cr2O3 mass fractions. The aforementioned effects were then examined through X-ray diffraction, scanning electron microscope, and leaching experiments. Results showed that Cr2O3 content affects spinel phase in vanadium slag. With the increase in Cr2O3 content, chromium was observed in the (Mn, Fe)(V, Cr)2O4 phase with vanadium in a homogeneous form, while the diffraction peak positions of (Mn, Fe)(V, Cr)2O4 shifted by a large angle from the lattice distortion. Further, the average grain size of spinel gradually decreased because of the increase in the number of crystallization centers, and the distribution of Cr, V, and Ti in the spinel phase were gradually homogenized instead of having obvious stratification. After calcification roasting, vanadium and chromium existed in the form of vanadate and (Fe0.6Cr0.4)2O3, achieving the complete separation of them after acid leaching. The increase in Cr2O3 content had no significant effect on the leaching behavior of vanadium. Additionally, increasing the roasting temperature and accelerating the heating process contributed to restraining chromium extraction. These results provide a research basis for the resource utilization of vanadium slag and vanadium chromium slag.

A Comparative Study of Extracting Vanadium from Vanadium Titano-Magnetite Ores: Calcium Salt Roasting Vs Sodium Salt Roasting

ABSTRACT In this study, a new vanadium extraction process from vanadium titano-magnetite(VTM) featuring calcification roasting and (NH4)2C2O4 solution leaching has been proposed. Compared with the traditional sodium roasting, the calcification roasting can avoid the production of waste gas and the sodium free tailings can be used for iron recovering by steel-making. However, the leaching rate of (NH4)2C2O4 was lower than that in sodium salt roasting-waterleaching. The reaction kinetics and mechanism of these two process were studied and compared in detail. It was found thatCaV2O6was formed during calcification and the porous structure of calcine facilitated the mass transfer. In the subsequent (NH4)2C2O4 leaching, theCaC2O4was formed and it would precipitate at the calcine particle surface and pores, which hindered the vanadium leaching. The leaching kinetics study showed that the diffusion through the solid product layer was the rate-determiningstep. Mechanical activation method was proposed to improve the leaching reaction kinetics in this work. It has been evident to be an effective method to intensify the leaching process. Under the optimal roasting and leaching conditions, the vanadium leaching rate could reach 81%, which was similar to that of the sodium salt roasting process. This is a promising alternative process for vanadium extraction from high grade VTM.

Evaluation of a green-sustainable industrialized cleaner production for FeV50 and FeV80 alloys from vanadium slag by calcification roasting–ammonia on-line cycle

Conventional calcification roasting–ammonium precipitate for ferrovanadium preparation have been exposed many technical problems such as roasting temperature control, leaching kinetics problem, precipitating vanadium liquor loss, reducing-melting vanadium evaporation loss and smelting vanadium evaporation loss in the process of industrialization. Therefore, a green-sustainable industrialized cleaner production for FeV50 and FeV80 alloys from vanadium slag by calcification roasting–ammonia on-line cycle is discussed. This process involves several steps including vanadium pretreatment and Fe recycling, pre-calcified vanadium slag circulating roasting, two-step circulating leaching, continuous vanadium precipitating and wastewater recycling, reducing-melting and NH3 recycling, three-stage ferrovanadium smelting. According to the theoretical base about conventional chemical, thermodynamics principles, phase diagram, dissolution kinetics, solution state diagram, separation gravity, problems, challenges and reasons analysis, the several steps including six cycles of FeV50 and FeV80 preparation were designed and industrialized. Through before and after process optimization and heat discharge, TG–DSC, XRD, SEM–EDS analysis, the mechanisms from vanadium slag to ferrovanadium help understand the increasing of the whole process vanadium yield from 57.21% to 80.81%, including vanadium oxide yield increased from 59.90% to 82.88%, ferrovanadium yield increased from 95.50% to 97.50%, respectively. All results and conclusions had guiding significance and demonstration effect on vanadium industry.

A sustainable green technology for separation and simultaneous recovery of rare earth elements and fluorine in bastnaesite concentrates

The current metallurgical process for the treatment of bastnaesite concentrates was developed when comprehensive utilization of resources and environmental impacts were not important issues. Today, these issues need to be addressed through designing more efficient processes that enable cleaner production and achieve sustainable development. A novel beneficiation-metallurgy combination process mainly comprised of calcification roasting, gravity separation and hydrochloric acid leaching was proposed in this work. Compared with current production process, the new process can reduce the dosage of chemical reagents and energy consumption, and significantly inhibit the generation and emission of fluorine containing wastes. In addition to rare earths, fluorine in the concentrates and the auxiliary calcium can also be effectively recovered, resulting in higher economic benefits. The experimental results show that, under the optimum conditions, the recoveries of rare earths, fluorine and calcium can reach 98.07 wt%, 64.76 wt% and 85.48 wt%, respectively. The new method can make the process and products more sustainable, and is supposed to be suitable for the treatment of bastnaesite concentrates around the world.

Recovery of vanadium from vanadium slag with high phosphorus content via recyclable microemulsion extraction

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.

Process and Kinetic Assessment of Vanadium Extraction from Vanadium Slag Using Calcification Roasting and Sodium Carbonate Leaching

The leaching process of vanadium from the calcification-roasted vanadium slag by sodium carbonate was researched. The effect of the main parameters on the sodium carbonate leaching process was investigated, and a kinetics analysis for the process using a new shrinking core model is presented. The results indicate that the leaching rate of vanadium significantly depends on the leaching temperature. Under the conditions of 6% CaO additive content in the roasted samples, 10:1 ml g−1 liquid–solid ratio, 80 g L−1 Na2CO3, and 30 min at 90°C, the leaching rate of vanadium is 86.64%. The clean and efficient utilization of vanadium slag can be achieved by the calcification roasting and sodium carbonate leaching process. Scanning electron microscopy/energy dispersive x-ray spectroscopy analysis shows that the vanadium slag can be effectively leached by sodium carbonate with few impurities drawn into the solution. The leaching kinetics of this process shows that the interfacial transfer and diffusion across the product layer affect the leaching at the same time. Moreover, the calculated activation energy of the leaching process is 40.93 kJ/mol, and the reaction order of the sodium carbonate concentration is 0.49.

Efficient separation of chromium and vanadium by calcification roasting–sodium carbonate leaching from high chromium vanadium slag and V2O5 preparation

Calcification roasting–sodium carbonate (Na2CO3) leaching process was carried out to separate chromium and vanadium efficiently from high chromium vanadium slag (HCVS). Then vanadium existed in the form of ammonium metavanadate (NH4VO3) after precipitation from the purified leaching liquid, and highly pure V2O5 was prepared, while chromium remained in the vanadium tailings in the form of (Fe0.6Cr0.4)2O3. The effects of separation behaviors of chromium and vanadium under different roasting and leaching conditions were studied systematically. In order to elucidate the phase evolution, XRD and SEM were used during the whole process. After calcification roasting and Na2CO3 leaching, 93.19% of vanadium and 0.04% of chromium was extracted when CaO was added to HCVS in a mole rate n(CaO)/n(V2O5) of 0.5, roasted at 900 °C and maintained for 60 min. The roasted samples were added to 160 g/L Na2CO3 solution with the mass ratio of liquid to solid (L/S) of 10, then heating at 80 °C for 60 min. CaO tended to combine with vanadium and form alkali soluble calcium vanadate, while almost all of chromium was more likely to react with iron and form (Fe0.6Cr0.4)2O3. 94.00% of vanadium was then precipitated as NH4VO3 from the vanadium–containing supernatant after CO32– removing, when NH4Cl was added with the mole rate of n(NH4+)/n(V) of 6 and precipitated for 120 min at 5 °C. The purity of V2O5 was 99.68%, which was prepared by roasting NH4VO3. This process achieved the high efficiency separation of chromium and vanadium from HCVS compared with the traditional calcification roasting–acid leaching process. And the chromium-containing vanadium tailings can be used as the raw material to extract chromium and prepare Fe-Cr alloy.

Roasting and leaching behaviors of vanadium and chromium in calcification roasting–acid leaching of high-chromium vanadium slag

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(V2O5)), 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 (Fe0.6Cr0.4)2O3. 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(V2O5) 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(V2O5) ratios of 0.5 and 5, respectively.

Efficient Separation and Extraction of Vanadium and Chromium in High Chromium Vanadium Slag by Selective Two-Stage Roasting–Leaching

Vanadium and chromium are important rare metals, leading to a focus on high chromium vanadium slag (HCVS) as a potential raw material to extract vanadium and chromium in China. In this work, a novel method based on selective two-stage roasting–leaching was proposed to separate and extract vanadium and chromium efficiently in HCVS. XRD, FT-IR, and SEM were utilized to analyze the phase evolutions and microstructure during the whole process. Calcification roasting, which can calcify vanadium selectively using thermodynamics, was carried out in the first roasting stage to transfer vanadium into acid-soluble vanadate and leave chromium in the leaching residue as (Fe0.6Cr0.4)2O3 after H2SO4 leaching. When HCVS and CaO were mixed in the molar ratio CaO/V2O3 (n(CaO)/n(V2O3)) of 0.5 to 1.25, around 90 pct vanadium and less than 1 pct chromium were extracted in the first leaching liquid, thus achieving the separation of vanadium and chromium. In the second roasting stage, sodium salt, which combines with chromium easily, was added to the first leaching residue to extract chromium and 95.16 pct chromium was extracted under the optimal conditions. The total vanadium and chromium leaching rates were above 95 pct, achieving the efficient separation and extraction of vanadium and chromium. The established method provides a new technique to separate vanadium and chromium during roasting rather than in the liquid form, which is useful for the comprehensive application of HCVS.

Phase evolutions, microstructure and reaction mechanism during calcification roasting of high chromium vanadium slag

Excess CaO was added to high chromium vanadium slag (HCVS) to systematically and comprehensively investigate the reaction mechanisms during calcification roasting. Samples roasted at specific temperatures according to thermal analysis (TG-DSC) were analyzed by XRD, FT-IR, SEM, XPS and leaching experiments from different perspectives. Reaction thermodynamics and kinetics were employed to demonstrate the mechanism theoretically. The results show that dehydration, oxidation of free iron and olivine, and preliminary and further oxidation and calcification of spinel were the major steps during calcification roasting. The formation of calcium-containing components followed the order of calcium vanadate > calcium chromate > calcium silicate, both practically and theoretically. Normal V-spinel in HCVS converted to inverse V-spinel at lower temperatures and then combined with CaO to generate Ca2V2O7. At higher temperatures, the final oxidation and calcification product of V-spinel with excessive CaO was Ca3V2O8, which was controlled by reaction kinetics rather than thermodynamics. Cr-spinel was more stable than V-spinel, which reacted with CaO and gradually formed CaCrO4 and Ca3(CrO4)2. With further temperature increases, Cr tended to conjugate to Fe to form acid-insoluble solid solutions (Fe0.6,Cr0.4)2O3 instead of reacting with CaO. Oxidation and calcification of spinel were controlled by a 2.50 order reaction. The overall apparent activation energy Ea and frequency factor A were 157.34 kJ mol−1 and 4.23 × 107 min−1, respectively.

Comparison of Ultrasound-Assisted and Regular Leaching of Vanadium and Chromium from Roasted High Chromium Vanadium Slag

Ultrasound-assisted leaching (UAL) was used for vanadium and chromium leaching from roasted material obtained by the calcification roasting of high-chromium–vanadium slag. UAL was compared with regular leaching. The effect of the leaching time and temperature, acid concentration, and liquid–solid ratio on the vanadium and chromium leaching behaviors was investigated. The UAL mechanism was determined from particle-size-distribution and microstructure analyses. UAL decreased the reaction time and leaching temperature significantly. Furthermore, 96.67% vanadium and less than 1% chromium were leached at 60°C for 60 min with 20% H2SO4 at a liquid–solid ratio of 8, which was higher than the maximum vanadium leaching rate of 90.89% obtained using regular leaching at 80°C for 120 min. Ultrasonic waves broke and dispersed the solid sample because of ultrasonic cavitation, which increased the contact area of the roasted sample and the leaching medium, the solid–liquid mass transfer, and the vanadium leaching rate.

Effect of Mechanical Activation Treatment on the Recovery of Vanadium from Converter Slag

The high roasting temperature and low leaching efficiency of vanadium from vanadium-bearing converter slag are regarded as the main factors significantly influencing the application of calcification roasting–acid leaching processes in the cleaner production of vanadium. In this study, a mechanical activation treatment was performed to enhance the extraction of vanadium from converter slag. The enhancement effects obtained from mechanical activation were comprehensively evaluated through indices such as the roasting temperature and leaching efficiency. The effects of mechanical activation time, roasting temperature, leaching temperature, solid to liquid ratio, particle size, and acid concentration on the leaching efficiency were investigated. Microstructure morphology and elemental analyses of the raw materials and leaching residue were also investigated using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results demonstrated that the mechanical activation significantly decreased the optimum roasting temperature from 1173 K to 1073 K (900 °C to 800 °C) and increased the leaching efficiency from 86.0 to 90.9 pct.

Thermodynamic Mechanism Analysis of Calcification Roasting Process of Bastnaesite Concentrates

A novel calcification roasting decomposition method for bastnaesite concentrates has been proposed previously. In this work, the thermodynamic mechanism was investigated via simultaneous measurements of thermogravimetry and differential thermal analyses, combined with X-ray diffraction analyses. Rare earth oxides and calcium fluorides were generated after bastnaesite and calcium hydroxide broke down, respectively. The generation and decomposition of calcium carbonate occurred at the same time. Considering the difficulties in obtaining pure substances, theoretical calculations were applied to determine the standard enthalpy of formation (Δf H 298), Gibbs free energies of formation (Δf G 298), and heat capacities at constant pressure (C p) of some rare earth minerals (CeFCO3 and CeOF). Based on these results, the standard Gibbs energy of reaction at different temperatures (Δr G T) was ascertained, and the major reactions were verified to be thermodynamically reasonable.

A novel process for recovery of rare earth and fluorine from bastnaesite concentrates. Part I: calcification roasting decomposition

Abstract Environmental pollution and valuable resource waste exist commonly in current metallurgical processes of bastnaesite concentrates. A novel associated process of calcification roasting, mineral beneficiation and acid leaching was proposed. This paper focused on the prior calcification roasting decomposition procedure. By studying the influence of roasting conditions on cerium oxidation, the optimum technology conditions were obtained: operated at 650°C for 60 min with 20% calcium hydroxide. After roasting, the leaching rate of rare earths can reach 98.84%. Bastnaesite can be sufficiently decomposed at lower temperature with calcium hydroxide added and the emission rate of fluorine decreased by over 98% compared with that during the roasting without additives. After the roasting, the main existence form of fluorine turned calcium fluoride, which made it possible for resource utilization and environmental protection. Particle sizes and scanning electron microscope and energy dispersive spectrometer analyses indicated that rare earth oxides gathered in particles of >48 μm, while generated calcium fluoride with fluffy cotton morphology distributed evenly.