Separation Of Chromium Research Articles

Preconcentration of heavy metal ions using Konjac gum- Co3O4 magnetic hydrogel prior to their determination by ICP-OES

In this study, a hydrogel embedded with magnetic cobalt nanoparticles was synthesized from natural Konjac gum through a simple and low-cost method and its potential for separation and preconcentration of lead, copper, zinc, chromium, cobalt, and cadmium ions was investigated. Determination of the extracted metal ions was carried out using inductively coupled plasma /optical emission spectroscopy. The magnetic property of the hydrogel helps the separation from the solution and improves the adsorption capacity. The proper synthesis of the magnetic hydrogel was confirmed with different characterizations techniques, such as Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The effective parameters on the sorbent synthesis and extraction process were studied. Under optimized conditions, the linear range and detection limit were found to be 0.3–100.0 µg L−1 and 34.0 ng L−1 for lead, 0.1–100.0 µg L−1 and 17.0 ng L−1 for chromium, 0.07–100.0 µg L−1 and 10.0 ng L−1 for zinc, 0.07–100.0 µg L−1 and 12.0 ng L−1 for copper, 0.1–100.0 µg L−1 and 15.0 ng L−1 for cadmium and 0.1–100.0 µg L−1 and 21.0 ng L−1 for cobalt, respectively. The developed method was successfully employed for the analysis of the above ions in the real samples including water, fruit and soil.

Efficient separation of Chromium(III) from Lanthanide(III) via reductive boronization in molten chloride

It is an easy way to recover metals in molten salt by the precipitation-based method, but the selectivity yet remains challenging. Herein, a new separation method employing reductive boronization is proposed, and it is validated by the separation of trivalent chromium and lanthanide ions in molten LiCl-KCl. Although no Cr(III) and La(III) separation was achieved by using NaBH4, Cr(III) was successfully removed via the formation of insoluble CrB2 when B powder was used as the boronization reagent with La(III) remaining entirely in the melt. More than 97% Cr(III) can be removed from the CrCl3-LaCl3-LiCl-KCl melt after a reaction time of 300 min, and the removal rate was retained when the La/Cr ratio varied from 0.1:1 to 10:1. Such reductive boronization method is also valid in other Ln(III)/Cr(III) systems. The boronization process involves the reduction of Cr(III) and the reaction between zero valent metal and boron rather than the simple combination of anions and cations to give precipitates as evidenced by the XPS analyses. The difference in reactivity between Cr(III) and La(III) toward B can be rationalized in terms of their significant difference in the ΔG values of the boronization reactions that mainly correlates with the much lower reduction potential of La(III)/La(0), which makes B an ideal boronization reagent for the separation of trivalent chromium and lanthanide ions in molten chloride.

Efficient separation of vanadium and chromium by the complexation with sulfate ions in solvent extraction using EHEHPA

The significant chemical similarity between vanadium and chromium complicates the process of efficient extracting V(Ⅳ) from the solution containing Cr(Ⅲ) to prepare high-purity vanadyl sulfate electrolyte. In this study, the separation of vanadium and chromium with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (EHEHPA) was enhanced by increasing the concentration of SO42−. Under the extraction equilibrium pH of 2.5, the extraction of Cr(III) was suppressed by increasing the concentration of SO42− anions, which hardly affected the extraction efficiency of V(IV), achieving a separation factor as high as 5780.6 at SO42− concentration of 1.75 mol·L−1. Furthermore, after pretreatment of the water-leaching solution of sodium-roasted vanadium slag, extraction was carried out under the conditions of equilibrium pH of 1.8 and SO42− concentration of about 2.00 mol·L−1, and after stripping, the vanadyl sulfate electrolyte containing 2.12 mol·L−1 of vanadium and only 0.11 mg·L−1 of chromium was obtained. It was proved that Cr(Ⅲ) mainly extracted in the form of CrSO4+ into organic phase by one EHEHPA dimer as [CrSO4(H2O)]+ under higher SO42− concentrations (e.g., ≥1.50 mol·L−1), while Cr(Ⅲ) was extracted by two EHEHPA dimers as Cr3+ without SO42− in the solution. Based on the density functional theory, the complex structures of Cr(III) were optimized and the energy changes of Cr(III) extraction reactions were calculated, indicating the complexation between SO42− and Cr(III) under higher SO42− concentrations resulting in the inhibition of Cr(III) extraction, and thus enhancing the separation of vanadium and chromium.

Observations and simulations for separation mechanism of vanadium and chromium: Progressive study based on oxides, spinels and vanadium-chromium slag

In this study, V2O3-CaO-Cr2O3 oxides system, Fe2VO4-CaO-FeCr2O4 spinels system and V-Cr slag-CaO system were established progressively to investigate the separation effect of vanadium and chromium components in vanadium-chromium slag (V-Cr slag). Then, the separation mechanism was proposed by XRD, SEM and leaching experiments. The results show that the reaction ability of vanadium with calcium is far stronger than that of chromium. In oxides and spinels systems, as CaO increases, CaV2O6, Ca2V2O7, and Ca3V2O8 are generated sequentially. In V-Cr slag-CaO system, additive CaO, along with manganese, magnesium and iron components in V-Cr slag reacts with vanadium, resulting in the complex composition of vanadate. As to chromium component, Cr2O3 in oxides system will be converted into CaCrO4 as n(CaO)/n(V2O3) is higher than 2. Iron in the spinels system reacts with chromium and form solid solution (FexCr1-x)2O3, resulting in less chromium reacting with calcium to produce CaCrO4. In V-Cr slag-CaO system, SiO2 generated by the decomposition of silicate phase combines with part of calcium expected to react with chromium, making CaCrO4 generation more difficult, promoting the separation of vanadium and chromium further. Consequently, during H2SO4 leaching, chromium leaching ratios are 98.75%, 45.77% and 5.91%, respectively, in oxides, spinels and V-Cr slag system when n(CaO)/n(V2O3) is 5. And when n(CaO)/n(V2O3) is 2, more than 90% of vanadium can be leached, however, the leaching ratios of chromium are 0.22%, 0.17% and 0.094% in these three systems. Furthermore, the variation regularities of chromium leaching ratios with CaO amount are described by regression equations. These findings would provide the theoretical support for the calcification roasting process with V-Cr slag.

Green redox separation and efficient extraction of vanadium and chromium from leaching solution of chrome-vanadium slag

Green separation and efficient extraction of vanadium and chromium from vanadium-chromium leaching solution are serious challenges for the utilization of chrome-vanadium slag. A green sucrose reduction-H2O2 selective oxidation route is proposed for deep separation of vanadium and chromium from vanadium-chromium leaching solution based on different redox properties. Eh-pH diagram of V-Cr-H2O system and existence forms of vanadium and chromium ions are calculated. Obvious difference of redox properties between V(V) and Cr(VI) exists in acidic environment. The dependences of selective separation on pH for reduction, temperature, m(sucrose)/m(Cr(VI)) and n(H2O2)/n(V(V)) are studied. The concentration ratio of vanadium to chromium in solution after selective separation of chromium decreases from 1.6 to 0.06. The extraction ratios of Cr2O3 and V2O5 are 96.3% and 93.8%, respectively. The redox behavior of V(V) and Cr(VI) is revealed. Cr(VI) and V(V) are reduced to Cr(Ⅲ) and V(IV) by 5-hydroxymethylfurfural, a hydrolysate of sucrose, and then V(IV) is selectively oxidized to V(V) by H2O2. Cr2O3·n(H2O) and ammonium polyvanadate obtained by hydrolysis and ammonium precipitation are calcined to Cr2O3 and V2O5, respectively. Cr2O3 with the purity of 99.4% can be used as high-quality pigment. The purity of V2O5 meets the requirements of YB/T 5304–2011 for 98 V2O5.

Method Development and Optimization of Liquid-Liquid Microextraction Based on the Decomposition of Deep Eutectic Solvent for the Determination of Chromium (VI) in Spinach: Assessment of the Greenness Profile Using Eco-scale, AGREE, and AGREEprep

A simple, effective, and ligandless liquid-liquid microextraction (LLME) procedure based on the decomposition of hydrophobic deep eutectic solvents (HDES) was developed for the separation and pre-concentration of chromium (VI) ions in spinach leaves, before the determination by flame atomic absorption spectrophotometry. In the proposed study, the first stage involved the leaching of chromium (VI) from spinach leaves with 0.1 M Na2CO3, and in the second stage, chromium (VI) extract was preconcentrated with the LLME procedure using a DES prepared from the combination of DL-menthol and formic acid as a chelating agent and extraction solvent. The DES decomposed in an aqueous donor phase resulting in the dispersion of menthol and extraction of Cr (VI) ions. Under optimal experimental conditions, the limits of detection (LOD) and quantification (LOQ) were 0.63 and 2.1 µg L−1, respectively. The relative standard deviation (RSD) was less than 7%, and the pre-concentration factor (PF) was found to be 31.25. The accuracy of the present methodology was tested by recovery experiments. The greenness of the developed method was assessed using three quantitative green metrics tools: Analytical Eco-scale, AGREE, and AGREEprep, with only Analytical Eco-scale qualifying the proposed method as green.

Green and efficient separation of vanadium and chromium from high-chromium vanadium slag: a review of recent developments

Strategies for efficient extraction and separation of vanadium and chromium from high-chromium vanadium slag with green chemistry principles are summarized.

Efficient, fast, simple, and eco-friendly methods for separation of toxic chromium(VI) ions based on ion exchangers and polymer materials impregnated with Cyphos IL 101, Cyphos IL 104, or D2EHPA

In this study, we present the results of the first comparison of the elimination of toxic Cr(VI) ions, which are hazardous contamination of the environment, from aqueous solutions using ion exchangers (IEs) and polymer materials (PMs) impregnated with D2EHPA or ionic liquids (Cyphos IL 101 and Cyphos IL 104). Sorption of Cr(VI) ions and desorption from the formulated sorption materials were carried out. In comparison, classical solvent extraction was accomplished. Fourier transform infrared-attenuated total reflectance spectroscopy (FTIR-ATR), scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and atomic force microscopy (AFM) have been used for characterization of the structure of developed IEs and PMs. The highest efficiency of adsorption of Cr(VI) ions was obtained using PMs with ionic liquids (>82%). Desorption from these materials were also very efficient (>75%). On the contrary, the application of IEs allowed for obtaining the best results of both, sorption and desorption processes when using D2EHPA (75% and 72%, respectively). The application of PMs and IEs is part of the green chemistry, and the conducted elimination of chromium(VI) ions using developed materials allows for the conclusion that they can potentially be used on a larger scale, e.g., for the treatment of industrial wastewater rich in Cr(VI) ions.

Separation of vanadium and chromium from vanadium-chromium slag by high-temperature heating

A method to separate vanadium (V) and chromium (Cr) from vanadium-chromium (V-Cr) slag was developed to treat the hazardous substances effectively. This approach was achieved by heating V-Cr slag with Na2CO3 in air within a temperature range of 30 °C to 1400 °C. Through TG-DSC, XRD, SEM-EDS and XPS tests, the results showed that Na2CO3 reacted with V compounds at lower temperatures, producing NaVO2 and Na3VO4. At the high-temperature stage, Na2CO3 reacted with Cr compounds, resulting in Na2CrO4 and Cr2O3 formation on the slag surface. As the temperature exceeded 1200 °C, volatiles (Na2CrO4, NaCrO2, and other Cr compounds) were generated from the residuals and collected by condensation to separate V and Cr. This method provides a novel strategy for eco-friendly resource utilization of V-Cr slag, which is highly efficient, minimizes hazardous wastes, and can be further promoted in the industry.

Recovery and Reuse of Chromium from Tan Yard Solid Waste in Leather Manufacturing

Chrome tanning is the most popular and widely used method utilizing basic chromium salts in leather processing. Only 60-70% of these salts react with collagen to form leather. The rest remains unreacted being released as toxic waste and causing severe environmental pollution in many developing countries. In the current study, a significant approach was made to utilize solid waste with a clean environment perspective. The chromium was extracted as basic chromium sulfate using H2SO4 from tannery waste and reused in the leather manufacturing procedure. Extracted solid sludge was examined by Atomic Absorption Spectrometry and elemental analysis before and after the separation of chromium (III). It revealed that 97% of chromium was extracted from tan yard sludge. Recovered chromium sulfate was reused in goat skin processing. Batch experiments were carried out by applying recovered basic chromium sulfate, and a combination of fresh and recovered basic chromium sulfate solutions separately. Fresh basic chromium sulfate was used as the control method. The structure and morphology of the final processed leather were characterized by Field Emission Scanning Electron Microscope (FESEM) and Thermogravimetric analysis (TGA). The identical structural morphologies of all processed leather were confirmed in the FESEM study. The physical and chemical characteristics of all finished leather were found very similar. The TGA analysis data proved that raw leather processed by recovered chromium is thermally more stable than others. These research findings signify a new potential effort of separating important chemicals from solid sludge and reusing them. This technique is simple, cost-effective, eco-friendly, and sustainable as it reduces environmental pollution from tannery chromium waste.

Electrically Controlled Adsorptive Membranes with Tunable Affinity for Selective Chromium (VI) Separation from Water.

Ionic contaminants such as Cr(VI) pose a challenge for water purification using membrane-based processes. However, existing membranes have low permeability and selectivity for Cr(VI). Therefore, in this study, we prepared an electrically controlled adsorptive membrane (ECAM-L) by coating a loose Cl--doped polypyrrole layer on a carbon nanotube substrate, and we evaluated the performance of ECAM-L for Cr(VI) separation from water. We also used electrochemical quartz crystal microbalance measurements and molecular dynamics and density functional theory calculations to investigate the separation mechanisms. The adsorption and desorption of Cr(VI) could be modulated by varying the electrostatic interactions between ECAM-L and Cr(VI) via potential control, enabling the cyclic use of the ECAM-L without additional additives. Consequently, the oxidized ECAM-L showed high Cr(VI) removal performance (<50 μg/L) and treatment capacity (>3500 L/m2) at a high water flux (283 L/m2/h), as well as reusability after the application of a potential. Our study demonstrates an efficient membrane design for water decontamination that can selectively separate Cr(VI) through a short electric stimulus.

Melamine functionalized mesoporous silica SBA-15 for separation of chromium (VI) from wastewater

In this study, a Melamine-functionalized mesoporous silica-SBA-15 (Melamine-MS-SBA-15) adsorbent was synthesized to remove Cr(VI) from wastewater. The mesoporous silica-SBA-15 adsorbent was first synthesized using the hydrothermal method and post-synthesis under toluene reflux. Then, 3-aminopropyl trimethoxy silane was added to the adsorbent surface and it was further modified by melamine to obtain the final product. SBA-15 well-performed after Melamine functionalization against the Cr(VI) removal due to the conversion of physisorption to chemisorption adsorption. The adsorption of Cr(VI) using the Melamine-MS-SBA-15 was studied. XRD, BET, SEM, FTIR, TGA, and zeta potential analyses were used to characterize the adsorbent. Parameters affecting adsorption including pH (3–9), initial concentration (20–200 ppm), contact time (1–24 h), adsorbent dose (1.5–15 mg L−1), and temperature (18–30 °C). Optimal results were pH = 3, an initial concentration of 20 ppm, an adsorbent dose of 4 mg L−1, a contact time of 6 h, and a temperature of 18 °C. The results of isotherm and kinetics model studies were consistent with Temkin and pseudo-second-order models, respectively. The thermodynamics parameters confirmed the spontaneous reaction. Experimental results showed that functionalization of the adsorbent surface of MS-SBA-15 with melamine increased the adsorption efficiency and adsorption capacity. The highest adsorption capacity for Cr(VI) was about 50 mg/g. The maximum adsorption efficiency for solutions containing Cr(VI) was about 84%. Increasing the adsorption concentration in a fixed value of the heavy metal concentration increased the adsorption capacity and increasing the heavy metal concentration, increased the adsorption capacity.

Separation, speciation and quantification of both chromium (VI) and chromium (III) in tanned leather samples: a comparative study and validation of analytical methods

In the present work, a comparative study of analytical methods for the simultaneous and quantitative determination of trivalent and hexavalent chromium is presented. For the analysis by ion chromatography-inductively coupled plasma-mass spectrometry, two different columns were tested, as well as different mobile phases and different pH of the samples. The optimized analytical method permitted the separation of Cr(III) and Cr(VI) using 75 mmol/L NH4NO3 pH 3 as chromatographic eluent. The method was validated and applied to real samples, allowing the determination of both species simultaneously, even when there is a huge difference of concentration between Cr(III) and Cr(VI). Limit of detection and limit of quantification for Cr(III) were found to be 0.016 and 0.054 upmug/L (0.3 and 1.1 upmug/kg), respectively, and for Cr(VI) 0.13 and 0.43 upmug/L (7 and 22 upmug/kg), respectively. Possible species interconversions were monitored through the use of chromium isotopic standards, which confirmed that the optimized methodology preserves chromium speciation during extraction and analysis. Fourier-transform ion cyclotron resonance-mass spectrometry permitted the structure elucidation of the complex formed during ethylenediaminetetraacetic acid extraction.Graphical

Chemical Investigation and Separation of Chromium from Chrome Cake of BSCIC Tannery Industrial Estate at Hemayetpur, Dhaka, Bangladesh

Leather tanning mainly depends on chrome tanning. A huge amount of basic chromium sulfate (BCS) is used in leather tanning. About 60–70% of BCS has been taken by leather and the rest of the amount is discharged as effluent and solid waste. In the Common Effluent Treatment Plant (CETP) of BSCIC Tannery Industrial Estate (Hemayetpur, Savar, Dhaka), the effluent which contained a high concentration of chromium is precipitated as solid chromium hydroxide with other elements which is called a chrome cake. Chrome cake is not exposed directly in the open space due to its toxic effect on human health as well as the environment. Human occupational experience distinctly indicates that, when inhaled, chromium compounds are respiratory tract irritants, resulting in airway irritation, airway obstruction, and lung, nasal, or sinus cancer. It is strongly suggested to extract Cr from the chrome cake before dumping it; otherwise, it will be a potential hazard to the environment. Herein, the chrome cake is characterized by inductively coupled plasma-optical emission spectroscopy (ICP-OES), X-ray fluorescence (XRF), UV-visible spectrophotometer, etc., and develops a method to separate chromium from chrome cake. ICP-OES and XRF analyses show that the total chromium contained in chrome cake is ∼17.45% and 20.7%, respectively. UV-visible spectrophotometer indicates that ∼0.04% of chromium is hexavalent. Afterward, chromium has been separated by using H2SO4 where the optimized concentration was found to be 7%. The separation efficiency of chromium from the chrome cake for optimized condition is obtained at ∼95%.

Molecular dynamic simulation and artificial neural network (ANN) modeling of the functionalized graphene oxide membranes on Cr (VI) ion removal through electrodialysis method

In this study, the separation of chromium (VI) ion as a dangerous heavy metal material from water by graphene oxide (GO) membrane was investigated using molecular simulation method. Pores were created in the middle of GO membrane and then the membrane pores were functionalized by adding -F, -H, and -OH chemical groups. The external voltages were applied to the studied system to improve the efficiency of Cr (VI) and water separation process. To study the functionalized GO membrane performance under applied voltage in the separation process, analyzes were performed, which include permeation, artificial neural network (ANN), radial distribution function, hydrogen bond, ion tracking path, water density map and diffusion coefficient of ion. The outcomes demonstrate that the GO membrane can be constructed with an adequate functional porosity and a sufficient applied voltage, and that it performs well throughout the heavy metal separation procedure.

Enhanced selective separation of vanadium(V) and chromium(VI) using the CeO2 nanorod containing oxygen vacancies.

Adsorption of vanadium from wastewater defends the environment from toxic ions and contributes to recover the valuable metal. However, it is still challenging for the separation of vanadium (V5+) and chromium (Cr6+) because of their similar properties. Herein, a kind of CeO2 nanorod containing oxygen vacancies is facilely synthesized which displays ultra-high selectivity of V5+ against various competitive ions (i.e., Fe, Mn, Cr, Ni, Cu, Zn, Ga, Cd, Ba, Pb, Mg, Be, and Co). Moreover, a large separation factor (SFV/Cr) of 114,169.14 for the selectivity of V5+ is achieved at the Cr6+/V5+ ratio of 80 with the trace amount of V5+ (~ 1mg/L). The results show that the process of V5+ uptake is the monolayer homogeneous adsorption and is controlled by external and intraparticle diffusions. In addition, it also shows that V5+ is reduced to V3+ and V4+ and then formation of V-O complexation. This work offers a novel CeO2 nanorod material for efficient separation of V5+ and Cr6+ and also clarifies the mechanism of the V5+ adsorption on the CeO2 surface.

Mechanism of Chromium Separation and Concentration from Tannery Wastewater by Membrane Methods

The article specifies conditions for a nanofiltration process employing a diafiltration method with a constant volume diafiltration (NF-CVD) for exhausted chromium tannery wastewater treatment and describes a mechanism of the examined process carried out for model wastewater. The authors prove that a decrease in salt concentration in the NF-CVD process is an important factor that enables effective concentration of chromium. Based on the proposed chromium separation and concentration mechanisms, it was found that this effect may be achieved by (1) limiting the formation of an ionic adsorption-polarization layer and (2) reducing the increase in the osmotic pressure caused by a change in the separation properties of the membrane. The article shows that in the analyzed system a higher amount of the solvent introduced at the diafiltration stage and a lower process pressure that ensures a reduction in salt retention translate to a high level of salt removal. In regenerates, after the NF-CVD processes in which at least the same volume of a washing diluent as the volume of the retentate after the pre-concentration step was used, salt concentration below 10 g L-1 and chromium concentration about three times higher than in the case of the feed solution were obtained. Therefore, the proposed solution implements the circular economy strategy in the tannery.

Separation of chromium(VI) by adsorption onto garlic peels: kinetics, thermodynamic and isotherm study

Separation of chromium(VI) by adsorption onto garlic peels: kinetics, thermodynamic and isotherm study

Effective separation and recovery of iron and chromium from laterite residue in the presence of calcium chloride

In nitric acid pressure leaching (NAPL) for the treatment of limonitic laterite ores, the comprehensive utilization of leach residue is significant for resource recovery and environmental protection. In this work, the recovery and separation of iron and chromium from NAPL residue by metallization reduction roasting−magnetic separation with calcium chloride as additive was studied. The following optimum parameters were obtained: 1100 °C roasting temperature, 25 % reductant dosage, 40 min roasting time, 7 % calcium chloride dosage, 200 mT magnetic field intensity, and 40 s rod mill time (D50 = 7.20 µm). Under these optimum conditions, 81 wt% iron content in the concentrate and 7.4 wt% chromium in the tailings were obtained. The corresponding recovery rates of iron and chromium were 95 % and 64 %, respectively. The microstructure and composition of leach residue and process products were investigated by SEM, EDS, and XRD to study the phase transition and polymerization of substances during roasting. The results showed that iron was mainly enriched in the magnetic concentrate, and chromite and silicate minerals dominated the tailings. Analysis of the action of calcium chloride in the reduction roasting revealed that calcium chloride was beneficial for the liberation of Fe from fayalite and the migration and polymerization of iron.

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.