Extraction and separation of chromium from the solution after hydrolysis precipitation of vanadium

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.

Efficient extraction and separation of vanadium and chromium in high chromium vanadium slag by sodium salt roasting-(NH4)2SO4 leaching

A cleaner and efficient process for extraction of vanadium from high chromium vanadium slag: Leaching in (NH4)2SO4-H2SO4 synergistic system and NH4+ recycle

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

ABSTRACTCalcification roasting-acid leaching were conducted to investigate the extraction behavior of vanadium and chromium from high-chromium vanadium slag (HCVS). The conditions were optimized by response surface methodology (RSM). Results showed that when HCVS and CaO were mixed in m(CaO)/m(V2O5) of 0.62, then roasted from room temperature to 840 °C and maintained for 170 min, a maximum vanadium leaching rate of 87.74% was achieved. Additionally, 0.68% chromium was co-leached, achieving the separation of vanadium and chromium. The roasting factors affecting vanadium extraction followed this order: roasting temperature>m(CaO)/m(V2O5)=holding time. For the chromium extraction, the interaction between m(CaO)/m(V2O5) and roasting temperature was significant.

A novel roasting process to extract vanadium and chromium from high chromium vanadium slag using a NaOH-NaNO3 binary system

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

An efficient utilization of high chromium vanadium slag: Extraction of vanadium based on manganese carbonate roasting and detoxification processing of chromium-containing tailings.

Charles F. Baes Robert E. Mesmer The hydrolysis of cations 1976 John Wiley Interscience Londres

Selective recovery of vanadium from high-chromium vanadium slag by a mechanically activated low-sodium salt roasting-water leaching process

The process of electroflotation is used for treatment of wastewaters carrying heavy and non-ferrous metals in the form of poorly soluble compounds if the concentrations of contaminants are too high to be handled by adsorption process. The problem of raising the efficiency of electroflotation process is currently of relevance. This paper examines how the composition of the medium, i.e. the nature of the electrolyte, surfactants and hardness salts, can influence the extraction of iron, aluminum and chromium hydroxides from aqueous solutions by electroflotation. It was found that the electrolyte (NaCl, Na2SO4) nature has no significant effect on the process. The hydroxide extraction performance can be impacted by the presence of calcium ions regardless of the electrolyte nature. It happens due to the adsorption of Ca2+ on the hydroxide surface, which makes it more hydrophilic. The degree of dispersed phase extraction can be increased due to the introduction of surfactants: didecyldimethylammonium chloride, sodium dodecyl sulfate and a mixture of primary oxyethylated synthetic alcohols. Sodium dodecyl sulfate, which is an anionic surfactant, proved to deliver the best result. The high process efficiency in terms of dispersed phase extraction is due to the hydrophobization of the particle surface by adsorbed sodium dodecyl sulfate and the stabilization of gas bubbles. The particle sizes of iron and chromium hydroxides vary in the range of 0.04 to 4 microns. At the same time, most of the aluminum hydroxide particles are bigger than 10 microns, which can be attributed to the high polymerization ability of aluminum ions and subsequent particle coagulation. The efficiency of electroflotation extraction of chromium, aluminum and iron hydroxides in the presence of calcium ions using anionic surfactant is at least 90%. Additional filtration is recommended to ensure the treated wastewater is in compliance with applicable standard.

Change in phase, microstructure, and physical-chemistry properties of high chromium vanadium slag during microwave calcification-roasting process

This paper describes a systematic study into the role of metallic chromium and chromium (III) oxide films of varying thickness in slowing or preventing the corrosion-driven cathodic disbondment of an organic overcoat applied to chromium/oxide coated steel. A graded wedge of chromium metal or chromium (III) oxide is applied to a steel substrate using physical vapour deposition (PVD) in conjunction with a stepping motor driven sliding shutter arrangement. An overcoat of electrically insulating polyvinyl butyral (PVB) lacquer is then applied and this acts as model organic coating. Corrosion is initiated from an artificially created coating defect, penetrating to the steel substrate, though the introduction of an aqueous sodium chloride electrolyte. Scanning Kelvin probe (SKP) potentiometry is then used to follow the resulting kinetics of PVB coating delamination in air at high relative humidity. The variation in layer thickness across the PVD wedge allows for a high-throughput investigation of the effect of the layer thickness for both metallic chromium and chromium (III) oxide on the rate of corrosion driven cathodic coating delamination, as shown schematically in the figure below. Varying chromium metal layer thickness between 100 nm and 1000 nm produced very little change in the rate of PVB film delamination and the delamination kinetics remained parabolic throughout. Parabollic kinetics are consistent with rate limitation by the mass transport of (sodium) cations through electrolyte layer forming beneath the delaminated coating. Conversely, increasing the thickness of chromium (III) oxide from 10nm to 200 nm (applied over a 500 nm metallic chromium layer), resulted in a significant decrease in rates of PVB delamination. At chromium oxide layer thicknesses ≥ 120 nm delamination kinetics became linear (zero order with respect to time). Linear kinetics are consistent with rate limitation by cathodic electron transfer to oxygen across the chromium (III) oxide layer. For chromium (III) oxide thicknesses of 200 nm PVB delamination was prevented over the entire 48 hour experimental time period. This level of inhibition is comparable to the protection provided by electroplated hexavalent chromium/ hydrated chromium oxide (ECCS) material used in packaging steel products. These finding indicate the ability of PVD to produce corrosion resistant coatings of controlled thickness and composition and provides relevant information regarding the likely relative importance of metallic metal and chromium (III) oxide in potential alternatives to coatings produced using hexavalent chromium. Figure I. Schematic representation of: a) the process by which a wedge of chromium metal or chromium (III) oxide is formed using a sliding shutter mechanism and b) how the PVB overcoated wedge sample is oriented with respect to the cathodic delamination cell. Figure 1

Effect of microwave irradiation and conventional calcification roasting with calcium hydroxide on the extraction of vanadium and chromium from high-chromium vanadium slag

Separation and recovery of vanadium and chromium from acidic leach solution of V-Cr-bearing reducing slag