Leaching Of Chromium Research Articles

Effect of in situ CO2 mixing of cement paste on the leachability of hexavalent chromium (Cr(VI))

In situ CO2 mixing technology is a potential technology for permanently sequestering CO2 during concrete manufacturing processes. Although it has been approved as a promising carbon capture and utilisation (CCU) method, its effect on the leachability of heavy metals from cementitious compounds has not yet been studied. This study focuses on the effect of in situ CO2 mixing of cement paste on the leaching of hexavalent chromium (Cr(VI)). The tank leaching test of the CO2 mixing cement specimen resulted in a Cr(VI) cumulative leaching of 0.614 mg/m2 in 28 d, which is ten times lower than that of the control mixing specimens. The results in thermogravimetric analysis indicated that a relatively significant amount of CrO42− is immobilised as CaCrO4 during the CO2-mixing, and a higher Cr–O extension is observed in the Fourier transform infrared spectra. Furthermore, a portion of the monocarboaluminate is inferred from microstructural analyses to incorporate CrO42− ions. These results demonstrate that in situ CO2 mixing is beneficial not only in reducing CO2 emissions, but also in controlling the leaching of toxic substances.

Selective recovery of europium from real acid mine drainage using modified Cr-MIL and SBA15 adsorbents

The successful adoption and widespread implementation of innovative acid mine drainage treatment and resource recovery methods hinge on their capacity to demonstrate enhanced performance, economic viability, and environmental sustainability compared to conventional approaches. Here, an evaluation of the efficacy of chromium-based metal–organic frameworks and amine-grafted SBA15 materials in adsorbing europium (Eu) from actual mining wastewater was conducted. The adsorbents underwent comprehensive characterization and examination for their affinity for Eu. Cr-MIL-PMIDA and SBA15-NH-PMIDA had a highest Langmuir adsorption capacity of 69 mg/g and 86 mg/g, respectively, for an optimum level of pH 4.8. Preferential adsorption tests followed using real AMD collected at a disused mine in the north of Norway. A comparative study utilizing pH-adjusted real AMD revealed that Cr-MIL-PMIDA (88%) exhibited slightly higher selectivity towards Eu compared to SBA15-NH-PMIDA (81%) in real mining wastewater. While Cr-MIL-PMIDA displays excellent properties for the selective recovery of REEs, practical challenges related to production costs and potential susceptibility to chromium leaching make it less appealing for widespread applications. A cost–benefit analysis was then undertaken to quantify the advantages of employing SBA15-NH-PMIDA material. The study disclosed that 193.2 g of EuCl3 with 99% purity can be recovered by treating 1000 m3 of AMD.

Influence of iron content of chemically and mineralogically modified electric arc furnace slag on the hydration and environmental behaviour of composite cements

This work investigates the influence of the iron content of tailored electric arc furnace slag (EAFS) on hydration and strength development as well as associated heavy metal leaching properties of Portland composite cement. Further, the impact of limestone additions was investigated. EAFS from scrap smelting plant was used as starting material. Tailored EAFS was produced by re-melting, conditioning, and water quenching. By that, a glassy material with defined chemistry was obtained. The tailored EAFS strongly contributed to the compressive strength development between 7 and 28 days. Composite cements containing 35 wt.-% EAFS reached an activity index above 85 % after 28 days. The addition of limestone and amine-based quality improvers resulted in an increase of the reached compressive strength at all tested ages. That is linked to the accelerated and increased AFm phase formation. This effect is more pronounced for EAFS with high iron content. Contrary, C-S-H formation was promoted if EAFS with low iron content was used. Chromium leaching was not critical despite the high content in the tailored EAFS. The lowest vanadium leaching was observed for EAFS with low iron content.

Advances in adsorption technologies for hexavalent chromium removal: Mechanisms, materials, and optimization strategies

In the realm of environmental engineering and water treatment, significant attention has been devoted to the removal of hexavalent chromium Cr (VI) from wastewater. Delving into the mechanisms of adsorption reveals a complex interplay of ion exchange, surface complexation, and electrostatic interactions dictating the binding of Cr (VI) to various adsorption materials. Utilizing diverse adsorbents like 2-D materials, metal oxides, and bio-based substances is driven by their exceptional absorptive capacity and specificity. Key parameters such as pH, temperature, initial concentration, and dosage are scrutinized to optimize the efficiency of adsorbent removal and ascertain the absorptive nature of the adsorbate. Beyond natural sources, human activities have exacerbated chromium contamination across ecosystems, posing a threat to food chains due to chromium's non-biodegradable nature and persistence. Chromium affects a wide range of life forms, including humans, aquatic organisms, and terrestrial species, through the accumulation and repercussions of chromium discharge. The leaching of chromium into ground and surface water triggers various health issues such as dermatitis, allergic reactions, skin ulcerations, bronchial carcinoma, asthma, and gastroenteritis. This review intended to list different treatment technologies for chromium removal along with their mechanism. Different types of sensors used for chromium detection have also been explored.

Oxidative Leaching of Vanadium and Chromium from Vanadium Slag via a Mechanochemical Activation─Assisted Microbubbles Method

Oxidative Leaching of Vanadium and Chromium from Vanadium Slag via a Mechanochemical Activation─Assisted Microbubbles Method

Leachability of hexavalent chromium from fly ash-marl mixtures in Sarigiol basin, Western Macedonia, Greece: environmental hazard and potential human health risk

Hexavalent chromium (Cr (VI)) is an environmental contaminant brining high concerns due to its higher toxicity and mobility in comparison with trivalent chromium Cr(III). Cr (VI) has been linked with several adverse health effects, including respiratory diseases, lung cancer, and skin irritation. The primary sources of it in the environment are industrial activities.Most of the time, fly ash made of lignite can release Cr(VI) when it comes into contact with water in an aquatic environment. The objective of this study is the investigation of Cr (VI) concentration in leachates of fly ash and marl mixtures and the determination of its solubility under different pH conditions. Samples of fly ash were collected from the Power Plant of Agios Dimitrios. Additionally, samples of marl were collected from the mine of South Field, and both samples were mixed and prepared in in different proportions (% w.t.). The leaching experiments were carried out according to the EN-12457/1-4 (2003) standard under different pH conditions and chemical analysis of the leachates were performed by spectrophotometry with diphenylcarbazide (DPC). The environmental footprint of Cr (VI) in the study area was significant, especially in mixtures containing higher concentrations of fly ash. A critical pH range between 6 to 12 is observed. At acidic pH values, a high release of Cr (VI) was observed, while at the mentioned critical values (pH 10–12), a gradual decrease in its leachability was noticed. The high concentrations of Cr (VI) in the industrial area studied require immediate actions in terms of managing and limiting the potential hazardous impacts on the environment and by extension on the public health by developing appropriate prevention strategies.Graphical abstract

Laboratory weathering studies to evaluate the water quality impact of a lithium mining in Portugal

Lithium mining driven by the growing demand for lithium-ion batteries, has environmental consequences linked to soil and water pollution. Nevertheless, research on the environmental impacts of lithium extraction still needs to be improved, highlighting the imperative for additional research. The article addresses the potential impact of the C57 lithiniferous feldspar mine on water quality, specifically focusing on surface, groundwater and spring water samples collected at the mining site and surrounding area in Gonçalo (Guarda, Portugal). The objective is to evaluate the environmental consequences of mining activities, with particular emphasis on mineral leaching. This study aims to evaluate the water quality around the C57 mine and the potential environmental impacts of mining operations. Water samples were collected from different sources, such as surface, underground, and spring waters, and chemical analyses were carried out to determine concentrations of different parameters, which were later compared with national and international reference guidelines. In addition to analysing the water samples, weathering tests were carried out using the Soxhlet extractor method to simulate the leaching of minerals over a shorter period (about 125 days). The concentrations of the analysed elements by atomic absorption spectroscopy (Al, Ca, Cd, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb and Zn) in the weathering solutions were generally low and decreased throughout the testing period, with significant concentrations of aluminium and chromium exceed Canadian environmental quality guidelines for surface waters. The detected lithium concentrations are quite different, ranging from 8.7 to 19.8 μg/L in surface waters, from 6.9 to 74.1 μg/L in groundwater, and from 25.6 to 35.4 μg/L in spring waters, but are all below the US EPA (2021) recommendations threshold of 0.7 mg/L. Based on the findings, the article concludes that there is currently no clear evidence to indicate the environmental impact of mining activities on water quality in the analysed samples. However, weathering tests suggest potential long-term implications regarding the leaching of specific chemical elements, particularly aluminium 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.

Proposal of an Encapsulation-led Disposal Method for Tannery Sludge – A Circularity Approach

In the context of achieving sustainable development goals, continuously pushing possible extended research and attempting to implement the respective outcomes in expanding a circular economy for a broad range of products are high priorities. In this paper, we considered disposable tannery sludge as a matter of concern and proposed an innovative framework for placing tannery sludge in the economic value chain via an encapsulation technique-based construction product development. We used polypropylene plastic and a cement-water matrix as encapsulation materials, and the encapsulated tannery sludge bodies were tested for their drop strength, water absorbing behaviour, ability to leach chromium and tendency to lose weight upon ignition. Value of water absorption for the prepared double layered encapsulated tannery sludge bodies was 1.332%, the drop strength performance index arrived was 90% and 0.0001 µg/g of Chromium leaching was found in Toxicity Characteristic Leaching Procedure (TCLP) and shown 67% weight loss in thermogravimetric (TGA) analysis. The results confirmed the possibility of ecocompatible disposal and recirculation of tannery sludge for the sustainable production of building blocks in the form of encapsulated bodies. The outcomes of our work add upon a new perspective to the existing literature regarding the environmentally positive utilization of tannery sludge in the production of building blocks.

Eco-friendly Chrome Tanning of Leather using Ultrasound Technique

This article describes the development of an environmentally friendly chrome tanning process of leather using ultrasound. Most of the leathers are tanned by the conventional method using basic chromium sulfate. It is one of the most polluting and time-consuming steps in leather processing. Investigations were carried out on ultrasound assisted eco-friendly tanning process so that the chrome tanning agent could provide better quality leather. Effects of using ultrasound in chrome tanning process were studied at different pH, tanning time, tanning agent dosage, and then compared with that of conventional method. Tanned leathers were characterized by scanning electron microscopy (SEM), photomicrographic analysis, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and energy dispersive X-ray (EDX). SEM analyses of the surface and cross-section of the tanned leather showed that fiber structures were not affected by ultrasound. It was also found that the shrinkage temperature of leather tanned with ultrasound was increased by about 5-29 °C. Chrome uptake and content were found to increase by 30-50% and 1-7%, respectively. Tanning time was shortened from 6 hours to 2 hours and the quantity of leachable chromium in ultrasound assisted chrome tanned leather was also decreased significantly. The noteworthy enhancing effects have been attributed largely because of the increased penetration of tanning agents into pickled leather. Photomicrographic analysis of the cross-section of the tanned leather also showed a higher penetration of tanning agents in presence of ultrasound.

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.

Research on the environmental stability performance of chromite ore processing residue solidified products.

Chromite ore processing residue (COPR) is a hazardous waste because of leachable chromium, especially Cr(vi). Therefore, ascorbic acid (AA) and blast furnace slag (BFS) have been used to detoxify and solidify COPR. On this basis, environmental stability experiments with high temperature and freeze-thaw cycles were carried out to explore the stability performance of a solidified body with 40% COPR. The environmental stability performance was analyzed through changes in edge length, mass loss, compressive strength development, and leaching concentration of Cr(vi). The result indicated that the high-temperature environment had much more effect on the solidified body than the freeze-thaw cycle environment in these four aspects: after being maintained at 900 °C for 2 h, the compressive strength of the solidified bodies reached its minimum value (35.76 MPa). However, in the freeze-thaw cycle experiments, the compressive strength of the solidified bodies consistently remained above 80 MPa, and the leaching of hexavalent chromium was below the limit (5 mg L-1). In addition, X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR) analysis verified that COPR was effectively solidified through physical and chemical means. Moreover, high temperature changes the molecular structure of the solidified body, thus reducing the compressive strength and curing ability of the solidified body, while the freeze-thaw cycle experiment has little effect on it.

Stabilization of Chromium Waste by Solidification into Cement Composites.

This article deals with the study of hazardous chromium leaching, stabilized/solidified by cement CEM II after 28 days of curing, in an acidic environment. The mortars subjected to this study were investigated by X-ray diffraction (XRD) characterization to evaluate the influence of chromium waste on their mineralogical structure. In the study range (0.6-1.2%), increasing the mass percentage of Cr2O3 in the mortars indicates that chromium accelerates the hydration process and setting of the mortar and increases the mechanical strength of the mortars compared to the control sample. It was observed that the release of chromium during the Toxicity Characteristic Leaching Procedure (TCLP) test and the efficiency of the stabilization/solidification process depended on the initial Cr concentration and the leaching time. The use of XRD allowed the identification of new crystallized phases in the cement matrices, namely, CaCrO4·2H2O and chromium-ettringite Ca6Cr2(SO4)3(OH)12·26H2O, which confirms the immobilization of chromium and the efficiency of the stabilization/solidification process. In this research, the release mechanism was found to be primarily a surface phenomenon by modeling the experimental data (dissolution or precipitation).

Valorization and enhancement mechanism of ferrochrome slag as aggregate for manufacturing ultra-high performance concrete (UHPC)

Ferrochrome slag (FCS) is a by-product discharged in the smelting of ferrochrome alloys. This high-volume waste can be effectively valorized by utilizing it as aggregate in ultra-high performance concrete (UHPC), which is beneficial for resolving the environmental issue induced via its buildup and potential risk of chromium leaching. Additionally, it can also compensate for the shortage of natural aggregate (NA), and reduce the cost of UHPC. Its feasibility as aggregate in UHPC was explored. The enhancement mechanisms of FCS aggregate dosage, pre-wetting water, and steel fiber on the performances of UHPC were systematically investigated. The results indicated that FCS with rough texture, higher water absorption and lower strength can substitute NA in the manufacturing of UHPC. The mechanical and drying shrinkage properties of UHPC mixed with FCS were improved, which was attributed to the synergistic effects including the reduction of effective water-binder ratio and porosity, the enhanced interface structure, and the internal curing to matrix. The water film layer enriched surrounding aggregate absorbed by FCS, which reduced the enrichment and directional growth of portlandite at interface. This also inhibited the water absorption of UHPC, and may hinder the transport of harmful ions inside UHPC. With the incorporation of FCS, its autogenous shrinkage increased, this matter can be ameliorated by the pre-wetted aggregates with water not exceeding 45%–65% of the saturated water absorption rate. Furthermore, the reinforcement of steel fiber on UHPC strength gradually decreased due to the fiber dispersion was affected by the declined workability and aggregate morphology.

Effects of Carbonation and Saturation on the Leaching Characteristics of Recycled Concrete Aggregates

Abstract This study assessed the efficacy of water leach tests (WLTs) and pH-static leach tests in evaluating the leaching behavior of distinctly carbonated recycled concrete aggregates (RCA). The leaching of barium (Ba), calcium (Ca), chromium (Cr), magnesium (Mg), and sulfate (SO4) from seven RCA samples were studied. WLTs at several liquid-to-solid ratios (L/S) and pH-static leach tests were conducted to examine the effects of carbonation on the release of elements. In addition, a novel experimental approach was introduced to gauge the impact of moisture saturation on the leaching attributes of RCA. The saturation effect on the leaching potential was explored by inducing eight different matric suctions in laboratory-compacted RCA cores. Moreover, geochemical modeling was performed to evaluate the leaching mechanisms of the elements. Results showed that a carbonation-based leaching assessment of RCA could be premised on laboratory WLTs and pH-static leach tests. Ba and Ca leaching decreased while Cr and SO4 leaching increased with the RCA degree of carbonation. The L/S ratio could be used as a substitute for RCA carbonation. At a higher L/S ratio, fresher and aged RCA samples had similar leaching fingerprints. The pH-dependent leaching of the elements was regulated by the RCA degree of carbonation, especially in the alkaline pH range. Irrespective of carbonation level, geochemical modeling suggested solubility-controlled leaching mechanisms. The leaching of metals from RCA was a dynamic process, and the changes in matric suction and consequently saturation could diversely influence the leaching characteristics of RCA.

Effect of ferrous sulfate replacing gypsum on properties and reducing Cr(VI) of cement paste

Ferrous sulfate has a negative effect on the properties of cement when reducing chromium (VI) in cement. Ferrous sulfate was used to replace gypsum in cement because of its similarity to gypsum. The effect of ferrous sulfate on cement properties and reducing chromium (VI) was characterized by setting time, compressive strength, X-ray diffraction (XRD), scanning electron microscopy (SEM), the leaching of chromium (VI). Ferrous sulfate can adjust the setting time of cement paste, and the compressive strength was the highest when the amount of substitution is 25%. Furthermore, the content of portlandite in hydration products were reduced. The reduction efficiency of chromium (VI) was 88.11%, 98.00%, 98.91% and 98.57% respectively when the replacement amount of ferrous sulfate is 25%, 50%, 75% and 100%, the chromium (VI) was reduced to chromium (III) to form Cr3+-ettringite. Ferrous sulfate replacement gypsum can not only solve the negative effect of gypsum on chromium (VI) immobilization, but also further reduce the leaching amount of chromium (VI).

Statistical analysis and profiling of chromium leaching characteristics in Basic Chrome Sulphate (BCS) sludge dumping at Khanchandpur-Rania, district Kanpur Dehat, Uttar Pradesh (India)

The present investigation has been conducted to study the leaching behaviour of chromium species in immobilised hazardous waste containing Basic Chrome Sulphate (BCS) dumped at Khanchandpur-Rania, Kanpur Dehat district of Uttar Pradesh, India. The pH of sludge was found to be basic in nature. The concentration of total and Toxicity Characteristic Leaching Procedure (TCLP) based Cr was observed at 26,208 and 215, 36,102 and 370, and 42,812 and 516 mg kg−1 in the pre-monsoon and 26,194 and 200, 36,237 and 340, and 42,570 and 471 mg kg−1 in the post-monsoon at 0–15, 15–75 and 75–150 cm depth, respectively. The concentration of total and TCLP based Cr6+ was found at 9652 and 107, 243,384 and 151 and 24,936 and 237 mg kg−1 in the pre-monsoon and 9724 and 102, 24,400 and 144, and 24,830 and 228 mg kg−1 in the post-monsoon at 0–15, 15–75, 75–150 cm depth, respectively. Results indicated that the concentration of total and TCLP-based Cr and Cr 6+ increased with depth. A similar trend was also observed in total and TCLP-based Cr 3+, total Fe, total Mn and TDS contents, which strongly justified the leaching characteristic of salts increasing with the increasing depth level of the dumpsite.

Evaluation of chromium leaching in concrete by immersion and irrigation methods

RESUMO A busca por materiais na construção civil ecoeficientes pode ser realizada adicionando ou substituindo as matérias-primas por resíduos gerados em outros setores industriais. Muitos destes resíduos são classificados como perigosos, sendo que a inertização dos compostos que conferem periculosidade pode ser realizada através da estabilização por solidificação (E/S) que ocasiona o encapsulamento e a fixação química de substâncias tóxicas. No entanto, no Brasil não há uma norma regulamentada ou mesmo uma recomendação técnica, que seja específica para produtos E/S utilizados como componentes de construção. Neste contexto, o presente estudo teve como objetivo avaliar a lixiviação do cromo em matriz de concreto de cimento Portland pelos métodos de imersão e irrigação, com vistas ao emprego destes métodos na avaliação ambiental de materiais e componentes da construção civil. Para isso, foram confeccionados corpos de prova de 25x200x400 mm com e sem adição de 2% de Cr2O3 (óxido de cromo) em relação a massa do cimento Portland, os quais foram submetidos a testes de lixiviação por imersão e irrigação. Os resultados obtidos permitiram verificar o encapsulamento do cromo no concreto e que os testes de lixiviação propostos em monólitos de concreto, durante a fase de uso, mostraram-se aplicáveis em 28 dias.

Oxidation leaching of chromium from electroplating sludge: Ultrasonic enhancement and its mechanism.

The oxidation leaching of chromium from electroplating sludge was investigated, and ultrasonication was introduced for the enhancement of the leaching process. Two different types of Cr-bearing electroplating sludge were selected for the study, and the effects of the reagent dosage, temperature, and ultrasonic pulse ratio on the leaching efficiency were tested through oxidation leaching experiments. The experimental results show that hydrogen peroxide and sodium hypochlorite exhibit different leaching effects on different types of electroplating sludge. The control of reagent dosage is crucial for the oxidation leaching of Cr, while the effect of temperature turns out to be small. Hydrogen peroxide turns out to be a more effective oxidizer for chromium sludge, and the leaching efficiency of Cr could be promoted from 77.52% to 87.08% using ultrasonic enhancement under optimum conditions. Interestingly, sodium hypochlorite exhibited better leaching efficiency than hydrogen peroxide for the mixed sludge since the organic matter in the mixed sludge will lead to the rapid decomposition and consumption of hydrogen peroxide. The leaching efficiency of Cr from the mixed sludge could also be promoted from 56.82% to 67.10% using ultrasonic enhancement under optimum conditions. According to the scanning electron microscope imaging, ultrasonic enhancement can create voids and cracks on the surface of the sludge particles, hence promoting the contact between electroplating sludge and leaching agents, and promoting the oxidation leaching efficiency. In addition, ultrasound seems to be able to remove the coverings on the surface of the mixed sludge particles, which may facilitate the oxidation reaction.

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.