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Recovery of Vanadium from Spent Catalysts of Sulfuric Acid Plant by Using Inorganic and Organic Acids: Laboratory and Semi-Pilot Tests

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Recovery of Vanadium from Spent Catalysts of Sulfuric Acid Plant by Using Inorganic and Organic Acids: Laboratory and Semi-Pilot Tests

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Abstract

Catalysts are used extensively in industry to purify and upgrade various feeds and to improve process efficiency. These catalysts lose their activity with time. Spent catalysts from a sulfuric acid plant (main elemental composition: 5.71% V2O5, 1.89% Al2O3, 1.17% Fe2O3 and 61.04% SiO2; and the rest constituting several other oxides in traces/minute quantities) were used as a secondary source for vanadium recovery. Experimental studies were conducted by using three different leaching systems (citric acid with hydrogen peroxide, oxalic acid with hydrogen peroxide and sulfuric acid with hydrogen peroxide). The effects of leaching time, temperature, concentration of reagents and solid/liquid (S/L) ratio were investigated. Under optimum conditions (1:25 S/L ratio, 0.1M citric acid, 0.1M hydrogen peroxide, 50°C and 120min), 95% V was recovered in the presence of hydrogen peroxide in citric acid leaching.

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... Currently, environmentally acceptable organic acids (e.g., oxalic acid, citric acid and others) have been studied as alternative leaching reagents for metal extraction [16][17][18][19][20][21][22][23][24][25][26][27]. Organic acids may dissolve minerals via the following two mechanisms: (1) acid attack and displacement of metal ions by H + (acidolysis) and (2) formation of soluble metal-ligand complexes and chelates (complexolysis) [16,26]. ...
... Therefore, the use of oxalic acid as a leaching reagent provides an environmentally friendly leaching process. Extensive studies have been performed to efficiently extract vanadium from spent catalysts using oxalic acid [17,18,[22][23][24]. However, there are very few published studies on vanadium extraction from stone coal using oxalic acid. ...
... Therefore, the vanadium and iron leaching efficiencies at a water-mineral ratio of 0.6 mL/g were 5.5% and 2.4%, which were lower than at a water-mineral ratio of 1.0 mL/g. When the water-mineral ratio exceeded 1.5 mL/g, the vanadium and iron leaching efficiencies exhibited a downward trend that resulted from the decrease of the leaching reagent concentration [17,34]. Considering the vanadium concentration and amount of water used in the leaching process, 1.0 mL/g was chosen as the optimal water-mineral ratio. ...
... The steel industry is the largest consumer of vanadium. Today, its consumption in metallurgy is up to 85% of total vanadium consumption; vanadium is used as an alloying component introduced into steel as ferro-vanadium (Erust et al. 2016;Nikiforova et al. 2016). Furthermore, vanadium is widely used for the producing of vanadium redox flow batteries (VRBs) (Wang et al. 2011;Skyllas-Kazacos et al. 2011;Cheng et al. 2011). ...
... One source is vanadium-containing waste: spent vanadium catalyst (SVC), fly ash, converter and smelter slag Zharski et al. 2012). SVC is one of the most preferable secondary raw materials for vanadium extraction, as it contains 5-10 wt% of vanadium along with other valuable components, such as Cu, Ni, Mo, and Co, in the form of oxides or sulfates (Akcil et al. 2015;Erust et al. 2016). The average service life of this catalyst is about 2-5 years (up to 10 years) (Ullmann 's 1994). ...
... It is well known that vanadium can be extracted from solution by hydrolysis as V 2 O 5 (Muzgin and Khamzina, 1981). Some authors (Vegliծ et al. 2006;Ognyanova et al. 2009;Erust et al. 2016) reported about using hydrogen peroxide (H 2 O 2 ) as an oxidizing agent for vanadium leaching, leading to an intensification of the V 2 O 5 hydrolytic extraction. Our previous studies showed the possibility to use H 2 O 2 for oxidation of SVC leaching solutions and further extraction of V 2 O 5 from solutions by thermohydrolysis with boiling time 5 min (Orehova et al. 2013). ...
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Spent vanadium catalysts of sulfuric acid production (main elemental composition in wt%: 7.5 V, 9.1 K, 10.2 S, 23.2 Si and 1.4 Fe) can be used as a secondary source of vanadium. Extraction of vanadium was studied using two-step leaching (acidic and reductive) of spent vanadium catalysts with further oxidizing of leaching solutions. The factors leaching and hydrolysis temperature, concentration of leaching (H2SO4, Na2SO3) and oxidizing ((NH4)2S2O8) reagents, solid/liquid ratio, mixing parameters, and time of leaching and thermohydrolysis were systematically investigated. The solubility of V2O5 was investigated as a function of temperature, pH of sulfuric acid solutions, and concentration of Na2SO3. The kinetics of V2O5 solubility and reduction were also studied. The vanadium leaching yield after a two-step recovery was 98 wt% after acidic (H2SO4, pH 1.2–1.3) leaching with ultrasonic treatment for 5 min at ambient temperature, followed by reductive leaching in 0.01 Mol/L Na2SO3 solution for 15 min at ambient temperature. The highest vanadium extraction yield from leaching solutions was 98 wt% obtained through oxidizing of leaching solutions by 30 wt%. (NH4)2S2O8 with a molar ratio n(V2O5)/n((NH4)2S2O8) of 5/1 for a reaction time of 5 min at 80–90 °C. the extracted vanadium product was V2O5 with a purity of 85–87 wt%. The technological scheme has been developed to recycle all obtained products and sub-products
... What is important is that its presence in the exhausts can cause corrosion as well [12,13]. In the industrial applications of NH 3 -SCR, the catalyst can be easily deactivated by sulphur compounds formed in the combustion chamber due to their presence in fuel [14]. Thus, it lowers the activity of DeNO x catalysts [3,5,11,15]. ...
... As already mentioned, the main two reasons of deactivation of Cu-doped catalysts used for SCR is the formation of copper and ammonium sulphates [10,14]. The effect of the formation of those compounds can be explained by the difference of desorption temperature between ammonia (150- It can be noted that in the case of all of the tested materials, increasing the reaction temperature accelerates NO conversion. ...
... As already mentioned, the main two reasons of deactivation of Cu-doped catalysts used for SCR is the formation of copper and ammonium sulphates [10,14]. The effect of the formation of those compounds can be explained by the difference of desorption temperature between ammonia (150-400 • C) and sulphur oxide (>400 • C). ...
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A series of materials based on activated carbon (AC) with copper deposited in various amounts were prepared using an incipient wetness impregnation method and tested as catalysts for selective catalytic reduction of nitrogen oxides with ammonia. The samples were poisoned with SO2 and regenerated in order to analyze their susceptibility to deactivation by the harmful component of exhaust gas. NO conversion over the fresh catalyst doped with 10 wt.% of Cu reached 81% of NO conversion at 140 °C and about 90% in the temperature range of 260–300 °C. The rate of poisoning with SO2 was dependent on Cu loading, but in general, it lowered NO conversion due to the formation of (NH4)2SO4 deposits that blocked the active sites of the catalysts. After regeneration, the catalytic activity of the materials was restored and NO conversion exceeded 70% for all of the samples.
... Several scholars conducted extraction by oxalic acid in spent catalysts, such as HDS. Heavy metals, such as V, Mo, Ni, and Fe, can be extracted using oxalic acid as leaching agent (Erust et al., 2016;Lee et al., 1992;Mazurek, 2013;Szymczycha, 2011). However, few studies have reported on the recovery of spent SCR catalysts by oxalic acid. ...
... In addition, the highest leaching efficiency at the same temperature was observed in Fe, indicating that the reaction rate of Fe was the fastest among the elements evaluated. However, when the solution temperature was above 90°C, oxalic acid easily volatilized and was thermally decomposed (Erust et al., 2016;Hu et al., 2017). Thus, the optimized temperature was considered as 90°C. ...
Article
Large amounts of selective catalytic reduction (SCR) denitrification catalysts with poor mechanical property are disposed and difficult to be regenerated, resulting in environmental pollution. For spent SCR denitrification catalyst, the ratio of V⁴⁺/V⁵⁺ decreased by about 45% and Fe impurity increased >10 times, which influenced the recycling of the supporter. Selective leaching of V and Fe by oxalic acid and its reaction mechanism were investigated. Under the optimized leaching condition: oxalic acid concentration of 1.0 mol/L, reaction temperature of 90 °C, liquid-to-solid ratio of 20 mL/g, <75 μm particle size and leaching time of 180 min, the leaching efficiencies of V and Fe reached over 84% and 96%, respectively. The reaction mechanism for the selective leaching of these metals was determined through UV-VIS spectrophotometry and CO2 emission analyses. After dissolution and complexation, VO2⁺ and Fe³⁺ were reduced to water-soluble cations VO²⁺ and Fe²⁺. When V and Fe was in the specific forms of VOC2O4 and Fe(C2O4)2²⁻ at 0.33 pH, high leaching efficiency was obtained. It indicated that redox reactions led to the broken of dissolution and complexation equilibriums for VO2⁺, VO⁺ and Fe³⁺. For W and Ti, only dissolution and complexation reactions occurred and the leaching efficiency was limited by the solubility. The leaching residue with anatase TiO2 was recovered as carrier and used for synthesis of a new SCR catalyst.
... However, this illustrates that this phenomenon requires more investigation in the field of kinetics for the leaching process, and will be the topic of our next research manuscript. In addition, oxalic acid easily volatilized and thermally decomposed when the solution temperature was higher than 95 • C [9,20]. Therefore, the optimized leaching temperature was regarded to be 95 • C. Figure 7 presents the results of experimental studies designed to determine the leaching efficiencies of compounds from the spent catalyst at different leaching temperatures. ...
... However, this illustrates that this phenomenon requires more investigation in the field of kinetics for the leaching process, and will be the topic of our next research manuscript. In addition, oxalic acid easily volatilized and thermally decomposed when the solution temperature was higher than 95 °C [9,20]. Therefore, the optimized leaching temperature was regarded to be 95 °C. ...
Article
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The problem of spent fluid catalytic cracking (SFCC) catalyst resource utilization, draws more and more attention to system analysis. SFCC was leached in an oxalic solution for comprehensive utilization. The results showed that for a D50 ≤ 17.34 μm, the catalyst leached for 240 min at 95 °C in the presence of a 2 mol/L oxalic acid solution, and the extent of leaching of V, Ni, Fe, and Al was 73.4%, 32.4%, 48.2%, and 36.8%, respectively. Studies on the occurrence state of the main ions (V, Ni, Fe, and Al) in the leaching solution were presented. Additionally, the separation of the main ions from such a solution by the “solvent extraction-stripping-hydrothermal precipitation-comprehensive recovery of valuable metal” process was studied. The immobilization rates of vanadium and nickel in geopolymers can be obtained using the toxicity characteristic leaching procedure (TCLP) test, and the geopolymers prepared by SFCC leaching residues can be considered a non-hazardous material. A process diagram of the comprehensive utilization of SFCC catalysts is presented.
... The catalytic activity will recover and it can be further applied for another 3 years. Unfortunately, the activity of regenerated catalyst may decrease to an extremely low level and further regeneration is not be feasible (Erust et al. 2016). Therefore, this completely abandoned waste SCR catalyst has been classified into hazardous solid waste in China. ...
... Generally, pyrometallurgical and hydrometallurgical processes with high energy consumption, long process flow, and specific reaction equipment have been used to extract valuable metals such as W, V, and Ti from waste catalysts such as alkaline roasting and pressure leaching methods (Shang et al. 2012;Zhao et al. 2015). Most of previous works focused on the valuable metal extraction, but ignore the comprehensive utilization of waste catalyst (Choi et al. 2018;Erust et al. 2016). Refer to the structure of V 2 O 5 -WO 3 /TiO 2 , anatase type TiO 2 is used as a support to disperse the V 2 O 5 and WO 3 . ...
Article
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In this work, an environmental friendly industrial regeneration approach has been proposed to remove the surface poisoning and recover the catalytic activity of waste V2O5-WO3/TiO2 catalyst. Alkaline treatment and acid wash are combined for the waste catalyst regeneration process, which is applied for the arsenic and alkali metal removal, respectively. The crystal structure was well maintained as anatase phase and the surface area was increased during the regeneration, which is favorable for the following active component addition step and regenerated process. The XPS results illustrated that the surface contaminants (arsenic and sodium) were removed and V(IV) was loaded on the regenerated catalyst. Based on the deNOx evaluations, the catalytic activity of the regenerated sample is increased to the level of commercial fresh catalyst. The present industrial regeneration process provides a promising method for the comprehensive recovery of waste catalyst and further understanding in the field of secondary resource recycle.
... It should be noted that some reports have achieved 90 wt% leaching efficiency of Mo even without the addition of hydrogen peroxide. 41,58 Vanadium is another major metal that can be found in many spent catalysts 42,45,53,54,58,61 and is reported to form only soluble oxalates as shown in Figure 3, Table 1, and Table 2. Mazurek 53 and Erust et al. 54 attempted to recover V from a spent catalyst using oxalic acid. Vanadium(IV) oxalate is formed, which is soluble in the aqueous phase. ...
... It should be noted that some reports have achieved 90 wt% leaching efficiency of Mo even without the addition of hydrogen peroxide. 41,58 Vanadium is another major metal that can be found in many spent catalysts 42,45,53,54,58,61 and is reported to form only soluble oxalates as shown in Figure 3, Table 1, and Table 2. Mazurek 53 and Erust et al. 54 attempted to recover V from a spent catalyst using oxalic acid. Vanadium(IV) oxalate is formed, which is soluble in the aqueous phase. ...
Article
Energy-efficient metal recovery and separation processes from a mixture of valuable metals is vital to the metallurgy and recycling industries. Oxalate has been identified as a sustainable reagent that can provide both the selectivity and efficient leaching capabilities for a variety of mixed metals under mild reaction conditions. The oxalate process has great potential to replace many of the existing metal recovery processes that use inorganic acids such as sulfuric, hydrochloric, and nitric acid. In this review, the use of oxalate chemistry in four major metal recovery applications is discussed, namely, spent lithium-ion batteries, spent catalysts, valuable ores, and contaminated and unwanted waste streams. Recycling of critical and precious metals from spent lithium-ion batteries and catalysts has significant economic opportunity. For energy-efficient metals recovery, reaction conditions (e.g., temperature, pH, time, and concentration), metal-oxalate complex formation, oxidation and reduction, and metal precipitation must all be well-understood. This review provides an overview from articles and patents for a variety of metal recovery processes along with insights into future process development.
... Therefore, (bio)hydrometallurgical approaches are believed to be more environment-friendly due to low-energy demand. The reagents used in hydrometallurgical studies were both inorganic and organic, acidic, and alkaline [23][24][25][26][27]. In particular, organic acids such as citric acid might be used in metal extraction due to their environmental safety, natural origin, and high degradability [25,26]. ...
... The possible ways to improve recovery rates of V from spent catalysts are: (a) addition of an oxidizing/reducing agent, such as hydrogen peroxide (H 2 O 2 ), (b) the increase of CA molar concentration, and (c) increase of the temperature during the extraction. For example, the study of Erüst et al. [23] showed that the addition of 0.1 M H 2 O 2 and the increase of CA molar concentration to 0.2-M lead to 95% vanadium extraction yield. The similar yield has been achieved when the temperature increased to 80 °C. ...
Article
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Spent catalysts being considered hazardous wastes exhibit a high metal content in mobile forms. In addition, growing demand for circular economy policy applications requires proper utilization of these wastes. This study aimed at the assessment of vanadium leaching from spent desulfurization catalyst derived from sulfuric acid plant dump located nearby a copper smelter. Chemical and phase composition of the catalyst has been characterized. The extraction has been performed using chemical (0.1-M and 1-M citric acid) and biological (biotic solution with Acidithiobacillus thiooxidans) methods, using different experimental parameters (pulp density, particle size, leaching time) to observe V leaching behavior and kinetics. The results revealed that both citric acid and bacteria carried out the extraction process well. The optimal parameters for acid leaching were < 0.2-mm particle size and 2% pulp density, which allowed to leach out 95% of V from spent catalyst within 48 h. The bacterially mediated extraction resulted in 93% V leached out within 21 days with 2% pulp density. The experiments showed that V present in the catalyst is susceptible to bioleaching and organic acid leaching with the latter being a quicker process.
... Vanadium and vanadium alloys are consumed in steel industry, titanium alloy, chemical industries and alloying agent [1,2]. Aluminumvanadium alloys have been widely applied in the military and civilian industry due to its high working temperature, strong corrosion resistance and high specific strength [3,4]. ...
Article
A novel recycling process was developed to produce vanadium aluminum (AlV55) alloy using vanadium aluminum (AlV65) alloy scrap and aluminum (Al) under vacuum. The theoretical calculation indicates that Al can be evaporated under vacuum. Excessive Al would be consumed during melting process when the reaction temperature ranges from 1823 to 2123 K, according to the theoretical calculation, which indicates Al could evaporate under vacuum. The experimental results present that Al was effectively dissolved in molten AlV65 alloy, the impurities (N, O, and C) decreased and the content of V increased gradually with reducing Al addition.
... So far, most processes for treating spent vanadium oxide containing catalysts have been performed toward recovery of vanadium pentoxide by using a 3-step approach, involving acid leaching, oxidation and precipitation [2,[23][24][25]. Drawbacks of this pathway to the situation of spent sulfuric acid catalysts lay in the low content of vanadium to be recovered from the spent catalyst, operation requirement at elevated temperatures with large amount of high concentration acid solution as well as recovery efficiency versus vanadium oxide purity trade-off. ...
Article
In this work, the efficiency of the regeneration process of spent V2O5 catalyst from sulfuric acid plant under different atmospheres (5%O2/N2 or air) was evaluated. Temperature-programmed results showed that the observed reduction profiles of the samples are attributed to the reduction of amorphous V⁺⁵ and low-valence V+5−x species at low temperatures followed by the reduction of their crystalline structures at high temperatures. Significantly low values of SO2 conversion of the spent samples can be explained by the significant drop in quantity of all vanadium species, coupled with their structural change to more thermally stable forms. It was found that the exposure of the spent catalyst to 5%O2/N2 stream at 550 °C for 1 h allowed at first the re-oxidation of amorphous low-valence V species and second the dissolution of crystalline low-valence V species, thus resulted in recovery of their catalytic activity for SO2 oxidation. However, the regeneration in air was less effective than in 5%O2/N2 stream. This is supposedly due to the differential behaviors of the spent sample in different oxidative streams toward re-oxidizing low-valence V species and re-dissolving V precipitates.
... Valuable metals could be completely or selectively dissolved in the leachate by leaching processes, such as acid leaching, alkali leaching and salt leaching [14,17]. Then, according to the composition of the leachate, the metals can be separated by adsorption, ion exchange, precipitation, solvent extraction or molecular recognition [18][19][20][21][22][23]. Finally, the products such as CoSO 4 or NiSO 4 , CoC 2 O 4 , Al 2 O 3 , MoO 3 and CaMoO 4 can be successfully recovered from spent hydrotreating catalysts [20,24,25]. ...
Article
Currently, roasting-leaching is the main treatment process of spent hydrodesulfurization (HDS) catalyst, but it will produce impurities, such as nickel molybdate and cobalt molybdate (NiMoO4 or CoMoO4), which is adverse to recover valuable metals. In this paper, a combined ultrasonic-microwave method was developed to remove oil and recover molybdenum (Mo) from the spent HDS catalyst. Firstly, ethanol was used to extract the surface oil of the spent MoNiCo/Al2O3 catalyst with ultrasonic assistance. Effects of temperature, ultrasonic time, liquid-solid ratio and ultrasonic power on the oil removal rate were investigated systematically and the process conditions were optimized using response surface methodology (RSM). The results showed that the oil removal rate was over 99% under the optimum conditions of temperature 55 °C, ultrasonic time 2 h, liquid to solid ratio 5:1, and ultrasonic power 600 W. After oil removal, the sample was roasted in microwave field at 500 °C for 15 min. The generation of toxic gas could be effectively avoided and no hardest-to-recycle impurity CoMoO4 was found. At last, the roasted sample was subjected to ultrasonic leaching with sodium carbonate (Na2CO3) solution for recovering Mo. Extraction of Mo of the deoiled sample after microwave roasting reached 94.3%, which is about 7% higher than that of oily sample. Moreover, microwave roasting method resulted in a much higher Mo extraction than traditional method for both the oily and deoiled spent catalyst. It was concluded that the ultrasonic-microwave assisted method could remarkably improve the recovery of Mo and greatly shorten the processing time.
... Particle size plays an important role, since the smaller the particle size, the less Cu leaching [11]. In addition, citric acid in combination with H 2 O 2 has the capacity to recover metals from secondary sources, since it has been observed that it can leach up to 96.4% of V present in spent catalysts [12]. It has also been reported that for Co and Zn, the citric acid produced by Aspergillus niger presents higher percentages of leaching than commercial citric acid [36].The above shows that the efficiency in the recovery of metals between chemical leaching and biological leaching depends on the metal, the metal matrix and the study conditions. ...
Article
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Electronic waste (E-Waste) is consumed at high speed in the world. These residues contain metals that increase their price each year, generating new research on the ability of microorganisms to recover the metals from these wastes. Therefore, this work evaluated the biologic lixiviation of Cu, Ag and Au from printed circuit boards (PCB) of mobile phones by three strains of Aspergillus niger, Candida orthopsilosis, Sphingomonas sp. and their respective consortia, in addition to leaching with citric acid. The microorganisms were cultured in mineral media with 0.5 g of PCB, and the treatments with 1M citric acid were added the same amount of PCB. All treatments were incubated for 35 days at room temperature. The results showed that Sphingomonas sp. MXB8 and the consortium of C. orthopsilosis MXL20 and A. niger MXPE6 can increase their dry biomass by 147% and 126%, respectively, in the presence of PCB. In the bioleaching of metals, the inoculation of A. niger MXPE6, the consortium of Sphingomonas sp. MXB8/C. orthopsilosis MXL20 and Sphingomonas sp. MXB8 leached 54%, 44.2% and 35.8% of Ag. The consortium of A. niger MX5 and A. niger MXPE6 showed a leaching of 0.53% of Au. A. niger MX5 leaching 2.8% Cu. Citric acid increased Cu leaching by 280% compared to treatments inoculated with microorganisms. Although further research is required, A. niger MXPE6 and the consortium of Sphingomonas sp. MXB8/C. orthopsilosis MXL20 could be an alternative to recover Ag from PCB of mobile phones.
... 86.7% of vanadium can be extracted at the optimum conditions (Nejad et al., 2018). Erust used citric acid (Erust et al., 2016) to leach vanadium from spent catalysts containing 5.71% V 2 O 5 , achieving 95% V recovery under the optimum conditions (1:25 S/L ratio, 0.1 M citric acid, 0.1 M hydrogen peroxide, 50°C and 120 min). Nazari et al. investigated the simultaneous recovery of V and Ni from power plant heavy fuel fly-ash containing 2.2 wt% vanadium, using a hydrometallurgical process consisting of sulfuric acid leaching. ...
Article
The petroleum coke is the main raw material for the preparation of pre-baked anode materials for aluminum electrolysis. However, the presence of vanadium in petroleum coke negatively affects its properties. In the present study, microwave-ultrasonic assisted leaching is used to enhance the removal of vanadium from petroleum coke. The leaching efficiency of vanadium can reach above 90%, under the optimum conditions: ultrasonic power of 1000 W, microwave power of 500 W, temperature of 95 °C, NaOH concentration of 150 g/L, Na atomic ratio of NaOH and Na2CO3 of 3. The results showed that the contact angle and the surface tension between leaching solution and petroleum coke were notably reduced, resulting in an improved leaching efficiency.
... After 3 to 5 years, the SCR catalyst comes to its life end and is classified as solid industrial waste [4,5]. Serious environmental and potential safety problems are raised [6][7][8]. Hence, the spent SCR catalyst needs to be treated urgently. At the same time, spent SCR catalyst has also been viewed as a potential secondary resource due to the presence of precious natural resources, titanium, tungsten, and vanadium [9,10]. ...
Article
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PurposeTiO2 recovered from spent SCR catalyst, a hazardous industrial solid waste, was modified by g-C3N4 to produce the recovered TiO2 (R-TiO2)/g-C3N4 photocatalyst to protect valuable Ti resources and revamp its shortage of underutilization of visible light.Methods TiO2 recovered from spent SCR catalyst by an alkali leaching method was used to prepare the R-TiO2/g-C3N4 photocatalyst via self-assembly procedure. The photodegradation efficiencies of the prepared catalysts were evaluated by degradation of Rhodamine B (RhB) under visible light.ResultsThe XRD patterns indicate that R-TiO2 remains the crystal structure of the standard anatase TiO2 phase intact throughout the recovery process. The photodegradation efficiencies of the R-TiO2/g-C3N4 photocatalysts evaluated by degradation of RhB under visible light optimally reached 97.11% when the systems were irradiated for only 40 min. For comparison, the best RhB degradation rate constant from the R-TiO2/g-C3N4 photocatalyst was about 1.9 times that of the pure TiO2/g-C3N4 photocatalyst.Conclusion The R-TiO2/g-C3N4 photocatalyst with the 97.616 wt% purity R-TiO2 has the highest visible light photocatalytic degradation RhB activity which is almost 1.9 times that of pure TiO2/g-C3N4 photocatalysts. The results demonstrate that the TiO2/g-C3N4 photocatalyst with recovered TiO2 from spent SCR catalyst shows excellent photodegradation efficiency for RhB.Graphical abstract
... These catalysts deactivate after repeating catalytic processing for crude oil and eventually become solid wastes [2], implying a potential serious threat to human health and environmental system [3]. In another hand, due to the presence of metals like aluminum (15-30%), molybdenum (4-12%), cobalt (1-5%), nickel (1-5%), vanadium (1-5%), etc [4], the spent HDS catalysts becomes an important resource supply when the mineral resource supply cannot meet the growing demand of the said metals [5,6]. Therefore, the harmless dispose and metal recovery of spent HDS catalysts is significant for the resource preservation and environmental protection [7]. ...
Article
It is urgently desired to develop a promising method for deep removal of vanadium from molybdate solution for the efficient recycle of spent hydrodesulfurization (HDS) catalyst. In this paper, a novel method was investigated to deeply remove vanadium using γ-Fe2O3 particles as adsorbent. The properties of synthesized adsorbent were analyzed by a series of characterization methods. The adsorbent composed of γ-Fe2O3 nanoparticles with a diameter of 10−15nm shows superparamagnetism and the saturation magnetization is about 56 emu·g⁻¹. The performance of this adsorbent including the vanadium removal efficiency and adsorbent stability was evaluated. The vanadium removal rate is up to 97.6% and the co-adsorbed Mo is lower than 5% at a pH of 10 within only 30 minutes. Furthermore, both magnetism and adsorption capacity of the γ-Fe2O3 adsorbent are nearly unchanged after 30 days storage. The adsorption mechanism was revealed that polymeric vanadium ions exhibit higher affinity with γ-Fe2O3 than MoO4²⁻, and the adsorption follows ion exchange mechanism between hydroxyls covered on the adsorbent. The γ-Fe2O3 adsorbent presents a series of advantages of excellent V-removal performance, good recyclability, excellent stability, which may have significant potential for industrial-scale applications.
... The poisoning effect is observed mainly in the low-temperature range of SCR (below 300 • C). Since vanadium catalysts are commonly used for sulphur dioxide oxidation in the technology of sulphuric acid production, the active phase of commercial NH 3 -SCR system is capable to oxidize SO 2 to SO 3 [46,58]. The main problem of the exposition of the catalyst to SO x is the formation of ammonium bisulphates (NH 4 HSO 4 ) and ammonium sulphates ((NH 4 ) 2 SO 4 ) on its surface [59]. ...
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One of the most harmful compounds are nitrogen oxides. Currently, the common industrial method of nitrogen oxides emission control is selective catalytic reduction with ammonia (NH3-SCR). Among all of the recognized measures, NH3-SCR is the most effective and reaches even up to 90% of NOx conversion. The presence of the catalyst provides the surface for the reaction to proceed and lowers the activation energy. The optimum temperature of the process is in the range of 150–450 °C and the majority of the commercial installations utilize vanadium oxide (V2O5) supported on titanium oxide (TiO2) in a form of anatase, wash coated on a honeycomb monolith or deposited on a plate-like structures. In order to improve the mechanical stability and chemical resistance, the system is usually promoted with tungsten oxide (WO3) or molybdenum oxide (MoO3). The efficiency of the commercial V2O5-WO3-TiO2 catalyst of NH3-SCR, can be gradually decreased with time of its utilization. Apart from the physical deactivation, such as high temperature sintering, attrition and loss of the active elements by volatilization, the system can suffer from chemical poisoning. All of the presented deactivating agents pass for the most severe poisons of V2O5-WO3-TiO2. In order to minimize the harmful influence of H2O, SO2, alkali metals, heavy metals and halogens, a number of methods has been developed. Some of them improve the resistance to poisons and some are focused on recovery of the catalytic system. Nevertheless, since the amount of highly contaminated fuels combusted in power plants and industry gradually increases, more effective poisoning-preventing and regeneration measures are still in high demand.
... These preliminary results show that sulfuric acid is the most efficient leaching agent for the treatment of these Co/ Mo catalysts. Alternative acidic treatments have been tested for the recovery of metals from ores and catalysts or spent materials using organic acids [3,34], including oxalic acid [35]. Some tests were carried out for the recovery of Al, Co and Mo from the catalyst material using oxalic acid at the concentration of 50 g L −1 ; the leaching efficiency remained very low: 1.46-1.63% ...
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Two different strategies have been designed for the acid and alkaline leaching steps of hydrodesulphurization catalysts. Tests have been performed on out-of-range catalysts issued from catalyst manufacturing process. Experimental conditions have been screened for these different processes considering the effects of concentration, temperature, solid/liquid ratio, etc. The best conditions have been used for producing two leachates that were treated by precipitation for recovery of valuable metals such as cobalt and molybdenum. Post-treatments have also been designed for the selective separation of Co from Mo: X-ray diffraction analyses on selective precipitates (as sulfide) confirm the purity of produced materials. Two flow sheets are proposed that allow selectively recovering more than 95% of the valuable metals.
... Composition of the catalyst waste differ. Erust et al. determined composition with approximately 6% V 2 O 5 , 2% Al 2 O 3 , 1% Fe 2 O 3 and 60% SiO 2 ; and the rest constituting several other oxides were in traces/minute quantities (Erust et al., 2016). Another work reported that catalysts contained 27% of V 2 O 5 but much larger content of Al 2 O 3 (40%) (Villarreal et al., 1999). ...
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This paper addresses the sustainability of vanadium, taking into account the current state-of-the-art related to primary and secondary sources, substitution, production, and market developments. Vanadium plays a critical role in several strategic industrial applications including steel production and probable widespread utilization in next-generation batteries. Confirming the importance of vanadium, the European Commission identified and formally registered this metal on the 2017 list of Critical Raw Materials for the European Union. The United States and Canada have also addressed the importance of this metal. Like the European economy, the American and Canadian economies rely on vanadium and are not globally independent. This recognized importance of vanadium is driving many efforts in academia and industry to develop technologies for the utilization of secondary vanadium resources using hydrometallurgical and pyrometallurgical techniques. In this paper, current efforts and their outcomes are summarized along with the most recent patents for vanadium recovery.
... Catalysts are extensively used in sulfuric acid production and petroleum refining [70,71]. More than 100,000 tons of spent hydrodesulphurization catalysts are produced every year, which usually contain the valuable elements V, Mo, Ni, and Co [72]. ...
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Vanadium as a rare element has a wide range of applications in iron and steel production, vanadium flow batteries, catalysts, etc. In 2018, the world’s total vanadium output calculated in the form of metal vanadium was 91,844 t. The raw materials for the production of vanadium products mainly include vanadium-titanium magnetite, vanadium slag, stone coal, petroleum coke, fly ash, and spent catalysts, etc. Chlorinated metallurgy has a wide range of applications in the treatment of ore, slag, solid wastes, etc. Chlorinating agent plays an important role in chlorination metallurgy, which is divided into solid (NaCl, KCl, CaCl2, AlCl3, FeCl2, FeCl3, MgCl2, NH4Cl, NaClO, and NaClO3) and gas (Cl2, HCl, and CCl4). The chlorination of vanadium oxides (V2O3 and V2O5) by different chlorinating agents was investigated from the thermodynamics. Meanwhile, this paper summarizes the research progress of chlorination in the treatment of vanadium-containing materials. This paper has important reference significance for further adopting the chlorination method to treat vanadium-containing raw materials.
... Son numerosos los estudios relacionados con la recuperación de vanadio de catalizadores agotados mediante lixiviación, donde se evalúa la extracción utilizando diferentes agentes lixiviantes: ácidos, básicos y orgánicos (Erust et al. 2016). ...
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In the production of sulfuric acid by the contact method, catalysts with more than 4 % vanadium pentoxide are used, which go out of service once they are completely exhausted. In the present work, the recovery, by acid leaching, of the vanadium contained in exhausted catalysts from the Patricio Lumumba Factory was evaluated. A full factorial design of experiments was carried out (23) where the following were analyzed as independent variables: temperature, solid/liquid ratio and sulfuric acid concentration and as dependent variables: vanadium concentration and leaching performance. The processing allowed obtaining a liquid phase composed of the sulfates of the metals leached with sulfuric acid, which have vanadium concentrations between 1,448 mg/l and 3,730 mg/l. The evaluated processing allows, from the liquid phase obtained, recovering the vanadium for its industrial use, where the solid waste generated is not polluting, which is favorable for the protection of the environment.
... citric acid, oxalic acid) as well as oxidants and alkalis (e.g. NaOH, KOH) [61][62]. In our studies the vanadium based catalyst was leached using hydrochloric acid (5% m/m), sulphuric acid (5% m/m), sodium hydroxide (15% m/m) and potassium hydroxide (15% m/m). ...
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It is well known that removal of vanadium ions from the natural environment has become a great challenge in recent years. Due to this fact, the present study concerns the application of binary oxides such as TiO2-ZrO2 (molar ratio 9:1) and TiO2-ZnO (molar ratio 7:3) synthesized by the sol-gel method with calcination at 873 K (TZ1 sample) or by the hydrothermal method at 433 K (TZ2 and T7Zn3 samples), respectively. The fabricated adsorbents were subjected to the detailed physicochemical analysis including: dispersive properties, morphology, crystalline and textural properties as well as chemical composition. The vanadium(V) ions adsorption on the binary oxides was optimized by the experimental conditions such as pH (2-10), adsorbent dose (0.01-0.1 g), vanadium concentration (10-500 mg/L), agitation time (1 min-24 h) and temperature (293-333 K). The pseudo-first-order (PFO), pseudo-second-order (PSO) and intraparticle diffusion (IPD) kinetic models as well as the Langmuir, Freundlich, Temkin and Dubinin-Raduskievich isotherm models were applied for the description of V(V) adsorption. The adsorption capacities were found to be 129.3 mg/g for TZ1, 170.8 mg/g for TZ2 and to 195.9 mg/g for T7Zn3. The endothermic and spontaneous character of V(V) adsorption on the binary oxides was confirmed by the values of thermodynamic parameters. The best fitting of kinetic experimental data to the pseudo-second-order model was obtained. The maximum desorption yield (%D) was achieved using the 1 mol/L NaOH (97.96%-T7Zn3, 75.81%-TZ2, 62.88%-TZ1) solution. Applicability of the inorganic oxides in V(V) and Fe(III) removal from spent catalyst leaching solutions was proved.
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... The carbon adsorption and desorption process include solubilization of vanadium, adsorption on activated charcoal, desorption, and precipitation of vanadium pentoxide, has been used mainly on a laboratory scale for extracting vanadium from red mud, and it is not clear that this process can be used in industrial and economic scale [33][34][35]. Spent catalysts have good potential for extracting valuable elements (Ni, V, Mo, Co, etc.) due to depletion of primary resources mines, increasing vanadium demand by the industry, and landfilling environmental problems as hazardous wastes [19,36,37]. The hydrometallurgical (acid or alkali leaching and solvent extraction processes) in the combination of roasting and bio-hydrometallurgical (bacterial leaching based on the ability of microorganisms, bacteria, or fungi as leaching reagents) methods have been reported for the extraction of vanadium from the spent catalysts at room temperature and atmospheric pressure [38][39][40][41][42]. ...
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To alleviate the energy consumption and the effluent of traditional oxidizing roasting and leaching process of vanadium extraction, a novel method to extract the vanadium from iron vanadate spinel mineral (Fe3-xVxO4) by one leaching step was developed. In this method, the Fe powder was found as a synergist of oxalic acid to leach the vanadium as [V(C2O4)3]³⁻ complex under hydrothermal condition. With the synergy of Fe powder, the leaching efficiency of V³⁺ ions from iron vanadate spinel concentrate was enhanced significantly, and simultaneously Fe³⁺ ions present as impurity in the pregnant leachate were eliminated effectively by forming FeC2O4·2H2O precipitate. Using the most suitable conditions, the leaching efficiency of vanadium can reach 95%, reducing Fe³⁺ to less than 100 mg/L. Furthermore, FeC2H2O4·2H2O with 98% purity could be obtained as a by-product by washing the filtered cake.
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The leaching mechanism of the spent selective catalytic reduction (SCR) catalyst was investigated by density functional theory (DFT) calculations and experiments. Three models, namely V2O5/TiO2, WO3-V2O5/TiO2, and WO3/TiO2, were created to simulate the spent SCR catalyst. Interaction between the surface clusters and the leaching agents of NaOH, H2SO4, HCl and HNO3 was investigated by DFT calculations. The adsorption site was determined through electrostatic potential and adsorption energy. The calculations showed that NaOH tended to be adsorbed on V and W atoms. H2SO4, HCl and HNO3 tended to be adsorbed on specific O atoms. H2SO4 dissociated on all three models, HCl dissociated on V2O5/TiO2 and WO3-V2O5/TiO2, while HNO3 dissociated only on V2O5/TiO2. The order of leaching ability among leaching agents was NaOH>H2SO4>HCl>HNO3. Experiments showed that the leaching ratios of V and W in NaOH solution were 82.4% and 54.3%. In acid solution, the leaching ratio of V was 69.0% for H2SO4, 52.5% for HCl, and 42.2% for HNO3, while W was hardly leached out. After acid leaching, the change in the TiO2 lattice parameter was greater than that after alkaline leaching. The experimental results were found to be consistent with the calculations.
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Metal‐ion batteries emerged as promising candidates for energy storage system due to their unlimited resources and competitive price‐performance ratio. Vanadium‐based compounds have diverse oxidation states rendering various open‐frameworks for ions storage. To date, some vanadium‐based polyanionic compounds have shown great potentials as high‐performance electrode materials. However, there has been a growing concern regarding the cost and environmental risk of vanadium. In this review, we comprehensively summarize the whole links in the industry chain of vanadium‐based electrodes. Starting with an analysis of the resources, applications, and price fluctuation of vanadium. We discuss the manufacturing processes of the vanadium extraction and recovery technologies. Moreover, the commercial potentials of some typical electrode materials are critically appraised. We then evaluate the environmental impact and sustainability of the industry chain. We hope this critical review will provide a clear vision of the prospects and challenges of developing vanadium‐based electrode materials.
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In order to control nitrogen oxides emissions, V2O5-WO3/TiO2 catalysts are widely applied in coal-fired power plants. Consequently, a large number of V2O5-WO3/TiO2 catalysts are spent annually because of their short operating life. Although these spent catalysts contain amounts of heavy metals, they have also been regarded as a potential secondary resource for the recovery of valuable elements titanium, tungsten, and vanadium. Therefore, this study developed an efficient method for selective leaching of heavy metal vanadium with an “H2SO4 + Na2SO3” acid reduction system. The use of this leaching solution achieved nearly 100% efficiency in vanadium removal. And the effects of the leaching parameters on the vanadium leaching efficiencies were investigated. Subsequently, the titanium-enriched residue obtained from the leaching process was used to produce high-performance WO3-TiO2 photocatalysts with dominant {001} facets via a hydrothermal treatment. The influence of the amount of hydrogen fluoride on the morphology and percentage exposure of the {001} facets of the photocatalysts was studied systematically. The method proposed in this study constitutes a novel and sustainable approach for the disposal of spent V2O5-WO3/TiO2 catalysts.
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The catalyst Mo–Ni/Al2O3 is commonly used in the hydrodesulphurization of petroleum fractions. The catalyst is discarded when its catalytic activity does not meet the requirement of the process, and the spent catalyst is usually classified as hazardous waste due to its significant heavy-metal content. The spent catalyst usually has a high commercial recovery value as a secondary resource for high-value metals, but the simple and high efficiency recovery method is still lacking. A high-efficiency recovery method for Mo and Ni from spent Mo–Ni/Al2O3 catalyst via soda roasting and solvent extraction was developed in this study. MoO3 interacts with Al2O3 and forms a new phase, Al2(MoO4)3, during blank roasting at 600–700 °C. Al2(MoO4)3 further transforms into NaMoO4 during soda roasting at 950 °C, and over 99.1% of Mo can be leached using hot water (60 °C). Solvent extraction with the trioctyl tertiary amine (N235) is employed to separate Mo from the leaching solution, and approximately 99.45% of Mo can be enriched through single-stage extraction. Around 99.2% of Mo can be stripped from loaded N235 using 8 M NH3•H2O. Further, PO4³⁻ and SiO3²⁻ can be removed from the stripping solution using Mg(NO3)2, and Mo is recycled in the form of MoO3, i.e., a product of the ammonium precipitation and calcining process. Over 99.3% of Ni can be leached from the solid residue using 30% volume fraction of H2SO4 and the solvent extraction can be enriched using diiso-octylphosphate (DP). Ni is finally recycled from the stripping solution as NiSO4•2H2O via evaporative crystallization. The total Mo and Ni recovery efficiencies of the newly developed integrated approach are 97.8% and 98.1%, respectively. Al is also recycled in the form of α-Al2O3 via chemical precipitation and calcination. The proposed approach is simple, with a high recovery rate and high selectivity, and can be applied to the recycling and disposal of spent Mo–Ni/Al2O3 catalyst.
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Coal tar in the glass furnace flue gas can poison the V2O5-WO3/TiO2 (VWTi) catalyst used for ammonia selective catalytic reduction (NH3-SCR) of NOx. Herein, naphthalene (Nap), as one of the main components of coal tar, was selected to investigate the poisoning effect of coal tar on VWTi catalyst in the range of 200–280 ℃. The experimental results showed that the activity of VWTi catalyst decreased sharply with the introduction of Nap vapor, and the NOx conversion was less than 20% after the introduction of 1 h at the temperature range of 200–280 ℃. The poison processing and mechanism were systematically investigated. It was found that the Nap preferentially consumes active oxygens on the catalyst to form phthalic anhydride (PA) with a higher boiling point, which covers the active sites and leads to the deactivation of VWTi catalyst. Temperature affects the accumulation of deposits and the conversion rate of Nap, thus poisoning effect of Nap on VWTi is temperature-sensitive. The deposited Nap can be removed at high temperatures. Therefore, the inactivated catalysts can be regenerated by high temperature treatment.
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A cleaner and novelty leaching medium, (NH4)2SO4-H2SO4 synergistic system was introduced into the leaching process for extracting vanadium efficiently after calcification roasting with high chromium vanadium slag (HCVS), and then V2O5 was prepared after precipitation and roasting. The effects of leaching and precipitation conditions were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). 93.45% vanadium and 0.24% chromium were leached when the calcification roasted sample was leached in the (NH4)2SO4-H2SO4 synergistic system at 20 °C for 60 min with a liquid–solid ratio (L/S) of 10, achieving the efficient separation of vanadium and chromium in HCVS. The optimal (NH4)2SO4-H2SO4 synergistic system was composed with 250 g/L (NH4)2SO4 and 3.75 mol/L H2SO4, the amount of H2SO4 was 1 mL in every 30 mL leaching system. The introduction of (NH4)2SO4 provided much NH4⁺, which could promote the acid leaching reaction. 99.75% vanadium was precipitated further from vanadium-containing leaching liquid when heating the liquid at 60 °C for 60 min after adjusting the system pH at 8.0, and the deposit was ammonium polyvanadate (NH4)2V6O16. Then, V2O5 with a purity of 95.71% was prepared after roasting, and recovery rate of vanadium from HCVS was higher than 93%. After precipitation, the supernatant containing a large amount of NH4⁺ could be recycled as the new leaching medium with some (NH4)2SO4 adding according to NH4⁺ loss after vanadium precipitation. This process achieved the efficient extraction of vanadium from HCVS and provided a new thinking for the leaching process based on the (NH4)2SO4-H2SO4 synergistic system.
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This study investigated heavy metal chemical speciation and leaching behavior from a board-type spent selective catalytic reduction (SCR) catalyst containing high concentrations of vanadium, chromium, nickel, copper, zinc, and lead. A three-step sequential extraction method, standard toxicity characteristic leaching procedure (TCLP), and leaching characteristic tests have been performed. It was found that the mobility of six heavy metals in the spent SCR catalyst was significantly different. The mobility of the six heavy metals exhibited the following order: Ni > Zn > V > Cr > As > Cu. Meanwhile, TCLP test results revealed relatively high Zn and Cr leaching rate of 83.20% and 10.35%, respectively. It was found that leaching rate was positively correlated with available contents (sum of acid soluble, reducible and oxidizable fractions). Leaching characteristics tests indicated that pH substantially affected the leaching of these heavy metals. In particular, the leaching of Cr, Ni, Cu, and Zn was positively influenced by strong acid, while V and As were easily released in the presence of strong acid and strong alkali (pH < 3 or pH > 11). In terms of kinetics, the leaching of Cr, Ni, Cu, Zn, and As within the spent catalyst was dominated by erosion and dissolution processes, which were rapid reaction processes. V was released in large amounts within 1 h, but its leaching amount sharply decreased with time due to readsorption.
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The extensive use of selective catalytic reduction (SCR) catalysts will afford many spent SCR catalysts. The mass fraction of the titanium component is over 80% in spent SCR catalysts, but currently, it is usually thrown away without proper recycling. This work aims to develop a clean, green, and economical approach to recovering titanium and regenerating TiO2 photocatalysts from spent SCR catalysts based on the conversion of the titanium component. This titanium component is converted into metastable α-Na2TiO3 with high efficiency (> 98%) using a NaOH molten salt method, and the optimal conditions were found to be a roasting temperature of 550 °C, a NaOH-to-spent-SCR-catalysts mass ratio of 1.8:1, a roasting time of 10 min, and a NaOH concentration of 60-80 wt.%. And a possible chemical reaction mechanism is proposed. A subsequent hydrothermal treatment of α-Na2TiO3 regenerates TiO2 photocatalysts with high purity (> 99.0%) that can satisfy commercial requirements. In addition, the present iron element contained in spent SCR catalysts is doped into regenerated TiO2 photocatalysts, resulting in providing visible-light-driven photocatalytic activities. The regenerated TiO2 photocatalysts possess superior photocatalytic degradation capacities for dye pollutants and can be used to efficiently treat wastewater. This work introduces a promising technology for the cyclical regeneration of titanium from spent SCR catalysts.
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The extraction mechanism and the oxidation of extractants are essential to optimize the extraction process. To investigate the two problems for selective extraction of V(V) and Cr(VI), the extraction complexes of V(V) and Cr(VI) formed in the process of extraction with primary amines were obtained by solvent-out crystallization, respectively. The average compositions of the extraction complexes were determined by element analysis, X-ray photoelectron spectroscopy, and inductive couple plasma-optical emission spectrometry. The chemical functional groups of the extraction complexes were confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy. The structures of the extraction complexes of V(V) were speculated with their functional groups and average compositions. The hydrogen bond association mechanism of V(V) extraction was illustrated with the structure of the complexes, and the oxidation reaction of extractants with Cr(VI) was also demonstrated. According to the oxidation reaction of extractants with Cr(VI) and experiment conditions for the initial pH value, the optimized operation condition of the initial pH value ≥5.5 was determined to prevent the oxidation of extractants. The interaction of V(V) and Cr(VI) for the vanadium extraction and extractant oxidation was also investigated.
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Aluminum recovery is a key issue for the overall recycling of valuable metals from spent catalysts. This paper focuses on the recovery and regeneration of alumina with high additional value from the spent hydrodesulfurization catalyst CoMo/Al2O3. The results indicate that 98.13% alumina is successfully leached from the treated spent catalysts by an alkaline leaching process under the conditions of 5 mol·L⁻¹ sodium hydroxide, a liquid/solid ratio of 20 ml·g⁻¹, a temperature of 160 °C and a reaction time of 4 h. In the leaching residue, no difficult leaching compound is found and cobalt and nickel are enriched, both of which are conducive to the subsequent metal recovery step. The reaction order of aluminum leaching is 0.99. This reaction fits well with the interfacial chemical reaction model, and its apparent activation energy is calculated as 45.50 kJ·mol⁻¹. Subsequently, γ-Al2O3 with a high specific surface area of 278.3 m²·g⁻¹, a mean size of 2.2 μm and an average pore size of 3.10 nm is then regenerated from the lixivium, indicating its suitability for use as a catalyst carrier. The recovery and regeneration of alumina from spent catalysts can not only significantly contribute to the total recycling of such hazardous spent catalysts but also provide a new approach for the preparation of γ-Al2O3 with a high specific surface area using spent catalysts as the aluminum sources.
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An environmentally friendly hydrometallurgical process was developed to recover vanadium and cesium selectively from spent sulfuric acid catalysts, and it has high recovery efficiency and economic advantages.
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Titanium white waste acid (TWWA) is strongly acidic, and has high metatitanic acid (TiO(OH)2) and n-hexane (C6H14) content. In this study, the effects of polyvinyl alcohol (PVA) on the modification of TWWA deacidification were evaluated via pilot testing. The results showed that the PVA solution can significantly improve the deacidification performance of TWWA. The TWWA specific resistance to filtration (SRF) decreased from the initial 2.42 × 10¹³ m/kg to 1.80 × 10¹² m/kg when 2% PVA solution was added at 25% (v/v). Furthermore, the amount of filter press-processed TWWA increased by 3.56 m³ relative to the control, and the moisture content of titanium white slag was only 42.02% after deacidification. In addition, distillation and phase separation was demonstrated to efficiently separate C6H14 and hydrochloric acid (HCl) from the mixed filtrate. Moreover, titanium white slag was converted into rutile after 60 min when the calcination temperature was 900 °C, with the titanium dioxide (TiO2) purity of rutile reaching 91.83%. Accordingly, the TWWA recycling process proceeded as follows: PVA modification, solid-liquid separation, filtrate distillation and phase separation, and titanium white slag calcination. Our findings demonstrate that this process has unique practical application value.
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The dissolution kinetics of vanadium from spent hydroprocessing catalyst was investigated by leaching with sulfuric acid at atmospheric pressure. The effects of stirring speed (400-800 rpm), initial sulfuric acid concentration (0.60-1.20 mol/l) and reaction temperature (373-423 K) on the vanadium dissolution were studied. The results showed that the vanadium dissolution ratio was practically independent of stirring speed at the investigated range, while increasing with the increases of sulfuric acid concentration and reaction temperature. The experimental data agreed quite well with the shrinking core model, with solid membrane diffusion as the rate controlling step. The apparent activation energy was calculated as 11.44 kJ/mol, and the reaction order with respect to sulfuric acid concentrations was determined to be 1.51. The kinetics equation of the leaching process was established as: 1-2x/3-(1-x)2/3=0.067[H2SO4]1.51exp[-11563RT]t.
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Selective leaching of vanadium and separation of iron from red mud by using oxalic acid and sodium sulfite were put forward. The main influencing factors of selective leaching were studied and the leaching mechanism was analyzed with XRD, SEM-EDS, thermodynamic theory and leaching kinetics. The results show that more than 90% of vanadium could be selectively leached into the acid solution with less than 10% of iron under the suitable leaching conditions. The acid leaching of vanadium is controlled by boundary layer diffusion with R² more than 0.98. The acid leaching of iron is controlled by surface chemical reaction with R² more than 0.99 under different oxalic acid concentrations. The apparent activation energy of vanadium and iron was 8.21 kJ/mol and 13.57 kJ/mol, respectively. H2C2O4 could selectively destroy the minerals of red mud resulted in the high recovery of vanadium. H2C2O4 reacted with Fe²⁺ to generate the precipitation of FeC2O4 in the leaching residue caused by the p-π conjugation of O--C--O of C2O4²⁻. The stable VO(C2O4)2²⁻ complex was present in the leaching solution due to the conjugated system of π-π with O--C--O of C2O4²⁻ and V=O of VO²⁺.
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Carbon black waste generated in Singapore oil refinery contains a high concentration of vanadium (>14000 ppm on dry weight basis). Considering the high market value of the waste vanadium component, in this work, an economic and eco-friendly production strategy of monoclinic bismuth vanadate (BiVO4) has been developed based on vanadium recovery from carbon black waste leachates. The total recovery of vanadium from the carbon black waste can reach 99%. Importantly, the BiVO4 could be utilized as photocatalysts to degrade organic dyes under visible-light irradiation. Further economic analysis on the industrial-scale production of BiVO4 was studied after scaling up the production process and evaluating the profitability associated with operations over a 10-year period. Considering a 30 tons/day processing rate of wet carbon black waste feed, the estimated discounted payback period at 8% discount rate is 1.36 years after plant commissioning.
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Nickel–cobalt–manganese ternary cathode materials for lithium‐ion batteries are prone to detrimental side reactions and deterioration performance at deep charge. Coating is one of the effective methods to boost electrochemical performance of materials. This work conducts an ultrathin LiV2O4 layer on the single‐crystal LiNi0.5Co0.2Mn0.3O2 (NCM523) particles and scrutinizes the optimal coating amount. It turns out that 0.3 wt% LiV2O4‐modified NCM523 cathode achieves a reversible discharging capacity of 131.2 mAh g−1 after 100 cycles (3.0–4.5 V vs Li/Li+), with a capacity retention of 80% (which is 50% higher than that of the pristine sample). The experimental data suggest that this lithium vanadate coating technique provides an innovative strategy to boost the performance of NCM cathodes. LiV2O4‐modified NCM523 single crystals with a coating thickness of ≈3 nm are achieved from a facile wet‐chemical procedure in VOSO4 and followed by annealing operations. Structures and electrochemical performances of the coating layer are investigated, which show that LiV2O4‐coated NCM523 from 0.3 wt% VOSO4 solution exhibits superior electrochemical activity and stability.
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The V-Cr-Fe ternary slime is an emerging heavy metal waste after a series of pyro- and hydro-metallurgical processes (so called “slime of the slag”), usually containing considerable metal resources and nearly 70 wt% H2O inside. In this study, a facile leaching-complexation method is proposed for the cleaner, efficient and selective recovery of V, Cr and Fe. After efficient leaching procedure in the H2SO4 solution, 94% V and 97% Fe were selectively precipitated out via the complexation with C5H10NNaS2. Subsequently, the V and Fe could be further separated through the dissociation in alkaline solution, in which the Fe(OH)3 solid and Ca2V2O7 (with the addition of CaO) were generated, respectively. Furthermore, the complexing agent could be regenerated for next cycles, minimizing the potential secondary wastewater or solid waste formation . As a result, a cleaner and sustainable metal recovery method was developed, providing further understanding of the solution chemistry and separation technologies.
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Recovery of valuable metals such as cobalt, molybdenum, nickel, and vanadium from spent catalysts has attracted much attention owing to the gradual depletion of high-grade ores. In this work, several hydrometallurgical methods have been reviewed for recovery of these metals from several spent catalysts. The main methods include adsorption, chelation, ion exchange, leaching, precipitation, and solvent extraction. The disadvantage of precipitation lies in the difficulty in recovering pure products. Acid leaching is generally preferred to basic leaching in the industry owing to high dissolution of valuable metals. Solvent extraction is effective in the separation of valuable metals. The adsorption and complexing with chelating agents offer useful means for selective metal recovery although the scale of its application in the industry is still limited. Ion exchange is suitable for the purification of metal ions. The combination of these techniques is recommended in developing a process. The heat treatment of spent catalysts facilitates the dissolution of valuable metals by the leaching and then the dissolved metal ions can be recovered by solvent extraction. The assessment of the environmental impacts, economics, and prediction of the industrial applicability of some processes have been discussed by the life cycle analysis (LCA). Employment of LCA method to evaluate the environmental aspects during the recovery of metals from spent catalysts is necessary in further research.
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The demand for V2O5-WO3/TiO2 catalysts is growing as many countries impose increasingly stricter limits on nitrogen oxide emissions. Unfortunately, after service, the spent V2O5-WO3/TiO2 catalyst is continuously and considerably discarded. The cost of the catalyst accounts for approximately 30–50% of the total investment in the denitration system. Additionally, the spent catalyst contains significant amounts of valuable metals and some heavy metals. Thus, the regeneration to form a new catalyst or recovery of valuable metals from the spent V2O5-WO3/TiO2 catalyst has gained widespread attention in recent years, not only for meeting the growing demand for corresponding critical metals/catalysts but also reducing the potential ecological and environmental hazards caused by inappropriate disposal. In this article, a systematic review of the literature was conducted to examine recently developed processes and technologies for recycling the spent V2O5-WO3/TiO2 catalyst to recover either new catalysts or valuable metals. Moreover, the challenges associated with process optimization for the regeneration to form a new catalyst and the recovery of valuable metals were analyzed. The aim of this article is to provide a guideline on how effective processes and techniques for the spent V2O5-WO3/TiO2 catalyst recycling can be developed and to motivate further studies in this theme for industrial-scale realization.
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Vanadium, iron and aluminum were recovered from the spent sulfuric acid catalyst with efficiency of 98%, 95% and 85%, respectively by using low temperature sulphuric acid baking followed by leaching. The optimum baking conditions were four grams of concentrated sulfuric acid per ten grams of spent catalyst at 300 C for two hours. Sulphuric acid baking followed by leaching was found to be the best and it is more effective in Iron and Aluminum dissolution. Sulfuric acid baking is expected to consume small amount of chemicals and generate much less waste effluents during the separation process of metals with alkali solutions. It is economically favorable, as it avoids us much more environmental contamination.
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Vanadium has many industrial uses and its contribution to environmental contamination is increasing all the time. Recovery of vanadium pentoxide from spent sulphuric acid catalysts was performed using a three-step process involving acid leaching, oxidation and precipitation. Several different acids were used in the leaching process. Finally, sulphuric acid was used in various concentrations, solid to liquid ratios, stirring times and temperatures. A high solid/liquid ratio in the leaching stage was used to obtain high concentration of vanadium pentoxide and low acid consumption that allowed direct precipitation without the use of extraction by rather expensive organic solvents. Sodium carbonate solution of one mole/liter concentration was used in the precipitation stage. An industrial application including material balance and operating conditions with an overall vanadium pentoxide recovery efficiency of (70%) was proposed.
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Recovery of vanadium from desilication residue obtained from the processing of a spent catalyst was investigated by leaching, purification and precipitation. In the leaching process, 96.4% vanadium can be extracted when the desilication residue (1:4 g/mL) was stirred at 800 rpm for 45 min at 80 °C with 100 g/L sodium bicarbonate. After purifying leach liquor in a two stage precipitation process, over 99% Al, 95% Si, 93% P and 95% As were removed under optimum conditions with less than 4% loss of vanadium. Adding 50 g/L NH4NO3 to the purified leach liquor and adjusting the pH to 8.2, promoted the crystallization and precipitation of 99.7% vanadium as ammonium metavanadate. After roasting ammonium metavanadate at 500 °C for 2 h, the purity of the V2O5 product was up to 98.3%. In terms of desilication residue and spent catalyst, the recovery of vanadium in the process reached 92.5% and 88.7%, respectively. The proposed leaching, purification and precipitation steps provide a feasible recovery of vanadium from desilication residue and a new approach for the comprehensive utilization of spent catalyst.
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The chemical, physical and mechanical properties of Va-base alloys and unalloyed Va, its interaction with molten metals and gases and its applications are described. The sources and processing methods are outlined. The properties of vanadium compounds (oxides, hydroxides, peroxy compounds, vanadates, vanadium bronzes, sulphates and nitrates, halides and oxyhalides, and interstitial compounds) are presented. The reduction of vanadium compounds, refining (pyrovacuum treatment, electrorefining, iodide refining, zone melting, electrotransport, gettering) and the toxicology of vanadium are discribed. (A.P.)
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Spent V catalyst from SO 2 oxidn. was leached with aq. soln. of NaOH to remove Fe, Cu, Zn, As and Pd and to recover the catalyst-contained V and K. After leaching under optimum conditions (temp, above 303 K, leaching time longer than 2 h, NaOH conc. 10% by mass, catalyst size below 750 urn, solid-liq. ratio above 1:15), the recovery degree were 90% for V and 99% for K.
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A review with 17 refs. covering wastes from process-gas purification step, oxidn. of SO2 and absorption of SO3, spent V catalyst and off-gases and their utilization methods.
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The recent U.S. Environmental Protection Agency's (EPA's) memorandum clarified that spent catalysts resulting from 'dual purpose' hydroprocessing reactors are hazardous waste. This article provides insight into the definitions in the EPA regulations that refiners must follow when determining how spent hydroprocessing catalysts should be classified.
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With the increase in environmental awareness, the disposal of any form of hazardous waste has become a great concern for the industrial sector. Spent catalysts contribute to a significant amount of the solid waste generated by the petrochemical and petroleum refining industry. Hydro-cracking and hydrodesulfurization (HDS) catalysts are extensively used in the petroleum refining and petrochemical industries. The catalysts used in the refining processes lose their effectiveness over time. When the activity of catalysts decline below the acceptable level, they are usually regenerated and reused but regeneration is not possible every time. Recycling of some industrial waste containing base metals (such as V, Ni, Co, Mo) is estimated as an economical opportunity in the exploitation of these wastes. Alkali roasted catalysts can be leached in water to get the Mo and V in solution (in which temperature plays an important role during leaching). Several techniques are possible to separate the different metals, among those selective precipitation and solvent extraction are the most used. Pyrometallurgical treatment and bio-hydrometallurgical leaching were also proposed in the scientific literature but up to now they did not have any industrial application. An overview on patented and commercial processes was also presented. Copyright © 2015 Elsevier Ltd. All rights reserved.
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The recovery and purification of vanadium (V) and tungsten (W) from honeycomb-type spent selective catalytic reduction (SCR) catalyst was investigated using an autoclave through a pressure leaching process. Spent SCR catalyst mainly consists of TiO2 and other oxides (7.73% WO3, 1.23% V2O5, etc.). The reaction temperature, NaOH concentration, time, additive concentration, and liquid–solid (L/S) ratio were varied during the leaching process. The optimal reaction conditions were identified for recovery of V and W. The addition of NaOH to Na2CO3 improved the amount of V and W recovered because of the enhancing effect of NaOH in Na2CO3. As the concentration of CaCl2 was increased during the precipitation process in order to separate the recovered V and W, the precipitation percentages of V and W increased, respectively. However, the use of Ca(OH)2 as the additive reduced the precipitation percentage of W. Therefore, despite full precipitation of V (98.6%), only 7.73% of W was precipitated when 3 equivalents of Ca(OH)2 was reacted with spent SCR catalyst for 30 min. The remaining W in the leaching solution was reacted with NH4OH to form ammonium tungstate, which was converted to ammonium paratungstate through evaporation. Consequently, V and W could be recovered and separated successfully through the process in this study.
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Molybdenum (Mo) and vanadium (V) were effectively extracted from the spent diesel exhaust catalyst (V2O5–MoO3/TiO2) by using an ammonia leaching method. Meanwhile, the structure of the spent catalyst carrier (TiO2) was not destroyed and might be reused. The effects of ammonia (NH3·H2O) concentration, leaching temperature and time, concentration of hydrogen peroxide (H2O2) and liquid to solid ratio on the extraction of Mo and V were systematically investigated. It is shown that the extraction efficiency of Mo increased from 68.68% to 96.45% while the extraction efficiency of V remained stable at 27% with increasing ammonia concentration from 2.95 to 7.38 mol/L, leaching temperature from 298.15 to 473.15 K, and reaction time from 1 to 8 h. With the concentration of H2O2 solution increasing from 1.0 to 2.5 mol/L, the extraction efficiency of V increased from 26.87% to 39.73%. Under the optimum conditions (the ammonia concentration of 4.5 mol/L, leaching temperature of 413.15 K, reaction time of 2 h, the H2O2 solution concentration of 1.0 mol/L and the liquid to solid ratio of 20/1 mL/g), the extraction efficiencies of Mo and V reached 95.13% and 46.25%. Moreover, the catalyst carrier TiO2 with anatase crystal phase was also obtained.
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In this study, recovery of vanadium and gallium from solids waste by-products (vanadium sludge and electrofilter dust of calcination plant) of Bayer process was investigated. An efficient purification process wasdevelopedbased on the removal of impurities such as phosphate by water leaching, neutralisation using CO2-enriched air and addition of aluminate solution. Recovery of V2O5 from the purified solution via the precipitation of ammonium metavanadate, its conversion into polyvanadate by the addition of ammonium sulphate and sulphuric acid, respectively, and then the ignition of the latter at 560°C was demonstrated. Effects of various parameters on the purification and precipitation processes were shown. A treatment process involving sintering and two-stage of carbonisation was also demonstrated to produce a Ga-rich precipitate. A gallate solution suitable for electrolysis of Ga was also shown to be prepared from this precipitate. A complete flowsheet was proposed for the treatment of vanadium sludge and electrofilter dust.
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MicroRNAs (miRNAs) encoded by the myosin heavy chain (MHC) genes are muscle-specific miRNAs (myomiRs) and regulate the expression of MHC isoforms in skeletal muscle. These miRNAs have been implicated in muscle fibre types and their characteristics by affecting the heterogeneity of myosin. In pigs, miR-208b and miR-499 are embedded in introns of MYH7 and MYH7b respectively. Here, we identified a novel single nucleotide polymorphism (SNP) in intron 30 of MYH7 by which porcine miR-208b is encoded. Based on the association study using a total of 487 pigs including Berkshire (n = 164), Landrace (n = 121) and Yorkshire (n = 202), the miR-208b SNP (g.17104G>A) had significant effects on the proportions of types I and IIb fibre numbers (P < 0.010) among muscle fibre characteristics and on drip loss (P = 0.012) in meat quality traits. Moreover, the SNP affected the processing of primary miR-208b into precursor miR-208b with a marginal trend towards significance (P = 0.053), thereby leading to significant changes in the levels of mature miR-208b (P = 0.009). These SNP-dependent changes in mature miR-208b levels were negatively correlated with the expression levels of its target gene, SOX-6 (P = 0.038), and positively associated with the expression levels of its host gene, MYH7 (P = 0.046). Taken together, our data suggest that the porcine miR-208b SNP differentially represses the expression of SOX-6 by regulating miRNA biogenesis, thereby affecting the expression of MYH7 and the traits of muscle fibre characteristics and meat quality.
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The catalytic removal of NOx technologies must pay attention to waste selective catalytic reduction (SCR) catalysts, which are the traditional commercial V2O5–WO3/TiO2 catalysts. Our work focuses on the progress in green reclamation and green chemistry for dealing with the spent SCR catalysts with sustainability perspectives. The problem outlined deals largely with the study of a feasible preparation way for visible-light-sensitive BiVO4/Bi2WO6 heterojunction photocatalyst, which was synthesized via a hydrothermal process through waste SCR catalysts. In this paper, the simulated waste SCR catalyst dissolved by sodium hydroxide (NaOH) solution was proposed. V2O5 and WO3 were dissolved heavily while TiO2 was rarely dissolved by sodium hydroxide. Afterword, the dissolved vanadium and tungsten in leaching solution were used to produce BiVO4/Bi2WO6 heterojunction through a hydrothermal process at 160 °C, which can be used as photocatalyst. The photocatalytic performance of the BiVO4/Bi2WO6 sample was evaluated by degradation of methylene blue in aqueous solution under visible light irradiation, which attributed to the improved separation efficiency of photogenerated hole-electron pairs generated by the heterojunction between Bi2WO6 and BiVO4.
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Leach solutions and wastes of Bayer process are important resources for metals such as aluminum and vanadium. Despite the fact that vanadium cake is precipitated and removed in the Seydisehir Eti Aluminum Facility (Turkey), it cannot be used due to low metal content and impurities it contains. Within the scope of this study, research and development of environmentally acceptable, technically sound and low-cost chemical leaching and recovery methods were conducted for the recovery of vanadium from the by-product cake of the Bayer process. In the conducted studies, a sample of vanadium cake was used after its detailed characterization. Roasting tests were performed in order to remove the arsenic in the vanadium cake; however, it was found that roasting was not effective in removing the arsenic from the cake. The performance of different reagents were examined in chemical leaching tests (H2O and H2SO4 leaching, H2SO4 leaching with the addition of NaSO3, and NH4F); in the H2SO4 leaching tests performed with the addition of Na2SO3, the concentration of the reagents and the effect of temperature on the efficiency of vanadium recovery (max. 93.09%) were determined with the full factorial experimental design method, the outcomes were evaluated with ANOVA (variance analysis) method, and empirical models were formed. In lab and semi-pilot scale leaching tests, vanadium recoveries were 96.34% and 94.76% respectively. Vanadium was precipitated with NaOH and FeSO4 and almost all vanadium (95.8%) was obtained as Fe3(VO4)2. Cost analysis and economic evaluation have shown the economic feasibility of the leaching and recovery processes proposed.
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A spent vanadium catalyst was leached in an oxalic acid solution to recover vanadium, potassium and iron. The effects of time, temperature, acid concentration, phase ratio and catalyst particle size were studied. The results showed that for a 180–250 μm catalyst leached for 4 h at 323 K in the presence of 2% oxalic acid solution at a liquid:solid ratio of 25:1, the extent of leaching of V, K and Fe was about 91%, 92% and 63%, respectively. Studies on the separation of vanadium from iron were conducted. The effect of pH on the concentration of the investigated compounds in post-leaching solution was presented. Additionally, separation of vanadium from such a solution was investigated by the ion exchange method. Three types of polymer strongly acidic ion exchangers were used. The ion exchange tests indicate that only potassium and iron were loaded from the post-leaching solution. On this basis a flowsheet for the proposed process of a complex utilization of spent vanadium catalyst is presented.
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This paper presents a brief review of extractive metallurgy of tantalum starting from processing of its ore to two pure intermediates K2TaF7 and Ta2O5 and their conversion to pure tantalum metal by various technically feasible processes. Though tantalum metal can be produced by several means only two processes – sodium reduction of K2TaF7 and fused salt electrolysis of K2TaF7 in the presence of oxide, have been successful on industrial scale. Besides providing salient features of these two processes, the paper presents brief accounts of studies carried out on the reduction of oxide by metallic reductants – calcium and aluminium as well as nonmetallic reductants – carbon and carbon–nitrogen. The crude metal obtained by various reduction techniques outlined are purified either by solid state pyrovacuum treatment or by melt refining in an electron beam furnace. Mechanism of refining processes taking place during these post reduction treatments are also included in the review.
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The leaching behaviors of Ni and V from a spent hydroprocessing catalyst were assessed in this study. The fractionations of Ni and V on the spent catalyst were determined. An automatic pH/ORP control apparatus was utilized to assess the leaching behaviors of Ni and V. When spent catalyst suspension was continuously aerated with nitrogen for 300 h, the pH did not change, and the redox potential decreased from 521 to 340 mV. Leached Ni and V concentrations did not change much during the aeration period, and were about 460 and 70 mg kg−1, respectively. The leaching experiments under equilibrium were first conducted at a pH of 5.0 and various redox potentials (− 100, 0, 100, 250, 330, 400 mV). Leached Ni concentrations did not change significantly with redox potential, while leached V concentrations decreased. At pH 8.0 and different redox potentials (− 330, − 300, − 200, − 100, 0, 150, 250 mV), leached Ni concentrations were relatively low, and increased with decreasing redox potential. Leached concentrations of V increased gradually with decreasing redox potential, and increased abruptly when the redox potential was changed from − 300 to − 330 mV. It is proposed that the exchangeable fraction of Ni was leached out, while the enhanced leaching of V could be attributed to both changes of fractionation and the reduction reactions of oxyanions of V.
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The metals deposited on spent atmospheric resid desulfurization (ARDS) catalyst can be effectively removed by acid extraction. We discovered that a reforming catalyst can be prepared by impregnating a suitable catalyst support with this metal-laden extraction liquor. Since nickel and iron oxides have a detrimental effect on the performance of the reforming catalyst, aqueous solution of oxalic acid was used to selectively extract vanadium (excluding nickel and iron) from spent ARDS catalyst for the catalyst preparation. Catalyst prepared with the recovered vanadium and other minor elements showed significant dehydrocyclization activity to convert paraffins to aromatics. For example, in a nonoptimized fluidized-bed reactor, this catalyst can improve the research octane number of a paraffinic naphtha from 55 to 87 with approximately 81 wt% liquid yield. Hydrogen pretreatment to reduce vanadium on the catalyst can substantially decrease the catalyst activity and selectivity.
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In the catalytic processing of heavy oils, chemically combined nickel and vanadium present in the oil deposit on the catalyst and markedly influence catalytic behavior. Small quantities of these metals change the selectivity in catalytic cracking, while larger deposits in residual oil desulfurization or hydrocracking cover the catalyst and lower activity. By using a dilute aqueous solution of a complexing agent, such as oxalic acid, dioxane, or acetylacetone, nickel and vanadium oxides can be removed to obtain a substantial improvement in catalytic activity and/or selectivity. In this work, a number of complexing agents were tested, and their selectivity for removing contaminating metals, catalytic metals, and alumina was studied. A study of the state of vanadium as it exists on the catalyst surface is also reviewed.
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A spent vanadium catalyst was leached in a urea solution to recover vanadium, potassium and iron. The effect of time, temperature, pH, concentration of urea, phase ratio and catalyst particle size was studied. Results showed that for 180–250 μm catalyst leached for 1 h at 20 °C in the presence of 40% urea solution at a liquid:solid ratio of 10:1, the extent of leaching of V, K and Fe were about 78%, 90% and 29% respectively. A flowsheet for the proposed process is presented.
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Solid catalysts containing metals, metal oxides or sulfides, which play a key role in the refining of petroleum to clean fuels and many other valuable products, become solid wastes after use. In many refineries, the spent catalysts discarded from hydroprocessing units form a major part of these solid wastes. Disposal of spent hydroprocessing catalysts requires compliance with stringent environmental regulations because of their hazardous nature and toxic chemicals content. Various options such as minimizing spent catalyst waste generation by regeneration and reuse, metals recovery, utilization to produce useful materials and treatment for safe disposal, could be considered to deal with the spent catalyst environmental problem. In this paper, information available in the literature on spent hydroprocessing catalyst waste reduction at source by using improved more active and more stable catalysts, regeneration, rejuvenation and reuse of deactivated catalysts in many cycles, and reusing in other processes are reviewed in detail with focus on recent developments. Available methods for recycling of spent hydroprocessing catalysts by using them as raw materials for the preparation of active new catalysts and many other valuable products are also reviewed.
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Catalysts are widely used in petroleum refining and chemical industries. Among secondary resources, spent catalysts are undoubtedly very important because of not only their large amounts and enormous economic values, but also because of the environmental concerns if disposed off. Spent hydrodesulphurisation catalysts usually consist of molybdenum sulphide mixed with sulphides of vanadium, cobalt and nickel on an alumina carrier. A wide variety of metallurgical processes are used to treat these catalysts. The processes vary in their selectivity for metals and complexity of operation, but adopt one of the following approaches: 1. acid leaching with either H2SO4, HCl or (COOH)2, often after roasting; 2. caustic leaching with NaOH, sometimes after roasting; 3. salt roasting with Na2CO3, NaCl or NaOH followed by leaching with water or Na2CO3; 4. smelting either directly or after calcination; 5. anhydrous chlorination; 6. bioleaching.Roasting followed by sulphuric acid leaching seems to be the best option since all of the valuable metals dissolve. However the downstream processes to produce separate products with high purity are relatively complex. Sodium carbonate roasting followed by water leaching is a good option since molybdenum and vanadium are selectively extracted over aluminium, nickel and cobalt. Bioleaching offers good prospects for recovering valuable metals and at the same time, generates much less environmental pollution. However, much more research work is needed before it can be commercialised.After leaching, the metals in leach solutions have to be separated and purified by conventional separation techniques such as precipitation, adsorption, ion exchange and solvent extraction. Part II of this review considers the application of these methods, especially, solvent extraction for treating such leach solutions.
Article
Vanadium is an important by-product that is used almost exclusively in ferrous and non-ferrous alloys due to its physical properties such as high tensile strength, hardness, and fatique resistance. Vanadium consumption in the iron and steel industry represents about 85% of the vanadium-bearing products produced worldwide. The ubiquitous vanadium is employed in a wide range of alloys in combination with iron, titanium, nickel, aluminum, chromium, and other metals for a diverse range of commercial applications extending from train rails, tool steels, catalysts, to aerospace. The global supply of vanadium originates from primary sources such as ore feedstock, concentrates, metallurgical slags, and petroleum residues. Vanadium-bearing host minerals consist of carnotite, mottramite, patronite, roscoelite, and vanadinite. Deposits of titaniferous magnetite, uraniferous sandstone, bauxite, phosphate rock, crude oils, oil shale and tar sands host vanadium. Apart from titanomagnetite and ilmenite ore deposits containing vanadium, slags from the ferrous industry are a major source of supply. At present, known world reserves are expected to supply the next century’s needs. Vanadium-bearing materials are treated by means of several processes such as calcium reduction, roast/leach, solvent extraction and ion exchange to recover vanadium either as metal, ferrovanadium, vanadium pentoxide, or in the form of various chemicals. The recovery of aluminum and magnesium metal from smelters and refineries generates vanadium and associated compounds. Countries such as China, South Africa, and Russia are the largest world producers of ferrovanadium and its toxic oxides while about 40 other countries contribute smaller quantities in different forms for global consumption. Australia is poised to become a major player for this essential substance during the next decade. The supply and demand of vanadium products during the past 20 years has been relatively stable and subject to a gradual decline in delivered price. The paper describes established industrial processes for recovery of vanadium from sources such as raw ore and process reverts. The comprehensive condensation of pertinent facts is intended to provide a single reference source rather than the reader perusing many articles.
Article
Spent catalyst from manufacture of sulfuric acid production (main elemental composition: 3.5% V, 0.63% Ni, 7.9% Fe and 9.64% Si) can be used as a secondary source of vanadium and nickel. Extraction of these metals was studied using two different leaching systems (alkaline and acidic). Statistical design of the experiments and ANOVA (analysis of variance) were performed in order to determine the main effects and interactions of the factors under research, which were roasting, leaching temperature, concentration of the leaching reagent (H2SO4 and NaOH), liquid/solid (L/S) ratio (at 100 mL of liquid reagent), and presence of hydrogen peroxide.The results obtained after acidic treatment show that nickel extraction yield of 96% is achieved after roasting at 600 °C, followed by leaching with 5 mL/g 1 M sulfuric acid at 80 °C for a 30 min reaction time. The highest vanadium extraction yield was 59% after roasting at 400 °C and leaching at 80 °C by 0.3 M sulfuric acid for 6 h and 10 mL/g L/S ratio.A full factorial experiment was also performed by application of sodium hydroxide for vanadium extraction in the second leaching system. The highest vanadium extraction yield after alkaline treatment was 78%, obtained through roasting at 400 °C, leaching at 80 °C by 4 M NaOH for 2 h and 10 mL/g L/S ratio. Because nickel is not dissolved by sodium hydroxide, a sequential acidic leaching was conducted using the alkaline leaching residue, obtaining a nickel extraction yield of 88%.
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Power plant process simulation software is well-suited for the modelling of energy systems and more importantly, tools for analysing the energy efficiency are often built into the software. This work presents the development of a simulation model for a sulphuric acid plant using a commercial software package for power plant process simulation. This will be of value to for instance small consultant and engineering companies involved with audits and analysis of energy systems. For small sized companies the cost of acquiring and maintaining many different specialised software packages will be noticeable. However, companies involved with audits and analysis of energy systems will in most cases have access to at least one software package for power plant process calculations. The use of this kind of software for also modelling chemical plants would be valuable to these companies. The results of this work shows that it is possible to use an inexpensive but powerful power plant process simulation software for modelling a common chemical process as a part of a large energy system.
Article
Petroleum refineries must pay attention to spent hydroprocessing catalysts particularly since they are hazardous toxic wastes. This review focuses on the progress in metal reclamation and disposal methods used for dealing with the environmental problem of spent hydroprocessing catalysts. Studies have been conducted with the aim either to increase the efficiency of metals recovery using established methods or to develop novel methods. Leaching studies used inorganic agents such as solutions of strong acids and bases, ammonium containing compounds and water soluble organic acids. The roasting of spent catalysts with sodium and/or potassium salts significantly enhanced solubility of some metals in water from where they could be recovered, in a pure form, either by selective precipitation or extraction using various extracting agents. The interests in bioleaching and electrochemical dissolution of metals were also reviewed. Commercial processes, involve either leaching out metals or roasting to make metals soluble in water. Markets and price trends for the metals in spent hydroprocessing catalysts are also discussed.To ensure the environmental acceptance, spent catalysts may require some pretreatments if disposal in landfills, is chosen as the last option. The aim is to make metals non-leachable by immobilizing them using thermal treatments with encapsulating agents. Consequently, the leachability of the metals is minimized. A number of methods and various agents have been evaluated for these purposes.
Article
The present work deals with the application of biotechnology for the mobilization of metals from different solid wastes: end of life industrial catalysts, heavy metal contaminated marine sediments and fluorescent powders coming from a cathode ray tube glass recycling process. Performed experiments were aimed at assessing the performance of acidophilic chemoautotrophic Fe/S-oxidizing bacteria for such different solid matrices, also focusing on the effect of solid concentration and of different substrata. The achieved results have evidenced that metal solubilization seems to be strongly influenced by the metal speciation and partitioning in the solid matrix. No biological effect was observed for Ni, Zn, As, Cr mobilization from marine sediments (34%, 44%, 15%, 10% yields, respectively) due to metal partitioning. On the other hand, for spent refinery catalysts (Ni, V, Mo extractions of 83%, 90% and 40%, respectively) and fluorescent powders (Zn and Y extraction of 55% and 70%, respectively), the improvement in metal extraction observed in the presence of a microbial activity confirms the key role of Fe/S oxidizing bacteria and ferrous iron. A negative effect of solid concentration was in general observed on bioleaching performances, due to the toxicity of dissolved metals and/or to the solid organic component.
Article
The kinetics of molybdenum, nickel, vanadium and aluminium leaching from a spent hydrodesulphurization catalyst in a solution containing oxalic acid and hydrogen peroxide was investigated. The effects of temperature and particle size were examined. In addition, the reaction mechanism for the dissolution of the spent catalyst was discussed. The results of the kinetic analysis for various experimental conditions indicated that the reaction rate of leaching process is controlled by chemical reaction at the particle surface. The values of the activation energies of 31±2, 36±4, 30±4 and 57±3 kJ mol(-1) for Mo, Ni, V and Al, respectively, are characteristic for mechanism controlled by chemical reaction.
Article
This study deals with bioremediation treatments of dredged sediments contaminated by heavy metals based on the bioaugmentation of different bacterial strains. The efficiency of the following bacterial consortia was compared: (i) acidophilic chemoautotrophic, Fe/S-oxidising bacteria, (ii) acidophilic heterotrophic bacteria able to reduce Fe/Mn fraction, co-respiring oxygen and ferric iron and (iii) the chemoautotrophic and heterotrophic bacteria reported above, pooled together, as it was hypothesised that the two strains could cooperate through a mutual substrate supply. The effect of the bioremediation treatment based on the bioaugmentation of Fe/S-oxidising strains alone was similar to the one based only on Fe-reducing bacteria, and resulted in heavy-metal extraction yields typically ranging from 40% to 50%. The efficiency of the process based only upon autotrophic bacteria was limited by sulphur availability. However, when the treatment was based on the addition of Fe-reducing bacteria and the Fe/S oxidizing bacteria together, their growth rates and efficiency in mobilising heavy metals increased significantly, reaching extraction yields >90% for Cu, Cd, Hg and Zn. The additional advantage of the new bioaugmentation approach proposed here is that it is independent from the availability of sulphur. These results open new perspectives for the bioremediation technology for the removal of heavy metals from highly contaminated sediments.
Article
A spent refinery processing catalyst was physically and chemically characterized, and subjected to one-step and two-step bioleaching processes using Aspergillus niger. During bioleaching of the spent catalysts of various particle sizes ("as received", 100-150 microm, <37 microm, and x =2.97 (average) microm) and pulp densities, the biomass dry weight and pH were determined. The corresponding leach liquor was analysed for excreted organic acids along with heavy metal values extracted from the catalyst. Chemical characterization of the spent catalyst confirmed the presence of heavy metal including Al (33.3%), Ni (6.09%) and Mo (13.72%). In general, the presence of the spent catalyst caused a decrease in the biomass yield and an increase in oxalic acid secretion by A. niger. The increase in oxalic acid secretion with a decrease in the catalyst particle size (up to <37 microm) led to corresponding increase in the extraction of metal values. The highest extraction of metal values from the spent catalyst (at 1% w/v pulp density and particle size <37 microm) were found to be 54.5% Al, 58.2% Ni and 82.3% Mo in 60 days of bioleaching. Oxalic acid secretion by A. niger in the presence of the spent catalyst was stimulated using 2-[N-Morpholino]ethanesulfonic acid (MES) buffer (pH 6), which resulted in comparable metal extraction (58% Al, 62.8% Ni and 78.9% Mo) in half the time required by the fungus in the absence of the buffer. Spent medium of A. niger grown in the absence and in the presence of MES buffer were found to leach almost similar amounts of Al and Ni, except Mo for which the spent medium of buffered culture was significantly more effective than the non-buffered culture. Overall, this study shows the possible use of bioleaching for the extraction of metal resources from spent catalysts. It also demonstrated the advantages of buffer-stimulated excretion of organic acids by A. niger in bioleaching of the spent catalyst.
Article
In order to reduce the environmental impact due to land disposal of oil fly ash from power plants and to valorize this waste material, the removal of vanadium was investigated using leaching processes (acidic and alkaline treatments), followed by a second step of metal recovery from leachates involving either solvent extraction or selective precipitation. Despite a lower leaching efficiency (compared to sulfuric acid), sodium hydroxide was selected for vanadium leaching since it is more selective for vanadium (versus other transition metals). Precipitation was preferred to solvent extraction for the second step in the treatment since: (a) it is more selective; enabling complete recovery of vanadate from the leachate in the form of pure ammonium vanadate; and (b) stripping of the loaded organic phase (in the solvent extraction process) was not efficient. Precipitation was performed in a two-step procedure: (a) aluminum was first precipitated at pH 8; (b) then ammonium chloride was added at pH 5 to bring about vanadium precipitation.
Article
This study focuses on recovering valuable metals from spent hydrodesulfurization (HDS) catalysts using a combined acid-leaching and fluidized-bed electrolysis process. The electrolytic cell was equipped with a glass bead medium, an iridium oxide mesh anode, and a stainless steel plate cathode. An acid solution consisting of concentrated HNO3/H2SO4/HCl with a volume ratio of 2:1:1 was found to be better than the other tested solution (HNO3/H2SO4=1:1) to leach the metals. For the three-acid mixture, the best solid/liquid ratio and leaching time were 40 g/L and 1 h, respectively, at 70 degrees C; under this condition, the leaching yields of target metals (Mo, Ni, and V) in the 1st stage of leaching reached 90, 99, and 99%, respectively, much higher than those in the 2nd/3rd/4th stages. When this acid leachate was electrolyzed for 2 h at 2 A constant current (current density=approximately 35.7 mA/cm2), a stable cell voltage of 5 V was observed. The electrolytic recoveries of Mo, Ni, and V were approximately 15, 61, and 66%, respectively, but extending the electrolysis time from 2 to 4 h did not increase the recoveries. For this operation, the total recoveries (leaching yieldxelectrolytic recovery) of Mo, Ni, and V were approximately 14, 60, and 65%, respectively.
Private interview. 01
  • Company Eti Mine
Eti Mine Company, 2013. Private interview. 01/04/2013.
Hazardous Waste Management System
USEPA (United Stated Environmental Protection Agency), 2003. Hazardous Waste Management System, vol. 68, Federal Register.