Analysis of the formation conditions and characteristics of interphase and random vanadium precipitation in a low-carbon steel during isothermal heat treatment

The characteristics of nanosized precipitates in steels depend on the heat-treatment parameters. The effects of characteristics of vanadium precipitates formed during isothermal heat treatment on the hardness of the ferrite matrix in low-carbon vanadium-alloyed steel were investigated through analysis of transmission electron microscopy images and microhardness measurements. The results show that, during isothermal holding in the temperature range from 675 to 750℃, only interphase precipitation occurs, whereas only random precipitation occurs in the ferrite matrix during holding at 600℃. Furthermore, during isothermal heat treatment between 600 and 675℃, both random and interphase precipitates occurred in the ferrite. Nanoscale vanadium carbides with different atomic ratios of vanadium(V) and carbon(C) were the dominant precipitates in the random and interphase precipitates. The sizes of random precipitation carbides were smaller than those of interphase ones. Also, the sample isothermally heat treated at 650℃ for 900s exhibited a higher hardness with a narrower hardness distribution.

Ammonium Metavanadate Fabricated by Selective Precipitation of Impurity Chemicals on Inorganic Flocculants

High purity ammonium metavanadate(NH_(4)VO_(3))is the most vital chemical to produce V2O5,VO2,VN alloy,VFe alloy and VOSO4,which have some prospective applications for high strength steel,smart window,infrared detector and imaging,large scale energy storage system.NH_(4)VO_(3)is usually produced by spontaneous crystallization from the aqueous solution due to its sharp dependence of solubility on the temperature.However,hazardous chemicals in industrial effluent,include phosphorate,silicate and arsenate,causing severe damage to the environment.In this work,these impurities are selectively precipitated onto inorganic flocculants,while the vanadate dissolved in an aqueous solution keeps almost undisturbed.Therefore,high purity NH_(4)VO_(3)is produced by the crystallization from the purified solution.By screening various flocculants and precipitating parameters,polyaluminum sulfate with an optimal amount of 50 g/L,is demonstrated to selectively remove phosphorate,silicate and arsenate,corresponding to the removing efficiency of 93.39%,97.11%and 88.31%,respectively.NH_(4)VO_(3)from the purified solution holds a purity of 99.21%,in comparison with 98.33%in the product from the crude solution.This purifying technology cannot only produce NH_(4)VO_(3)with high added value,but also reduce the environmental pollution of waste liquid.

Stability of highly supersaturated vanadium electrolyte solution and characterization of precipitated phases for vanadium redox flow battery

The vanadium redox flow battery(VRFB)has been receiving great attention in recent years as one of the most viable energy storage technologies for large-scale applications.However,higher concentrations of vanadium species are required in the H_(2)O-H_(2)SO_(4) electrolyte in order to improve the VRFB energy density.This might lead to unwanted precipitation of vanadium compounds,whose nature has not been accurately characterized yet.For this purpose,this study reports the preparation ofⅤ^((Ⅱ)),ⅤV^((Ⅲ)),Ⅴ^((Ⅳ))andⅤ^((Ⅴ))supersaturated solutions in a 5 M H_(2)SO_(4)-H_(2)O electrolyte by an electrolytic method,from the only vanadium sulfate compound commercially available(VOSO_(4)).The precipitates obtained by ageing of the stirred solutions are representative of the solids that may form in a VRFB operated with such supersaturated solutions.The solid phases are identified using thermogravimetric analysis,X-ray diffraction and SEM.We report that dissolvedⅤ^((Ⅱ)),Ⅴ^((Ⅲ))andⅤ^((Ⅳ))species precipitate as crystals of VSO_(4),V_(2)(SO_(4))3 and VOSO_(4) hydrates and not in their anhydrous form;conversely V^((Ⅴ))precipitates as an amorphous V_(2) O_(5) oxide partially hydrated.The measured hydration degrees(respectively 1.5,9,3 and 0.26 mol of H_(2)O per mol of compound)might significantly affect the overall engineering of VRFB operating with high vanadium concentrations.

Cyclic metallurgical process for extracting V and Cr from vanadium slag: Part Ⅱ. Separation and recovery of Cr from vanadium precipitated solution

Cyclic metallurgical process for separation and recovery of Cr from vanadium precipitated solution by precipitation with PbCO_(3)and leaching with Na_(2)CO_(3)was investigated.The concentration of Cr residue in the solution decreases from 2.360 to 0.001 g/L by adding PbCO_(3)into vanadium precipitated solution according to Pb/Cr molar ratio of 2.5,adjusting the pH to 3.0 and stirring for 180 min at 30℃.Then,the precipitates were leached with hot Na_(2)CO_(3)solution to obtain leaching solution containing Na_(2)CrO_(4)and leaching residue containing PbCO_(3).The leaching efficiency of Cr reaches 96.43%by adding the precipitates into 0.5 mol/L Na_(2)CO_(3)solution with the mass ratio of liquid to solid(L/S)of 10:1 mL/g and stirring for 60 min under pH 9.5 at 70℃.After filtration,leaching residue is reused in Cr precipitation and leaching solution is used to circularly leach the Cr precipitates until Na_(2)CrO_(4)approaches the saturation.Finally,the product of Na_(2)CrO_(4)·4H_(2)O is obtained by evaporation and crystallization of leaching solution.

废SCR催化剂含钒砷碱浸液选择性分离工艺

碱浸法被广泛应用于从废脱硝催化剂中浸取回收钒、钨等有价资源。由于钒和砷的化学性质相似,在碱浸过程中,砷与钒一同溶解到浸出液,导致后续钒元素回收困难,并且处理过程产生有毒废水,危害环境安全。提出了同步钙沉—酸溶—铁盐除砷—钙盐沉钒工艺,在钙沉过程中,通过加入氢氧化钙将钒和砷转化为钒酸钙和砷酸钙固定下来,实现了钒砷高效沉淀与碱溶液回收。酸溶后,采用硫酸亚铁沉淀法实现了酸液中钒砷的有效分离,砷以砷酸铁的形式固定在沉淀渣中。最佳工艺条件为:H 2O 2预氧化30 min、溶液初始pH=3.0、反应温度30℃、反应时间3 h。砷的沉淀率为97.26%,钒的损失率为1.84%。向获得的含钒滤液中加入氢氧化钙得到钒酸钙。该工艺实现了废SCR脱硝催化剂碱性浸出液中钒、砷的高效分离,同时实现了高碱度溶液的回收。

钒钛磁铁矿提钒尾渣钙化碱浸试验研究

由于钒钛磁铁矿提钒尾渣中Na2 O含量高,作为炼铁配矿使用时会造成高炉结瘤问题,难以规模化利用。本文针对此问题,以承钢钒钛磁铁矿提钒尾渣为原料,进行了钙化碱浸-偏钒酸铵沉钒试验,目的是对提钒尾脱碱的同时提取其中有价金属钒。试验主要考察了浸出温度、碱浓度、氧化钙添加量和液固比对钠和钒浸出率的影响,结果表明,在浸出温度160℃、碱浓度100 g·L^(-1)、氧化钙添加量15%、液固比6:1、浸出时间60 min的条件下,钒和钠的浸出率分别达到82.25%和85.36%;对含钒碱浸液进行偏钒酸铵沉钒,得到了纯度大于97%的V_(2)O_(5)产品;终渣中Na_(2)O含量小于0.5%,Fe_(2)O_(3)含量达到30.10%,结合承钢高炉的碱金属平衡数据,可满足高炉炼铁配矿使用。本文研究结果可为相关企业钒钛磁铁矿提钒尾渣的规模化利用提供参考。

含钒页岩酸浸提钒废水处置的研究进展

含钒页岩酸浸提钒过程中会产生两类废水:酸性废水以及氨氮废水。基于提钒废水的性质特点,评述了其处置的研究进展。处理酸性废水时,中和沉淀法操作简单,但存在重金属离子时还需进行二阶段处理;膜分离法避免了中和沉淀法产生污泥多的情况,但膜易结垢使得寿命较短;酸性废水循环主要是将其返回至前端的浸出过程,利用废水中的H+等,可明显节约成本。处理氨氮废水时,吹脱法简单高效,但废水氨氮浓度较高时还需要进行二次脱氮;磷酸铵镁结晶法不仅操作简便,其产物还可作为肥料使用,但其消耗药剂较多,这增加了成本;离子交换法虽运行成本低、效率高,但尚有吸附容量小、金属负载型树脂离子易洗脱等关键问题待解决;催化氧化法效率高且产物清洁,但其使用成本高以及反应稳定性差。最后,展望了提钒废水处置的方向与趋势。

镧负载方式对Y分子筛抗钒性能的影响

分别采用不同方式在Y分子筛上负载相同量的稀土元素镧(La),制备得到了Y2、Y3、Y4分子筛样品,系统考察了La引入方式对Y分子筛理化性质和微反活性的影响。结果表明:在采用浸渍法负载La得到的Y2分子筛中,La以离子态存在,且在焙烧过程中La离子更易于迁移到分子筛内部结构中,并更多进入分子筛的α笼;在采用沉淀法负载La得到的Y3和Y4分子筛中,La以非离子态存在,且在焙烧过程中La物种较少向分子筛内部迁移,更多存在于分子筛表面上;与Y2分子筛相比,采用La与草酸先沉淀后负载到分子筛上的方式制备的Y3分子筛具有更好的水热稳定性和微反活性,说明赋存在分子筛表面上的La可以更好地改善分子筛的抗钒性能。

感应回火对含钒900 MPa级高强钢组织与性能的影响

对含钒Q960E高强钢进行热轧和900℃淬火,并对其分别在450、550和600℃下进行感应回火处理。通过扫描电子显微镜(SEM)与投射电子显微镜(TEM)研究了Q960E高强钢不同感应回火温度下的组织特征。结果表明:淬火后Q960E钢板组织由马氏体+贝氏体复相组织组成,并通过提高终轧和卷曲温度保证了感应回火前的板形质量。高温回火后组织为回火索氏体。通过V的添加,在感应回火过程中均匀弥散析出尺寸小于100 nm的析出相,保证了感应高温回火后的板材强度,并随回火温度的升高,部分回火马氏体消失,形成回火索氏体组织。在900℃/15 min淬火,(550~600℃)/15 min高频感应回火可以获得Q960E的最佳力学性能,通卷横向强度波动小于10 MPa,通卷纵向强度波动范围小于30 MPa,通卷横、纵向伸长率稳定在12%以上。

膜电解钒酸钠溶液制备五氧化二钒

钒渣提钒的传统方法钠化提钒工艺以铵盐为介质实现钒酸钠阴阳离子的解离,但是会产生大量的氨氮废水和硫酸钠固废,使得钒产品制备过程环境污染严重,工艺复杂,成本高。基于此,提出了膜电解技术处理含钒浸出液,使钠离子扩散到阴极,钒保留在阳极,随后通过水解沉钒,煅烧获得五氧化二钒产品,阴极液蒸发浓缩回收氢氧化钠的工艺技术。系统考察了电解电压、电解时间和沉钒温度等的影响规律,在电压5 V、电解时间135 min的条件下,可分离回收浸出液中85%的钠;电解后的浸出液在120℃加热90 min,沉钒率可达99%,获得的五氧化二钒产品满足行业标准要求。

碳氮化物析出行为对钒微合金化套管钢屈服强度的影响

钒微合金化套管钢调质处理后的屈服强度对回火温度有较高的敏感性。研究了碳氮化物析出行为对钒微合金化套管屈服强度的影响。分析了钒微合金化的作用与N含量的关系,研究了VN和VC的析出行为以及析出相的强化作用。分析认为:V含量与材料热处理后的强度波动存在近似定量关系,V含量每增加0.03%,在回火温度变化10℃时将产生3~4 MPa的附加屈服强度波动。因此,可据此对钒微合金化钢种进行成分优化设计和产品性能控制,以增加实际生产中套管强度指标的稳定性。

铌钒微合金化对高碳针布钢线材组织的影响

利用直读光谱仪、万能试验机、金相显微镜和扫描电镜等设备,分析研究了针布用钢线材82B和82NbV的差异,探明了铌钒微合金化对高碳针布钢82B性能的影响。结果表明:基于82B成分基础上添加0.1%V和0.02%Nb,采用斯泰尔摩冷却,吐丝温度控制在900℃,辊道速度0.9 m/s,风冷时保证相变温度在600℃以上,线材的抗拉强度能从1180 MPa提高到1260 MPa,珠光体实际晶粒度从8级提高到9.5级,珠光体组织片层间距从150 nm缩小到100 nm,同时析出大量的(Nb,V)(C,N)的析出物,尺寸约115 nm。由于Nb、V微合金的添加降低索氏体相变温度、细化晶粒同时细化索氏体片层间距,提高了钢丝拉拔加工硬化能力,通过Nb、V微合金的合理匹配,提高了针布钢丝的表面硬度和细化了钢丝组织的晶粒度,最终实现了成品针布的高耐磨性。

A review of electrolyte additives and impurities in vanadium redox flow batteries

As one of the most important components of the vanadium redox flow battery （VRFB）, the electrolyte can impose a significant impact on cell properties, performance and capital cost. In particular, the electrolyte composition will influence energy density, operating temperature range and the practical applications of the VRFB. Various approaches to increase the energy density and operating temperature range have been proposed. The presence of electrolyte impurities, or the addition of a small amount of other chemical species into the vanadium solution can alter the stability of the electrolyte and influence cell perfor- mance, operating temperature range, energy density, electrochemical kinetics and cost effectiveness. This review provides a detailed overview of research on electrolyte additives including stabilizing agents, im- mobilizing agents, kinetic enhancers, as well as electrolyte impurities and chemical reductants that can be used for different purposes in the VRFBs.

Effects of RE and Vanadium on Microalloyed Steel

The effects of RE were studied by TEM, SEM, ICP and thermal simulation methods in vanadium microalloyed steel. The content of RE in the solid solution can reach the order of 10 -5 ～10 -4 in steel. The solid solution of RE was found to reduce the stability of precipitated V(C,N), impede the precipitation of V(C,N) in austenite, and accelerate and refine the precipitation of V(C,N) in ferrite. The combined effect of RE and V is to delay the dynamic recrystallization, refine the grains and second phase particles, and to promote the precipitation of V(C,N) obviously. Thus the microalloying with RE and V leads to raising the strength and toughness of steel.

Thermodynamic analysis for separation of vanadium and chromium in V(Ⅳ)-Cr(Ⅲ)-H_2O system

To recycle vanadium and chromium from the V?Cr-bearing reducing slag,the thermodynamics of separating V(IV)and Cr(III)at 298 K was summarized in the form of potential-pH diagram and activity-pH diagram.The potential-pH diagrams of V-Mn-H2O and Cr-Mn-H2O systems show that the electrode potential of MnO2/Mn2+is higher than that of VO2+/VO2+but lower than that of Cr2O7 2-/Cr3+,which proves that it is feasible to selectively oxidize low valent vanadium using MnO2.The activity-pH diagrams of V(V)-H2O and Cr(III)-H2O systems show that the precipitation pH of V(V)is far lower than that of Cr(III),and therefore V(V)and Cr(III)can be separated through precipitation method.Based on the thermodynamic analysis,the flowsheet of recovery of vanadium and chromium from the V-Cr-bearing reducing slag is designed.

Recovery of vanadium from black shale

The recovery of vanadium from a black shale from Guizhou Province of China was performed using a three-step process, which consists of a leaching step in the H2SO4-HF-NaClO system under atmospheric pressure,the vanadium separation from leachate by solvent extraction and stripping,followed by precipitation of ammonium vanadate and thermal decomposition.Under the optimum leaching conditions of 100 g/L sulfuric,15 g/L hydrofluoric acid,1.5 g/L NaClO,6 h leaching at 90℃and oxygen partial pressure of 1 200 kPa,and the liquid-to-solid ratio of 2,about 91%vanadium extraction is achieved.The vanadium extraction yields of solvent and stripping are 99.83%and 97.66%when using 10%(volume fraction)P204,5%TBP and 85%sulfonated berosene as organic phase and 15%(mass fraction)sulphuric acid as stripping agent.After thermal decomposition the purity of powder vanadium pentoxide products is 99.18%and the overall vanadium recovery is over 81%in the whole process.

Cyclic metallurgical process for extracting Ⅴ and Cr from vanadium slag: Part Ⅰ. Separation and recovery of Ⅴ from chromium-containing vanadate solution

The separation and recovery of V from chromium-containing vanadate solution were investigated by a cyclic metallurgical process including selective precipitation of vanadium,vanadium leaching and preparation of vanadium pentoxide.By adding Ca(OH)_(2) and ball milling,not only the V in the solution can be selectively precipitated,but also the leaching kinetics of the precipitate is significantly improved.The precipitation efficiency of V is 99.59%by adding Ca(OH)_(2) according to Ca/V molar ratio of 1.75:1 into chromium-containing vanadate solution and ball milling for 60 min at room temperature,while the content of Cr in the precipitate is 0.04%.The leaching rate of V reaches 99.35%by adding NaHCO_(3) into water according to NaHCO_(3)/V molar ratio of 2.74:1 to leach V from the precipitate with L/S ratio of 4:1 mL/g and stirring for 60 min at room temperature.The crystals of NH_(4)VO_(3) are obtained by adjusting the leaching solution pH to be 8.0 with CO2 and then adding NH_(4)HCO_(3) according to NH_(4)HCO_(3)/NaVO_(3) molar ratio of 1:1 and stirring for 8 h at room temperature.After filtration,the crystallized solution containing ammonia is reused to leach the precipitate of calcium vanadates,and the leaching efficiency of V is>99%after stirring for 1 h at room temperature.Finally,the product of V_(2)O_(5) with purity of 99.6%is obtained by calcining the crystals at 560℃ for 2 h.

Morphology and orientation relationship of VC precipitates in HSLA steel

The morphology and distribution of VC precipitates in HSLA steel as well as the orientation relationship between VC precipitate and α-Fe were studied by transmission electron microscopy （TEM）. The chemical composition of the VC precipitate was analyzed qualitatively by using analytical electron microscopy （AEM） equipped with an energy dispersive spectrum （EDS） system. The VC precipitate is needle-like in shape with a size of about 10 nm in length and is homogeneously dispersed in the α-Fe matrix. The smaller lattice misfit along the 〈100〉 lattice direction of α-Fe matrix leads to VC precipitate forming with its long axes nearly parallel to the 〈100〉 lattice direction of α-Fe matrix. It is confirmed that the orientation relationship between VC precipitate and α- Fe is the ＂N-W＂ orientation relation by selected area electron diffraction （SAED） patterns.

Solution and aging behavior of precipitates in laser melting deposited V-5Cr-5Ti alloys

V-5Cr-5Ti alloys have been fabricated using a laser melting deposition(LMD)additive manufacturing process,showing precipitates aggregated near the grain/dendrite boundaries.Since the mechanical properties of vanadium alloys considerably depend on the precipitates,solution and aging treatments have been applied to eliminating the aggregations of the precipitates.The results show that as the solution temperature increases from 800 to 1560℃,the densities and the lengths of the precipitates are reduced,while the widths of the precipitates are increased.When the solution temperature reaches 1560℃,most impurity elements diffuse into the matrix and form into a nearly uniform supersaturated solid solution.Aging treatments have been applied to the 1560℃solution treated samples.It shows that as the aging temperature increases from 800 to 1200℃,the precipitate length increases,and the shapes of precipitates change from near-spherical to lath-like.Compared to 800 and 1200℃,aging at 1000℃results in the highest precipitate density.Compared to the LMD and solution-treated samples,the aged samples have the highest micro-hardness,due to the precipitation strengthening.

Thermodynamic simulation of stepwise precipitation of NH_(4)VO_(3)and NaHCO_(3)from carbonating Na_(3)VO_(4)solution

Thermodynamic simulation was conducted to design a new process of stepwise precipitating NH_(4)VO_(3)and NaHCO_(3)from regulating the CO_(2)carbonation of Na_(3)VO_(4)solution.Firstly,a new V(V)speciation model for the aqueous solution containing vanadate and carbonate is established by using the Bromley-Zemaitis activity coefficient model.Subsequently,thermodynamic equilibrium calculations are conducted to clarify the behavior of vanadium,carbon,sodium,and impurity species in atmospheric or high-pressure carbonation.To ensure the purity and recovery of vanadium products,Na_(3)VO_(4)solution is initially carbonated to the pH of 9.3-9.4,followed by precipitating NH_(4)VO_(3)by adding(NH_(4))_(2)CO_(3).After vanadium precipitation,the solution is deeply carbonated to the final pH of 7.3-7.5 to precipitate NaHCO_(3),and the remaining solution is recycled to dissolve Na_(3)VO_(4)crystals.Finally,verification experiments demonstrate that 99.1%of vanadium and 91.4%of sodium in the solution are recovered in the form of NH_(4)VO_(3)and NaHCO_(3),respectively.