Reaction Process of Chromium Slag Reduced by Industrial Waste in Solid Phase

M, a particular industrial waste, was selected to detoxify chromium slag at a high temperature. The carbon remaining in M reduced Cr （ Ⅳ ） of Na2 CrO4 borne in the chromium slag to Cr （ Ⅲ ） in the solid phase reaction, and its thermodynamics and kinetics were studied. The reduction process of Na2CrO4 by carbon produced CO, whiCh＇was endothermic. Under the experimental condition, the apparent activation energy was 4. 41 kJ·mol^-1 , the＇apparent order of reaction for Na2 CrO4 was equal to one, and the partial pressure of CO was only 0.22 Pa at 1 330℃.

Thermal stabilization of chromium slag by sewage sludge: Effects of sludge quantity and temperature

To investigate the feasibility of detoxifying chromium slag by sewage sludge, synthetic chromium slag containing 3% of Cr（Ⅵ） was mixed with sewage sludge followed by thermal treatment in nitrogen gas for stabilizing chromium. The effects of slag to sludge ratio （0.5, 1 and 2） and temperature （200, 300, 500, 700 and 900℃） on treatment efficiency were investigated. During the mixing process before thermal treatment, 59.8%-99.7% of Cr（Ⅵ） was reduced, but Cr could be easily leached from the reduction product. Increasing heating temperature and decreasing slag to sludge ratio strengthened the reduction and stabilization of Cr（Ⅵ）. When the slag to sludge ratio was 0.5 and thermal treatment temperature was 300℃, the total leached Cr and Cr（Ⅵ） declined to 0.55 mg/L and 0.17 mg/L respectively, and 45.5% of Cr in the thermally treated residue existed as residual fraction. A two-stage mechanism was proposed for the reduction and stabilization of Cr.

Preparation of Chromium-iron Metal Powder from Chromium Slag by Reduction Roasting and Magnetic Separation

Chromium slag（CS）has become one of the most hazardous solid waste containing chromium and iron.Based on its characteristics,the technology of reduction roasting and magnetic separation was employed to treat CS.The major impurity element of CS is magnesium and it exists in magnesium ferrite phase,which is hard to recover iron in the absence of additives.During reduction roasting,additives（Al2O3and CaF2）could destroy the structure of magnesium ferrite and improve the iron grade and recovery.The final product,i.e.chromium-iron powder,contains 72.54% Fe and 13.56% Cr,with the iron recovery of 80.34% and chromium recovery of 80.70%.

Roasting and leaching behaviors of vanadium and chromium in calcification roasting–acid leaching of high-chromium vanadium slag

Calcification roasting–acid leaching of high-chromium vanadium slag(HCVS)was conducted to elucidate the roasting and leaching behaviors of vanadium and chromium.The effects of the purity of Ca O,molar ratio between Ca O and V_2O_5(n(Ca O)/n(V_2O_5)),roasting temperature,holding time,and the heating rate used in the oxidation–calcification processes were investigated.The roasting process and mechanism were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM),and thermogravimetry–differential scanning calorimetry(TG–DSC).The results show that most of vanadium reacted with Ca O to generate calcium vanadates and transferred into the leaching liquid,whereas almost all of the chromium remained in the leaching residue in the form of(Fe_(0.6)Cr_(0.4))_2O_3.Variation trends of the vanadium and chromium leaching ratios were always opposite because of the competitive reactions of oxidation and calcification between vanadium and chromium with Ca O.Moreover,Ca O was more likely to combine with vanadium,as further confirmed by thermodynamic analysis.When the HCVS with Ca O added in an n(Ca O)/n(V_2O_5)ratio of 0.5 was roasted in an air atmosphere at a heating rate of 10°C/min from room temperature to 950°C and maintained at this temperature for 60 min,the leaching ratios of vanadium and chromium reached91.14%and 0.49%,respectively;thus,efficient extraction of vanadium from HCVS was achieved and the leaching residue could be used as a new raw material for the extraction of chromium.Furthermore,the oxidation and calcification reactions of the spinel phases occurred at 592and 630°C for n(Ca O)/n(V_2O_5)ratios of 0.5 and 5,respectively.

Technological progress on detoxification and comprehensive utilization of chromium containing slag

Chromium salt is an important industrial material, but vast waste slag containing chrome(Ⅵ) is brought out in the process of its production. The slag is seriously harmful to environments and human health. The technologies on detoxification and comprehensive utilization of chromium containing slag were summarized abroad and at home. And various methods were also described for the detoxification mechanism, technology process, and practical application effects in detail. A new concept for detoxification of chromium containing slag, furthermore, was put forward by using microorganism.

Spatial distribution of chromium in soils contaminated by chromium-containing slag

To evaluate the metal chromium (Cr) contamination of soil at a chromium-containing slag site by ferrochromium production, the contaminated sites, under slag heap, in the vicinity of slag heap and arable soils near the outlet of sewer channel, and unpolluted site 5 km away from one ferroalloy plant in Hunan Province, China, were selected. The concentrations of total Cr and water soluble Cr in bulk soil samples and profile depth samples were determined. The results show that the soils in the vicinity of slag heap have the highest total Cr content followed by the soils under the slag heap and near the outlet of sewer channel of the factory. The mean concentrations of total Cr in the top soils at above three contaminated locations exceed the critical level of Secondary Environmental Quality Standard for Soil in China by 3.5, 5.4 and 1.8 times. In most Cr polluted soils, total Cr has a relative accumulation in soil depth of 40-60 cm, but this trend is not found in unpolluted soils. The average concentrations of water soluble Cr (Ⅵ) in top soils under slag heap and in the vicinity of slag heap are 176.9 times and 52.7 times higher than that in the uncontaminated soils, respectively. However, water soluble Cr (Ⅵ) contents in soils near sewer channel are all low and the values are close to that in the uncontaminated soils. Although water soluble Cr (Ⅵ) content in soil profiles decreases with soil depths, it in soils under slag heap maintains a high level even at a depth of 100-150 cm. The results imply that the transportation of Cr (Ⅵ) can result in a potential risk of groundwater system in this area.

Selective leaching of chromium-containing slag by HCl

A batch of column experiments was carried out to investigate the change of Cr(Ⅵ) concentration leached out from chromium-containing slag with HCl as leaching agent, and to study influences of pH, ratio of solid mass to solution volume, flow velocity and temperature on Cr(Ⅵ) leaching. The optimal parameters were obtained for Cr(Ⅵ) leaching and a fitting model was established to describe the procedure of Cr(Ⅵ) leaching. The results show that Cr(Ⅵ) concentration in leachate increases with decreasing pH and increasing flow velocity and temperature. Moreover, Cr(Ⅵ) leaching percentage increases with increasing ratio of solid mass to solution volume. The optimal parameters for Cr(Ⅵ) selective leaching are as follows: pH=3.0, 1-5 of ratio of solid mass to solution volume, 180 mL/min of flow velocity and 40 ℃ of temperature. The procedure of Cr(Ⅵ) leaching fits well with the model: v=1.87t-0.54, indicating that the leaching rate of Cr(Ⅵ) declines in an exponential order of -0.54.

Thermodynamic Study on BaO－BaF_2－Fe_xO Slags Used for Dephosphorization of Chromium－Containing Hot Metal

Electrochemical measurements of the solid-oxide galvanic cell, Mo|Mo+MoO2|ZrO2 (MgO)| Fe+ (FexO)+Ag| Fe, have been made at temperatures of 1473K and 1573K in order to obtain the activities of FexO in BaO-BaF2-FexO slags used for dephosphorization of chromium-containing hot metal. The FexO activities show a significant dependence upon the molar ratio of BaO/BaF2. Within the homogeneous liquid region, the substitution of BaF2 for BaO has an effect of raising the FexO activity. From these activity data, the phase diagrams of the system BaO -BaF2-FexO are drawn at 1473K and 1573K. The temperature dependence of the activity coefficient of FexO at a fixed BaO/ BaF2 molar ratio can be expressed by formula RTlnγ(FexO)=constant.

钒钛磁铁矿冶炼渣场周边土壤-鱼塘-河流系统中钒铬分布特征及生态风险评价

为探究冶炼废渣中钒(V)和铬(Cr)对周边环境的影响,采集渣场周边土壤、沉积物、鱼塘底泥、鱼塘水和河水样品,分析V和Cr的浓度、赋存形态,并采用富集因子法、地质累积指数法和潜在生态风险指数法对V和Cr的污染状况和生态风险进行评价。结果表明,研究区土壤中V和Cr平均含量分别约为四川省背景值的2.6和4.0倍,富集程度分别为轻微和中度富集;沉积物中V、Cr平均含量分别约为对照沉积物的5.0和3.2倍,底泥中V、Cr平均含量分别约为对照沉积物的5.5和1.4倍,V和Cr富集程度均为中度和轻微富集;水样表现为V污染,鱼塘水和河水V平均浓度分别约为金沙江水样的17.6和1.8倍。研究区V和Cr主要以残渣态形式存在于土壤中,其占比分别为57.1%和89.4%,沉积物和底泥中V和Cr残渣态占比分别为20.1%和74.9%,各环境介质中V的生物可利用率及迁移率要远高于Cr;结合V和Cr地球化学性质分析,研究区环境介质中V和Cr可能主要以V 5+和Cr 3+形式存在。污染评价结果表明,土壤中V、Cr污染程度分别为轻微和中度污染,沉积物与底泥中V、Cr污染程度分别为中度和轻微污染,V和Cr均对生态系统构成轻微风险。因此,为保护研究区域生态系统和公共健康,应尽快修复受污染土壤和沉积物。

钒铬渣钙化焙烧—酸浸过程多组元浸出行为

以钒铬渣钙化焙烧熟料为原料,探究了浸出pH值、浸出温度、浸出时间和浸出液固比对钒铬渣中钒以及铬、锰、硅、钛、铁组元浸出率(质量分数,下同)的影响.结果表明:在酸浸过程中浸出pH值为2.8、浸出温度为60℃、浸出时间为60 min、浸出液固比为5的条件下,钒浸出率达到87.81%,此时铬、锰、硅、钛、铁浸出率分别为0.44%,23.91%,2.28%,0.23%,0.03%;此外,延长浸出时间、提高浸出温度、适当增大浸出液固比均有利于钒的分离提取.

铬渣无害化及资源化处理的试验研究

为实现铬渣的环境友好处理,对铬渣进行了无害化及资源化处理试验研究。试验结果表明,在活性炭投加量为1%、铬还原剂投加量与六价铬的比值为2.0、钠水玻璃投加量为10%的条件下,对铬渣进行无害化处理,可以将铬渣浸出液中的六价铬浓度降低至5 mg/L以下,达到环保排放标准;铁铝基复合材料中的铁、铝、镁、钙、硫、抗压强度、10~50 mm粒度范围比例、六价铬浓度及总铬浓度等指标均符合相关要求。

复合固废制备微晶玻璃性能研究

由于微晶玻璃具有多种优良的性能,使其在很多领域得到了广泛的发展应用,同时还有很多潜在的应用价值有待于开发。利用工业矿渣和冶金废渣制备微晶玻璃为固体废弃物的综合利用提供了一条新的途径。煤矸石在各种工业废渣中排放量最大,铁尾矿、高碳铬铁渣在我国工业固体废弃物中也占有很大比重。以廉价的工业固废为主要原料生产高附加值的微晶玻璃可以减少污染、保护生态环境,具有很好的经济和社会效益。文章以煤矸石、铁尾矿、高碳铬铁渣为主要原料,采用烧结法制备堇青石微晶玻璃。利用差热分析仪确定基础玻璃的热处理制度,使用X射线衍射仪及扫描电镜对烧结制品进行物相分析和微观形貌观察,并测定烧结制品的硬度、耐酸碱性、密度和吸水性。研究结果表明,所制备的微晶玻璃主晶相为堇青石,其各项性能表现良好。该研究为工业固废处理提供了有益参考。

高纯五氧化二钒制备过程钒铬分离的研究进展

全钒液流电池因资源禀赋好、自给率高,有望成为我国大规模储能市场的主力军。全钒液流电池以高纯五氧化二钒为原料,对铬等杂质含量要求严格。目前,我国五氧化二钒主要从含钒钢渣中提取,但钒铬难以深度分离,导致产品中铬含量较高。因此,从含钒钢渣中提取并制备电池级五氧化二钒,以及钒铬深度分离问题亟待解决。本文综述了高纯五氧化二钒制备过程钒铬分离的研究进展,对化学沉淀法、溶剂萃取法、离子交换法、吸附法及结晶法分离钒铬进行比较,并通过绘制298 K下V-Cr-H_(2)O系电位(E)-pH图,获得钒铬选择性分离的热力学窗口。与其他方法相比,化学沉淀法具有成本低、操作简单等优势,可根据钒铬氧化还原的电位差异,通过选择性氧化或还原沉淀,实现钒铬的深度分离。

Cr3和Cr5系支承辊大型锻件脱氧工艺研究

由于Cr3和Cr5系支承辊钢液中铬含量增加会抑制铝脱氧反应的进行。本文以Cr3和Cr5系支承辊冶金过程中脱氧工艺为研究背景,通过实验室脱氧实验,利用FactSage 8.1软件计算Cr3和Cr5系轧辊钢中氧含量,绘制铝脱氧平衡曲线,将Wagner模型与炉渣共存理论相结合,建立了钢渣反应模型,探讨铬含量对钢液中铝脱氧效果的影响。结果表明,钢液中铬含量在一定范围内增加会抑制铝脱氧反应进行;在精炼过程中,当Cr3系支承辊中铝含量控制在0.03%左右、Cr5系支承辊中铝含量控制在0.05%左右时,可将氧含量有效控制在10^(-5)以下;而与之相匹配的最佳炉渣成分的碱度为2.5~3.0,w(Al_(2)O_(3))>20%。

Effect of FeO on the formation of spinel phases and chromium distribution in the CaO-SiO_2-MgO-Al_2O_3-Cr_2O_3 system

Synthetic slag samples of the CaO-SiO2-MgO-A1203-Cr203 system were obtained to clarify the effect of FeO on the formation of spinel phases and Cr distribution. X-ray diffraction （XRD） and scanning electron microscopy （SEM） equipped with energy-dispersive spectroscopy （EDS）, as well as the thermodynamic software FactSage 6.2, were used for sample characterization. The results show that the addition of FeO can decrease the viscosity of molten slag and the precipitation temperatures of melilite and merwinite. The solidus temperature significantly decreases from 1400 to 1250℃ with the increase of FeO content from 0wt% to 6wt%. The addition of FeO could enhance the content of Cr in spinel phases and reduce the content of Cr in soluble minerals, such as merwinite, melilite, and dicalcium silicate. Hence, the addition of FeO is conducive to decreasing Cr leaching.

不锈钢渣高温改性-析晶调控解毒研究现状及发展趋势

截止到目前,钢铁工业普通固废(高炉铁渣)循环利用技术取得了重要进展,但仍存在固废顽疾亟需处理.不锈钢冶炼产生的含铬(Cr)渣长期以来缺乏有效的无害化处置方法,环境隐患巨大.国内外专家学者通过添加还原物质、高温调质及调节冷却方式等以改变渣中铬元素的赋存状态,控制Cr6+的溶出,进而实现不锈钢渣的解毒.其中,高温改性-析晶调控方法可以通过调整钢渣组分和控制温度制度促进含铬尖晶石相的形成和长大,提高铬元素在尖晶石相中的富集程度,有望成为最有效且安全的无害化处理技术,在近些年得到快速发展.本文从不锈钢渣高温改性-析晶调控解毒的热力学机理和结晶动力学原理出发,针对不锈钢渣的高温调质改性、解毒方面的研究进展进行了综述.基于高温调质-选择性析晶的核心问题,重点阐述了改善解毒效果的方法和措施.另外,针对不锈钢渣高温改性-析晶调控解毒存在的问题提出了今后的发展方向.

FeO含量对不锈钢渣微晶玻璃铬的迁移分布规律及固铬效果的影响

利用不锈钢渣制备微晶玻璃,系统研究了FeO含量对Cr在微晶玻璃中的赋存分布状态、迁移行为及固铬效果的影响。研究表明,在形核阶段,随着FeO含量增加,铬尖晶石类晶核数量增大,玻璃相中Cr逐渐向铬尖晶石中迁移。在晶化阶段,铬尖晶石纳米晶体生成透辉石晶相。TEM与XPS分析表明,一部分Cr赋存于透辉石晶格中,另一部分Cr仍赋存于被透辉石包裹的铬尖晶石中。玻璃相中的Cr也随着透辉石晶体的生成而不断扩散迁移进透辉石晶格中。FeO含量为4.80%(指质量分数,下同)时,95.23%Cr赋存于透辉石晶相中,Cr^(3+)浸出浓度仅为0.007 mg/L,微晶玻璃抗压强度为235 MPa,维氏硬度为949.3。本研究结果为强化固铬效果,实现不锈钢渣无害化、高值化利用提供理论与技术支持。

铬渣资源化利用研究进展

为解决目前铬渣无害化处理不彻底且未对其中的铬进行资源化利用的问题,综述了国内外铬渣处理现状,介绍了铬渣来源和成分,重点梳理和分析了有钙焙烧渣在钢铁行业的应用、无钙焙烧渣中金属回收以及液相氧化渣的资源利用。通过总结和比较,提出了采用烧结炼铁工艺处理有钙焙烧渣、采用碱浸法回收无钙焙烧渣中金属以及液相氧化渣直接用作炼铁原料的建议,指出了铬盐行业在未来发展的同时,应该加强源头创新,实现工业共生,最终达到清洁生产的目的。

Growth and aggregation control of spinel by shear-force-based melting modification of stainless steel slag

To improve the efficiency of melting modification for stainless steel(SS) slag, a shear force was introduced in this work and its effects on the spinel and silicate melt were experimentally investigated. The results indicated that the use of shear force changed the nucleation and growth behaviors of spinel and that the effects of shear force varied with its intensity. The aggregation behavior of spinel under different shear-force conditions was studied, revealing that large spinel clusters could be formed when the stirring speed was controlled. However, no notable change in the melt structure of the silicate was detected in this study. The optimal stirring speed for the melting modification treatment was 50 r·min^(-1), which substantially promoted spinel growth and aggregation, resulting in modified SS slag with excellent chromium sequestration capability.

不锈钢尾渣制备低碱高强度硅酸盐水泥熟料的技术研究

基于不锈钢尾渣的物性研究及新型干法水泥工艺现状调研,采用FactSage热力学软件理论分析计算和实验室研究表明,由不锈钢尾渣制成的水泥熟料对环境友善可靠。不锈钢尾渣掺配比例最大21%,最佳烧成温度1350℃,烧成时间1.5~2.0 h。烧成温度比传统原料低100℃。研制的低碱高强熟料,理化性能指标及重金属溶出含量均满足相关产品规范和质量标准。经测算,煤耗可降低10%~15%,生料粉磨电耗降低3~5 kWh/t,窑台时产量提高10%~15%,熟料成本降低4.5~5.5元/t。节能、减排、增效效果显著,高度契合当前我国“碳达峰、碳中和”政策导向。