氯化物熔盐中铬的价态对镍基合金腐蚀性的影响

氯化物熔盐的腐蚀性是制约其应用的重要因素,对富铬金属材料的腐蚀会导致金属中铬元素优先流失到熔盐中。探讨进入熔盐中不同价态的铬对后续腐蚀的影响,是了解熔盐长期运行中金属持续受腐蚀的关键。通过浸没腐蚀实验研究在三元NaCl-MgCl₂-CaCl₂熔盐中引入Cr⁰、Cr²⁺与Cr³⁺后,对一种贫铬Hastelloy B-2(HB-2)和两种富铬Hastelloy C-276(HC-276)、Hastelloy X(HX)镍基合金腐蚀性的影响。通过比较腐蚀前后质量变化、X射线衍射(XRD)、扫描电子显微镜(SEM)以及能谱分析(EDS)的结果,探讨含不同价态铬的熔盐对贫铬与富铬金属的腐蚀性差异。实验结果表明,Cr⁰和Cr²⁺能消耗熔盐中H₂O、O₂等氧化性物种,从而有效抑制腐蚀;Cr³⁺会抑制贫铬HB-2的腐蚀,但能促进富铬HC-276和HX的腐蚀;SEM和XRD分析结果表明,Cr³⁺在增强富铬金属铬优先流失的同时也会增强铁流失。热力学理论计算结果表明,CrCl₃氧化Cr、Fe的反应进行得很彻底;而CrCl₃氧化Ni、Mo的反应进行程度有限。因此,熔盐中含CrCl₃会氧化合金中Cr和Fe从而促进富铬合金腐蚀,而含Cr⁰和CrCl₂能降低熔盐中的氧化性物质含量而抑制腐蚀。     

不同异位修复工艺对高浓度铬渣污染土壤中Cr的去除特性

以我国某铬盐厂的两种不同污染特性铬渣污染土壤（A土和B土）为研究对象,探讨了三种异位修复工艺（淋洗、稳定化、湿法解毒）去除铬渣污染土壤中总Cr和Cr（Ⅵ）的效果,并采用改进BCR顺序提取法分析了不同修复工艺对土壤中各形态Cr的去除效果。实验结果表明,三种异位修复工艺对铬污染土壤中Cr（Ⅵ）的去除效果为湿法解毒 > 稳定化 > 淋洗,湿法解毒工艺对A土、B土中Cr（Ⅵ）的去除率分别高达83.26%、92.94%;对铬污染土壤总铬去除效果最佳的是异位淋洗工艺,异位淋洗工艺对A土、B土总铬消减分别达54.87%、80.16%。异位淋洗工艺实现了对水溶态Cr（Ⅵ）、酸溶态Cr（Ⅵ）的泥水分离,是总铬消减的主要原因;稳定化工艺和湿法解毒工艺降低了土壤pH,促进了水溶态Cr、酸溶态Cr及可还原态Cr向可氧化态Cr的转化,因此土中总Cr并未发生显著消减。高浓度铬渣污染土壤经三种异位修复工艺处理后,A土Cr（Ⅵ）仍然残留736.6 mg·kg^-1,B土Cr（Ⅵ）仍然残留245.47 mg·kg^-1,酸溶态Cr的残留是导致三种工艺修复Cr（Ⅵ）效果受限的主要原因。     

氯化物熔盐中铬的价态对镍基合金腐蚀性的影响

氯化物熔盐的腐蚀性是制约其应用的重要因素,对富铬金属材料的腐蚀会导致金属中铬元素优先流失到熔盐中。探讨进入熔盐中不同价态的铬对后续腐蚀的影响,是了解熔盐长期运行中金属持续受腐蚀的关键。通过浸没腐蚀实验研究在三元NaCl-MgCl₂-CaCl₂熔盐中引入Cr⁰、Cr²⁺与Cr³⁺后,对一种贫铬Hastelloy B-2(HB-2)和两种富铬Hastelloy C-276(HC-276)、Hastelloy X(HX)镍基合金腐蚀性的影响。通过比较腐蚀前后质量变化、X射线衍射(XRD)、扫描电子显微镜(SEM)以及能谱分析(EDS)的结果,探讨含不同价态铬的熔盐对贫铬与富铬金属的腐蚀性差异。实验结果表明,Cr⁰和Cr²⁺能消耗熔盐中H₂O、O₂等氧化性物种,从而有效抑制腐蚀;Cr³⁺会抑制贫铬HB-2的腐蚀,但能促进富铬HC-276和HX的腐蚀;SEM和XRD分析结果表明,Cr³⁺在增强富铬金属铬优先流失的同时也会增强铁流失。热力学理论计算结果表明,CrCl₃氧化Cr、Fe的反应进行得很彻底;而CrCl₃氧化Ni、Mo的反应进行程度有限。因此,熔盐中含CrCl₃会氧化合金中Cr和Fe从而促进富铬合金腐蚀,而含Cr⁰和CrCl₂能降低熔盐中的氧化性物质含量而抑制腐蚀。     

实验室COD废水处理研究

实验室COD废水含有大量的Cr⁶⁺、Ag⁺和Hg²⁺等重金属离子,若不经处理直接排放,会对生态环境造成不利影响。采用氧化还原法和中和沉淀法处理实验室COD废水中重金属离子,通过单因素实验和正交实验优化了处理条件。结果表明,当葡萄糖加量为10 g时,废水中Cr⁶⁺完全转化为Cr³⁺;当氯化钠加量为2.1 g时,废水中Ag⁺去除率为100%;在氢氧化钠加量为5.0 g、反应时间为20 min、反应温度为20℃的最佳条件下,总Cr和Hg²⁺综合去除效率最佳,去除率分别为75.13%、86.51%。     

分步投加FeSO_4·7H_2O、H_2O_2法预处理皮革鞣制废液试验研究

对皮革鞣制废液采用分步投加FeSO_4·7H_2O、H_2O_2法进行预处理,考察了FeSO_4·7H_2O、H_2O_2的投加方式与投加量、反应温度、pH值、反应周期等的影响。结果表明,最佳工艺参数为:温度50℃,pH值5,FeSO_4·7H_2O投加量5 mmol/L,H_2O_2用量50 mmol/L,反应周期3 h。在此工艺条件下,可使废液色度从40 000倍降为10倍,COD、总铬和Cr⁽⁶⁺⁾浓度分别从2 700,19.27,18.78 mg/L降为426.7,0.162,0.15 mg/L,达到了《制革及毛皮加工工业水污染物排放标准》(GB 30486—2013)要求。方法主要是利用先投加FeSO_4·7H_2O还原Cr(6+)浓度分别从2 700,19.27,18.78 mg/L降为426.7,0.162,0.15 mg/L,达到了《制革及毛皮加工工业水污染物排放标准》(GB 30486—2013)要求。方法主要是利用先投加FeSO_4·7H_2O还原Cr⁽⁶⁺⁾,搅拌反应一段时间后,再投加H_2O_2形成Fenton试剂。其去除机制有别于传统Fenton试剂,主要是针对皮革鞣制废液中的Cr(6+),搅拌反应一段时间后,再投加H_2O_2形成Fenton试剂。其去除机制有别于传统Fenton试剂,主要是针对皮革鞣制废液中的Cr⁽⁶⁺⁾浓度高这一水质特色,先用Fe(6+)浓度高这一水质特色,先用Fe⁽²⁺⁾还原Cr(2+)还原Cr⁽⁶⁺⁾,并利用Cr_2O_72-的强氧化性,在酸性条件H+与H_2O_2的共同作用下,形成Fe(6+),并利用Cr_2O_72-的强氧化性,在酸性条件H+与H_2O_2的共同作用下,形成Fe⁽²⁺⁾、Fe(2+)、Fe⁽³⁺⁾、Cr(3+)、Cr⁽³⁺⁾、Cr(3+)、Cr⁽⁶⁺⁾、H_2O_2、·OH、OH-等离子的共氧化和共沉淀体系,实现色度、Cr(6+)、H_2O_2、·OH、OH-等离子的共氧化和共沉淀体系,实现色度、Cr⁽⁶⁺⁾、COD和总铬的同步去除。     

粘质沙雷氏菌对重金属的耐受性和去除作用

微生物修复是治理重金属污染的重要手段之一。本文考察了粘质沙雷氏菌对重金属Cu²⁺、Zn²⁺和Cr⁶⁺耐受性和去除作用。结果表明,粘质沙雷氏菌对重金属Cu²⁺、Zn²⁺、Cr⁶⁺具有良好的耐受性,耐受程度表现为：Zn²⁺> Cu²⁺>Cr⁶⁺。不产灵菌红素时,最大耐受浓度分别为100～150 mg/L、200～250 mg/L、50～100 mg/L;产灵菌红素时能增加菌体对重金属的耐受性,最大耐受浓度分别为150～200 mg/L、>250 mg/L、150～200 mg/L。菌体对重金属的去除效果表现为Zn²⁺>Cr⁶⁺> Cu²⁺,48 h内最大去除率分别为分别为63.3%、44.5%、32.3%。     

三价铬电沉积机理研究及镀层表征

在硫酸盐三价铬电沉积体系中,通过赫尔槽实验对不同络合剂含量进行了筛选,得到络合剂最佳含量配比为甲酸铵80 g/L、草酸铵20 g/L以及尿素30 g/L,最佳电流密度范围为5.11 A/dm²～20.68 A/dm²;通过循环伏安曲线和阴极极化曲线分析三价铬电沉积机理,发现三价铬的沉积过程分两步进行：第一步为Cr³⁺+e→Cr²⁺,过程不可逆;第二步为Cr²⁺+2e→Cr,可逆;草酸铵会增大阴极极化,甲酸铵和尿素会降低阴极极化;电沉积20 min得到的铬镀层,XPS分析表面镀层由单质Cr、Cr₂O₃及Cr(OH)₃构成;微观结构观测发现,随着电沉积时间增加,镀层由表面平整形貌逐渐转变为瘤状结构形貌;镀层呈现明显的(110)择优取向;电化学研究表明,相比20 min铬镀层,5 min铬镀层的耐蚀性较好,腐蚀电位由-0.6377 V提高至-0.5633 V,腐蚀电流由6.1030×10^-6 A/...     

磷酸盐分步沉淀不锈钢酸洗污泥浸出液铬铁镍

不锈钢酸洗污泥含有高浓度的Fe、Cr、Ni金属离子,属于危险固体废弃物。本文对不锈钢酸洗污泥浸出液有价组分梯级分离展开研究,探讨了磷酸钠用量、浸出液初始pH、反应温度、搅拌时间对酸洗污泥中浸出液中Fe、Cr、Ni分离效果的影响。确定Cr³⁺沉淀的最佳工艺条件：P/Cr摩尔比为1.00,初始pH为1.00,反应温度为90℃,反应时间70min。Cr³⁺平均沉淀率为94.47%,Fe²⁺、Ni²⁺平均沉淀率为0.88%、0.78%。Fe³⁺优化条件为P/Fe体积比0.80、初始pH为1.00、反应温度为45℃、搅拌时间为60min,Fe³⁺沉淀率最高为99.83%、Ni²⁺沉淀率稳定在0.68%,证明了磷酸盐沉淀法可以有效分离不锈钢酸洗污泥浸出液中Fe、Cr、Ni,为不锈钢酸洗污泥铁、镍、铬分离提供理论依据和技术应用参考。     

功能纳米银材料的可控制备及其3价铬离子可视化检测的研究

针对目前水溶液中铬离子检测中存在的问题，设计、合成了功能纳米银材料，并构建了水溶液中Cr³⁺离子检测体系。考察了双氧水、柠檬酸三钠和聚乙烯吡咯烷酮对银纳米材料合成的影响。以功能银纳米材料为探针，初步考察了该探针对水溶液中Cr³⁺离子的检测效果。研究结果表明，双氧水、柠檬酸三钠和聚乙烯吡咯烷酮浓度可以有效调控功能纳米银的合成，可调控制备10～245 nm粒径范围内的纳米银，不同粒径之间表现出不同颜色。当柠檬酸三钠、双氧水和聚乙烯吡咯烷酮浓度分别为1.61×10^-3、2.13×10^-2、3.73×10^-5 mol/L时，所制备的功能化纳米银材料平均粒径为16 nm,该功能材料对水溶液中Cr³⁺离子具有较好的可视化检测效果。     

季铵盐改性玻璃纤维滤纸吸附去除水中Cr(Ⅵ)研究

采用二甲基十八烷基[3-(三氧甲基硅基)丙基]氯化铵(TPMMC)与经过等离子体预处理后的玻璃纤维滤纸进行接枝改性获得负载有季铵盐基团的玻纤材料,对其进行了表征,探讨了改性前后玻璃纤维滤纸在不同溶液Cr6+含量和p H下对水中Cr⁶⁺吸附性能的差异及形成原因。结果表明,改性后玻璃纤维材料表面ζ电位大幅上升,由负转为正。未改性的玻璃纤维材料对Cr⁶⁺几乎没有吸附能力,改性后吸附能力明显升高,在Cr⁶⁺的质量浓度为1 mg/L时,改性后的玻璃纤维较原始材料对Cr6+的吸附去除率提高了51.13%。且改性后玻纤对Cr⁶⁺的吸附效果受p H影响较大,在一定范围内,p H越低吸附效果越好。     

Investigation of a transparent chromate (III) passive film on electroless Ni–P coating by XPS and electrochemical methods

A transparent passive film on electroless nickel phosphorus coating (ENPC) was obtained in a chromate (Cr³⁺) bath. An ENPC sample passivated in a Cr⁶⁺-containing bath was used for comparison. The corrosion properties were tested by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). SEM, XPS, and EDX were employed to analyze the chemical composition and surface morphology of the films. SEM results indicate that the passive film is too thin to be observed by SEM. The potentiodynamic polarization tests show that the corrosion currents of the two passivated samples are only about 1/25 of the un-passivated coating. The XPS analysis illustrate that the Cr⁶⁺-treated film comprises Cr, Ni and O, while the Cr³⁺-treated film is made up of Cr, C, O, Ni, P and N. High-resolution XPS analysis show that, both in Cr⁶⁺-treated and Cr³⁺-treated films, element Cr is only in the form of trivalent compounds, no hexavalent chromium existing. By XPSpeak analyzing, trivalent chromium compounds on the two treated surfaces were fitted as Cr(OH)₃ and Cr₂O₃. However, for the Cr³⁺ and Cr⁶⁺ passivation routes, the Cr(OH)₃ and Cr₂O₃ contents in passive films are widely divergent.     

Reducing Cr6+ emissions from gas tungsten arc welding using a silica precursor

Hexavalent chromium (Cr⁶⁺) emission from stainless steel welding operations poses a serious threat to worker safety and ambient air quality. In this study, tetraethyloxysilane (TEOS) was used as a silica precursor additive to welding shield gas during gas tungsten arc welding (GTAW) operations to determine the feasibility of using these chemicals for Cr⁶⁺ exposure reduction. Fume aerosol samples were analyzed for Cr⁶⁺ concentration using ion chromatography (IC) and for total Cr by inductively coupled plasma with atomic emission spectroscopy (ICP-AES).At high temperature, silica precursors are pyrolyzed to form amorphous silica (SiO₂) which can condense on the existing metal aerosols. The inert silica layer surrounding the aerosols can prevent further chromium oxidation by insulating chromium aerosols. Experimental results showed approximately 45% Cr⁶⁺ reductions when 3.0% TEOS was added to the shield gas. Nitrate concentration also decreased by 53%, indicating that reactive oxygen species were also reduced. Transmission electron microscopy (TEM) images of collected fume aerosols showed SiO₂ coating on metal particles, verifying the proposed mechanism.     

A simple sulfuric acid pretreatment method to improve the adsorption of Cr(VI) by chitosan

An optimum pH of 5.0 for the adsorption of Cr⁶⁺ by chitosan was determined by using a stirred‐batch reactor method at constant pH. When a column containing chitosan was used to bind Cr⁶⁺ in a situation where pH could not be held constant because of pH changes caused by the chitosan itself, significant binding occurred only at solution pH 1 and 2. When chitosan was pretreated with sulfuric acid in a range of 7–70 mol % sulfuric acid : moles glucosamine residue, maximum binding occurred at pH 6.0. Under these conditions, a column containing 0.500 g acid‐treated chitosan (35% mole ratio) reduced the concentration of Cr⁶⁺ in 713 bed volumes of 25 ppm Cr⁶⁺ solution to ≤5 ppm in the effluent. A similar column of pretreated chitosan reduced Cr⁶⁺ concentration in 1042 bed volumes of industrial chromium plating rinse water initially containing 18 ppm Cr⁶⁺ to ≤5 ppm. Capacity experiment results indicated 60 mg chromium bound per gram of treated chitosan at pH 6.0. Commercial resin IRA‐67 was also investigated as a Cr⁶⁺ binding agent. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2808–2814, 2004     

Optimization of chromium removal by the chromium resistant mutant of the cyanobacterium Anacystis nidulans in a continuous flow bioreactor

BACKGROUND: Chromium removal potential of the cyanobacterium Anacystis nidulans and its chromium resistant strain Cr^rI8 has been optimized. Optimized parameters include biomass load, pH, temperature and dilution rate of the bioreactor. RESULTS: Results show that chromium resistant strain has high EC₅₀ dose for chromium compared to wild strain. Chromium removal potential of both strains is strongly influenced by various factors. Optimized conditions in batch system included pH 6.5, temperature 28 °C, biomass load 150 µg protein mL^?1 for 30 µmol L^?1 Cr⁶⁺ solution. In continuous flow bioreactor at optimum pH (6.5) and temperature (28 °C) at a fixed biomass of 10 mg protein and 30 µmol L^?1 Cr⁶⁺, metal removal efficiency varied with dilution rate. For A. nidulans continuous flow bioreactor, optimum dilution rate was 0.076 h^?1 (64.6 per cent metal removal) while for Cr^rI8 it was 0.152 h^?1 (85.8 per cent metal removal). Operative time of the Cr^rI8 bioreactor was also more (85 h) compared to A. nidulans bioreactor (45 h). CONCLUSION: Under optimized conditions resistant strain Cr^rI8 removed more Cr⁶⁺ compared to A. nidulans and thus has the potential to be exploited for Cr⁶⁺ removal from industrial effluents at large scale. Copyright © 2007 Society of Chemical Industry     

Oxidative Dehydrogenation of Propane with CO2 Over Cr/H[B]MFI Catalysts

Abstract  

Cr/silicalite-1 and Cr/H[B]MFI catalysts were prepared by the impregnation method, and Cr/H[B]MFI were further treated by steaming. The catalysts were employed for the oxidative dehydrogenation of propane to propylene with CO₂ as the oxidant. Cr/H[B]MFI showed significantly higher catalytic activity than Cr/silicalite-1, and steamed Cr/H[B]MFI was superior in the reaction stability to Cr/H[B]MFI. The nature of the supported chromium species have been characterized by a number of physicochemical techniques, such as Raman, UV–vis and NMR. It is concluded that the steaming led to the auto-reduction of some Cr⁶⁺ to Cr³⁺, and resultant Cr³⁺ species might be located near the boron center in the borosilicate framework to counterbalance the negative charge of the framework. The transformation of Cr⁶⁺ species to Cr³⁺ species, facilitated by the steaming process and the presence of boron in the catalyst, is responsible for the enhanced stability of oxidative dehydrogenation of propane to propylene with carbon dioxide as the oxidant.     

Effect of thermal history on high‐valence chromium ion dissolution in merwinite (3CaO·MgO·2SiO2)

Solubility and local structure of transmission elements in calcium silicate compounds has not been well understood. We investigate the local structure of chromium ions dissolved in merwinite (3CaO·MgO·2SiO₂) of a monoclinic crystal structure. The acceptance of doping elements into merwinite has not been reported before. We found that chromium ions are soluble in merwinite in air and that chemical valence of the dissolved Cr ions varies with annealing temperature. The absorption edge in the x‐ray absorption near edge structure (XANES) of Cr‐doped merwinite indicated that octahedrally coordinated Cr³⁺ ions were mainly formed when annealed at 1673 K in air. A pre‐edge peak was also detected, indicating the existence of tetrahedrally coordinated high‐valence Cr ions. Conversely, through annealing of merwinite at 1123 K in air, tetrahedrally coordinated Cr⁶⁺ ions were found to be the main form of chromium. XANES spectra simulated by first‐principle calculations were used to explain the structural features in the observed spectra. We propose the coexistence of Cr³⁺ ions in octahedral Mg²⁺ sites and high‐valence Cr ions in tetrahedral Si⁴⁺ sites. In addition, a change in the chromium ion oxidation state in tetrahedral coordination sites was suggested by XANES spectroscopy of Cr‐doped merwinite synthesized at 1673 K and reannealed at 1123 K.     

Adsorption of chromium (III) ion from aqueous solution using rice hull ash

Rice hull was calcined to rice hull ash (RHA) at 500 °C under 20 mL air/s for 50 min. The RHA thus prepared has been found to be able to remove chromium (III) ion from aqueous solution, though not very efficient. The experiments indicated that the rate of removal of Cr³⁺ and the removal of Cr³⁺ at equilibrium was increased upon decreasing the RHA dosage. The removal could also be enhanced upon increasing the initial chromium concentration, or adsorption temperature. However, pH in the range of 2.5-5.4 or stroke speed higher than 120 stroke/min could not change the removal. The dependence of the RHA dosage and the initial chromium concentration on the removal have been found to be strong, while that of adsorption temperature is mild. An empirical equation correlating the relationship between the removal of Cr³⁺ and the adsorption time was determined.     

Influence of photoirradation on reduction of hexavalent chromium by zero-valent iron in the presence of organic acids

Reduction of hexavalent chromium (Cr(VI)) by zero-valent iron (Fe⁰) was investigated systematically in the present study. No change in Cr(VI) concentration occurs using untreated Fe⁰ powders even after a long contact time. The Fe⁰ powders treated with acid washing shows a weak activity and a poor long-term performance to reduction of Cr(VI). The activity and long-term performance of treated Fe⁰ powders is not effectively improved in the presence of citric acid. In contrast, introduction of photoirradiation not only dramatically increases the reduction rate of Cr(VI) in the presence of citric acid but also effectively stabilizes the activity of Fe⁰ powders and films. Such enhancement should be attributed to photoreductive dissolution of the oxide layer on Fe⁰ surface. For this newly developed system, effective reduction of Cr(VI) is favored at low pH values and oxalic and tartaric acid are also effective as complex reagents.     

On the La–Cr–O Phase Change During Methane Catalytic Combustion Investigated with in situ HT-XRD

La₂CrO₆ (Cr6), LaCrO₃ (Cr3), LaCrO₃–La₂CrO₆ (Cr6–Cr3) and LaCrO₃–La₂O₃ (Cr3-L) catalysts were synthesised and investigated with in situ X-ray diffraction (ISXRD) during methane catalytic combustion in order to characterise the solid phases present under reactants and to determine the effect of chromium oxidation state on the catalytic activity. Methane conversion was evaluated over a temperature range of 300–800 °C, using oxygen-to-methane ratio of 4 and GHSV of 8,000 h^?1. The TPR provided information about the oxygen depletion temperatures characteristic of lattice oxygen mobility in the samples and ISXRD results evidenced a cooperative effect of Cr3 and Cr6 phases at low temperatures (<725 °C) and of Cr3 and LaCrO₄ (Cr4) phases at high temperatures (>750 °C). The relative phase composition determined the oxygen activation capability and hence the corresponding activity for the oxidation of methane. It was observed that while direct and back Cr6 ? Cr4 transition temperatures were unaffected by Cr6 content in the samples, the methane conversion was strongly modified. This suggests that Cr³⁺/Cr⁶⁺ and Cr³⁺/Cr⁵⁺ species involved substantial modification of the surface chemistry which affected the catalytic activity. These results provide the first direct evidence of the presence of Cr4 metastable phase during methane combustion over La–Cr–O catalysts.