The electro-reduction of chromium oxide（Cr2O3） was investigated in an equimolar mixture of CaCl2-NaCl molten salt at 800℃ for developing a more efficient process for chromium preparation. Cyclic voltammetry and pot...The electro-reduction of chromium oxide（Cr2O3） was investigated in an equimolar mixture of CaCl2-NaCl molten salt at 800℃ for developing a more efficient process for chromium preparation. Cyclic voltammetry and potentiostatic electrolysis were used to study the electro-reduction of the Cr2O3-loaded metallic cavity electrode. In addition, a number of parameters affecting the rate and extent of Cr2O3 electrolysis were considered to better understand the electrolysis process. The results demonstrate that CaCl2-NaCl molten salt is applicable for preparing Cr directly from Cr2O3 and the electrolysis parameters exert great influence on the cathode product. Under optimal experimental conditions, nodular Cr with an oxygen content of 0.5%（mass fraction） was obtained without any chromium carbides detected by XRD. Furthermore, the relatively high solubility of CaO and quite rapid crystal growth result in the formation of large platelet CaCr2O4, and the addition of NaCl to CaCl2 results in several variations on the electrolysis process and the product morphology from pure CaCl2 molten salt.展开更多
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 vanadi...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.展开更多
Pyrochemical reprocessing utilizing a molten LiCl-KCl eutectic medium is regarded as the most promising approach for recovering uranium and transuranic elements from spent metallic nuclear fuels.However,the harsh corr...Pyrochemical reprocessing utilizing a molten LiCl-KCl eutectic medium is regarded as the most promising approach for recovering uranium and transuranic elements from spent metallic nuclear fuels.However,the harsh corrosiveness of molten chloride poses a significant challenge to the durability of structural materials.Herein,we report the corrosion behavior of 304 SS,316H SS and Inconel 800H in LiCl-KCl eutectic salt at 550°C for 100 h under an argon atmosphere.Experimental results indicate that all three materials can form a rather continuous Cr_(2)O_(3)-based scale through oxidation reaction at the beginning,but only the scale developed on 800H maintains excellent protection against corrosion throughout the entire exposure period.In contrast,both 304 SS and 316H SS experience considerable active dissolution on the bare substrate under a detached scale.We suggest that the primary reasons for the outstanding resistance of 800H to molten salt corrosion are the high concentration of noble Ni in the system,which lowers the inclination for active dissolution,and the beneficial addition of Al,which accelerates the formation of a less defective Cr_(2)O_(3)-based scale.Our work offers an in-depth understanding on the corrosion performance of high-Cr alloys in molten chloride,insights critical for the selection and subsequent development of structural materials for pyrochemical reprocessing applications.展开更多
Solid oxide membrane-assisted electrolytic reduction of solid Cr_(2)O_(3) to Cr in molten CaCl_(2) was performed using a sintered porous Cr_(2)O_(3) cathode paired with an yttria-stabilized zirconia(YSZ)tube anode con...Solid oxide membrane-assisted electrolytic reduction of solid Cr_(2)O_(3) to Cr in molten CaCl_(2) was performed using a sintered porous Cr_(2)O_(3) cathode paired with an yttria-stabilized zirconia(YSZ)tube anode containing carbon-saturated liquid copper alloy.Analyses of the reduction mechanism,ion migration behavior,and effects of cathode pellet porosity and particle size on the electrolysis products and reduction rate revealed that the cathode microstructure and electrolytic conditions were key factors influencing the electrolysis process.Optimal results were obtained when the cathode was characterized by high porosity and a small particle size because this combination of features contributed to ion migration.Good electrochemical activation was observed when cathode pellets prepared by 4 MPa molding followed by 2 h of sintering at 1150℃ were applied.The electrode reduction process(Cr^(3+)→Cr^(2+)→Cr)was promoted by high electrode voltages,and Cr metal was efficiently formed.The proposed method appears to be well suited for electrolytic Cr production because it does not require expensive pre-electrolysis techniques or generate harmful by-products.展开更多
Cr(VI) is a widespread environmental contaminant and a known human carcinogen. Biosorption is a very common method to remove toxic Cr(VI) from industrial waste water. In biosorption Cr(VI) is reduced to less toxic Cr(...Cr(VI) is a widespread environmental contaminant and a known human carcinogen. Biosorption is a very common method to remove toxic Cr(VI) from industrial waste water. In biosorption Cr(VI) is reduced to less toxic Cr(III) and adsorbed in biosorbent as Cr(III). Effective biosorbents contain hydroxy groups;it may be aliphatic or aromatic. Kinetics of reduction of Cr(VI) by an aromatic alcohol, benzyl alcohol, (which is an important volatile component of flowers of some night blooming plants) in micellar media have been studied spectrophotometrically. Micellar media is a probe to establish the mechanistic paths of reduction of Cr(VI) to Cr(III). Effects of electrolytes are studied to support the proposed reaction mechanism. Suitable surfactant & suitable concentration of electrolyte enhance the biosorption property.展开更多
A novel organic-inorganic chromium(III) hybrid salt, triethylammonium<em> trans</em>-diaquabis(oxalato-<em>κ</em><sup>2</sup>O<sup>1</sup>,O<sup>2</sup>)chr...A novel organic-inorganic chromium(III) hybrid salt, triethylammonium<em> trans</em>-diaquabis(oxalato-<em>κ</em><sup>2</sup>O<sup>1</sup>,O<sup>2</sup>)chromate(III), (C<sub>6</sub>H<sub>16</sub>N)[Cr(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>] (1), has been synthesized in aqueous solution and characterized by elemental and thermal analyses, FTIR and UV-Vis spectroscopies, and by single crystal X-ray structure determination. Compound 1 crystallizes in the orthorhombic system, <em>Pbcn</em> space group with the unit cell parameters <em>a</em> = 11.1776(10), <em>b </em>= 7.6105(10), <em>c</em> = 17.5654(2) <span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">Å</span>, <em>α</em> = <em>β</em> = <em>γ</em> = 90<span style="white-space:nowrap;">°</span>, <em>V</em> = 1494.24(3) <span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">Å</span>3, <em>Z</em> = 4 and <em>Z’</em> = 1/2. The structure of 1 consists of [Cr(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]<span style="white-space:nowrap;"><sup>−</sup></span> mononuclear anions and triethylammonium [(C<sub>2</sub>H<sub>5</sub>)<sub>3</sub>NH]<sup>+</sup> cations. In the anionic unit, the CrIII ion is six coordinated, in a distorted octahedral geometry, by four equatorial O atoms of two oxalate anions acting as chelating ligands and two O atoms from <em>trans</em>-coordinated water molecules occupying the apical positions with longer metal-oxygen distances. In the solid, O-H … O and N-H … O intra and inter molecular hydrogen bonding interactions connect the components into a 3D network. The triethylammonium cations are disordered among two possible orientations with occupancies rates around 50% for C4, N1, C1a, C1b, C4<sup>ii</sup>, N1<sup>ii</sup>, C1a<sup>ii</sup>, C1b<sup>ii</sup> (ii = <span style="white-space:nowrap;">−</span><em>x</em> + 1, <em>y</em>, <span style="white-space:nowrap;">−展开更多
基金Project(2013CB632600)supported by the National Basic Research Program of ChinaProjects(21376251,21406233)supported by the National Natural Science Foundation of ChinaProject supported by the Fund of Hubei Zhenhua Chemical Co.,Ltd.,China
文摘The electro-reduction of chromium oxide（Cr2O3） was investigated in an equimolar mixture of CaCl2-NaCl molten salt at 800℃ for developing a more efficient process for chromium preparation. Cyclic voltammetry and potentiostatic electrolysis were used to study the electro-reduction of the Cr2O3-loaded metallic cavity electrode. In addition, a number of parameters affecting the rate and extent of Cr2O3 electrolysis were considered to better understand the electrolysis process. The results demonstrate that CaCl2-NaCl molten salt is applicable for preparing Cr directly from Cr2O3 and the electrolysis parameters exert great influence on the cathode product. Under optimal experimental conditions, nodular Cr with an oxygen content of 0.5%（mass fraction） was obtained without any chromium carbides detected by XRD. Furthermore, the relatively high solubility of CaO and quite rapid crystal growth result in the formation of large platelet CaCr2O4, and the addition of NaCl to CaCl2 results in several variations on the electrolysis process and the product morphology from pure CaCl2 molten salt.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51974369)the Postgraduate Research Innovation Project of Central South University,China(2019zzts244).
文摘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.
基金financially supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA0410203).
文摘Pyrochemical reprocessing utilizing a molten LiCl-KCl eutectic medium is regarded as the most promising approach for recovering uranium and transuranic elements from spent metallic nuclear fuels.However,the harsh corrosiveness of molten chloride poses a significant challenge to the durability of structural materials.Herein,we report the corrosion behavior of 304 SS,316H SS and Inconel 800H in LiCl-KCl eutectic salt at 550°C for 100 h under an argon atmosphere.Experimental results indicate that all three materials can form a rather continuous Cr_(2)O_(3)-based scale through oxidation reaction at the beginning,but only the scale developed on 800H maintains excellent protection against corrosion throughout the entire exposure period.In contrast,both 304 SS and 316H SS experience considerable active dissolution on the bare substrate under a detached scale.We suggest that the primary reasons for the outstanding resistance of 800H to molten salt corrosion are the high concentration of noble Ni in the system,which lowers the inclination for active dissolution,and the beneficial addition of Al,which accelerates the formation of a less defective Cr_(2)O_(3)-based scale.Our work offers an in-depth understanding on the corrosion performance of high-Cr alloys in molten chloride,insights critical for the selection and subsequent development of structural materials for pyrochemical reprocessing applications.
基金the National Natural Science Foundation of China(Nos.51664005,51774102,U1812402,and 51804088)Talents of Guizhou Science and Technology Cooperation Platform(Platform Talent[2017]5626 and KY(2015)334)。
文摘Solid oxide membrane-assisted electrolytic reduction of solid Cr_(2)O_(3) to Cr in molten CaCl_(2) was performed using a sintered porous Cr_(2)O_(3) cathode paired with an yttria-stabilized zirconia(YSZ)tube anode containing carbon-saturated liquid copper alloy.Analyses of the reduction mechanism,ion migration behavior,and effects of cathode pellet porosity and particle size on the electrolysis products and reduction rate revealed that the cathode microstructure and electrolytic conditions were key factors influencing the electrolysis process.Optimal results were obtained when the cathode was characterized by high porosity and a small particle size because this combination of features contributed to ion migration.Good electrochemical activation was observed when cathode pellets prepared by 4 MPa molding followed by 2 h of sintering at 1150℃ were applied.The electrode reduction process(Cr^(3+)→Cr^(2+)→Cr)was promoted by high electrode voltages,and Cr metal was efficiently formed.The proposed method appears to be well suited for electrolytic Cr production because it does not require expensive pre-electrolysis techniques or generate harmful by-products.
文摘Cr(VI) is a widespread environmental contaminant and a known human carcinogen. Biosorption is a very common method to remove toxic Cr(VI) from industrial waste water. In biosorption Cr(VI) is reduced to less toxic Cr(III) and adsorbed in biosorbent as Cr(III). Effective biosorbents contain hydroxy groups;it may be aliphatic or aromatic. Kinetics of reduction of Cr(VI) by an aromatic alcohol, benzyl alcohol, (which is an important volatile component of flowers of some night blooming plants) in micellar media have been studied spectrophotometrically. Micellar media is a probe to establish the mechanistic paths of reduction of Cr(VI) to Cr(III). Effects of electrolytes are studied to support the proposed reaction mechanism. Suitable surfactant & suitable concentration of electrolyte enhance the biosorption property.
文摘A novel organic-inorganic chromium(III) hybrid salt, triethylammonium<em> trans</em>-diaquabis(oxalato-<em>κ</em><sup>2</sup>O<sup>1</sup>,O<sup>2</sup>)chromate(III), (C<sub>6</sub>H<sub>16</sub>N)[Cr(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>] (1), has been synthesized in aqueous solution and characterized by elemental and thermal analyses, FTIR and UV-Vis spectroscopies, and by single crystal X-ray structure determination. Compound 1 crystallizes in the orthorhombic system, <em>Pbcn</em> space group with the unit cell parameters <em>a</em> = 11.1776(10), <em>b </em>= 7.6105(10), <em>c</em> = 17.5654(2) <span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">Å</span>, <em>α</em> = <em>β</em> = <em>γ</em> = 90<span style="white-space:nowrap;">°</span>, <em>V</em> = 1494.24(3) <span style="font-family:Verdana, Helvetica, Arial;white-space:normal;background-color:#FFFFFF;">Å</span>3, <em>Z</em> = 4 and <em>Z’</em> = 1/2. The structure of 1 consists of [Cr(C<sub>2</sub>O<sub>4</sub>)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]<span style="white-space:nowrap;"><sup>−</sup></span> mononuclear anions and triethylammonium [(C<sub>2</sub>H<sub>5</sub>)<sub>3</sub>NH]<sup>+</sup> cations. In the anionic unit, the CrIII ion is six coordinated, in a distorted octahedral geometry, by four equatorial O atoms of two oxalate anions acting as chelating ligands and two O atoms from <em>trans</em>-coordinated water molecules occupying the apical positions with longer metal-oxygen distances. In the solid, O-H … O and N-H … O intra and inter molecular hydrogen bonding interactions connect the components into a 3D network. The triethylammonium cations are disordered among two possible orientations with occupancies rates around 50% for C4, N1, C1a, C1b, C4<sup>ii</sup>, N1<sup>ii</sup>, C1a<sup>ii</sup>, C1b<sup>ii</sup> (ii = <span style="white-space:nowrap;">−</span><em>x</em> + 1, <em>y</em>, <span style="white-space:nowrap;">−
