The practice ofin-situ leaching of the ion-adsorption type rare earths ore with ammonium sulfate could only leach most of rare earth in ion-exchangeable phase, but not the colloidal sediment phase. Therefore, the redu...The practice ofin-situ leaching of the ion-adsorption type rare earths ore with ammonium sulfate could only leach most of rare earth in ion-exchangeable phase, but not the colloidal sediment phase. Therefore, the reduction leaching of rare earth from the ion-adsorption type rare earths ore with ferrous sulfate was innovatively put forward. The soak leaching process and the column leaching process were investigated in the present study. It was determined that ion-exchangeable phase could be released, and part of colloidal sediment phase rare earth could be reduction leached by the cations with reduction properties. The mechanism of reduction leaching was discussed with the Eh-pH diagram of cerium. Moreover, the stronger reduction of reductive ions, the greater acidity of leaching agent solution, and the higher reductive ion concentration, could result in the higher rare earth efficiency and the bigger ce-rium partition in the leaching liquor. In the ferrous sulfate column leaching process, the rare earth leaching rate and the rare earth effi-ciency were a little higher than with (NH4)2SO4 agent, and the rare earth efficiency and the partitioning of cerium in leaching liquor could be about 102% and 5.31%, respectively. However, the ferrous sulfate leaching process revealed some problems, so compound leaching with magnesium sulfate and a small amount of ferrous sulfate was proposed to an excellent alternative leaching agent for further studies, which may realize efficiency extraction and be environment-friendly.展开更多
Reduction roasting-acid leaching process was utilized to process high-iron-content manganese oxide ore using black charcoal as reductant. The results indicate that, compared with the traditional reductant of anthracit...Reduction roasting-acid leaching process was utilized to process high-iron-content manganese oxide ore using black charcoal as reductant. The results indicate that, compared with the traditional reductant of anthracite, higher manganese extraction efficiency is achieved at lower roasting temperature and shorter residence time. The effects of roasting parameters on the leaching efficiency of Mn and Fe were studied, and the optimal parameters are determined as follows: roasting temperature is 650 °C, residence time is 40 min, and black charcoal dosage is 10%(mass fraction). Under these conditions, the leaching efficiency of Mn reaches 82.37% while that of Fe is controlled below 7%. XRD results show that a majority of MnO2 and Fe2O3 in the raw ore are reduced to MnO and Fe3O4, respectively.展开更多
Zinc ferrite is the principal constituent in zinc neutral-leach residue(NLR) which is commonly treated by hot-acid leaching in electrolytic zinc plants. Reductive leaching of zinc ferrite with sphalerite concentrate...Zinc ferrite is the principal constituent in zinc neutral-leach residue(NLR) which is commonly treated by hot-acid leaching in electrolytic zinc plants. Reductive leaching of zinc ferrite with sphalerite concentrate as a reducing agent was performed. It was found that leaching of zinc ferrite in the presence of sphalerit concentrate was a viable process that effectively extracted zinc and indium and converted Fe^3+ into Fe^2+ at the same time. Reflux leaching tests by two stages were performed to achieve extractions of 98.1% for zinc and 97.5% for indium, and a Fe^2+/Fe^3+ molar ratio of 9.6 in leach solution was also obtained. The leaching behaviors of other elements, such as iron, copper and tin were also studied. The results showed that iron and copper were completely leached, whereas tin presented lower extraction values.展开更多
Zinc neutral leaching residue(ZNLR) from hydrometallurgical zinc smelting processing can be determined as hazardous intermediate containing considerable amounts of Cd and Zn which have great threats to the environme...Zinc neutral leaching residue(ZNLR) from hydrometallurgical zinc smelting processing can be determined as hazardous intermediate containing considerable amounts of Cd and Zn which have great threats to the environment. The ZNLR contained approximately 35.99% Zn, 15.93% Fe and 0.26% Cd, and Cd mainly existed as ferrites in the ZNLR in this research. Reductive acid leaching of ZNLR was investigated. The effects of hydrazine sulfate concentration, initial sulfuric acid concentration, temperature, duration and liquid-to-solid ratio on the extraction of Cd, Zn and Fe were examined. The extraction efficiencies of Cd, Zn and Fe reached 90.81%, 95.83% and 94.19%, respectively when the leaching parameters were fixed as follows: hydrazine sulfate concentration, 33.3 g/L; sulfuric acid concentration, 80 g/L; temperature, 95 °C; duration of leaching, 120 min; liquid-to-solid ratio, 10 m L/g and agitation, 400 r/min. XRD and SEM-EDS analyses of the leaching residue confirmed that lead sulfate(Pb SO4) and hydrazinium zinc sulfate((N2H5)2Zn(SO4)2) were the main phases remaining in the reductive leaching residue.展开更多
The kinetics of reductive leaching of manganese from low grade pyrolusite in dilute sulfuric acid in the presence of molasses alcohol wastewater was investigated. The shrinking core model was applied to quantify the e...The kinetics of reductive leaching of manganese from low grade pyrolusite in dilute sulfuric acid in the presence of molasses alcohol wastewater was investigated. The shrinking core model was applied to quantify the effects of reaction parameters on leaching rate. The leaching rate increases with reaction temperature, concentrations of H 2 SO 4 and organic matter in molasses alcohol wastewater increase and ore particle size decreases. The leaching process follows the kinetics of a shrinking core model and the apparent activation energy is 57.5 kJ·mol –1 . The experimental results indicate a reaction order of 0.52 for H2SO4 concentration and 0.90 for chemical oxygen demand (COD) of molasses alcohol wastewater. It is concluded that the reductive leaching of pyrolusite with molasses alcohol wastewater is controlled by the diffusion through the ash/inert layer composed of the associated minerals.展开更多
Hydrazine sulfate was used as a reducing agent for the leaching of Li,Ni,Co and Mn from spent lithium-ion batteries.The effects of the reaction conditions on the leaching mechanism and kinetics were characterized and ...Hydrazine sulfate was used as a reducing agent for the leaching of Li,Ni,Co and Mn from spent lithium-ion batteries.The effects of the reaction conditions on the leaching mechanism and kinetics were characterized and examined.97%of the available Li,96%of the available Ni,95%of the available Co,and 86%of the available Mn are extracted under the following optimized conditions:sulfuric acid concentration of 2.0 mol/L,hydrazine sulfate dosage of 30 g/L,solid-to-liquid ratio of 50 g/L,temperature of 80℃,and leaching time of 60 min.The activation energies of the leaching are determined to be 44.32,59.37 and 55.62 k J/mol for Li,Ni and Co,respectively.By performing X-ray diffraction and scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy,it is confirmed that the main phase in the leaching residue is MnO2.The results show that hydrazine sulfate is an effective reducing agent in the acid leaching process for spent lithium-ion batteries.展开更多
The kinetics of reductive leaching of manganese from a low-grade manganese oxide ore were studied using cellulose as reductant in dilute sulfuric acid medium.It was found that when the stirring speed was higher than 2...The kinetics of reductive leaching of manganese from a low-grade manganese oxide ore were studied using cellulose as reductant in dilute sulfuric acid medium.It was found that when the stirring speed was higher than 200 r/min,the effect of gas film diffusion on manganese extraction efficiency could be neglected,and the kinetic behavior was investigated under the condition of elimination of external diffusion influence on the leaching process.Effects of leaching temperature,mass ratio of cellulose and ore,and the sulfuric acid concentration on manganese extraction efficiency were discussed.The kinetic data were analyzed based on the shrinking core model,which indicated that the leaching process was dominated by both ash layer diffusion and chemical reaction at the initial stage,with the progress of leaching reaction,the rate-controlling step switched to the ash layer diffusion.It was also concluded that the sulfuric acid concentration had the most significant influence on the leaching rate,the reaction orders with respect to the sulfuric acid concentration were 2.102 in the first 60 min,and 3.642 in the later 90 min,while the reaction orders for mass ratio of cellulose and ore were 0.660 and 0.724,respectively.An Arrhenius relationship was used to relate the temperature to the rate of leaching,from which apparent activation energies were calculated to be 46.487 kJ/mol and 62.290 kJ/mol at the two stages,respectively.Finally,the overall leaching rate equations for the manganese dissolution reaction with cellulose in sulphuric acid solution were developed.The morphological changes and mineralogical forms of the ore before and after the chemical treatment were discussed with the support of SEM and XRD analyses.展开更多
The present study evaluates the reductive leaching of indium from indium-bearing zinc ferrite using oxalic acid as a reducer in sulfuric acid solution.The effect of main factors affecting the process rate,including th...The present study evaluates the reductive leaching of indium from indium-bearing zinc ferrite using oxalic acid as a reducer in sulfuric acid solution.The effect of main factors affecting the process rate,including the oxalic-acid-to-sulfuric-acid ratio,stirring rate,grain size,temperature,and the initial concentration of synergic acid,was precisely evaluated.The results confirmed the acceptable efficiency of dissolving indium in the presence of oxalic acid.The shrinking-core model with a chemical-reaction-controlled step can correctly describe the kinetics of indium dissolution.On the basis of an apparent activation energy of 44.55 kJ/mol and a reaction order with respect to the acid concentration of 1.14,the presence of oxalic acid was found to reduce the sensitivity to temperature changes and to increase the effect of changes in acid concentration.Finally,the equation of the kinetic model based on the factors under study is presented.展开更多
An innovative method for recovering valuable elements from vanadium-bearing titanomagnetite is proposed. This method involves two procedures: low-temperature roasting of vanadium-bearing titanomagnetite and water lea...An innovative method for recovering valuable elements from vanadium-bearing titanomagnetite is proposed. This method involves two procedures: low-temperature roasting of vanadium-bearing titanomagnetite and water leaching of roasting slag. During the roasting process, the reduction of iron oxides to metallic iron, the sodium oxidation of vanadium oxides to water-soluble sodium vanadate, and the smelting separation of metallic iron and slag were accomplished simultaneously. Optimal roasting conditions for iron/slag separation were achieved with a mixture thickness of 42.5 mm, a roasting temperature of 1200°C, a residence time of 2 h, a molar ratio of C/O of 1.7, and a sodium carbonate addition of 70 wt%, as well as with the use of anthracite as a reductant. Under the optimal conditions, 93.67% iron from the raw ore was recovered in the form of iron nugget with 95.44% iron grade. After a water leaching process, 85.61% of the vanadium from the roasting slag was leached, confirming the sodium oxidation of most of the vanadium oxides to water-soluble sodium vanadate during the roasting process. The total recoveries of iron, vanadium, and titanium were 93.67%, 72.68%, and 99.72%, respectively.展开更多
The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate ofPanzhihua ilmenite. The as-pretreated ilmenite was leached with 20% HCI at 105 ℃, The leac...The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate ofPanzhihua ilmenite. The as-pretreated ilmenite was leached with 20% HCI at 105 ℃, The leaching process was controlled by the phases and microstructures that evolved during the pretreatment processes. The leaching kinetics of pure hematite, ilmenite and pseudobrookite were characterized to clarify the phase effect on the iron-leaching rate; the rate of iron leaching occurs in the following order in the HCI solution: hematite (ferric iron) 〉 ilmenite (ferrous iron) 〉〉 pseudobrookite (ferric iron). Therefore, the often-cited notion that ferrous iron dissolves faster in HCl solutions than ferric iron when explaining the pretreatment effects is inaccurate. Moreover, the oxidation pretreatment (at 600-1000 ℃ for 4 h) cannot destroy the dense structure of the Panzhihua ilmenite. Therefore, the influence exerted by the oxidation on the leaching process is primarily determined by the phase change; oxidation at 600 and 700℃ slightly increased the rate of iron leaching because the ilmenite was transformed into hematite, while the oxidation at 900-1000℃ significantly reduced the rate of iron leaching because a pseudobrookite phase formed. The reduction effect was subsequently investigated; the as-oxidized ilmenite was reduced under H2 at 750 ℃ for 30 min. The reduction significantly accelerated the rate of subsequent iron leaching such that nearly all of the iron had dissolved after leaching for 2 h in 20% HCl at 105 ℃. This enhanced iron-leaching rate is mainly attributed to the cracks and holes that formed during the reduction process.展开更多
A hydrometallurgical process for the recovery of cobalt oxalate from spent lithium-ion batteries was used to recycle cobalt compound by using alkali leaching, reductive acid leaching and chemical deposition of cobalt ...A hydrometallurgical process for the recovery of cobalt oxalate from spent lithium-ion batteries was used to recycle cobalt compound by using alkali leaching, reductive acid leaching and chemical deposition of cobalt oxalate. The recycled cobalt oxalate was used to synthesize nano-Co3O4 anode material by sol-gel method. The samples were characterized by thermal gravity analysis and differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and charge/discharge measurements. The influence of molar ratio of Co2+ to citric acid and calcination temperature on the structure and electrochemical performance of nano-Co3O4 was evaluated. As the molar ratio of Co2+ to citric acid is 1:1, the face-centered cubic (fcc) Co3O4 powder shows the discharge capacity of 760.9 mA h g-1, the high coulombic efficiency of 99.7% in the first cycle at the current density of 125 mA g-l, and the excellent cycling performance with the reversible capacity of 442.3 mA h g-1 after 20 cycles at the current density of 250 mA g-1.展开更多
基金Project supported by National Science and Technology Support Program of China(2015BAB16B01)Training Program of Major Academic and Technical Leaders in Jiangxi Province(20142BCB22005)Top Youth Talent Training Program of "Gan Po 555 Talents Project" of Jiangxi Province
文摘The practice ofin-situ leaching of the ion-adsorption type rare earths ore with ammonium sulfate could only leach most of rare earth in ion-exchangeable phase, but not the colloidal sediment phase. Therefore, the reduction leaching of rare earth from the ion-adsorption type rare earths ore with ferrous sulfate was innovatively put forward. The soak leaching process and the column leaching process were investigated in the present study. It was determined that ion-exchangeable phase could be released, and part of colloidal sediment phase rare earth could be reduction leached by the cations with reduction properties. The mechanism of reduction leaching was discussed with the Eh-pH diagram of cerium. Moreover, the stronger reduction of reductive ions, the greater acidity of leaching agent solution, and the higher reductive ion concentration, could result in the higher rare earth efficiency and the bigger ce-rium partition in the leaching liquor. In the ferrous sulfate column leaching process, the rare earth leaching rate and the rare earth effi-ciency were a little higher than with (NH4)2SO4 agent, and the rare earth efficiency and the partitioning of cerium in leaching liquor could be about 102% and 5.31%, respectively. However, the ferrous sulfate leaching process revealed some problems, so compound leaching with magnesium sulfate and a small amount of ferrous sulfate was proposed to an excellent alternative leaching agent for further studies, which may realize efficiency extraction and be environment-friendly.
基金Project(2013JSJJ028)supported by the Teachers’Research Fund of Central South University,ChinaProject supported by Co-Innovation Center for Clean and Efficient Utilization of Strategic Mineral Resources,China
文摘Reduction roasting-acid leaching process was utilized to process high-iron-content manganese oxide ore using black charcoal as reductant. The results indicate that, compared with the traditional reductant of anthracite, higher manganese extraction efficiency is achieved at lower roasting temperature and shorter residence time. The effects of roasting parameters on the leaching efficiency of Mn and Fe were studied, and the optimal parameters are determined as follows: roasting temperature is 650 °C, residence time is 40 min, and black charcoal dosage is 10%(mass fraction). Under these conditions, the leaching efficiency of Mn reaches 82.37% while that of Fe is controlled below 7%. XRD results show that a majority of MnO2 and Fe2O3 in the raw ore are reduced to MnO and Fe3O4, respectively.
基金Project(2014CB643404)supported by the National Basic Research Program of ChinaProjects(51564030,51474117,51304093,51364022)supported by the National Natural Science Foundation of China+1 种基金Project(0120150070)supported by Yunnan Applied Basic Reach Project,ChinaProject(ZD2014003)supported by the Education Department of Yunnan Province,China
文摘Zinc ferrite is the principal constituent in zinc neutral-leach residue(NLR) which is commonly treated by hot-acid leaching in electrolytic zinc plants. Reductive leaching of zinc ferrite with sphalerite concentrate as a reducing agent was performed. It was found that leaching of zinc ferrite in the presence of sphalerit concentrate was a viable process that effectively extracted zinc and indium and converted Fe^3+ into Fe^2+ at the same time. Reflux leaching tests by two stages were performed to achieve extractions of 98.1% for zinc and 97.5% for indium, and a Fe^2+/Fe^3+ molar ratio of 9.6 in leach solution was also obtained. The leaching behaviors of other elements, such as iron, copper and tin were also studied. The results showed that iron and copper were completely leached, whereas tin presented lower extraction values.
基金Project(2012FJ1010)supported by the Key Project of Science and Technology of Hunan ProvinceChina+2 种基金Project(51474247)supported by the National Natural Science Foundation of ChinaProject(2012GS430201)supported by the Science and Technology Program for Public WellbeingChina
文摘Zinc neutral leaching residue(ZNLR) from hydrometallurgical zinc smelting processing can be determined as hazardous intermediate containing considerable amounts of Cd and Zn which have great threats to the environment. The ZNLR contained approximately 35.99% Zn, 15.93% Fe and 0.26% Cd, and Cd mainly existed as ferrites in the ZNLR in this research. Reductive acid leaching of ZNLR was investigated. The effects of hydrazine sulfate concentration, initial sulfuric acid concentration, temperature, duration and liquid-to-solid ratio on the extraction of Cd, Zn and Fe were examined. The extraction efficiencies of Cd, Zn and Fe reached 90.81%, 95.83% and 94.19%, respectively when the leaching parameters were fixed as follows: hydrazine sulfate concentration, 33.3 g/L; sulfuric acid concentration, 80 g/L; temperature, 95 °C; duration of leaching, 120 min; liquid-to-solid ratio, 10 m L/g and agitation, 400 r/min. XRD and SEM-EDS analyses of the leaching residue confirmed that lead sulfate(Pb SO4) and hydrazinium zinc sulfate((N2H5)2Zn(SO4)2) were the main phases remaining in the reductive leaching residue.
基金Supported by the National Natural Science Foundation of China (20866001) the Natural Science Foundation of GuangxiProvince (0832035)
文摘The kinetics of reductive leaching of manganese from low grade pyrolusite in dilute sulfuric acid in the presence of molasses alcohol wastewater was investigated. The shrinking core model was applied to quantify the effects of reaction parameters on leaching rate. The leaching rate increases with reaction temperature, concentrations of H 2 SO 4 and organic matter in molasses alcohol wastewater increase and ore particle size decreases. The leaching process follows the kinetics of a shrinking core model and the apparent activation energy is 57.5 kJ·mol –1 . The experimental results indicate a reaction order of 0.52 for H2SO4 concentration and 0.90 for chemical oxygen demand (COD) of molasses alcohol wastewater. It is concluded that the reductive leaching of pyrolusite with molasses alcohol wastewater is controlled by the diffusion through the ash/inert layer composed of the associated minerals.
基金Project(51674298)supported by the National Natural Science Foundation of ChinaProject supported by Anhui Province Research and Development Innovation Program,China。
文摘Hydrazine sulfate was used as a reducing agent for the leaching of Li,Ni,Co and Mn from spent lithium-ion batteries.The effects of the reaction conditions on the leaching mechanism and kinetics were characterized and examined.97%of the available Li,96%of the available Ni,95%of the available Co,and 86%of the available Mn are extracted under the following optimized conditions:sulfuric acid concentration of 2.0 mol/L,hydrazine sulfate dosage of 30 g/L,solid-to-liquid ratio of 50 g/L,temperature of 80℃,and leaching time of 60 min.The activation energies of the leaching are determined to be 44.32,59.37 and 55.62 k J/mol for Li,Ni and Co,respectively.By performing X-ray diffraction and scanning electron microscopy in conjunction with energy dispersive X-ray spectroscopy,it is confirmed that the main phase in the leaching residue is MnO2.The results show that hydrazine sulfate is an effective reducing agent in the acid leaching process for spent lithium-ion batteries.
基金Project(2010FJ1011)supported by the Major Project of Science and Technology of Hunan Province,China
文摘The kinetics of reductive leaching of manganese from a low-grade manganese oxide ore were studied using cellulose as reductant in dilute sulfuric acid medium.It was found that when the stirring speed was higher than 200 r/min,the effect of gas film diffusion on manganese extraction efficiency could be neglected,and the kinetic behavior was investigated under the condition of elimination of external diffusion influence on the leaching process.Effects of leaching temperature,mass ratio of cellulose and ore,and the sulfuric acid concentration on manganese extraction efficiency were discussed.The kinetic data were analyzed based on the shrinking core model,which indicated that the leaching process was dominated by both ash layer diffusion and chemical reaction at the initial stage,with the progress of leaching reaction,the rate-controlling step switched to the ash layer diffusion.It was also concluded that the sulfuric acid concentration had the most significant influence on the leaching rate,the reaction orders with respect to the sulfuric acid concentration were 2.102 in the first 60 min,and 3.642 in the later 90 min,while the reaction orders for mass ratio of cellulose and ore were 0.660 and 0.724,respectively.An Arrhenius relationship was used to relate the temperature to the rate of leaching,from which apparent activation energies were calculated to be 46.487 kJ/mol and 62.290 kJ/mol at the two stages,respectively.Finally,the overall leaching rate equations for the manganese dissolution reaction with cellulose in sulphuric acid solution were developed.The morphological changes and mineralogical forms of the ore before and after the chemical treatment were discussed with the support of SEM and XRD analyses.
文摘The present study evaluates the reductive leaching of indium from indium-bearing zinc ferrite using oxalic acid as a reducer in sulfuric acid solution.The effect of main factors affecting the process rate,including the oxalic-acid-to-sulfuric-acid ratio,stirring rate,grain size,temperature,and the initial concentration of synergic acid,was precisely evaluated.The results confirmed the acceptable efficiency of dissolving indium in the presence of oxalic acid.The shrinking-core model with a chemical-reaction-controlled step can correctly describe the kinetics of indium dissolution.On the basis of an apparent activation energy of 44.55 kJ/mol and a reaction order with respect to the acid concentration of 1.14,the presence of oxalic acid was found to reduce the sensitivity to temperature changes and to increase the effect of changes in acid concentration.Finally,the equation of the kinetic model based on the factors under study is presented.
基金financially supported by the National Basic Research Program of China(Nos.2013CB632601 and 2013CB632604)the National Science Foundation for Distinguished Young Scholars of China(Nos.51125018 and 51504230)+3 种基金the Key Research Program of the Chinese Academy of Sciences(No.KGZD-EW-201-2)the National Natural Science Foundation of China(Nos.51374191,21106167,2160624,and 51104139)the Financial Grant from the China Postdoctoral Science Foundation(Nos.2012M510552 and 2013T60175)the Nonprofit Industry Research Subject of Environmental Projection(No.201509053)
文摘An innovative method for recovering valuable elements from vanadium-bearing titanomagnetite is proposed. This method involves two procedures: low-temperature roasting of vanadium-bearing titanomagnetite and water leaching of roasting slag. During the roasting process, the reduction of iron oxides to metallic iron, the sodium oxidation of vanadium oxides to water-soluble sodium vanadate, and the smelting separation of metallic iron and slag were accomplished simultaneously. Optimal roasting conditions for iron/slag separation were achieved with a mixture thickness of 42.5 mm, a roasting temperature of 1200°C, a residence time of 2 h, a molar ratio of C/O of 1.7, and a sodium carbonate addition of 70 wt%, as well as with the use of anthracite as a reductant. Under the optimal conditions, 93.67% iron from the raw ore was recovered in the form of iron nugget with 95.44% iron grade. After a water leaching process, 85.61% of the vanadium from the roasting slag was leached, confirming the sodium oxidation of most of the vanadium oxides to water-soluble sodium vanadate during the roasting process. The total recoveries of iron, vanadium, and titanium were 93.67%, 72.68%, and 99.72%, respectively.
基金financial support from the National Basic Research Program of China(grant No. 2013CB632603)the Chinese Academy of Sciences(project No.KGCX2-EW215)
文摘The present study investigated the influence of high temperature oxidation and reduction pretreatments on the leaching rate ofPanzhihua ilmenite. The as-pretreated ilmenite was leached with 20% HCI at 105 ℃, The leaching process was controlled by the phases and microstructures that evolved during the pretreatment processes. The leaching kinetics of pure hematite, ilmenite and pseudobrookite were characterized to clarify the phase effect on the iron-leaching rate; the rate of iron leaching occurs in the following order in the HCI solution: hematite (ferric iron) 〉 ilmenite (ferrous iron) 〉〉 pseudobrookite (ferric iron). Therefore, the often-cited notion that ferrous iron dissolves faster in HCl solutions than ferric iron when explaining the pretreatment effects is inaccurate. Moreover, the oxidation pretreatment (at 600-1000 ℃ for 4 h) cannot destroy the dense structure of the Panzhihua ilmenite. Therefore, the influence exerted by the oxidation on the leaching process is primarily determined by the phase change; oxidation at 600 and 700℃ slightly increased the rate of iron leaching because the ilmenite was transformed into hematite, while the oxidation at 900-1000℃ significantly reduced the rate of iron leaching because a pseudobrookite phase formed. The reduction effect was subsequently investigated; the as-oxidized ilmenite was reduced under H2 at 750 ℃ for 30 min. The reduction significantly accelerated the rate of subsequent iron leaching such that nearly all of the iron had dissolved after leaching for 2 h in 20% HCl at 105 ℃. This enhanced iron-leaching rate is mainly attributed to the cracks and holes that formed during the reduction process.
基金supported by Project Supported by the Planned Science and Technology Project of Hunan Province, China(Nos.2011F J3160,2011GK2002)Project Supported by Scientific Research Fund of Hunan Provincial Education Department(10B054)
文摘A hydrometallurgical process for the recovery of cobalt oxalate from spent lithium-ion batteries was used to recycle cobalt compound by using alkali leaching, reductive acid leaching and chemical deposition of cobalt oxalate. The recycled cobalt oxalate was used to synthesize nano-Co3O4 anode material by sol-gel method. The samples were characterized by thermal gravity analysis and differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and charge/discharge measurements. The influence of molar ratio of Co2+ to citric acid and calcination temperature on the structure and electrochemical performance of nano-Co3O4 was evaluated. As the molar ratio of Co2+ to citric acid is 1:1, the face-centered cubic (fcc) Co3O4 powder shows the discharge capacity of 760.9 mA h g-1, the high coulombic efficiency of 99.7% in the first cycle at the current density of 125 mA g-l, and the excellent cycling performance with the reversible capacity of 442.3 mA h g-1 after 20 cycles at the current density of 250 mA g-1.