The recovery of titanium with citric acid in sulfuric acid from red mud was put forward to strengthen acid leaching efficiency.The main factors on the recovery of titanium such as citric acid addition,sulfuric acid co...The recovery of titanium with citric acid in sulfuric acid from red mud was put forward to strengthen acid leaching efficiency.The main factors on the recovery of titanium such as citric acid addition,sulfuric acid concentration,leaching temperature,time and liquid-to-solid ratio were studied.The kinetics analysis of titanium leaching from red mud was deeply investigated.The results show that the citric acid could increase the recovery of titanium and decrease the consumption of sulfuric acid.The recovery of titanium was increased from 65% to 82% and the consumption of sulfuric acid was decreased by about 30% with using 5% citric acid.The dissolution of perovskite,brookite,and hematite in red mud could easily be dissolved using citric acid.The acid leaching process was controlled by internal diffusion of shrinking core model（SCM） and the correlation coefficient was above 0.98.The apparent rate constant was increased from 0.0012 to 0.0019 with 5% citric acid at 90 °C.The apparent activation energy of titanium leaching decreased from 39.77 k J/mol to 34.61 k J/mol with 5% citric acid.展开更多
The accumulation of citric acid and associated correlative strain indexes were investigated in the seedlings of Puccinellia tenuiflora (Griseb.) Scribn. et Merr. stressed with 0-175 mmol/L Na 2CO 3. The results ...The accumulation of citric acid and associated correlative strain indexes were investigated in the seedlings of Puccinellia tenuiflora (Griseb.) Scribn. et Merr. stressed with 0-175 mmol/L Na 2CO 3. The results showed that the citric acid accumulation is a specific physiological respond of this plant to alkali_stress. On the contrary, the citric acid content decreased slightly in this plant stressed with 0-400 mmol/L neutral salt NaCl. The accumulation of citric acid increased with increasing strength of alkali_stress, the citric acid content increased gently when the strength was lower than 100 mmol/L Na 2CO 3, but increased obviously when the strength was higher than 100 mmol/L Na 2CO 3. The citric acid rapidly accumulated at early alkali_stress, an obvious raise can be mensurated after 4 h. About 48 h after treatment, the amount of citric acid accumulated nearly reached the maximum. In various parts of P. tenuiflora seedlings alkali_stressed for 144 h, the order of citric acid content from high to low is: old leaf, mature leaf, old leaf sheath, young leaf sheath, young stem, old stem, and young leaf. In the mature leaf, the citric acid content gradually increased with increasing strength of alkali_stress, while the citric acid content increased sharply in old leaf and sheath just for strength higher than 125 mmol/L. There was little change of citric acid content in stem, but no change in young leaf. The results of the experiment showed that citric acid was outstanding among accumulated organic acid caused by alkali_stress. The contribution of other organic acids was negligible.展开更多
A novel and facile wet-chemical method for synthesis of silver microwires was developed.The well-defined particles were prepared by adding an iron（Ⅱ） sulfate heptahydrate solution into a silver nitrate solution con...A novel and facile wet-chemical method for synthesis of silver microwires was developed.The well-defined particles were prepared by adding an iron（Ⅱ） sulfate heptahydrate solution into a silver nitrate solution containing citric acid drop by drop at 50 °C.The resulting products were characterized by scanning electron microscopy and X-ray diffraction.It was found that the particles consisted of numerous silver microwires.The reaction temperature greatly affected the morphologies of the as-prepared particles.Both of the mean length and width of the silver microwires increased with the decrease of the concentration of silver nitrate.And the lower concentration was unfavorable for the formation of more silver microwires.Similar findings were also observed when the concentration of iron（Ⅱ） sulfate was decreased.The amount of citric acid also greatly affected the shape of the as-prepared particles.It was concluded that citric acid was the key role in the formation of silver microwires via the Oswald ripening mechanism.展开更多
Platinum nanoparticles supported on carbons（Pt/C,60%,mass fraction） electrocatalysts for direct methanol fuel cell（DMFC） were prepared by citrate-stabilized method with different reductants and carbon supports.The...Platinum nanoparticles supported on carbons（Pt/C,60%,mass fraction） electrocatalysts for direct methanol fuel cell（DMFC） were prepared by citrate-stabilized method with different reductants and carbon supports.The catalysts were characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM） and cyclic voltammetry（CV）.It is found that the size of Pt nanoparticles on carbon is controllable by citrate addition and reductant optimization,and the form of carbon support has a great influence on electrocatalytic activity of catalysts.The citrate-stabilized Pt nanoparticles supported on BP2000 carbon,which was reduced by formaldehyde,exhibit the best performance with about 2 nm in diameter and 66.46 m2/g（Pt） in electrocatalytic active surface（EAS） area.Test on single DMFC with 60%（mass fraction） Pt/BP2000 as cathode electrocatalyst showed maximum power density at 78.8 mW/cm2.展开更多
Aluminum capacitor foils with a tunnel etch structure were reacted with boiling water and then anodized at 530 V in boric acid solution or boric acid＋citric acid mixed solution.The microstructure and crystallinity of...Aluminum capacitor foils with a tunnel etch structure were reacted with boiling water and then anodized at 530 V in boric acid solution or boric acid＋citric acid mixed solution.The microstructure and crystallinity of the resulting anodized film were examined by TEM and XRD.The special capacitance,resistance and withstanding voltage of the film were explored with electrochemical impedance spectroscopy（EIS）,LCR meter and small-current charging.The results show that the high voltage anodized oxide film consists of an inner layer with high crystallinity and an outer layer with low crystallinity.However,the crystallinity of the film formed in boric acid＋citric acid mixed solution is higher than that of the film formed in only boric acid solution,leading to an increase in film＇s field strength and special capacitance.Meanwhile,there are more defects from phase transformation in the out layer of the film formed in boric acid＋citric acid mixed solution than in that of film formed in only boric acid solution,leading to a decrease in film＇s resistance and withstanding voltage.展开更多
Effects of citrate concentration and pH on the electrochemical reduction process of Co（Ⅱ） were investigated by cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）. The results show that Co（...Effects of citrate concentration and pH on the electrochemical reduction process of Co（Ⅱ） were investigated by cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）. The results show that Co（Ⅱ） is reduced into two species which are free Co2＋ and [Co（C6H607）] in the solution composed of 0.05 mol/L CoS04·5H2O, 0.20 mol/L Na2SO4 and 0-0.40 mol/L C6H5O7Na3·2H2O in the pH range of 3-9. The reduction behavior depends on the pH of the solution. Co（H） is mainly reduced into the form of free Co^2＋ at pH 3 and into the form of [Co（C6H6O7）] at the pH range of 4-6 in citrate solution. The [Co（C6H6O7）] is first reduced to an intermediate state and then to Co°. Adsorption of the intermediate state exists on the surface of the electrode. Co（Ⅱ） is difficult to be reduced in the solution with the pH above 7, because the existing Co（Ⅱ）-citrate complex species [Co（C6H5O7）]- and [Co（C6H4O7）]2- are more difficult to be reduced than the hydrogen ion.展开更多
基金Project(B2014-012)supported by the Doctoral Foundation from Henan Polytechnic University,China
文摘The recovery of titanium with citric acid in sulfuric acid from red mud was put forward to strengthen acid leaching efficiency.The main factors on the recovery of titanium such as citric acid addition,sulfuric acid concentration,leaching temperature,time and liquid-to-solid ratio were studied.The kinetics analysis of titanium leaching from red mud was deeply investigated.The results show that the citric acid could increase the recovery of titanium and decrease the consumption of sulfuric acid.The recovery of titanium was increased from 65% to 82% and the consumption of sulfuric acid was decreased by about 30% with using 5% citric acid.The dissolution of perovskite,brookite,and hematite in red mud could easily be dissolved using citric acid.The acid leaching process was controlled by internal diffusion of shrinking core model（SCM） and the correlation coefficient was above 0.98.The apparent rate constant was increased from 0.0012 to 0.0019 with 5% citric acid at 90 °C.The apparent activation energy of titanium leaching decreased from 39.77 k J/mol to 34.61 k J/mol with 5% citric acid.
文摘The accumulation of citric acid and associated correlative strain indexes were investigated in the seedlings of Puccinellia tenuiflora (Griseb.) Scribn. et Merr. stressed with 0-175 mmol/L Na 2CO 3. The results showed that the citric acid accumulation is a specific physiological respond of this plant to alkali_stress. On the contrary, the citric acid content decreased slightly in this plant stressed with 0-400 mmol/L neutral salt NaCl. The accumulation of citric acid increased with increasing strength of alkali_stress, the citric acid content increased gently when the strength was lower than 100 mmol/L Na 2CO 3, but increased obviously when the strength was higher than 100 mmol/L Na 2CO 3. The citric acid rapidly accumulated at early alkali_stress, an obvious raise can be mensurated after 4 h. About 48 h after treatment, the amount of citric acid accumulated nearly reached the maximum. In various parts of P. tenuiflora seedlings alkali_stressed for 144 h, the order of citric acid content from high to low is: old leaf, mature leaf, old leaf sheath, young leaf sheath, young stem, old stem, and young leaf. In the mature leaf, the citric acid content gradually increased with increasing strength of alkali_stress, while the citric acid content increased sharply in old leaf and sheath just for strength higher than 125 mmol/L. There was little change of citric acid content in stem, but no change in young leaf. The results of the experiment showed that citric acid was outstanding among accumulated organic acid caused by alkali_stress. The contribution of other organic acids was negligible.
基金Project (2011CDC114) supported by the Hubei Provincial Natural Science Foundation of China
文摘A novel and facile wet-chemical method for synthesis of silver microwires was developed.The well-defined particles were prepared by adding an iron（Ⅱ） sulfate heptahydrate solution into a silver nitrate solution containing citric acid drop by drop at 50 °C.The resulting products were characterized by scanning electron microscopy and X-ray diffraction.It was found that the particles consisted of numerous silver microwires.The reaction temperature greatly affected the morphologies of the as-prepared particles.Both of the mean length and width of the silver microwires increased with the decrease of the concentration of silver nitrate.And the lower concentration was unfavorable for the formation of more silver microwires.Similar findings were also observed when the concentration of iron（Ⅱ） sulfate was decreased.The amount of citric acid also greatly affected the shape of the as-prepared particles.It was concluded that citric acid was the key role in the formation of silver microwires via the Oswald ripening mechanism.
基金Project(50573041)supported by the National Natural Science Foundation of China
文摘Platinum nanoparticles supported on carbons（Pt/C,60%,mass fraction） electrocatalysts for direct methanol fuel cell（DMFC） were prepared by citrate-stabilized method with different reductants and carbon supports.The catalysts were characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM） and cyclic voltammetry（CV）.It is found that the size of Pt nanoparticles on carbon is controllable by citrate addition and reductant optimization,and the form of carbon support has a great influence on electrocatalytic activity of catalysts.The citrate-stabilized Pt nanoparticles supported on BP2000 carbon,which was reduced by formaldehyde,exhibit the best performance with about 2 nm in diameter and 66.46 m2/g（Pt） in electrocatalytic active surface（EAS） area.Test on single DMFC with 60%（mass fraction） Pt/BP2000 as cathode electrocatalyst showed maximum power density at 78.8 mW/cm2.
基金Project supported by University New Materials Disciplines Construction Program of Beijing Region
文摘Aluminum capacitor foils with a tunnel etch structure were reacted with boiling water and then anodized at 530 V in boric acid solution or boric acid＋citric acid mixed solution.The microstructure and crystallinity of the resulting anodized film were examined by TEM and XRD.The special capacitance,resistance and withstanding voltage of the film were explored with electrochemical impedance spectroscopy（EIS）,LCR meter and small-current charging.The results show that the high voltage anodized oxide film consists of an inner layer with high crystallinity and an outer layer with low crystallinity.However,the crystallinity of the film formed in boric acid＋citric acid mixed solution is higher than that of the film formed in only boric acid solution,leading to an increase in film＇s field strength and special capacitance.Meanwhile,there are more defects from phase transformation in the out layer of the film formed in boric acid＋citric acid mixed solution than in that of film formed in only boric acid solution,leading to a decrease in film＇s resistance and withstanding voltage.
基金Project(200800560002)supported by the Ph.D.Programs Foundation of Ministry of Education of China
文摘Effects of citrate concentration and pH on the electrochemical reduction process of Co（Ⅱ） were investigated by cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）. The results show that Co（Ⅱ） is reduced into two species which are free Co2＋ and [Co（C6H607）] in the solution composed of 0.05 mol/L CoS04·5H2O, 0.20 mol/L Na2SO4 and 0-0.40 mol/L C6H5O7Na3·2H2O in the pH range of 3-9. The reduction behavior depends on the pH of the solution. Co（H） is mainly reduced into the form of free Co^2＋ at pH 3 and into the form of [Co（C6H6O7）] at the pH range of 4-6 in citrate solution. The [Co（C6H6O7）] is first reduced to an intermediate state and then to Co°. Adsorption of the intermediate state exists on the surface of the electrode. Co（Ⅱ） is difficult to be reduced in the solution with the pH above 7, because the existing Co（Ⅱ）-citrate complex species [Co（C6H5O7）]- and [Co（C6H4O7）]2- are more difficult to be reduced than the hydrogen ion.
