In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coa...In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coating on Mg alloy AZ91D, the process of copper transition coating plated in the cyanides bath can be replaced. A new bath composed of NiSO4 was established by orthogonal test. The results show that zinc transition coating can increase the adhesion and protect the Mg alloy substrate from the bath corrosion. The optimal plating bath composition is NiSO4·6H2O 20 g/L, NaH2PO2·H2O20g/L and C6H8O7·H2O 2.5 g/L, and optimal bath acidity and optimal plating temperature are pH 4.0 and 95℃, respectively. The present process flow is composed of ultrasonic cleaning→alkaline cleaning→acid pickling→activation→double immersing zinc→electroplating zinc→electroless nickel plating→passivation treatment. The present non-cyanide process of electroless nickel plating is harmless to our surroundings and Ni-P coating on Mg alloy AZ91D produced by present process possesses good adhesion and corrosion resistance.展开更多
The effects of non-cyanide zincation process parameters on the microstructure of the zincation layer on A356 alloy were investigated by scanning electronic microscope.With the increasing of zincation time,the zinc gra...The effects of non-cyanide zincation process parameters on the microstructure of the zincation layer on A356 alloy were investigated by scanning electronic microscope.With the increasing of zincation time,the zinc grain size and the number density increase gradually,and the zinc grains adhere each other.The zinc grain obtained in the double-dipping process is finer,compacter and more homogeneous than that obtained in the single-dipping process.With the increasing of the zincation temperature,the morphology of zinc grains changes from spherical shape to flake-like shape.However,higher zincation temperature results in the flaking off of the zincation layer from the matrix.The optimized zincation temperature is 20-30 ℃.The quality of the zincation layer obtained in a low concentration,non-cyanide and multi-element zincation solutions is much better than these obtained in conventional high concentration zincation solution,dilute zincation solutions or a dilute zincation solution containing nickel.In addition,the matrix alloy and the pre-treatment also have significant influence on the morphology of the zincation layer.展开更多
The thermodynamic equilibria and kinetic aspect of gold dissolution in iodine-iodide leaching were studied with emphasis on the effects of pH value and temperature on the system.The results of thermodynamic analysis o...The thermodynamic equilibria and kinetic aspect of gold dissolution in iodine-iodide leaching were studied with emphasis on the effects of pH value and temperature on the system.The results of thermodynamic analysis of iodine in aqueous solution were given and numerous forms of iodine exist mainly in the acid region of pH values.An increase of the potential of the system results in an increase of iodine speciation.The oxidizing potential of the system will increase by the addition of element iodine.The IO^(3-)anions are stable in the potential range from-2.0 to-0.75 V and at pH value greater than 12.1.An increase of the temperature shifts boundaries of existence of various iodine species in the acid region of pH values.Some of them become unstable.The determined values of the diffusion coefficients and the thickness of the diffusion boundary layer,as well as the solvent concentration on the disc surface(14 mg/L) indicate that the process proceeds in the external diffusion region.Thus,while choosing the conditions of leaching from gold-containing materials of different origins of iodide solvents,it is necessary to carry out the process within the acidic region of pH values,where I^-,I_3^- and IO_4^- ions are capable to form complex compounds with metals.展开更多
Effective silver recovery is usually restricted by either environmental pollution or high recovery costs. To tackle the issues, this study introduces a novel method for the effective recovery of silver by utilizing th...Effective silver recovery is usually restricted by either environmental pollution or high recovery costs. To tackle the issues, this study introduces a novel method for the effective recovery of silver by utilizing the alkaline sodium thiosulfate-potassium ferricyanide leaching system. The reaction kinetics of silver dissolution in this system was investigated via the rotating disk electrode technology. The influences of important parameters, including the rotation speed, sodium thiosulfate concentration, potassium ferricyanide concentration, and temperature, on the silver dissolution rate were systematically investigated. The activation energy was measured to be 17.96 kJ·mol^(-1) when the silver dissolution was controlled by a diffusion process. When the silver dissolution was in the region of mixed control, the reaction orders of ferricyanide and thiosulfate were found to be 0.57 and 0.19, respectively, and the reaction orders of ferricyanide and thiosulfate were 0.55 and 0.22, respectively, when the silver dissolution was controlled by surface reaction. This study has great potential for the development of an environmentally friendly silver recovery process from end-of-life products.展开更多
The dissolution of silver with thiosulfate and copper ions was studied in a batch-stirred reactor at 25 °C in the absence and presence of various ammonium ions and oxygen concentrations in the aqueous solution. L...The dissolution of silver with thiosulfate and copper ions was studied in a batch-stirred reactor at 25 °C in the absence and presence of various ammonium ions and oxygen concentrations in the aqueous solution. Leaching silver with 4 mg L-1oxygen in the aqueous solution requires high concentration of ammonium and thiosulfate ions. High silver dissolution is achieved at pH of high cupric tetraamine concentration, around pH 9.8, but a high degradation of thiosulfate ions is resulted from their oxidation by the presence of oxygen. When the oxygen concentration is below 1 mg L-1, dissolved silver thiosulfate species are fairly stable and the degradation of thiosulfate ions in the aqueous solution is low. Under these conditions,high silver dissolution is attained using low thiosulfate concentration. At the oxygen concentration of 4 mg L-1,dissolved silver thiosulfate species precipitate out of the aqueous solution significantly affecting silver dissolution.Precipitation of dissolved silver thiosulfate species occurs because of oxidation of the thiosulfate bonding to the silver.展开更多
文摘In this research we presented a non-cyanide plating process of Ni-P alloy coating on Mg alloy AZ91D. By applying a new process flow of electroless nickel plating in which zinc coating is used as transition of Ni-P coating on Mg alloy AZ91D, the process of copper transition coating plated in the cyanides bath can be replaced. A new bath composed of NiSO4 was established by orthogonal test. The results show that zinc transition coating can increase the adhesion and protect the Mg alloy substrate from the bath corrosion. The optimal plating bath composition is NiSO4·6H2O 20 g/L, NaH2PO2·H2O20g/L and C6H8O7·H2O 2.5 g/L, and optimal bath acidity and optimal plating temperature are pH 4.0 and 95℃, respectively. The present process flow is composed of ultrasonic cleaning→alkaline cleaning→acid pickling→activation→double immersing zinc→electroplating zinc→electroless nickel plating→passivation treatment. The present non-cyanide process of electroless nickel plating is harmless to our surroundings and Ni-P coating on Mg alloy AZ91D produced by present process possesses good adhesion and corrosion resistance.
文摘The effects of non-cyanide zincation process parameters on the microstructure of the zincation layer on A356 alloy were investigated by scanning electronic microscope.With the increasing of zincation time,the zinc grain size and the number density increase gradually,and the zinc grains adhere each other.The zinc grain obtained in the double-dipping process is finer,compacter and more homogeneous than that obtained in the single-dipping process.With the increasing of the zincation temperature,the morphology of zinc grains changes from spherical shape to flake-like shape.However,higher zincation temperature results in the flaking off of the zincation layer from the matrix.The optimized zincation temperature is 20-30 ℃.The quality of the zincation layer obtained in a low concentration,non-cyanide and multi-element zincation solutions is much better than these obtained in conventional high concentration zincation solution,dilute zincation solutions or a dilute zincation solution containing nickel.In addition,the matrix alloy and the pre-treatment also have significant influence on the morphology of the zincation layer.
文摘The thermodynamic equilibria and kinetic aspect of gold dissolution in iodine-iodide leaching were studied with emphasis on the effects of pH value and temperature on the system.The results of thermodynamic analysis of iodine in aqueous solution were given and numerous forms of iodine exist mainly in the acid region of pH values.An increase of the potential of the system results in an increase of iodine speciation.The oxidizing potential of the system will increase by the addition of element iodine.The IO^(3-)anions are stable in the potential range from-2.0 to-0.75 V and at pH value greater than 12.1.An increase of the temperature shifts boundaries of existence of various iodine species in the acid region of pH values.Some of them become unstable.The determined values of the diffusion coefficients and the thickness of the diffusion boundary layer,as well as the solvent concentration on the disc surface(14 mg/L) indicate that the process proceeds in the external diffusion region.Thus,while choosing the conditions of leaching from gold-containing materials of different origins of iodide solvents,it is necessary to carry out the process within the acidic region of pH values,where I^-,I_3^- and IO_4^- ions are capable to form complex compounds with metals.
基金financially supported by the Key Research Program of the Chinese Academy of Sciences (No. ZDRW-ZS-2018-1-2)the the Material Chemistry and Engineering Group, Institute of Process Engineering, Chinese Academy of Sciences
文摘Effective silver recovery is usually restricted by either environmental pollution or high recovery costs. To tackle the issues, this study introduces a novel method for the effective recovery of silver by utilizing the alkaline sodium thiosulfate-potassium ferricyanide leaching system. The reaction kinetics of silver dissolution in this system was investigated via the rotating disk electrode technology. The influences of important parameters, including the rotation speed, sodium thiosulfate concentration, potassium ferricyanide concentration, and temperature, on the silver dissolution rate were systematically investigated. The activation energy was measured to be 17.96 kJ·mol^(-1) when the silver dissolution was controlled by a diffusion process. When the silver dissolution was in the region of mixed control, the reaction orders of ferricyanide and thiosulfate were found to be 0.57 and 0.19, respectively, and the reaction orders of ferricyanide and thiosulfate were 0.55 and 0.22, respectively, when the silver dissolution was controlled by surface reaction. This study has great potential for the development of an environmentally friendly silver recovery process from end-of-life products.
基金Research and Technology Development Center, Administrative Services of Pennoles for the financial support of this Research Project
文摘The dissolution of silver with thiosulfate and copper ions was studied in a batch-stirred reactor at 25 °C in the absence and presence of various ammonium ions and oxygen concentrations in the aqueous solution. Leaching silver with 4 mg L-1oxygen in the aqueous solution requires high concentration of ammonium and thiosulfate ions. High silver dissolution is achieved at pH of high cupric tetraamine concentration, around pH 9.8, but a high degradation of thiosulfate ions is resulted from their oxidation by the presence of oxygen. When the oxygen concentration is below 1 mg L-1, dissolved silver thiosulfate species are fairly stable and the degradation of thiosulfate ions in the aqueous solution is low. Under these conditions,high silver dissolution is attained using low thiosulfate concentration. At the oxygen concentration of 4 mg L-1,dissolved silver thiosulfate species precipitate out of the aqueous solution significantly affecting silver dissolution.Precipitation of dissolved silver thiosulfate species occurs because of oxidation of the thiosulfate bonding to the silver.
