Preparation Of Aurous-Cysteine None-cyanide Composition And Study On Its Gold-plated Performance

With the transfer of the international processing industry and the domestic industrial structure, the amount of Cyanide composition in the electroplating industry has been increasing year by year, which poses a potential and serious threat on ecological environment in China. The cyanide gold plating plays a irreplaceable role in industry. Though our country has been making rules and regulations to control and manage the selling and using of the cyanide, the non-cyanide gold plating has never been reaching its goal of industrialization.The purpose of this thesis is to synthesize a new kind of cyanide-free and water-soluble complex, using amino acid as ligand. At the same time, we characterize this kind of composition and study on its stability constant, then carry out research on the electrogilding performance of the aurous solution. And the complex of aurous is expected to instead of the transitional cyanide gold plating liquid which is posses of highly toxic element heavily polluting the environment.The research could be divided into several parts and shown as follows:(1) We use "selective reduction and the exchanges of ligand method" to synthesize the cyanide-free water soluble aurous complex and characterizing it.(2) investigating the influence of concentration of cysteine solution n(Au/HCys)and pH on the combining of aurous complex and finding the optimal condition. At the same time, we study on the stability of cyanide-free complex solution.(3) Exploring the optimal process conditions of the intermediate products-double Thoreau aurous.(4) making a comparative research on the stability constants of the complex of Au(Cys)2.(5) studying the electrogilding of KAu(Cys)2solution and investing the influence factor such as time, pH, electrical current density, temperature and concentration of the ligand influencing the planting rate and the apparent form of the cladding material,and further searching the optimum technological condition.The conclusions are:(1) After using the method including the ultraviolet spectroscopy、infra-red spectrum and elemental analysis to charaterize such complex, we can get the result that the molecular formula of cyanide-free aurous complexes is KAu(Cys)2,And its water-solution is perfect. The molar conductivity is430 S-cm2·mol-1,Thermal decomposition temperature is80℃.(2) After we carry on experiment of the comparative research method, we can make the conclusion that the stability constant of Au(Cys)2-range from1030(Na3Au(SO3)2) to1038(NaAu(CN)2).(3) The optimal condition of The double thiourea aurous:the chloroauric acid is25mg/ml、 the thiourea is20mg/ml, the temperature is50℃, the concentration ration is2.5, the temperature of crystallization is0℃.(4) The optimal condition of KAu(Cys)2: n(Au/HCys)=5:1, cysteine is30mg/ml, pH=9, and temperature is50℃, the concentration ration is2.5, the temperature of crystallization is0℃.(5) It is a appropriate way to keep away from sunshine to save the cyanide-free aurous solution and its temperature stays in less than65℃and its pH number ranging from7-9.(6) The optimal condition of electrogilding are:gold solution concentration is2g/L, current density is1.0A/dm2, concentration of ligand0.5mol/L, temperature is50℃, operation time is1.5min, pH9. Under this condition,the coating color and the binding force appears in a good and fine stateThe research shows that cyanide-free plating fluid system is mainly based on the KAu(Cys)2. it is not only meets the requirement of the zedoary process,but also can be used to replace the highly toxic chemical from environmental view. And that the cyanide-free plating fluid system which can reduce the harm to the environment and bring favorable influence in its wake can serve as a environmental products widely used.