Study On Electrowinning Nickel From A Leaching Solution Containing Ammonia

In this paper, the process of nickel electrodeposition was studied in three different baths by the various experimental conditions. The results show that dense nickel layer is electrodeposited in leaching solution containing ammonia and chloride, moreover, the current efficiency in its bath is above 90%. While nickel layer prepared in leaching solution containing ammonia and sulfate or carbonate prones to crack, the current efficiency is relatively low in both baths. Therefore, the optimized parameters in leaching solution containing ammonia and chloride, i.e., temperature 50癈, current density 400A籱~2, were determined.According to the principles of simultaneous equilibrium, equilibrium concentration of each specie in Ni (II )-NH3-NH4Cl-H2O system was calculated with computation method, and its application in the study of electro-crystallization mechanism was also introduced concisely.In the subsequent studies, kinetics law of nickel electrodeposition from leaching solution containing ammonia and chloride was investigated in terms of steady-state polarization curves. The electrochemical behavior of cathodic electrodeposition of nickel was studied by measuring polarization curves. The mechanisms of anodic reaction were demonstrated initially in terms of X-ray diffraction .cyclic voltammetry, vapor phase chromatograph. It is elucidated that anodic production is high valent nickel compound in the process of electrodeposition in terms of X-ray diffraction andchemical analysis. The amount of solid production formed on the electrode surface decreases with an increase in ammonium chloride concentration, increases with an increase in NiCl2-H2O concentration, and increases first, then decreases with decreasing in ammonia concentration by cyclic voltammetry analysis.. The amount of black nickel reaches the highest level when ammonia concentration is controlled at 1.00mol.L-1. It is proved by vapor phase chromatograph that the anodic gas species is mainly nitrogen.The process of nickel electrodeposition from leaching solution containing ammonia and sulfate was investigated by using differential anodic electrode. The gas species formed on anode was determined by vapor phase chromatograph, and then kinetics law of nickel electrodeposition from leaching solution containing ammonia and sulfate was studied in terms of steady-state polarization curves.Owing to the Ti based IrO2+Ta2O5 anode's superior property in leaching solution containing ammonia and sulfate, its morphology prepared under the different process was observed by means of scanning electron microscope(SEM), kinetics process of anode gas evolution was also investigated in terms of cyclic voltammetric technique.