Recovery of metallic zinc in waste zinc carbon batteries by hydrometallurgical method

In this study, the dissolution and kinetics, and the optimal dissolution conditions of metallic zinc in waste zinc-carbon batteries were determined in nitric acid solution. The effects of the experimental parameters on the dissolution of metallic zinc in nitric acid solutions were examined, and a mathematical model to represent the dissolution kinetics was purposed. The effects of the concentration of nitric acid, amount of metallic zinc (solid to liquid ratio), reaction temperature and stirring speed on the dissolution process were investigated. It was observed that the dissolution rate of zinc increased with increasing nitric acid concentration, stirring speed and reaction temperature and with decreasing solid to liquid ratio. A kinetic analysis using data obtained from the dissolution experiments was made, and it was found that the dissolution rate fit to the pseudo-first order kinetic. The activation energy for the dissolution process was found to be 12.89 kJ/mol, and it was determined that it was controlled by diffusion. Zinc ions in the resulting solution after the dissolution of metallic zinc was recovered by precipitation method. For this aim, sodium bicarbonate solution was used, and it was determined that zinc ions was precipitated as zinc hydroxy carbonate compound. In the precipitation process, pH, molar ratio of zinc/sodium bicarbonate, reaction time, and reaction temperature were taken to be 8, 1/2.5, 240 min, and 60 °C, respectively. Under these conditions, it was determined that zinc ions in the solution were fully recovered. Hydroxy carbonate compound obtained was subjected to the calcination process at a temperature of 300 °C for 4 h, and zinc oxide was produced. In the experiments performed to determine the optimal dissolution conditions, the concentration of nitric acid, reaction time, and zinc amount were selected as independent variables. The response surface method (RSM) was utilized to optimize the parameter values that have an effect on the dissolution of metallic zinc. To see the interactive effects of process variables, the multiple regression analysis to the experimental findings was performed, and a model equation was derived. At the end of the tests, it was found that the dissolution efficiency increased with an increase in the concentration of nitric acid and reaction time, and with a decrease in the amount of zinc.