Optimization in the Treatment of Spent Pot Lining and Enriching of Its Carbon Percentage by Hydrochloric Acid Leaching

Abstract

Due to a rise in demand of aluminium, the undesirable production of Spent Pot Lining in the Hall-Heroult process has been increasing side-by-side, owing to added environmental problems. The aim of this project is to optimize the process parameters so as to enrich maximum amount of graphitic carbon from Spent Pot Lining, by using sodium hydroxide followed by hydrochloric acid for the first time. The Taguchi method approach for optimization was adopted and significant process parameters such as temperature, alkali concentration, acid concentration and L/S ratio were optimized. Characterization of the various SPL samples was also done to qualify and quantify the samples, using XRD, SEMEDX, FESEM-EDX, CHNS analysis. The carbon percentage of SPL was increased from 43.39% to 70.44% which was confirmed from the ultimate analysis. From EDX data analysis, the carbon percentage was increased from 33.27% to 86.78%. Alkali concentration contributed 47.27% in the leaching process among the four factors, while acid concentration contributed only 1.02 %. The maximum leaching percentage was found to be 54.11% from experimentation. Finally, the analysis of the leaching capacity of four acids, HClO4, H2SO4, HNO3 and HCl was done graphically and comparisons were made.