Optimization in the treatment of spent pot lining - a hazardous waste made safe

Abstract

The increase in demand of aluminium leads to production of more Spent Pot Lining as well as more environmental problems. The objective of this study is to optimize the process parameters so as to get the maximum amount graphitic carbon by employing sodium hydroxide fallowed by percholoric acid and sodium hydroxide fallowed by sulfuric acid for the first time. Both “one factor at a time” and “taguchi method”, “Response Surface Methodology” approaches for optimization have been adopted to get the significant process parameters such as alkali concentration, acid concentration, L/S ratio and temperature. A feasibility study was also conducted in cryolite precipitation at two different pH. XRD, SEM-EDX, proximate and ultimate analysis were done on the SPL samples for mineralogical as well as elemental analysis. The carbon percentage of SPL has been increased from 42.19 to 87.03% as confirmed from the ultimate analysis. From the proximate analysis, the fixed carbon for perchloric acid treatment was found to be increase from 38.96% to 82.86 % from the raw to final treated SPL and for sulfuric acid treatment fixed carbon was found out to be increase from 38.96% to be 78.68%. From the calorific value determination it is seen that the heating value of raw SPL (2865.041 cal/g) has substantially increased to 6533.647 cal/g and 6689.694 cal/g respectively by using perchloric acid and sulfuric acid.