Recycling of spent pot lining (SPL) from aluminum smelters by water leaching

Spent pot lining (SPL) is a solid waste produced at the end of life of aluminum reduction cells. SPL is hazardous to the environment due to fluoride and cyanide compounds and is classified as toxic waste. Recovering the fluorine compounds in SPL can be used to eliminate the toxicity in these wastes and return part of the production costs, turning their carbon residues into purer materials for use in the steel and cement industry as fuel feed. In this research, sodium fluoride (NaF) contained in SPL was recovered with high purity using the water leaching process. The results of EDS analysis showed that water leaching was able to remove sodium and fluoride to a large extent and their amounts in SPL powder after the leaching process reached 0.17% and 0.21%, respectively. SEM images showed that the average particle size for recycled sodium fluoride was about 1.89 µm, and the average size of dispersed finer particles was about 451 nm. TEM images exhibited sheet-like particles having dimensions varying from 250 nm to 2.1 μm, accompanied by spherical and rod-like impurities. The optimal conditions obtained for the leaching process included a temperature of 85 °C, a stirring time of 30 min, and a ratio of liquid to solid of 10:1. According to the XRD analysis taken from the SPL powder after the leaching process, all the peaks related to sodium fluoride were removed. Some peaks related to compounds such as CaF2 and Na3AlF6 were removed, or their intensity was reduced. The results show that sodium fluoride is wholly recovered, other fluoride compounds are reduced, and the purity of the remaining graphite is increased.