Abstract
Coal ash (CA) is the waste material produced from the burning of coal for power generation. Coal ash is a hazardous waste, and its disposal requires careful consideration. Large quantities of CA have accumulated in Canada and globally due to coals prolonged and ongoing use. Coal ash is widely used as supplementary cementitious material to replace ordinary Portland cement, resulting in significant GHG reductions from the cement production industry. Prior to its use in cement, CA can be utilized for valuable metal recovery as it contains critical metals such as scandium. Coal ash can be acid leached for the recovery of scandium; the CA leach residue can then still be utilized for cement resulting in virtually no waste. CanmetMINING is developing a process to recover scandium from Canadian CA using acid leaching followed by a solvent extraction (SX) process. The pregnant leach solution (PLS) contains a few ppm of scandium and high concentrations of other elements. Solvent extraction can be used to selectively recover scandium while leaving the other elements in the PLS. Results indicate that scandium can be effectively leached from CA into the PLS. Scandium is then almost completely extracted from the PLS by SX. Impurities that are co-extracted with scandium can be removed with scrubbing and selectivity can be enhanced with the addition of complexing agents into the PLS. The scandium can then be stripped, and a scandium product can be produced. Further testing on the SX stripping solution is required to obtain highly pure scandium. Currently, results have been obtained from bench-scale batch experiments. Additional work including scaling up the process and performing continuous flow testing is required to advance to the overall pilot-plant operation objective.