Selective extraction and recovery of rare earth elements from coal fly ash by carboxylated mesoporous carbon

The separation of Rare Earth Elements (REEs) from non-conventional sources is very critical to maintain the supply-chain balance of REEs in the Western world. Despite Coal Fly Ash (CFA) being designated as a prominent non-conventional source of REEs and several studies have reported on the extraction of REEs from CFA, the selectivity of REEs with respect to non-REEs in the CFA has never been reported. In this work, for the time, we have reported the selectivity of REEs over non-REEs using carboxylated mesoporous carbon (CMC) as the sorbent. The CMC was produced by carboxylating the soft-templated mesoporous carbon and then it was characterized successfully for porosity, FTIR, and SEM-EDX. The leachate produced from REEs contains 16 REEs and 20 non-REEs from groups 1 through 3 and 6 through 15 of the modern periodic table. The REEs were extracted within 80-90% in the 3 cycles along with the elements from groups of 1,3, 5, 8, and 11. Although a few other elements were also extracted, the values of the distribution coefficient confirmed that the CMC has a much higher affinity towards REEs except the non-REEs from groups 1 and 3. In the recovery mode, the REEs were recovered in the range of 20-100%, and heavier REEs demonstrated a better recovery. The recovery percent of non-REEs was also much lower compared to that of REEs, except for the elements from groups 3, 8, and 11. The non-REEs from group 3 demonstrated the highest competition, which can be attributed to the fact the REEs also belong to the same group of the periodic table. The ratio of extracted and recovered REEs over non-REEs was always greater than unity, suggesting that the CMC was selective towards REEs over non-REEs in extraction and recovery. The overall results suggest that CMC can potentially be used for selective extraction and recovery of REEs from coal fly ash.