Leaching characteristics of rare earth elements from coal ash using organosulphonic acids

Extraction of valuable REEs from end of life products like coal ash is a viral topic. The potency of organosulphonic acids in leaching out REEs from coal ash matrix has not been exploited till date. In the present study, the leaching potential of methanesulphonic acid and p-toluenesulphonic acid was compared towards extraction of REEs from coal ash. The optimized conditions for extraction were determined to be at a temperature of 90 degrees C, for duration of 60 min in a liquid to solid ratio 100 at stirring speed of 600 rpm. At 0.5 M acid concentration, LREE was leached out in about 65-70% yield whereas HREEs could be only extracted in about 15-20% yield. XRD diffraction studies revealed that the leaching with organosulphonic acids did not destroy the aluminosilicate matrix of coal ash. MSA imparted good selectivity in leaching, wherein, it leached out 70% of REE along with minimal quantities of other coal ash elements (<10%). The leaching kinetics studies under varying temperature concluded the process to be diffusion controlled, following the shrinking core model. The leaching potency of organosulphonic acid was found to be at par with mineral acids (HNO3 and HCl), and hence it could be considered as a green alternative to mineral acids which are conventionally widely used in REE extraction from coal ash wastes.