Synthesis of nanosized Sm and Co oxides by liquid-liquid extraction scheme and investigation into separation chemistry employing tri-alkyl phosphine oxide as an extractant

Rare earth and transition metal-based permanent magnets are the jewels of smart and emerging technologies. Due to the increase in their demand in the industrial market, these metals will be at supply risk in near future. Spent Sm-Co magnets are the potential sources of Sm and Co, and recycling of these magnets is an alternative goal to sustain their resources. This present extraction investigation has been designed with an aim to avoid the use of high concentration of acids to reduce pollution and also to maintain sustainability. The solvent extraction process is executed with an organic solvent tri-alkyl phosphine oxide. This extractant has pronounced selectivity towards samarium resulting in complete separation of Sm/Co. By using 0.1 mol/L TAPO, Sm3+ was selectively extracted from the mother liquor containing Co2+, 3 mol/L NaNO3 at pH 3 and 1:1 organic-to-aqueous phase volume ratio. The extraction equilibrium was spontaneous and adversely affected by temperature. Cent per cent recovery of samarium was achieved with 0.2 mol/L HCl. From the stripped liquor, samarium oxide was recovered and cobalt oxide was reclaimed from the raffinate. With an increase in calcination time, the crystalline size of Sm2O3 and Co3O4 becomes finer. Regeneration studies revealed that tri-alkyl phosphine oxide could be reused for several cycles with an insignificant change in the extraction efficiency.

Automated summary

This study aims to recycle rare earth and transition metals to reduce supply risks. Using organic solvent extraction achieved complete separation of samarium and cobalt. Experimental results show that 100% recovery of samarium can be achieved through specific conditions.