ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

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

Nilam Swain and Sujata Mishra

Department of Chemistry, Institute of Technical Education and Research (FET), Siksha ‛O’ Anusandhan Deemed To Be University, Bhubaneswar, India

E-mail: drsujatamishra97@gmail.com

Received: 14 May 2021  Accepted: 2 October 2021

Abstract:

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.

Keywords: TAPO; Separation; Sm; Co; Simulated waste

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-021-01918-y

Chemical Papers 76 (2) 945–959 (2022)