Liquid-liquid extraction of cobalt(II) and zinc(II) from aqueous solutions using novel ionic liquids as an extractants

Extraction efficiencies of Co(II) and Zn(II) from aqueous phase with new ionic liquids (ILs) in comparison with already studied in literature ILs, but without addition of acids and at low temperatures are presented. Thus the new, environmental-friendly method of extraction of metal ions is proposed. A novel ammonium ILs, benzyldimethyloctadecylammonium bis(2,4,4-trimethylpentyl)phosphinate [N-Bz,N-1,N-1,N-18][BTMPP], didecyldimethylammonium saccharinate, [N-10,N-10,N-1,N-1][SACH] and didecyldimethylammonium acesulfamate, [N-10,N-10,N-1,N-1][ACE] were synthesized and used between others for this extraction. The solvent extraction behavior was compared to well known in this process ILs: methyltrioctylammonium chloride ([N-8,N-8,N-8,N-1][Cl]), Aliquat 336, trihexyltetradecylphosphonium chloride, ([P-6,P-6,P-6,P-14][Cl]), Cyphos IL 101 and trihexyltetradecylphosphonium bis (2,4,4-trimethylpentyl)phosphinate, ([P-6,P-6,P-6,P-14][BTMPP]). Extraction was provided with pure ILs and with addition of complexion agents, such as: 18-crown-6, 24-crown-8, alkanes C24H50, C27H56, Triton TM X-100 and L-histidine. It was shown that quick and efficient extraction, where N90% of Co(II) and Zn(II) may be obtained using pure IL, or with additives, using synergistic effects of mixture of two ILs, or using ILs in Aqueous Biphasic Systems (ABS) method with NaCl at low temperature T = 303 K. The tributyltetradecylphosphonium chloride, [P-4,P-4,P-4,P-14][Cl], tetraoctylphosphonium bromide, [P-8,P-8,P-8,P-8][Br], and benzalkonium chloride [N-Bz,N- 1,N-1,N-R][Cl] (R = C12H25-60%; C14H29-40%) were used in ABS experiment. The extraction behavior was carried out also using Deep Eutectic Solvents, DES non miscible with water, which presented lower efficiency. The extraction process confirmed the large efficiency and distribution ratio using [P-6,P-6,P-6,P-14][BTMPP] with addition of 18-Crown-6 at pH = 7 for Co(II), as well as using Cyphos IL 101 ([P-6,P-6,P-6,P-14][Cl]) with addition of 18-crown-6, or Triton TM X-100, or L-histidine at pH 1 (no addition of acid) for Zn(II). The same results for Zn(II) were obtained with ABS method with {[P-4,P-4,P-4,P-14][ Cl] + NaCl + Zn (II)}. However, the best results were obtained with trihexyltetradecylphosphonium thiocyanate, [P-6,P-6,P-6,P-14][SCN] for both metal ions. (C) 2020 Elsevier B.V. All rights reserved.