The Recovery of the Strategic Metals from the Nitrate Solutions of Zn-Pb Tailings Using a Solvent Extraction Process

The increasing demand for critical metals has intensified efforts to recover valuable metals from various sources, including secondary waste. Zn-Pb tailings contain both major and trace metals with economic and environmental significance. This study examined the extraction of transition metals from Zn-Pb tailings using inductively coupled plasma mass spectrometry (ICP-MS) at a constant time of 30 min. Metal extraction efficiencies were evaluated using N-Methyl-N,N,N-trioctylammonium chloride (Aliquat 336), methyl salicylate (MS), di(2-ethylhexyl) phosphoric acid (D2EHPA), tributyl phosphate (TBP),2,4,6-tris(allyloxy)-1,3,5-triazine (TAOT), and triethyl phosphate (TEP). Increasing mixing rates improved mass transfer, enhancing recoveries, with Hf4+, Ti4+, and Fe3+ reaching 88, 56, and 50%, respectively, at 1000 rpm (mixing rate; rotation per minute) using D2EHPA. At a mixing rate of 1000 rpm, 10% TEP recovered 25% of Cu2+ and 34% of Mn2+, while 150 g/L extracted 48% of Hf4+ and 46% of V4+. Additionally, 10% TBP extracted 33% of Mn2+ and 35% of V4+, 10% MS recovered 41% of Mn2+ and 39% of V4+, while TAOT extracted 35% of V4+. At room temperature (22.5 °C) and 1400 rpm, 10% of D2EHPA recovered 80% of Hf4+, 73% of Ti4+, and 61% of Fe2+. However, 10% TAOT selectively recovered 50% of V4+, while 10% MS, under the same conditions, recovered 50% of V4+ with co-extraction of Mn2+ and Cu2+ (<10%). A total of 150 g/L Aliquat 336 effectively extracted Hf4+ (66%), Zn2+ (19%), and V4+ (56%). A total of 10% TBP recovered 53% and 47% of Mn2+ and V4+, respectively. A total of 10% TEP recovered Cu2+ (45%), Mn2+ (55%), Zn2+ (29%), V (40%), and 26% of Ni2+. At room temperature (22.5 °C) and 1400 rpm, pH changes significantly affected extraction, with D2EHPA (10%) demonstrating 89% efficiency for Hf4+ at pH 1.3, while other metals showed lower recoveries. TEP (10%) increased Cu2+ and Hf4+ recovery to 52% and 80%, respectively, at pH 1.3, while 150 g/L Aliquat 336 favored Cu2+ (58%), with co-extraction of 16% of Zn2+ at pH 1.3. TBP (10%) extracted 60% and 61% of Cu2+ and Fe, respectively, at pH 1.3, while 10% of MS recovered 55% and 50% of V, respectively. A concentration of 10% D2EHPA favored the recovery of 90% of Hf4+ at pH 1.3, with less than 35% co-extraction of Cu2+, Mn2+, Zn2+, and Fe2+. At 1400 rpm, temperature also influenced extraction, with D2EHPA recovering 84% of Hf4+ at 35 °C, 77% of Ti (55 °C), and 79% of Fe (55 °C) and TBP extracting 73% of Cu2+, 67% of Mn2+, 68% of Zn, 60% of V4+, and 47% of Ni2+ at 55 °C. A concentration of 10% MS extracted 61% of V4+and 54% of Fe2+, while 150 g/L recovered 61% of V4+ at 55 °C. TAOT extracted 46% of Mn and 41% of V4+, while 10% TEP recovered 60% of Mn and 32% of V4+ at 55 °C. These outcomes contribute to an improved understanding of the solvent extraction mechanisms of different ligands.