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<p>This study proposes an innovative hydrometallurgical route for recovering zirconium (Zr) and hafnium (Hf) from tin (Sn) processing residues generated in Brazil, representing a previously unexplored secondary source of these strategic metals. The process integrates alkaline fusion with sodium hydroxide (NaOH), water leaching, and subsequent oxalic acid (H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>) leaching, the latter being a novel approach not reported in the literature for this type of residue. The flotation waste, composed primarily of Si (22.8%), Zr (11.7%), and Fe (5.8%), exhibited heterogeneous granulometry (D<sub>10%</sub> = 45.6&#xa0;μm, D<sub>50%</sub> = 105.4&#xa0;μm, and D<sub>90%</sub> = 220.8&#xa0;μm) and mineral phases such as ZrSiO<sub>4</sub>, SiO<sub>2</sub>, and NaAlSi<sub>3</sub>O<sub>8</sub>. Optimal alkaline fusion occurred at 700°C for 120&#xa0;min with a SiO<sub>2</sub>/NaOH mass ratio of 1:4, resulting in the formation of Na<sub>4</sub>Zr<sub>2</sub>Si<sub>3</sub>O<sub>12</sub> and Na<sub>2</sub>SiO<sub>3</sub> phases and 85% Si solubilization. Subsequent oxalic acid leaching under optimized conditions (1&#xa0;M H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>, 90°C, 120&#xa0;min, 1:10, 220&#xa0;μm) achieved recoveries of 92.4% for Zr and 91.0% for Hf. These results demonstrate the efficiency of oxalic acid as an alternative lixiviant, reducing reagent consumption and environmental impact compared to traditional inorganic acids. Unlike conventional mineral–acid-based systems, the proposed route integrates phase transformation control and ligand-assisted dissolution, enabling high selectivity toward tetravalent cations (Zr<sup>4+</sup> and Hf<sup>4+</sup>) while suppressing silicon re-dissolution. A mechanistic interpretation based on phase evolution and oxalate complex stability is provided to explain the synergistic effect between alkaline activation and selective complexation. The proposed route offers a sustainable and technically feasible method for valorizing tin tailings, aligning with the circular economy.</p>

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Recovery of Zirconium and Hafnium from Underexplored Tin Beneficiation Residues Using Oxalic Acid Leaching

  • 期刊论文

  • 发表日期：

    2026年3月30日

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  • Gabriel de Oliveira Rodrigues,
  • Bárbara da Rocha Pereira,
  • Denise Crocce Romano Espinosa

摘要

This study proposes an innovative hydrometallurgical route for recovering zirconium (Zr) and hafnium (Hf) from tin (Sn) processing residues generated in Brazil, representing a previously unexplored secondary source of these strategic metals. The process integrates alkaline fusion with sodium hydroxide (NaOH), water leaching, and subsequent oxalic acid (H2C2O4) leaching, the latter being a novel approach not reported in the literature for this type of residue. The flotation waste, composed primarily of Si (22.8%), Zr (11.7%), and Fe (5.8%), exhibited heterogeneous granulometry (D10% = 45.6 μm, D50% = 105.4 μm, and D90% = 220.8 μm) and mineral phases such as ZrSiO4, SiO2, and NaAlSi3O8. Optimal alkaline fusion occurred at 700°C for 120 min with a SiO2/NaOH mass ratio of 1:4, resulting in the formation of Na4Zr2Si3O12 and Na2SiO3 phases and 85% Si solubilization. Subsequent oxalic acid leaching under optimized conditions (1 M H2C2O4, 90°C, 120 min, 1:10, 220 μm) achieved recoveries of 92.4% for Zr and 91.0% for Hf. These results demonstrate the efficiency of oxalic acid as an alternative lixiviant, reducing reagent consumption and environmental impact compared to traditional inorganic acids. Unlike conventional mineral–acid-based systems, the proposed route integrates phase transformation control and ligand-assisted dissolution, enabling high selectivity toward tetravalent cations (Zr4+ and Hf4+) while suppressing silicon re-dissolution. A mechanistic interpretation based on phase evolution and oxalate complex stability is provided to explain the synergistic effect between alkaline activation and selective complexation. The proposed route offers a sustainable and technically feasible method for valorizing tin tailings, aligning with the circular economy.