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<p>This study presents an integrated experimental, kinetic, and thermodynamic investigation of neodymium (Nd) recovery from washed slag–residue bauxite (WSRB) using sulfuric acid. The effects of pH (0.5–5), temperature (30–90&#xa0;°C), and time (0.5–3&#xa0;h) were systematically examined, and process optimization was performed using Response Surface Methodology (RSM) based on Central Composite Design. Under strongly acidic conditions (pH &lt; 0.5) and elevated temperature (90&#xa0;°C), Nd dissolution reached 98.1%, whereas Al co-leaching remained below 10%, demonstrating high selectivity. Statistical modeling produced an excellent fit (<i>R</i><sup>2</sup> = 0.97), and the predicted optimum (pH 0.30, <i>T</i> = 105.7&#xa0;°C, <i>t</i> = 2.72&#xa0;h) was validated experimentally with 99.6% Nd recovery (0.4% deviation). Kinetic evaluation via the shrinking core model revealed an equilibrium-controlled leaching mechanism, with forward rate constants increasing from 0.1948 to 1.3810&#xa0;s<sup>−1</sup> as temperature increased from 303 to 363&#xa0;K. The activation energy (Ea = 26.45&#xa0;kJ&#xa0;mol<sup>−1</sup>) confirms chemically activated dissolution. Thermodynamic analysis yielded positive enthalpy (Δ<i>H</i> =  + 26.45&#xa0;kJ&#xa0;mol<sup>−1</sup>) and positive entropy (Δ<i>S</i> =  + 81.68&#xa0;J&#xa0;mol<sup>−1</sup>&#xa0;K<sup>−1</sup>), indicating an endothermic reaction with increased disorder. Negative Gibbs free energy values (− 785.3 to − 3235.8&#xa0;J&#xa0;mol<sup>−1</sup>) at elevated temperatures confirm increasing spontaneity. Post-leaching characterization identified quartz as the dominant phase (87.3 wt% SiO<sub>2</sub>), validating selective dissolution of Nd-bearing species. These results demonstrate the viability of sulfuric acid leaching supported by kinetic–thermodynamic insights for efficient and sustainable Nd recovery from industrial bauxite by-products.</p> Graphical Abstract <p></p>

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Comprehensive Kinetic, Thermodynamic, and Response Surface Analysis of Selective Neodymium Leaching from Slag–Residue Bauxite Using Sulfuric Acid

  • 期刊论文

  • 发表日期：

    2026年3月7日

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  • Jilda Sofiana Dewi,
  • Sariman,
  • Esti Handini,
  • Ferian Anggara,
  • Nuryadi Saleh,
  • Retno Wijayanti,
  • Titin Siti Fatimah,
  • Maitrise Adji Kawigraha,
  • Nur Ikhwani,
  • Vincent Sutresno Hadi Sujoto,
  • Himawan Tri Bayu Murti Petrus

摘要

This study presents an integrated experimental, kinetic, and thermodynamic investigation of neodymium (Nd) recovery from washed slag–residue bauxite (WSRB) using sulfuric acid. The effects of pH (0.5–5), temperature (30–90 °C), and time (0.5–3 h) were systematically examined, and process optimization was performed using Response Surface Methodology (RSM) based on Central Composite Design. Under strongly acidic conditions (pH < 0.5) and elevated temperature (90 °C), Nd dissolution reached 98.1%, whereas Al co-leaching remained below 10%, demonstrating high selectivity. Statistical modeling produced an excellent fit (R2 = 0.97), and the predicted optimum (pH 0.30, T = 105.7 °C, t = 2.72 h) was validated experimentally with 99.6% Nd recovery (0.4% deviation). Kinetic evaluation via the shrinking core model revealed an equilibrium-controlled leaching mechanism, with forward rate constants increasing from 0.1948 to 1.3810 s−1 as temperature increased from 303 to 363 K. The activation energy (Ea = 26.45 kJ mol−1) confirms chemically activated dissolution. Thermodynamic analysis yielded positive enthalpy (ΔH =  + 26.45 kJ mol−1) and positive entropy (ΔS =  + 81.68 J mol−1 K−1), indicating an endothermic reaction with increased disorder. Negative Gibbs free energy values (− 785.3 to − 3235.8 J mol−1) at elevated temperatures confirm increasing spontaneity. Post-leaching characterization identified quartz as the dominant phase (87.3 wt% SiO2), validating selective dissolution of Nd-bearing species. These results demonstrate the viability of sulfuric acid leaching supported by kinetic–thermodynamic insights for efficient and sustainable Nd recovery from industrial bauxite by-products.

Graphical Abstract