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<b>Abstract</b>— <p>In developing methods for the efficient extraction and concentration of rare earth elements (REE), as well as in the removal of associated metal impurities, the solubility of salts, in particular sulfates, which are often used in hydrometallurgy as intermediate products, is of great importance. The work considers the precipitation of complex potassium scandium sulfate KSc(SO<sub>4</sub>)<sub>2</sub>, the crystals of which are elongated hexagonal prisms 5–10 µm wide and 20–50 µm long. The DTA method shows the absence of crystallization water, as well as the presence of a reversible phase transition at about 447°C. The solubility of KSc(SO<sub>4</sub>)<sub>2</sub> in water at 25°C is found to be 0.28 ± 0.01 wt % Sc. Decreased solubility of KSc(SO<sub>4</sub>)<sub>2</sub> achieved by increasing the concentration of sulfuric acid to more than 3–4 mol/L H<sub>2</sub>SO<sub>4</sub>. Additional introduction of 0.5 mol/L K<sub>2</sub>SO<sub>4</sub> allows to reduce the solubility of scandium in the form of a complex compound by an order of magnitude and to increase the efficiency of scandium extraction from sulfate solutions. Experimental results on the solubility of KSc(SO<sub>4</sub>)<sub>2</sub> are described by the change in the ionic strength of the solution in the presence of the same ions (K<sup>+</sup> and <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\text{HSO}}_{4}^{ - }\)</EquationSource> <!--TFCE2660026Medyankina-m1--> </InlineEquation>). The degree of extraction of scandium from sulfate solutions with the addition of 0.5 mol/L K<sub>2</sub>SO<sub>4</sub> is more than 99%. A basic technological scheme for the extraction of scandium from red mud with crystallization of KSc(SO<sub>4</sub>)<sub>2</sub> is proposed. The results will be useful for developing methods for separating metals during sulfuric acid processing of raw materials and expanding methods for obtaining concentrates and pure metal oxides, as well as in studying the behavior of REE compounds with similar properties.</p>

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Crystallization and Solubility of KSc(SO4)2 to Increase the Efficiency of Scandium Extraction

  • 期刊论文

  • 发表日期：

    2025年10月1日

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  • I. S. Medyankina,
  • L. A. Pasechnik

摘要

Abstract—

In developing methods for the efficient extraction and concentration of rare earth elements (REE), as well as in the removal of associated metal impurities, the solubility of salts, in particular sulfates, which are often used in hydrometallurgy as intermediate products, is of great importance. The work considers the precipitation of complex potassium scandium sulfate KSc(SO4)2, the crystals of which are elongated hexagonal prisms 5–10 µm wide and 20–50 µm long. The DTA method shows the absence of crystallization water, as well as the presence of a reversible phase transition at about 447°C. The solubility of KSc(SO4)2 in water at 25°C is found to be 0.28 ± 0.01 wt % Sc. Decreased solubility of KSc(SO4)2 achieved by increasing the concentration of sulfuric acid to more than 3–4 mol/L H2SO4. Additional introduction of 0.5 mol/L K2SO4 allows to reduce the solubility of scandium in the form of a complex compound by an order of magnitude and to increase the efficiency of scandium extraction from sulfate solutions. Experimental results on the solubility of KSc(SO4)2 are described by the change in the ionic strength of the solution in the presence of the same ions (K+ and \({\text{HSO}}_{4}^{ - }\) ). The degree of extraction of scandium from sulfate solutions with the addition of 0.5 mol/L K2SO4 is more than 99%. A basic technological scheme for the extraction of scandium from red mud with crystallization of KSc(SO4)2 is proposed. The results will be useful for developing methods for separating metals during sulfuric acid processing of raw materials and expanding methods for obtaining concentrates and pure metal oxides, as well as in studying the behavior of REE compounds with similar properties.