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<p>Hydrometallurgical processes often result in the formation of a mixture of chrome alum and iron alum, necessitating their separation to continue the process. This study focuses on their separation using fractional crystallization, a straightforward technique requiring minimal equipment. A solubility difference between the two salts is induced by heating the solution above 70&#xa0;°C, which converts chrome alum into a green, non-crystallizable modification due to the covalent bonding of sulfate ions <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({\text{SO}}_{4}^{2-}\)</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mtext>SO</mtext> <mrow> <mn>4</mn> </mrow> <mrow> <mn>2</mn> <mo>-</mo> </mrow> </msubsup> </math></EquationSource> </InlineEquation> to Cr<sup>3+</sup>. Upon cooling, the green modification slowly reverts to the violet, crystallizable form, in which sulfate ions are bound to Cr<sup>3+</sup> by an ionic bond. The study examines key variables that influence the crystallization rate of chrome alum from a Cr/Fe alum mixture, including initial Cr alum concentration, pH, temperature, and stabilization (heating) time. A statistical model is proposed to predict crystallization rates under varying conditions. The findings have potential applications in purifying leach liquor from chromite ore leaching with H<sub>2</sub>SO<sub>4</sub> before electrolysis for pure chromium production and in separating Cr alum from Fe alum in acid-leached Cr/Fe scrap solutions.</p> Graphical Abstract <p></p>

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Separation of Chrome Alum from Iron Alum by Fractional Crystallization: Experimental Investigation and Predictive Modeling

  • 期刊论文

  • 发表日期：

    2025年12月3日

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  • M. G. Fouad,
  • M. A. Saad,
  • G. H. Sedahmed,
  • M. H. Abdel-Aziz,
  • I. K. Mohamed,
  • E.-S. Z. El-Ashtoukhy,
  • S. Mustafa

摘要

Hydrometallurgical processes often result in the formation of a mixture of chrome alum and iron alum, necessitating their separation to continue the process. This study focuses on their separation using fractional crystallization, a straightforward technique requiring minimal equipment. A solubility difference between the two salts is induced by heating the solution above 70 °C, which converts chrome alum into a green, non-crystallizable modification due to the covalent bonding of sulfate ions \({\text{SO}}_{4}^{2-}\) SO 4 2 - to Cr3+. Upon cooling, the green modification slowly reverts to the violet, crystallizable form, in which sulfate ions are bound to Cr3+ by an ionic bond. The study examines key variables that influence the crystallization rate of chrome alum from a Cr/Fe alum mixture, including initial Cr alum concentration, pH, temperature, and stabilization (heating) time. A statistical model is proposed to predict crystallization rates under varying conditions. The findings have potential applications in purifying leach liquor from chromite ore leaching with H2SO4 before electrolysis for pure chromium production and in separating Cr alum from Fe alum in acid-leached Cr/Fe scrap solutions.

Graphical Abstract