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Kinetics of platinum extraction from spent reforming catalysts in aqua-regia solutions

Baghalha, M ; Sharif University of Technology | 2009

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  1. Type of Document: Article
  2. DOI: 10.1016/j.hydromet.2008.06.003
  3. Publisher: 2009
  4. Abstract:
  5. Platinum content of two commercial spent reforming catalysts were extracted in aqua-regia solutions under atmospheric pressure and at temperatures up to 100 °C. Three factors, including presence of coke, catalyst particle size, and impeller agitation speed were first tested to study the relative importance of mass-transfer resistances during Pt extraction reaction. Catalyst particle sizes < 100 μm and agitation speeds > 700 rpm eliminated the internal and external mass-transfer resistances, respectively. The effect of other factors, including HNO3-to-HCl volume ratio, liquid-to-solid mass ratio, and the reaction temperature on the extraction rate of platinum were then examined. Pt extraction rate was significantly increased by increasing liquid-to-solid mass ratio and the reaction temperature. Kinetic modeling using power-law rate equation for Pt extraction revealed that increasing liquid-to-solid mass ratio increases the acid concentration, as a major reactant. This quantitatively accounted for the increased Pt extraction rate. The effect of temperature on Pt extraction kinetics was studied using the Arrhenius equation. The activation energy for the platinum surface dissolution reaction was calculated as 72.1 kJ/mol. This large value indicates that Pt extraction in aqua-regia solution is controlled by surface chemical reaction. The reaction order was 1.5 for Pt concentration in solid and 1.3 for the hydrogen ion molarity in solution. © 2008 Elsevier B.V. All rights reserved
  6. Keywords:
  7. Aqua-regia solution ; Extraction ; Kinetics ; Leaching ; Platinum ; Power-law ; Reaction rate ; Reforming catalyst ; Activation energy ; Atmospheric pressure ; Atmospheric temperature ; Catalysis ; Catalysts ; Chemical reactions ; Dissolution ; Hydrogen ; Mass transfer ; Particle size ; Reaction kinetics ; Reaction rates ; Reforming reactions ; Solvent extraction ; Surface reactions ; Acid concentrations ; Agitation speeds ; Aqua-regia solution ; Arrhenius equations ; Catalyst particle sizes ; Effect of temperatures ; External- ; Extraction kinetics ; Extraction rates ; Extraction reactions ; Hydrogen ions ; Kinetic modeling ; Molarity ; Platinum surfaces ; Rate equations ; Reaction orders ; Reaction temperatures ; Reforming catalysts ; Relative importances ; Solid masses ; Surface chemical reactions ; Transfer resistances ; Volume ratios
  8. Source: Hydrometallurgy ; Volume 95, Issue 3-4 , 2009 , Pages 247-253 ; 0304386X (ISSN)
  9. URL: https://www.sciencedirect.com/science/article/pii/S0304386X08002235