Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, I.R. IRAN
Platinum extraction from spent reforming catalysts in iodine solutions under atmospheric pressure at different temperatures, acid concentration, and iodine spices concentration, catalyst particle size, and impeller agitation speed have been studied in our group. In this system, platinum is oxidized from spent catalyst with I3¯ that is formed from the reaction of I2 and I¯ to produce PtI6-2 as its main product. It is obvious that some of the platinum ions in aqueous solution are precipitated as PtI4, especially at high temperatures. Power-law rate equation was used in extraction and precipitation reactions for kinetic modeling. The effect of temperature was studied using the Arrhenius equation. The activation energy for the platinum surface dissolution reaction was calculated as 53 kJ/mol in extraction reaction which indicated that the rate determining step is surface chemical reaction step. The reaction order was 3.01 for platinum concentration in solid and 0.45 for the hydrogen ion concentration, 0.1 for the iodine spices concentration in extraction reaction and 0.54 for platinum ions concentration in precipitation reaction. This model shows good agreement with experimental data.