Study On The Recovery Of Platinum And Aluminum From Spent Catalysts

Spent platinum catalysts posses extremely high recovery value due to its abundant resources and high grade as compared with platinum ore. Some Substrate of spent platinum catalysts can convert from γ-Al2O3to α-Al2O3under high temperature, which has resulted in the low leaching rate of platinum by active components dissolution because of the encapsulation of few platinum. The disadvantages of whole dissolution method include high consumption of regents and environmental pollution.In the present study, production processes including thermal acid ball-milling, alkali leaching with high pressure and sintering-leaching were adopted based on the disadvantages of whole dissolution method and active components dissolution method, as well as the comprehensive consideration of factors, such as utilization of secondary resources, production practice of factory and complex components of raw materials.Firstly, properties of raw material were analyzed using various analysis detection methods in order to elucidate the principle of the production process. Effect of various production parameters on the leaching process was studied. Also mechanical activation was used in the acid leaching process and its strengthening effect on the leaching process was discussed. The results showed:Aluminum in the spent reforming catalysts was appeared mainly in the form of γ-Al2O3with partially α-Al2O3. Few Al and Si were hosted in Na2O-Al2O3-SiO2-H2O system. The contents of C and SiO2were relatively high, which were6.16%and4.54%, respectively. Composition segregation of the raw materials was serious.Optimum process conditions for alkali leaching under high pressure were listed as follows:roasting at600℃for1h, concentration of NaOH in leaching solution was230g/L, leaching temperature260℃, caustic ratio1.6, leaching time2h. Slag ratio and leaching percentages of Al2O3and SiO2in the first leaching process was10.52%,95.93%and59.71%, respectively. Platinum content in slag was significantly increased from0.23%to2.08%after the leaching process, with the enrichment factor increased9.04times as compared to the raw materials.Optimum process conditions for sintering-leaching process were listed as follows:roasting at600℃for1h, sintering temperature800℃, molecule ratio1.2, sintering time2h, sintering products were digested at95℃for10min. Slag ratio and leaching percentages of Al2O3, SiO2and Na2O in the first leaching process was5.04%,98.10%,85.23%and99.25%, respectively. Platinum content in slag was significantly increased from0.23%to4.11%after the leaching process, with the enrichment factor increased17.87times as compared to the raw materials.Optimum process conditions for sintering-leaching process were listed as follows:roasting at550℃for2h, ball-to-powder weight ratio13:1, ball gradation Φ10:Φ6:Φ4=3:4:4, ball-mill speed6r/min, leaching temperature100℃, leaching time2h, H2SO4concentration50%, liquid-solid ratio5:1. Slag ratio and leaching percentages of Al2O3and SiO2in the first leaching process was10.56%,95.70%,9.56%, respectively. Platinum content in slag was significantly increased from0.25%to1.80%after the leaching process, with the enrichment factor increased7.20times as compared to the raw materials. Kinetics of thermal acid ball-milling showed apparent activation energy of Al2O3in the leaching process decreased by10.99kJ/mol compared to conventional stirring leaching process. Aluminum in the leaching solution of thermal acid ball-milling process was recovered by evaporation ammonia method. The product in the form of aluminum sulfate could meet the standard of the first grade in HG/T2225-2001Ⅰ.Though alkali dissolution (fusion) process could effectively reduce slag ratio, it still show some disadvantages, such as contradictory with existing process, and aluminum (Al) in the leaching solution can not be effectively recycled. Also sodium-silicon residue in slag exerted negative effect for subsequent recovery of platinum. Based on comprehensive consideration of the above factors, thermal acid ball-milling process was selected as optimum production for platinum recovery.