Hydrometallurgical Processes Of Rhodium Recovery From Automobile Exhaust Catalysts

Automobile exhaust catalysts is one of the most effective ways to eliminate the automobile exhaust emission, but also led to a dramatic increase in the amount of rhodium. Rhodium is a kind of rare and precious metal element of platinum group. With the widespread use of automobiles, there are many scrap automobiles every year. Recycling rhodium from this part of the automobile exhaust catalysts, will greatly reduce production costs and energy consumption.The Hydrometallurgical processes of rhodium recovery from automobile exhaust catalysts were studied in this research.The effects of the reaction time, temperatures and reagent concentration were discussed in the leaching experiments. The effects of the amount of resin, adsorption time, temperatures and pH value were discussed in the ion-exchange adsorption experiments. Furthermore, adsorption kinetics and adsorption uniform temperature types of rhodium adsorption on 201×7 ion-exchange resins were studied. The research conclusions were as follow:The leaching rate of rhodium increased with the increasing of the time, temperature, the concentration of acid A, acid B and H₂O₂, but the leaching rate of Rh reached the tap at the H₂O₂ concentration of 1.8 mol/L.The result shows that the extraction ratio of rhodium can reach to 79.58% respectively from the mixture solution of 5 mol/L the concentration of acid A, 6 mol/L acid B, 1.0 mol/L H₂O₂, stirring 2 hours under 100℃, and liquid-solid ratio of 4:1.The results of the static adsorption experiments indicated that the adsorption efficiency of Rh increased with the amount of resin used, and reached to 45% when the 1.5 g resin was used. The adsorption efficiency of Rh increased with a increase of the adsorption time, and reached to equilibrium at about 90 minutes(25℃). The adsorption efficiency of Rh increased with the increasing of the temperature, higher temperature and pH were both beneficial for the adsorption, and the process was endothermal. In the dynamic adsorption, the adsorption curve for the "S" type, through to saturation ratio is 0.39. The results showed that the proposed resin had strong adsorption performance in conditions of strong acid. The desorption curve was narrow. And the peak was high. The rhodium adsorbed on the resin can be desorpted by 5% thiourea + 0.75 mol/L HCl solution with the desorption rate reaching to 97%. Freundlich isotherm was more suitable for describing the adsorption process.The thermodynamic study of the adsorption process showed that the rhodium adsorption-ion exchange process is spontaneous and endothermal, and the entropy is positive. The adsorption kinetics of rhodium on the 201×7 resin followed the law of the first-order model of Lagergren.