Abstract:With the continuous increase in the number of motor vehicles and the tightening of environmental policies, the requirement for automotive exhaust purification catalysts is constantly increasing. When a large number of cars are scrapped, how to dispose of the spent automotive exhaust purification catalysts reasonably is a major social problem. Spent automotive exhaust purification catalysts contain a large amount of platinum group metals (PGMs) with high-value, which are important secondary resources of PGMs. In the current situation of scarce PGMs resources and long-term dependence on foreign imports, efficient recovery of PGMs from spent automotive exhaust purification catalysts plays an important role in the recycling of resources and alleviating the supply-demand contradiction of PGMs in China. Using pyrometallurgical technology and copper trapping method, efficient separation between base metal carriers and PGMs can be achieved. Using spent automotive exhaust purification catalysts as experimental materials and CuO as the trapping agent, CaO-SiO2-Al2O3-B2O3-MgO slag type was selected to conduct research on the pyrometallurgical technology and copper trapping of PGMs in spent automotive exhaust purification catalysts. The feasibility of copper trapping PGMs was analyzed from a thermodynamic perspective. In the process of copper trapping, using coke as a reducing agent, it is necessary to focus on analyzing the thermodynamic behavior of various metal oxides during carbon reduction process. The effects of melting temperature, melting time, basicity, the mass ratio of quartz sand and borax, and trapping agent dosage on the recovery rates of Pt, Pd, and Rh were systematically studied. The main chemical components of the experimental materials and products were analyzed using inductively coupled plasma optical emission spectrometer (ICP-OES) and spectrophotometer. The phase composition of the experimental materials and copper alloy were analyzed using X-ray diffractometer (XRD). The microstructure and energy spectrum of the copper alloy characterized by field emission scanning electron microscope and energy dispersive spectrometer (SEM-EDS). The thermodynamic research results indicate that the copper oxide and platinum group metal oxides can be reduced to their corresponding metals at high temperatures. Then, the PGMs generated by reduction were trapped and enriched in the copper alloy by the new ecological copper liquid, forming corresponding continuous solid solutions. The experimental research results show that when the temperature of reduction melting is continuously increased from 1 350 ℃ to 1 400 ℃, all the recovery rate of Pt, Pd, and Rh is improved. The recovery rate of Pt, Pd, and Rh gradually increases with the extension of the reduction smelting time, and then tend to stabilize. After six hours of smelting reaction, the copper trapping reaction basically reaches dynamic equilibrium. As the basicity increases, the recovery of PGMs rises firstly and then decreases. With the increase of borax dosage, the recovery of Pt, Pd, and Rh increases firstly and then decreases. Determining the appropriate amount of borax is crucial. After increasing the amount of trapping agent, the recovery rate of Pt, Pd, and Rh is gradually improved. Select an appropriate amount of capture agent based on production costs and recovery rate. Under the optimal conditions of melting temperature of 1 400 ℃, melting time of 6 h, basicity of 1.1, the mass ratio of quartz sand to borax of 1:2, and trapping agent dosage accounting of 16% of mass fraction of the raw material, the results of three parallel verification experiment indicate that the average grade of Pt, Pd and Rh in the melting slag is 1.4, 6.5 and 1.0 g/t, respectively, while the recovery rate of Pt, Pd and Rh reaches to 99.18%, 99.41% and 98.62%, respectively. The main component of the alloy product is Cu, with a grade of 92.84%. The grade of Pt, Pd, and Rh in copper alloy is 0.27%, 1.88% and 0.13%, respectively, indicating that they have been highly enriched. XRD patterns show that PGMs form phases such as Cu3Pt, CuPd, and CuRh in copper alloys, respectively. The results of energy dispersive spectroscopy analysis show that the non-precious metal elements in copper alloys are mainly composed of Cu, C, and O, and the Pt, Pd and Rh is unevenly distributed on Cu.