Slag design and iron capture mechanism for recovering low-grade Pt, Pd, and Rh from leaching residue of spent auto-exhaust catalysts

• Published in: The Science of the total environment 2022-01, Vol.802, p.149830-149830, Article 149830
• Main Authors: Zheng, Huandong, Ding, Yunji, Wen, Quan, Zhao, Shizhen, He, Xuefeng, Zhang, Shengen, Dong, Chaofang
• Format: Article
• Language: English
• Subjects: Iron capture; Mechanism; Platinum group metals; Slag design; Spent catalysts
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2021.149830

Recovery of platinum group metals (PGMs) from secondary resources has attracted worldwide attention from environmental and economic points of view. Pyrometallurgical routes exhibit the superiority in terms of efficiency and contamination control compared to hydrometallurgical process. However, traditional pyrometallurgical processes face the challenges of excessive flux and energy consumption. In this paper, an iron capture process was proposed to recover low-grade PGMs from leaching residue of spent auto-exhaust catalysts. Slag design was explored aimed at reducing the addition amount of flux. The optimized smelting conditions were as follows: 1400 °C for 30 min, adding 40.0 wt% CaO, 22.7 wt% Na2CO3, 5.0 wt% Na2B4O7, 5.0 wt% CaF2, 15.0 wt% Fe, and 5.0 wt% C. The concentrations of Pt, Pd and Rh remaining in the smelting slag were 0.83 g/t, 4.99 g/t, and 1.47 g/t, respectively. Furthermore, the 50 kg-scale experiment implied positive economic feasibility because of saving flux dosage and smelting time. The capture mechanism was revealed by investigating the formation of the metals phase and slag phase. Matrix formed slag phase and separate with metals phase owing to differences in chemical bonding, density, viscosity, and surface tension. PGMs were proved solubilized in α-Fe as substitutional solid solutions. The formation energies for FePt, FePd, and FeRh alloys were −4.149 eV, −4.040 eV, and −4.360 eV, respectively. Finally, the obtained CaO-SiO2-Al2O3-Na2O glass slag was used for producing glass ceramics. To sum up, the iron capture process realized low energy and material consumption, high recovery efficiency of PGMs, and resource utilization of the glass slag. [Display omitted] •An integrating method combining slag design and iron capture was proposed.•The concentration of PGMs remaining in slag was below 8.0 g/t.•The interaction mechanism of PGMs and iron was put forward.•Preliminary economic analysis shows the process is profitable.•Low energy consumption, non-pollution, and resource utilization were realized.