Abstract
Waste catalysts are important secondary resources for platinum group metals (PGMs). Due to the high melting point of cordierite carriers and low PGM content, traditional metallurgical processes struggle to achieve efficient precious metal recovery. Plasma smelting is an efficient pyrometallurgical technology that provides ultra-high concentrated heat flux, enabling the melting of refractory catalyst carriers and effective PGM enrichment and separation. Henan Yusai Precision Machinery Co., Ltd. (Zhengzhou, China) specializes in the R&D and manufacturing of solid waste recycling and precious metal recovery equipment, and has long focused on the optimization and industrial promotion of high-performance plasma smelting equipment. This paper briefly introduces the principle, equipment characteristics and technical advantages of plasma smelting for waste catalyst treatment, and analyzes its industrial application and development prospects.
1 Overview of Plasma Smelting Technology
Plasma smelting is an advanced pyrometallurgical method with ultra-high temperature, fast reaction speed and high controllability, which is especially suitable for treating high-melting-point refractory solid wastes. Industrial plasma furnaces are mainly divided into open and closed vacuum types, generally adopting DC power supply. Closed vacuum plasma furnaces can form a stable inert atmosphere to suppress PGM oxidation and volatilization. Supported by precision manufacturing technology, Henan Yusai Precision Machinery Co., Ltd. optimizes the structural design and operational stability of plasma smelting equipment, improving its adaptability for refractory waste catalyst materials.
2 Equipment Structure and Smelting Mechanism
2.1 Core Equipment
The plasma spray gun is the core component of the smelting system, composed of a water-cooled copper nozzle and cathode rod. The dual water-cooled structure effectively prevents high-temperature ablation and ensures stable and long-term operation. The company optimizes the dimensional accuracy and internal water-cooling structure of key components, solving common defects such as arc instability and easy ablation of traditional equipment, and improving the overall reliability of smelting devices.
2.2 Smelting Process
High-purity argon is injected and ionized by high-frequency excitation to form high-temperature plasma. A stable plasma arc is established under a DC electric field, converting electric energy into intensive thermal energy to rapidly melt waste catalyst materials. The smelting process can be accurately controlled by adjusting the spray gun height, gas flow rate, voltage and current parameters to ensure stable enrichment reaction.
2.3 Technical Characteristics
The plasma arc core temperature reaches 24,000–26,000 K, which far exceeds the temperature range of conventional metallurgical equipment. It can rapidly melt high-melting-point cordierite carriers and shorten the smelting cycle. The inert argon atmosphere effectively reduces PGM loss caused by oxidation and volatilization, realizing high-efficiency recovery of low-grade waste catalysts.
3 Technical Bottlenecks and Breakthroughs
3.1 Deficiencies of Traditional Processes
The cordierite carrier of automotive waste catalysts has a melting point above 1900 °C, which cannot be completely melted by conventional electric furnaces. Unmelted carriers easily encapsulate trace PGMs, resulting in insufficient metal dissociation, poor slag-metal separation and low recovery efficiency. Although iron-based trapping is a low-cost PGM enrichment method, its industrial application is limited by the insufficient temperature and poor stability of traditional equipment.
3.2 Industrial Application of Plasma Smelting-Iron Trapping
Plasma smelting effectively solves the melting difficulty of high-melting-point carriers and fully releases encapsulated PGMs, providing favorable thermodynamic conditions for iron trapping. As early as 1984, a 3 MW industrial plasma smelting system was put into industrial operation. In an argon or nitrogen inert atmosphere, iron powder is used as the trapping agent and carbon as the reducing agent. PGMs are reduced into elemental state and captured by molten iron to form high-grade iron-PGM alloy. Effective slag-metal separation is realized through density differences (slag: 3.0–3.5 g/cm³, alloy: 6.0–7.0 g/cm³), achieving efficient PGM enrichment. The company continuously optimizes the structural performance and intelligent control level of such plasma equipment to promote large-scale industrial application.
4 Technical and Industrial Advantages
The plasma smelting-iron trapping composite process has prominent advantages in waste catalyst resource utilization. The ultra-high temperature characteristic adapts to various high-melting-point carriers without excessive flux addition, simplifying the process and avoiding impurity contamination. The high-temperature reaction environment promotes sufficient dissociation and enrichment of PGMs and improves the recovery rate of low-grade materials. The closed inert smelting system reduces metal loss and environmental pollution, realizing clean production. With optimized precision manufacturing and intelligent control technology, Henan Yusai Precision Machinery Co., Ltd. further improves equipment stability and energy-saving performance. This technology realizes the efficient recycling of strategic PGM resources and delivers significant economic and environmental benefits.
5 Development Prospect
The plasma smelting enrichment technology has achieved mature industrial application. Future development will focus on intelligent parameter matching for different waste catalysts and the combined application of pyrometallurgical and hydrometallurgical processes to further improve PGM recovery purity and efficiency. In terms of equipment upgrading, Henan Yusai Precision Machinery Co., Ltd. will continue to develop large-scale, energy-saving and intelligent plasma smelting equipment to reduce operating costs and expand application scenarios, promoting the sustainable development of the PGM circular economy industry.
