Plasma arc melting, using a plasma arc as a heat source, is a highly efficient pyrometallurgical technique. It has applications in machinery, metallurgy, and aerospace, and is particularly suitable for producing high-melting-point metals and special functional alloy materials and devices. Plasma melting furnaces come in various types, including open furnaces and closed vacuum furnaces. The latter combines some characteristics of both electric arc melting and vacuum melting, and both typically use DC power.
The key equipment is the lance, which consists of a water-cooled copper nozzle and a water-cooled copper electrode rod (as the cathode). Argon gas is injected into the furnace through the lance sleeve, and a high-frequency electric field ignites the argon gas, ionizing it into a conductive argon gas fluid. The total number of positive and negative ions in the high-temperature fluid is equal, forming what is called plasma. After arc ignition, the lance height is adjusted, and under the influence of the furnace’s DC electric field, a working gaseous arc is formed between the lance and the furnace charge. Electrical energy is converted into the heat energy of the argon arc, catalyzing the furnace charge. Simultaneously, the argon flow rate and the main arc voltage and current are controlled by raising and lowering the lance to complete the melting process. This heating method features concentrated energy, high heat flux, very high arc core temperature (up to 24000-26000K), and fast melting speed.
There have been studies on using Fe to capture precious metals in certain low-grade catalysts [17], but the melting point of cordierite, the carrier of automotive waste catalysts, is very high (>1900℃), and it is difficult to reach the melting temperature of the carrier using ordinary smelting furnaces (including electric furnaces), making slag formation difficult. In 1984, a 3 MW furnace was built using iron powder as a collector and carbon as a reducing agent to capture platinum group metals by smelting under an argon or nitrogen atmosphere.
