High-Temperature Plasma Vitrification

1.0 INTRODUCTION

Nontransferred arc plasma technology represents a novel and powerful means for melting soil solids in an efficient and expedient manner. Plasma is the fourth state of matter and produces very high temperatures in the range over 4000°C. With a nontransferred arc plasma torch (see Figure 1 below), high temperatures can be controlled and directed at any desired target. This technology is capable of melting soils and rocks, as well as contaminated ground, thus creating a molten pool of surficial lava or subsurface magma. Tungsten has the highest melting point on earth, melting at 2450°C. The molten region eventually cools to form an inert glassy igneous rock, often similar to obsidian and in some instances similar to crystalline granite and/or basalt (Mayne, et al. 1994, 1996, 2000).

A plasma torch is a device that converts electrical energy into thermal energy (Camacho, 1988). Plasmas occur naturally in the form of lightning. The plasma arc creates a "flame" that has temperatures ranging from 4,000°C to 7,000°C. Thus, plasma torches operate at much higher temperatures, higher enthalpies, and at efficiencies much greater than those of fossil fuel burners. In addition, plasma torches require only about 5% of the gas necessary for fossil fuel burners. Therefore, the volume of effluent gas is greatly reduced, which allows the offgas to be collected and treated. Several plasma torch furnace processes for the destruction of hazardous and toxic wastes have been developed and successfully tested. The very high temperatures and energy densities, in conjunction with an ionized and reactive medium, have fully demonstrated the potential of plasma technology to remediate many waste and mixed-waste materials in an environmentally safe and cost-effective manner. Materials vitrified with plasma arc torches readily pass all standard leaching tests.