RADIOFREQUENCY GROUND HEATING FOR SOIL REMEDIATION - SCIENCE AND ENGINEERING

RF (radiofrequency) ground heating is a method of applying heat to soil at depth and affords a way of thermally desorbing organic contaminants for surface collection and destruction. Soil can be heated to high temperatures, and thus most organic contaminants, possibly including PCBs (polychlorinated biphenyls), can be desorbed. Applied heat greatly accelerates release and transport of the contaminants through the soil. This method therefore represents an advance over the widely-used method of vapor extraction. Laboratory desorption experiments demonstrate accelerated release of contaminants and non-exponential desorption rates. Measurements of soil electrical properties show high electrical losses in iron ores (hematite and magnetite) and soils with some small salt content, which indicates a possible mechanism for RF energy deposition at high temperatures when all water has been removed from the soil. We have carried out a field test and have heated a volume to 140-degrees-C. Vacuum tube RF amplifiers are, in general, touchy and unreliable, and our 50 kW amplifier has broken down several times. We have been working on simple, inexpensive solid-state amplifiers which can be combined to give multi-kilowatt and, ultimately, megawatt power levels at lower cost per watt than vacuum tube amplifiers. The development of solid-state RF power sources is important for a scaleup of RFGH systems, which should then be able to remediate, in a reasonable time, sites containing hundreds or thousands of tons of contaminated soil.