A tank furnace for the inertization of non-flammable batch, which contains hazardous substances, metals and less than 10% by weight of carbon, by vitrification with glass forming aggregates by producing a glassy melt. The furnace has a batch charging device and a tank, on the rim of which a furnace crown rests, electrodes for heating the melt, a supply of oxidizing gases to the melt and, as an outlet for the melt, an overflow channel which can be heated. Nozzles are installed in the bottom of the tank to introduce oxidizing gases in order to reduce the eluate values, and the electrodes are immersed in the melt from above. It is preferable to install the nozzles at sloping sidewalls of the tank which slope upwardly and outwardly.