Treatment of waste material containing alkali metals in a controlled atmosphere furnace

A method of treating waste material containing alkali metals in a multiple hearth furnace having a plurality of vertically spaced hearths, wherein waste material is introduced to the furnace at the top thereof and moves downwardly in a generally serpentine fashion alternately inwardly and outwardly across the hearths and is discharged at the bottom of the furnace, while simultaneously air is introduced thereto towards the bottom of the furnace and the gases of combustion are caused to flow in counter-current direction with respect to the material being processed and are exhausted at the top of the furnace, and wherein the furnace has a natural tendency to form zones of processing including sequentially from the top of the furnace to the bottom thereof, a drying zone, a charring and volatile burning zone, and a fixed carbon burning zone, said method further comprising the step of maintaining a maximum temperature in the furnace below about 1400.degree. F. directly adjacent the surface of the bed of material being processed.

Apparatus for treating waste material containing alkali metals comprising, in combination, a multiple hearth furnace having a plurality of vertically spaced hearths, a rotatable center shaft extending through the center of the furnace and passing through each hearth, a plurality of spaced rabble arms secured to the center shaft and extending radially outwardly over each hearth, alternate hearths having drop holes disposed towards the center shaft and the other hearths having drop holes disposed toward the outer periphery thereof, said furnace having an upper material inlet and a lower material dispensing outlet, and said furnace having an upper exhaust gas outlet, means disposed on successive hearths in said furnace for ascertaining the temperature at each hearth and means for maintaining a maximum temperature on that hearth below about 1400.degree. F.