The remaining 35 percent ends up in landfills. That's why the metals industry has long sought a process that can recycle dust with no emissions and at a low cost, Itaya says. The crude zinc that's recovered from dust has a zinc density of more than 60 percent. This makes it usable as a raw material for zinc smelting. The process has zero emissions, Itaya says.
Exhaust gas is recycled as fuel gas.
When the cost benefits of the recovered zinc, molten iron, slag, and fuel gas are factored in, the new furnace reduces dust-processing costs by about 40 percent compared with conventional methods. The direct production cost can be half that of current methods, Itaya says. One current zinc-recovery process uses rotary kilns with burners. But in this process, the slag has remnants of zinc and lead. Because of tightening pollution controls in Japan and elsewere, Itaya doubts that rotary kilns for recovering zinc from electric-furnace dust will continue operating for much longer.