EAF Dust
Recycling
Tel:+8617367842747
Gary Li
Zhengzhou Hengyang Industry Co., Ltd
Lead blast-furnace slag often contains sufficient zinc to make recovery profitable by rotary
kiln or submerged combustion slag fuming. In both cases zinc oxide in the slag is reduced to
metallic zinc (vapor) by carbon, oxidized by secondary air, and carried out in the furnace
gases for recovery of zinc oxide dust.
Zinc recovery rotary kilns (Waelz kilns) are up to 95 m long with an internal diameter of up
to 4.5 m and they are lined with refractory material. The granulated blast-furnace slag is
mixed with other zinc intermediates (steel dusts, etc.) and solid fuel reductant; it travels
down the kiln and is heated to reaction temperature by combustion gases from a burner at the
discharge end. In the slag-fuming process a mixture of coal dust and air is injected through
tuyeres into a liquid blast-furnace slag at 1150 - 1250 °C in a waterjacketed furnace. The slag
is delivered in liquid form directly from the lead blast furnace and may have up to 30 % of
solid granulated slag or slag skulls added to it. The process is typically operated in batch
mode in furnaces of 50 - 100 t capacity.
Reaction 1: Separation via Reduction and Volatization
ZnO(in ore) + C(coal) = Zn(gas) + CO(gas)
Reaction 2: Recovery via Re-Oxidation, Cooling and Settling
Zn(gas) + O2(g) + CO(g) = ZnO(s) + CO2(g)
The rotary kiln is only one part of a large unit, which is much larger than the kiln itself,
because it also contains charge preparation, equipment for gas blowing, for cleaning flue gas,
for the processing of the product from the furnace.
The linings in the rotary kiln are made of refractory material, whether brick or cast. When
the material is heated directly by gas or coal, the heat is transferred directly from the flame to
the material. The temperature of the flame and its flue gases reaches 2100 °C. The material is
further heated by the radiation of the furnace itself and by heat conduction from the
refractory material of the furnace. When the material is indirectly heated, the heat is
transferred to the material only by radiation from the inner shell of the furnace and by the
conduction of heat from the inner part of the refractory lining of the furnace.
Common to the recycled steel industry is to produce zinc oxide from electric arc kiln dust
(EAFD) and recover zinc-free iron. Known are 20 Waelz kilns applications (average capacity
75,000 tpy) that process approximately 3,400,000 tpy of EAFD with typical feeds of 35 wt%
ZnO.