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Nickel

 

Stainless steel furnaces worldwide generate significant tonnages of fine dust and fume which, because of their extremely finely sized nature, namely 100% minus 2mm, are difficult to re-process using conventional submerged-arc furnace technology. In this regard, AMRT is in the process of reprocessing such dusts and fumes produced at Columbus Stainless Steel Corporation, situated in South Africa, so as to recover its residual valuable nickel as well as its chromium and manganese components. By charging this material together with predetermined quantities of carbonaceous reductant and flux to a small 0.5 MVA furnace directly, three products are generated. These are a raw stainless steel, which is returned to Columbus Stainless Steel, a chemically inert slag and a gas containing, besides nitrogen and residual oxygen, carbon dioxide and water vapour. The reactions taking place in the AMRT melt reduction furnace are:

 

NiO + C = Ni + CO

Fe2O3 + 3C = 2Fe + 3CO

Cr2O3 + 3C = 2Cr + 3CO

Mn3O4 + 4C = 3Mn + 4CO

 

which combined draws 1320 kWh per metric ton of stainless steel furnace dust and fume mix. A spectrum of the compositions of the melt reduction furnace inputs and outputs is indicated in the following table:

 

AMRT melt reduction furnace technology as applied to a stainless steel dust/fume mixture ex Columbus Stainless Steel Corporation, South Africa

 

 

Furnace input

Furnace products

 

Steel furnace dust(%)

Metal
(%)

Slag
(%)

Gas
(% by volume)

Ni

2.52

4.65

0.07

 

Fe

41.2

76.1

1.1

 

Zn

3.9

0.07

0.1

1.3

Cr

9.1

14.4

3.7

 

Mn

2.3

3.6

0.9

 

SiO2

4.3

 

41.5

 

CaO

11.1

 

30.3

 

MgO

3.1

 

8.5

 

Al2O3

0.6

 

3.7

 

C

0.75

1.02

 

 

CO2

0

 

 

26.2

H2O

1

 

 

1.3

 

As is indicated in the above table, the bulk of the zinc that was present in the original dust/fume mixture reported to the off gas. This zinc was subsequently collected in the form of zinc oxide (ZnO) in an adjoining off gas filter unit, or bag house.

 

Examples of materials that have been produced by or processed in AMRT’s melt reduction furnaces are:

Copper

Cobalt

Nickel

Tin

Zinc and lead oxide and sulphides

Ferrochromium

Ferromanganese

Ferrotitanium

Precious metal-bearing wastes

Ancillary processes and procedures associated with AMRT’s furnace operations

 
 
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