(MERAF) for the Base Metals Smelting Sector - CCME

3.2.6. Falconbridge, Sudbury Division, Sudbury, Ontario 85
Figure 12 contains a schematic block flow diagram for Falconbridge’s
Nickel/Copper Smelter in Sudbury. This shows the general sequence of the
major unit operations, from the receipt of raw materials to the production of
metals. When these unit operations are referred to in the text, the corresponding
words starts with an upper case letter. This diagram is highly simplified and is
included solely to aid in the discussion and understanding of the pollution control
at the facility.
Nickel-copper concentrate is received from the Strathcona concentrator as a
slurry which is repulped to a consistent density prior to processing in the fluidized
bed roasters. Most of the nickel, copper, iron and sulphur in the smelter feed is
contained in sulphide minerals. Silica is proportioned to ensure a low viscosity
FeO-CaO-SiO 2 slag, with low nickel and copper content, in the subsequent
smelting step. The roasters oxidize part of the iron and approximately 60% of the
sulphide sulphur. Roaster off-gases are treated by a cyclone and electrostatic
precipitator to remove dust. The cleaned gases are treated by a single absorption
sulphuric acid plant to remove sulphur dioxide before being released to the
atmosphere. Weak acid from the gas cleaning section of the acid plant is
neutralized with lime.
The solid product from the roasters is charged to an electric furnace for smelting
together with custom concentrate and coke. The non-ferrous gangue minerals,
fluxes and iron oxides separate to form a molten oxide slag over the molten
nickel-copper-iron sulphide matte phase. Electric furnace slag is granulated and
pumped to the slag disposal area where the water is drained and recycled. Offgases
from the electric furnace are treated by cyclones and an electrostatic
precipitator for removal of dusts containing metals before being released to the
atmosphere. All dusts recovered from electric furnace off-gases are returned to
the electric furnace.
Electric furnace matte is transferred to conventional Peirce Smith converters
where iron and sulphide sulphur are further oxidized to iron oxide and sulphur
dioxide. Iron oxide and fluxes combine to form a molten oxide slag over the
molten nickel-copper matte, which also contains cobalt and some iron. The
higher density matte separates from the converter slag and is granulated,
dewatered, then shipped to Falconbridge’s Nikkelverk refinery in Norway.
Converter slag contains economic concentrations of metals and is cleaned prior
to disposal. Off-gases from the electric furnace are treated by cyclones and an
electrostatic precipitator for removal of dusts containing metals before being
85 Hatch Associates, Review of Environmental Releases for the Base Metals Smelting Sector,
prepared for Environment Canada, dated November 2000
71