(MERAF) for the Base Metals Smelting Sector - CCME

3.2.2. Sherritt International Corporation, Fort Saskatchewan, Alberta 79
The refinery consists of eight operating areas: Ammonia Leaching, Cobalt
Separation, Cobalt Conversion and Reduction, Copper Boil, Nickel Recovery,
Sulphide Precipitation, Ammonium Sulphate Recovery and Ammonia Recovery
circuits. Each of these areas is described in the subsections below.
Figure 4 contains a schematic block flow diagram for the Metals Refinery. 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.
The Nickel Powder Drying, Nickel Briquetting, Cobalt Powder Drying and Cobalt
Powder Briquetting circuits are also shown in Figure 4.
3.2.2.1. Ammonia leaching
There are three leach circuits in the Ammonia Leaching Plant. These are
Hexamine Leach, Adjustment Leach and Final Leach circuits. The purpose of
these leaching circuits is to dissolve the metals that are present in the feed
materials.
Prior to entering a leach circuit, the nickel feed is segregated into high and low
cobalt feeds.
The high cobalt feed materials are blended with ammonium sulphate liquor and
pumped to the Hexamine Leach autoclave circuit where the majority of the metal
sulphides, oxygen (in air) and ammonia react to form a soluble nickel and cobalt
hexamine complex. After additional treatment and solids separation, the leach
liquor, which contains the hexamine complexes, is pumped to the Cobalt
Separation Circuit. The autoclave vent gases are sent to the tail gas scrubber for
ammonia recovery.
The low cobalt feeds are sent directly to the Adjustment Leach circuit. The feed
is added to autoclaves where ammonia, air and other reagents are added. In the
pressurized and heated autoclaves, the nickel dissolves to form primarily nickel
amine. The resulting slurry is pumped into a lamella thickener and the solids are
separated. Any solids remaining are sent to the Final Leach Circuit. The
Adjustment Leach liquor is sent to the Copper Boil circuit area. The autoclave
vent gases are sent to the tail gas scrubber for ammonia recovery.
The Final Leach process is similar to the Hexamine and Adjustment Leach. In
the autoclaves, residual metals are extracted and a final iron oxide residue is
produced. The autoclave slurry is sent to thickeners and a centrifuge where the
solids and liquids are separated. The liquid is recycled to the process and the
residue is sent to the Metals Tailings Pond. Tailings pond return water is used to
79 Hatch Associates, Review of Environmental Releases for the Base Metals Smelting Sector,
prepared for Environment Canada, dated November 2000
53