2435
Selective Copper Flotation from a Copper/Nickel
Bulk Flotation Circuit
Bret Cousins
Lundin Mining Eagle Mine
ABSTRACT: The nickel/copper ore at the Eagle mine in Michigan undergoes a bulk flotation process as the
first step in producing nickel and copper concentrates. Due to the high grades of nickel and copper in the ore,
(nickel 2–4%, copper 1.5 to 2.1%) the flotation froth is overcrowded with material for several of the tank cells
of the rougher circuit, leading to nickel losses to the tails. With a large percentage of the copper floating in the
first cell, lab tests were carried out with copper selective collectors to determine if a much higher-grade product
could be produced. Its removal from the rest of the bulk rougher, cleaner and Cu/Ni separation circuits allow
them to run more efficiently in the recovery of nickel ores, reducing nickel losses to the copper concentrates.
INTRODUCTION
Eagle Mine’s Humboldt Mill consists of two balls mills and
three flotation circuits (bulk, cleaner and Cu/Ni separation).
The mill follows mineral processing convention, where
the copper (chalcopyrite) and nickel (pentlandite) miner-
als are floated together, and are separated in a later step,
exclusively using a xanthate as the only collector. However,
the flotation kinetics of copper minerals are much more
aggressive than nickel minerals. Applying the convention at
the Eagle Mine has shown copper minerals getting in the
way of nickel minerals floating in the bulk flotation circuit
when copper grades rise up towards equaling or exceeding
the nickel grades.
Testwork studying the possibility of floating off a near
nickel-less copper concentrate from the first flotation cell
has a goal of improving nickel recovery and final grade.
EAGLE MILL
The Ore
According to the XPS mineralogy report2, the Eagle Ore
sulphides consist of four primary minerals: pentlandite,
chalcopyrite, pyrrhotite and pyrite. Using the data from
Table 1, the nickel, copper, iron and sulphur assays were
converted to mineral assays of pentlandite, chalcopyrite,
pyrrhotite and pyrite. Each mineral’s molecular structure
was used to determine how much of the sulphur was used
for the pentlandite and chalcopyrite. The sulphur left over
was used up in pyrrhotite and pyrite, with a nine to one
weight ratio of pyrrhotite to pyrite. The remaining iron con-
tent in the ore was assumed to be oxides and silicates that
wouldn’t generally float. The non-sulphide gangue minerals
of concern are serpentine and orthopyroxene, representing
up to 35% of the ore, of which 14% floats in the rougher
circuit without magnesium mineral suppression chemistry.
With these feed grades, the ability of the froth to carry
the combined minerals efficiently is degraded. Table 2
shows the results of the first bulk rougher cell from the cir-
cuit survey, indicating that approximately 63% of the nickel
and 76% of the copper are carried into the froth of the first
rougher cell. Bubble definition is poor with so much mate-
rial is tied to them. Such froths are prone to retention of
gangue minerals trapped by their thickness. Copper min-
erals flotation kinetics also dominate over nickel minerals.
Selective Copper Flotation from a Copper/Nickel
Bulk Flotation Circuit
Bret Cousins
Lundin Mining Eagle Mine
ABSTRACT: The nickel/copper ore at the Eagle mine in Michigan undergoes a bulk flotation process as the
first step in producing nickel and copper concentrates. Due to the high grades of nickel and copper in the ore,
(nickel 2–4%, copper 1.5 to 2.1%) the flotation froth is overcrowded with material for several of the tank cells
of the rougher circuit, leading to nickel losses to the tails. With a large percentage of the copper floating in the
first cell, lab tests were carried out with copper selective collectors to determine if a much higher-grade product
could be produced. Its removal from the rest of the bulk rougher, cleaner and Cu/Ni separation circuits allow
them to run more efficiently in the recovery of nickel ores, reducing nickel losses to the copper concentrates.
INTRODUCTION
Eagle Mine’s Humboldt Mill consists of two balls mills and
three flotation circuits (bulk, cleaner and Cu/Ni separation).
The mill follows mineral processing convention, where
the copper (chalcopyrite) and nickel (pentlandite) miner-
als are floated together, and are separated in a later step,
exclusively using a xanthate as the only collector. However,
the flotation kinetics of copper minerals are much more
aggressive than nickel minerals. Applying the convention at
the Eagle Mine has shown copper minerals getting in the
way of nickel minerals floating in the bulk flotation circuit
when copper grades rise up towards equaling or exceeding
the nickel grades.
Testwork studying the possibility of floating off a near
nickel-less copper concentrate from the first flotation cell
has a goal of improving nickel recovery and final grade.
EAGLE MILL
The Ore
According to the XPS mineralogy report2, the Eagle Ore
sulphides consist of four primary minerals: pentlandite,
chalcopyrite, pyrrhotite and pyrite. Using the data from
Table 1, the nickel, copper, iron and sulphur assays were
converted to mineral assays of pentlandite, chalcopyrite,
pyrrhotite and pyrite. Each mineral’s molecular structure
was used to determine how much of the sulphur was used
for the pentlandite and chalcopyrite. The sulphur left over
was used up in pyrrhotite and pyrite, with a nine to one
weight ratio of pyrrhotite to pyrite. The remaining iron con-
tent in the ore was assumed to be oxides and silicates that
wouldn’t generally float. The non-sulphide gangue minerals
of concern are serpentine and orthopyroxene, representing
up to 35% of the ore, of which 14% floats in the rougher
circuit without magnesium mineral suppression chemistry.
With these feed grades, the ability of the froth to carry
the combined minerals efficiently is degraded. Table 2
shows the results of the first bulk rougher cell from the cir-
cuit survey, indicating that approximately 63% of the nickel
and 76% of the copper are carried into the froth of the first
rougher cell. Bubble definition is poor with so much mate-
rial is tied to them. Such froths are prone to retention of
gangue minerals trapped by their thickness. Copper min-
erals flotation kinetics also dominate over nickel minerals.