Note: Descriptions are shown in the official language in which they were submitted.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
A HYDROMETALLURGICAL SEPARATION PROCESS OF STEEL MILL
ELECTRIC ARC FURNACE (EAF) DUST AND THE PIGMENTS OBTAINED BY
THE PROCESS
FIELD OF THE INVENTION
The present invention relates generally to the field of steel mill dust
treatment.
More particularly, the invention comprises a hydrometallurgical separation
process of dust produced by electric arc furnaces in steel mills. This process
permits, on one hand, the decontamination of the dust and on the other hand,
the
production of ferrite and/or magnetite pigments useful in paints, plastics and
concrete. The invention also comprises the pigments produced from this
process.
PRIOR ART
Electric arc furnace (EAF) dust, also known under the name of (K061), is
classified as a dangerous material because it contains high concentrations of
soluble heavy metals such as cadmium, zinc, chromium and lead, but in
particular
lead. More specifically, EAF dust usually contains more than 5 ppm soluble
lead
and hence, does not meet the limits of lead specified by TCLP (Toxicity
Characteristic Leading Prodecure). This dust also contains spinel compounds,
notably magnetite (Fe304) -and diverse ferrites (MO2FezO3). These spinel
compounds as well as contaminants appear in the form of agglomerates and
aggregates. To the naked eye, the dust is brown and an observer, even with the
aid of a magnifying glass, will not notice the presence of black balls of
magnetite,
even if certain black balls can attain 150pm in diameter. The brown ferrite
contained in the dust is ultrafine, and as a pigment, coats by adsorption the
larger
particles of magnetite.
Table I shows the typical chemical composition of EAF dust coming from two
distinct steel mills. These compositions show elevated concentrations of
certain
heavy metals.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
2
TABLE I
CHEMICAL ANALYSES OF EAF DUST COMING FROM TWO DISTING STEEL
MILLS IN THE PROVINCE OF QUEBEC
il T SAMPLES
Elements Code 11 Units MILL I MILL 2
AL ICP90 ppm 7100 4500
Ba ICP90 ppm 157 120
Ca ICP90 ppm 107800 146000
Cd ICP90 ppm 153 200
Co ICP90 ppm 14 61
Cr ICP90 ppm 1200 1400
Cu ICP90 ppm 1720 1700
Fe ICP95 ppm >30 258000
K ICP90 ppm 17700 7400
Mg ICP90 ppm 49200 22200
Mn ICP90 ppm 15300 27200
Mo ICP90 ppm 18 41
Na ICP95 ppm 33300 9700
Ni ICP90 ppm 125 130
P ICP90 ppm 500 670
Pb ICP90 ppm 10950 9500
Si ICP95 ppm 15500 15800
Ti ICP90 ppm 700 600
V ICP90 ppm 98 n.d.
Zn ICP90 ppm 93900 162000
Most EAF dust treatment processes in the prior art aim at recovering or
removing
the heavy metals in an "aggressive" manner, attacking the cristallographic
structure of the spinels.
Also known in the prior art, is EP 0 853 648 (equivalent to US 6,022,406),
which
describes a hydrometallurgical process of EAF dust treatment with the aim to
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
3
produce pigments. This process comprises a step of magnetic separation of the
dust into two fractions, one fraction containing less magnetic elements, and
the
other fraction containing non magnetic elements, as well as treatment steps of
these two fractions to obtain zinc ferrite pigments. The process disclosed
also has
as an effect to attack the cristallographic structure of spinels other than
the zinc
ferrite spinel, and in this sense, is also an aggressive process.
Therefore, there is presently a need for a treatment process of EAF dust that
permits an efficient and unagressive recuperation of the different ferrites
and
magnetites present in the dust, as well as permitting the decontamination of
the
dust.
SUMMARY OF THE INVENTION
One objective of the invention is to propose a treatment process of EAF dust
that
responds to this need.
According to the present invention, that objective is accomplished with a
hydrometallurgical process for the treatment of steel mill electric arc
furnace (EAF)
dust containing agglomerates of small ferrite particles and larger magnetite
particles, the ferrite particles coating by adsorption the larger magnetite
particles,
the dust further containing calcium oxide, zinc oxide and a toxic amount of
leachable lead together with minor elements selected from the group consisting
of
Mg, Cr, Cu, Cd, V, and chlorides. The process comprises the steps of:
a) washing the EAF dust in water to dissolve soluble salts, metals and simple
oxides contained in the dust, the washing step being performed with an
alkaline
pH;
b) decanting the solution of step a) to obtain a supernatant liquid containing
the
dissolved salts, metals and simple oxides, and a slurry containing ferrites
and
magnetites, a non toxic amount of leachable lead and a reduced amount of
calcium;
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
4
c) separating the slurry and the supernatant liquid;
d) adding to the slurry obtained in step c) an anionic surfactant to disperse
the
ferrite particles adsorbed on the magnetite particles; and
e) treating the slurry from step d) to produce pigments selected from the
group
consisting of ferrite pigments, magnetite pigments and ferrite/magnetite
pigments.
Preferably, the sequence of steps a) to c) is performed more than one time
before
adding the anionic surfactant.
The use of an anionic surfactant was found to increase the efficiency and
quality
of further separation steps such as screening, and ferrite/magnetite
separation by
a magnetic separator. 'Steps a) to c) also enable the decontamination of the
dust
by leaching salts, metals and simple oxides such as lead oxide. This selective
solubilization is due to the alcaline pH solution, which is preferably greater
than
12, resulting from the first washing, and optional second washing, with water.
This
alcalinity promotes the solubilization of PbO and, with the addition of
surfactant,
enables the product to pass the test set out by the TCLP, which regulates
standards of dangerous materials.
Advantageously, the process of the invention also enables the separation of
the
ferrites from the magnetites without breaking the cristallographic structure
of the
spinels, so as to produce magnetite and/or ferrite pigments of different
grades,
whose different compositions have commercial values.
The process also permits the decontamination of EAF dust by hydrometallurgical
means while maintaining the most stable families of spinels intact.
The solution obtained is step a) described above has a positive zeta
potential, and
the anionic surfactant is preferably added in a concentration sufficient to
reduce
the zeta potential to or close to the isoelectric point, and more preferably
to the
isoelectric point.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
The anionic surfactant is preferably a phosphate or an equivalent thereof.
More.
preferably, sodium metaphosphate is used as the surfactant.
The use of sodium metaphosphate presents the following additional advantages
to the process. Sodium metaphosphate converts the calcium and calcium
5 hydroxydes present in the liquid phase into a calcium phosphate which is
precipitated with the solid. Therefore, this form of calcium sequestering
allows for
a quicker and sharper fractionation of the slurry by, for example, a drum
magnet,
and in addition when the slurry is eventually separated by screening, clogging
of
the mesh opening is minimized, and therefore requires less cleaning.
Step e) of treating the slurry preferably comprises the step of magnetically
separating the slurry into a first fraction composed essentially of brownish
ferrites
and a second fraction composed essentially of black magnetite, the first
fraction
being less magnetic than the second fraction.
The magnetic separation is preferably performed with a magnetic field in the
range of 400 to 700 gauss, more preferably around 550 gauss.
In accordance with preferred aspects of the invention, the process further
comprises steps of treating the first fraction to produce ferrite pigments
and/or
treating the second fraction to produce magnetite pigments.
Treatment of the first fraction (ferrite)
The step of treating the first fraction preferably comprises the steps of:
- removing from the first fraction, particles having a grain size of 20 pm or
more, to obtain a refined first fraction;
- leaching the refined first fraction with a solvent, to obtain a leached
slurry;
- separating the leached slurry into a solid fraction containing ferrite
pigments and a liquid fraction containing constituents of the first fraction
soluble
in the solvent; and
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
6
- drying the solid fraction to obtain dry pigments of ferrites.
In accordance with a first variant, the solvent is water and the ferrite
pigments
obtained are ferrite pigments of a first grade.
In accordance with a second variant, the solvent is sulphuric acid, the
leaching is
performed at a pH of 0,5 to 3 and the ferrite pigments obtained are ferrite
pigments of a second grade.
In accordance with a third variant, the solvent is nitric acid, the leaching
is
performed at a pH of up to 3, and the ferrite pigments obtained are ferrite
pigments of a third grade.
In accordance with a fourth variant, the process further comprises the step of
wet
grinding the solid fraction to obtain a fourth grade of pigments having a
finer mean
grain size and a lower concentration of lead as compared to the ferrite of the
third
grade.
Treatment of the second fraction (magnetite)
The step of treating the second fraction preferably comprises the step of
screening at 6 pm to obtain a first finer fraction with particles having a
grain size of
6 pm or less, and a coarser fraction with particles having a grain size
greater than
6 iam.
In that case, the process preferably further comprises the steps of: milling
the
coarser fraction, and removing from the milled coarser fraction the particles
having a grain size greater than 40 pm and returning these particles for
further
milling, and a second finer fraction having particles with a grain size of
less than
6 pm, resulting in the coarser fraction containing particles having a grain
size
between 40 and 6 pm.
In accordance with a fifth variant of the process, the coarser fraction is
preferably
wet grinded by attrition to attain a mean grain size of approximately 0,3 pm.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
7
The grinded product is thereafter filtered and dried to obtain a magnetite
pigment
of a first grade.
In accordance with a sixth variant, the first and second finer fractions,
which
contain particles of less than 6 pm, are purified by suspending residual
contaminants contained therein with an anionic surfactant, to obtain a
purified
magnetic fraction. The purified fraction is thereafter decanted, wet grinded
by
attrition, filtered and dried, to obtain a magnetite pigment of a second
grade.
Production of magnetite/ferrite particles
In accordance with a seventh variant of the invention, which does not involve
magnetic separation, the process preferably comprises the steps of:
- removing from the slurry obtained in step d), particles having a grain size
of 60 pm or less, to obtain a refined slurry;
- leaching the refined slurry in nitric acid at a pH of about 3, to obtain a
leached slurry with no or a controlled amount of ZnO, which retards the
setting of
concrete;
- separating!the leached slurry into a s"olid fraction containing a mixture of
ferrite and magnetite pigments and a liquid fraction containing constituents
soluble
in nitric acid; and
- drying the solid fraction to obtain dry pigments containing a mixture of
ferrite and magnetite.
The pigments obtained with this variant are suitable for use in concrete
formulation for retarding the setting of concrete or for coloring the same.
All the seven variants described above also preferably comprise the steps of:
- coating the pigments with an inorganic and/or organic coating; and
25' - micronizing the coated pigments.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
8
The present invention also concerns ferrite pigments and/or magnetite pigments
or a mixture thereof, obtained by the processes described above. It also
concerns
a ferrite pigment from EAF dust, showing a resistance to leaching; and
preferably
showing a color thermal stability at temperatures of 300 C and higher.
Preferably, the ferrite pigment provides anticorrosion properties to metallic
paint
formulation.
The present invention also concerns the use of a ferrite pigment as described
above for incorporation in anticorrosive paint formulation, plastic
formulation or
concrete formulation; and the use of a magnetite pigment as described above
for
incorporation in a paint formulation, plastic formulation or toner formulation
to
provide magnetic properties.
BRIEF DESCRIPTION OF THE DRAWING
The characteristics of the present invention will be best understood by
reading in
a broad manner the following description of a preferred embodiment for
carrying
out the invention, while referring to the annexed drawing in which:
Figure 1 is a flow chart of the process according to a first variant suitable
for
producing ferrite pigments of the first grade.
Figure 2 is a flow chart of the process according to a second variant suitable
for
producing ferrite pigments of the second grade.
Figure 3 is a flow chart of the process according to a third variant suitable
for
producing ferrite pigments of the third grade.
Figure 4 is a flow chart of the process according to a fourth variant suitable
for
producing ferrite pigments of the fourth grade.
Figure 5 is a flow chart of the process showing a fifth and a sixth variant
suitable
for producing magnetite pigments of the first grade and the second grade.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
9
Figure 6 is a flow chart of the process according to a seventh variant
suitable for
producing ferrite/magnetite pigments.
Figure 7 is a graph showing extraction values for calcium, chromium, zinc and
lead versus time, and using a hydrofoil impeller.
Figure 8 is a series of graphs representing the variation of the zeta
potential, ph
,and conductivity versus the concentration of sodium metaphosphate for a
partly
washed dust slurry.
Figure 9 is a graph showing extraction values for calcium, chromium, zinc and
lead versus time, and using a high shear impeller.
Figures 10 to 13 are graphs showing the granulometric distribution of the
first
fraction (ferrite fraction) after one or two passes in the grinder
Figure 14 is a photo of ferrite pigments taken with an AFM microscope after
wet
grinding by attrition, showing the state of agglomeration and the fine size of
the
constituent ferrite fragments.
DESCRIPTION OF PREFERRED PIGMENTS PRODUCED WITH THE
PROCESS OF THE INVENTION
Four grades of ferrite pigments, two grades of magnetite pigments and one
grade
of ferrite/magnetite pigments were produced in the pilot run. The ferrite
pigments
were produced according to the first, second, third and fourth variants of the
process shown in figures 1 to 4; the magnetite pigments were produced
according
to the fifth and sixth variant of the process shown in figure 5, and the
ferrite/magnetite pigments were produced according to the seventh variant of
the
process shown in figure 6.
All pigment grades have been obtained by a substantially similar treatment.
The
processes use the same physical manipulation techniques, but differ in the
specific leaching step which gives the pigments their desired chemical and
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
surface characteristics. In many cases, specific coating also gives the
pigments
even greater specific properties for more particular markets.
The novelty of the process for all grades of pigment resides in an initial
treatment
of the EAF dust with water with the addition of an anionic surfactant. This
5 surfactant increases the efficiency and quality of the ferrite/magnetite
separation
by the magnetic separator. This initial treatment also enables the
decontamination
of the dust by leaching salts, metals and simple oxides such as lead oxide.
This
selective solubilization is due to the alcaline pH>12 solution resulting from
the first
washing (first mixing) and rinsing (second mixing) with water (Table 2). This
10 alcalinity promotes the solubilization of PbO and enables for the product
to pass
the test set out by the TCLP; which regulates standards of dangerous materials
(Table 3).
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
11
TABLE 2
WATER ANALYSES
First Treatment
Chemical Analyses
Zn Pb Cr Cd Ca
ppm ppm ppm ppm ppM
S99# 28 IT H20 1.36 170 0.75 0 770
S99# 28 1 T H20/ LV 1.56 41 0.95 0 340
B99# 79 1 T H20 3.21 71.7 15.74 0 206
B99# 79 1 T H20/ LV 2.00 65.4 1.93 0 492
TABLE3
TCLP RESULTS
FM Grade Analysis of leachate
# pH Pb Cr Cd Zn
ppm ppm ppm ppm
1076 Ferrite pigments of 8.5 0 0.32 0 0
the first grade
1084 Ferrite pigments of 8.7 0 0 0 0.17
the first rade
1104 Ferrite pigments of 2 0.20 2 240
the first rade
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
12
Ferrite pigments
First grade (Fl)
The ferrite pigment of the first grade was produced with the aid of a solution
containing an optimal concentration of surfactant, the concentration being a
function of the isoelectric point of the dust to be treated, and with a
leaching
hereafter referred as to the second treatment) with water only.
The first grade ferrite pigment contained a high quantity of lead that cannot
be
easily leached under normal pH conditions. After ten months and many
agitations
in water, this pigment showed no leaching of heavy metals (Table 4) and is
comparable to pigments of the second and third grade described below. Heavy
metals, with the exception of 8% zinc in the resistant form of zincite, wave
present
and stabilized in the structure of certain ferrites and spinels.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
'a
G LO d:
ti W. J o~~O O~
0
O cO O~ O r..
M N
u.
~
a~ J N J '-
O LO
0oO 0
OD ~ N N
y ~--
U) LL
z d)
0 V
M
W s.. J J J r Cfl J d. O
o ~ G. v) 000 U. m y ~ ~ N
o U) L-
W
LU ~ M
m
m
Q z
N t/~ ~) J J Cfl OO cJ- ~
N
W _.a 0 o M p Cp N
O O O I'
cn
W
W 4)
r ct) :~.. r
tC O ~
0 =
N 0 O M0) LO N:
~
H
LZ m Q. CL tt. Q.
Q. 0. Q. M Q. m
~
tn +r
d
~ II EE .
~ (j) o
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
14
The varied acid leaching steps of the process left solid ferrites of varied
compositions and, as experience has taught, the ferrites rich in Ca were less
stable to leachings than zinc ferrites or other ferrites representing complex
oxides
of Ca, Fe, Zn, Mn, Mg, Ni, Cr, etc. The resistant ferrites left after
leaching, which
made up the pigment, gave the pigment a high thermal stability and resistance
to
leaching, which are a function of the ionic stoichiometry and of the type and
quality of the composite cristalline structures.
On the other hand, the ferrite pigments of the first grade demonstrated high
resistance to corrosion as demonstrated in the salt spray (mist) tests,
allowing
coated metallic plates to resist corrosion for more than 1500 hours in a salt
mist,
which is equal or superior to all other pigments, including those of
commercial
quality used in the tests.
The first grade ferrite pigment owes its corrosion (salt mist) resistance to
CaO,
which is sacrificed as Ca(OH)2 and/or to the resulting alcaline viscosity
(soapy
appearance) associated with Ca(OH)2 and the pigment's elevated alcalinity.
Second grade (F2)
The ferrite pigment of the second grade was produced in the same way as the
first grade, except that the second treatment was performed with sulphuric
acid.
The preparation steps for the second grade pigments were identical to those
used
for the ferrite pigments of the first grade, the addition of the surfactant
occurring
after the first washing but before the magnetic separation. For the second
grade
pigments, leaching using sulphuric acid at a pH between 0,5 and 3 allowed for
the
preservation of a certain quantity of hydrated calcium sulphate, the
solubilization
of all the Zn in the form of zincite (ZnO) and the stabilization of lead as a
solid
sulphate. Using this treatment, the effluents rich in zinc sulphate, are a
suitable
form of compound to be directly recycled back into an electrolysis process, in
order to recuperate the value of the zinc. The calcium sulphates generated by
the
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
leaching are not harmful in anticorrosion paints. Calcium sulphate is
frequently
used as a filler with pigments used in paints and is often desirable as a
pigmentary additive. This pigment did not require wet grinding by attrition,
nor did
it require a second magnetic separation and a second screening after acid
5 leaching. The pigment was filtered in order to obtain an allowable soluble
salt
concentration of 0.3g/I mg, and was then dried and micronized.
In consequence, the second grade of ferrite pigments allowed for the
conservation
of a fraction of calcium, the transformation of lead oxide into lead sulphate
(which
is very stable) and the solubilization of zinc oxide into zinc sulphate. These
10 characteristics of the second grade pigment make this pigment an excellent
colorant as well as a corrosion resistant pigment.
Third grade (F3)
The ferrite pigment of the third grade was produced in the same way as the
first
grade, except that the second treatment was performed with nitric acid.
15 The leaching with nitric acid enabled the preferential removal of lead and
other
heavy metals due to the oxidizing property of the acid. The leaching was
performed at a pH between 0 and 3, which permitted the elimination of certain
families of ferrites, as a function of,the pH, in order to minimize the total
lead in
the pigment and to give a pigment with a particular signature with regards to
its
composition, structure and surface characteristics. As an example, between a
pH
of 3 and 1.5, the ferrites displayed a zeta surface potential that is
positive, but this
potential became negative at a pH < 1.5. This charge characteristic influenced
the acceptable coatings and their associated mechanisms.
The different ferrites issuing from these leachings, showed high heat
resistant
capabilities, which are very valued pigmentary properties. This leaching also
minimized the difference between the pigment colours and enabled a delta of
variation of about 0.5 for pigments of different dust deliveries (Table 5).
The
properties were equal or superior to the pigments currently recognized on the
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
16
industrial market. This grade of pigment showed enhanced resistance to
corrosion
depending on the coating used and also displayed a thermal stability as they
preserve their colour tint at temperatures exceeding 300 to 400 C.
TABLE 5
E VARIATION OF FERRITE HS4 PIGMENTS (THIRD GRADE) FROM MILL I
FM COLOR Delta E --IF # L a 11 b
1317 27.13 2.27 7.38 0.2
1318 27.1 2.36 7.35 0.15
1319 26.81 2.34 7.15 0.21
1320 26.82 2.4 7.25 0.17
This thermal resistance is a requirement for plastics, powdered paint and
ceramics.
Fourth grade (F4)
The ferrite pigment of the fourth grade was produced in the same way as the
third
grade, with the addition of a wet grinding step.
This pigment can be used in concrete as a cement additive that increases the
fluidity and compression resistance of the concrete. This pigment had a finer
granulometry than the third grade, ferrite pigment and the ferrite/magnetite
pigment.
The ferrite pigments of the first, second, third and fourth gradse have
applications
in anticorrosive paints. The third grade can be used in plastics and powder
paints
due to its thermal resistance. This pigment can also be used as a cement
additive,
thinning agent and additive in high performance concrete. The major difference
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
17
between the second and third grade ferrite pigments lies in their surface
properties.
Magnetite pigments
First grade (M 1 )
The magnetite pigment of the first grade was produced by grinding with a ball
mill
the magnetic fraction issuing from the magnetic separation. The ground
fraction
was passed through a screening between 38 and 6 pm, and wet grinding by
attrition in order to result in a median granulometry of about 0,3pm. The
pigment
was then filtered, coated with an organic coating, dried and micronized.
Second grade (M2)
The magnetite pigment of the second grade was obtained by screening the
magnetic fraction, which had already undergone ball mill grinding, at 6pm.
This
fraction was purified by putting the silica, carbonate and residual ferrite
contaminants into suspension, with the aid of an anionic dispersive surface
active.
More particularly, this pigmentary grade of magnetite was obtained by
screening
at 6pm the magnetic fraction of the magnetic separation and the fractions less
than 6pm coming from the screening of the rough magnetite after its ball mill
grinding. This fraction, which contained a concentration of magnetite, was
purified
by putting the silica carbonate and ferrite residue contaminants into
suspension
with the help of a surfactant. Two successive treatments of adding surfactant,
followed by a decantation of the magnetite and separation of the suspension,
were required to obtain an adequately black product which was subjected to wet
grinding by attrition in order to attain a desired granulometry. The solid was
finally
filtered with an organic additive, dried and micronized. This step of
purification is
similar to the first treatment of the dust. The ferrites and contaminants were
put
into suspension, and the magnetite was decanted.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
18
A rough non pigmentary magnetite was also produced. It was obtained after
attrition grinding the magnetic fraction coarser than 30pm. The attrition
cleans the
surface of the magnetite spheres by wearing out the white coating of calcium
and
silicate initially present. This step improves the black color of the spheres
and
eliminates the magnetites which are less resistant to abrasion. The 70 and
30pm
product can be used as a toner in photocopy processing. The commercial niche
of
this solid depends on its granulometry, morphology, resistance to friction and
magnetic properties.
Ferrite/magnetite pigments (FM)
Ferrite/magnetite pigment suitable as a colorant for concrete was produced
with
nitric acid at a pH of 3 but without magnetic separation. The slurry from the
first
treatment was subjected to the following steps: screening at 6 pm, leaching in
nitric acid, filtration in order to reduce its soluble salt content, and
drying in a flash
dryer, yielding a coarse pigment made up of agglomerates having a median grain
size of 5pm.
The screening enabled the removal of coarser contaminants including silica,
coal
and other fragments. After this, the slurry containing a magnetic charge
underwent leaching with nitric acid at a pH of 3 in order to remove the
zincite,
since zincite delays the setting of cement. The product was filtered in order
to
reduce its soluble salt content, after which drying in a flash dryer gave the
pigment
a granulometry with a median of about 5 pm.
For this grade of pigments, the initial pilot process was greatly simplified,
which
translates into a reduced production cost.
Because its granulometry is too large, the pigment cannot be used as an
additive
in cement, in order to make high performance concrete.
For all grades of pigments, whether ferrite pigments, magnetite pigments or
ferrite/magnetite pigments, at the end of the treatment, an organic additive
was
provided for the finished product. in order to standardize the surface
charges, to
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
19
facilitate the incorporation of the dry pigment into paint resins, and to give
a
desired fluidity for its handling. It is however worth mentioning that the
coating
step is optional to the process.
DESCRIPTION OF PREFERRED VARIANTS OF THE PROCESS ACCORDING
TO THE INVENTION
The process for treating EAF dust according to the invention is a
hydrometallurgical process for the treatment of steel mill electric arc
furnace (EAF)
dust that contains agglomerates of small ferrite particles and larger
magnetite
particles, the ferrite particles coating by adsorption the larger magnetite
particles,
the dust further containing calcium and toxic amount of leachable lead
together
with minor elements selected from the group consisting of Mg, Cr, Cu, Cd, V,
and
chlorides.
Ferrites represent a complex family of compounds represented chemically by the
major elements Ca, Fe, Zn, Mg, which are the major and important elements in
this process together with minor elements selected from the group consisting
of
manganese, chromium, copper, cadmium, lead, vanadium and chlorides. Most of
the elements are represented as oxides; either complex oxides like the
ferrites or
simple oxides represented by PbO, ZnO, CaO some other salts and metals are
also present. This process also applies to EAF dust with low zinc content
generated from the use of pre-reduced iron ore pellets of hematite.
The process steps according to different preferred variants of the process are
illustrated in figures 1 to 6, for the different grades of pigments. They show
a
hydrometallurgical batch process with no atmospheric emissions. The dust
slurry
of the first washing step is composed essentially of ferrites (65-75%),
magnetites
(20-28%), zincite (ZnO) and litharge (PbO) (8%), CaO/Ca(OH)2 (5-12%) and
variable concentrations of silica and coal.
One difference between the process of the invention and the prior art of EAF
dust
treatment processes, lies in the fact that the profitability of the present
process is
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
not a function of the zinc concentration of the EAF dust. One of the steel
mills that
will be seen in an example uses an EAF feed of at least 50% pre-reduced
hematite, with 50% scrap iron of different grades. Depending on the required
production, the percentage of hematite and scrap iron can vary. For this steel
mill,
5 the dust's average zinc concentration is close to 9% compared to 16-22% for
dust
generated from feeds composed of scrap iron only. Table I shows two chemical
anaiyses of EAF dust from the two steel mills in Quebec, that were used for
testing the process.
The optimization and characterization of the test pilot run were effected by:
10 = conducting physiochemical analyses: chemical analyses, granulometric
distribution tests, and identification of chemical phases by X-ray diffraction
and
electronic microscopy, etc.;
= optimizing the efficiency of the yield at different stations by measuring
the
volume and concentration (g/1) of the slurry, the weights of their solid
fractions,
15 and the processing time; the pH and electric conductivity of the liquids
being also
measured, etc.;
= noting the pH and the electrical conductivity of the liquids;
= evaluating the pigments by noting the colour specifications of the solid,
humidity, oil absorption capacity, quality of dispersion, and salt mist tests,
etc.
20 FIRST TREATMENT i
The process comprises a first treatment which essentially consists of washing
and
rinsing the EAF dust for reducing the amount of calcium and soluble lead, to
thereafter facilitate further treatment of the dust to produce commercial
grade
pigments.
More specifically, the first treatment, which is performed in a tank (10)
comprises
the steps of :
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
21
a) washing the EAF dust (12) in water to dissolve soluble salts, metals and
simple:
oxides contained in the dust, the washing step being performed with an
alkaline
pH which is preferably greater than 12;
b) decanting the solution of step a) to obtain a supernatant liquid (14)
containing
the dissolve salts, metals and simple oxides and a slurry (16) containing
ferrites
and magnetites, a non toxic amount of leachable lead and a reduced amount of
calcium;
c) separating the slurry (16) and the supernatant liquid (14); and
d) adding to the slurry obtained in step c) an anionic surfactant (18),
preferably a
phosphate and most preferably sodium metaphosphate, to disperse the ferrite
particles adsorbed on the magnetite particles. It is worth mentioning that
another
anionic surfactant known in the art and that would have the same effect of
dispersing the adsorbed ferrite particles is within the scope of the present
invention.
Preferably, the sequence of steps a) to c) is performed more than one time
before
adding the anionic surfactant. Note that steps a) to c) are not shown in the
figures.
Steps a) to d) are performed in the tank (10) shown in each of figures 1 to 6.
After
the first treatment, the slurry (16) from step d) is sent to further stages of
the
process to produce pigments selected from the group consisting of ferrite
pigments, magnetite pigments and ferrite/magnetite pigments.
The treatment of the slurry (16) will vary depending on the grade of ferrite
or
magnetite to be produced. The production of each of these grades according to
the process of the invention will be described in further detail further
below.
Example
An example of the first treatment is now described in further detail.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
22
Washing and first agitation
The EAF dust was washed with water under agitation provided by a hydrofoil
impeller with a rotation speed of approximately 350 rpm in a tank. The height
of
the fluid level and the tank diameter had a ratio of 1:1. The tank agitation
system
also comprised four baffles, which acted as static agitators.
The concentration of the slurry was 16%. Tests were made with batches of 10,
20
and 30 kg of dust for 60 liters of liquid, corresponding to solid
concentrations of
16, 32 and 48% respectively..
The washing provided:
= an aqueous solution of alkaline pH>12;
= a dissolution of soluble salts, heavy metals and simple oxides under
alkaline conditions (see Table 2) (this chemical charge was the liquid that is
eliminated by decanting and pumping the supernatant liquid);
= the initiation of the break-up of ferrite particles that are weakly linked
(Figure 7);
= the dissolution of CaO and some calcium ferrites into soluble calcium and
CaOH2,and the dissociation of lead oxide;
= the transformation of the CaO fraction abundant in CaOH2 and the
dissolution of lead oxide;
= It is worth mentioning that greater agitation with other types of cutting
agitators may unfavorably result in elevated concentrations in Ca and Pb in
the
liquid, which could hinder subsequent treatment steps.
= The duration of agitation was 60 minutes and it was followed by a
decantation period of 60 minutes and a separation of the supernatant liquid.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
23
Given the high specific weights of the ferrites and magnetites, decantation of
the
slurry solid was used instead of filtration.
Rinsing and second agitation
The slurry from the washing was rinsed with water. Water is preferable:
= to recuperate the metals and alcaline water of pH 12 from the interstitial
water in the 20 liters of residual pulp of the first mixing; and
= to continue the leaching of the calcium, lead and zinc in the dust.
The rinsing was carried out for a period of 60 minutes, followed by a 60
minute
decantation and recuperation of the supernatant liquid.
Addition of surfactant
The addition of a surfactant had various objectives in the process. Firstly,
it
reduced the positive charge of the fine particles of the pulp represented by a
zeta
of 32 mV in order to attain the isoelectric point (zeta of 0 mV) for the
system
(slurry). This reduction of the charge of the chemical phases of the system
facilitated the fractionation of the composites. Further details on the effect
of the
surfactant on the charge of the chemical phases are given in the section
entitled
"Magnetic separation" hereinbelow. Secondly, when a phosphate such as sodium
metaphosphate was used, the surfactant temporarily confined the CaO coming
from the ferrites by coating the surface of the particles with phosphate.
Also, the
surfactant was able to convert the calcium already in solution into calcium
phosphate, which was insoluble in the solution and was concentrated with
solid. It
was also believed that some of the lead in solution is also precipitated in
the form
of a lead phosphate or in the form of a calcium and lead phosphate phase.
These deductions are supported by titration of the slurry with sodium
metaphosphate, which is the preferred surfactant (Figure 8). The conditions of
the
tests whose results are shown in Figure 8 were: 5% of solid in a slurry of
240m1;
titration with the sodium metaphosphate of 3.6% (w/w) (22m1 of the solution
was
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
24
used); zeta potential calculated by using a laser volume median; S.G. 4g/cc.
The
graph showing Zeta vs. Surfactant Concentration, shows the reduction of the
positive charge down to the isoelectric point. The graph showing Conductivity
vs.
Surfactant Concentration represents the concentration of ions in the
supernatant
liquid, which decreases with the addition of surfactant.
After the addition of surfactant, agitation was resumed in order to
standardize the
state of the mixture and the feed of the magnetic separator which was fed at a
flow rate of 1 I/min. The slurry was fed into the magnetic separator while
agitating
in such a way as to maintain the slurry homogenous in its magnetite and
ferrite
content throughout the tank.
After the agitation step and the two decantation steps, the alkaline solutions
of the
effluents (80 liters) were used in the effluent treatment. The alkaline liquid
was
mixed with the acid effluents of the second treatment which will be described
further below, in order to neutralize their acidity and to promote
precipitation of the
metals in solution.
This first treatment (washing) of the raw EAF dust, which generated an
alkaline
solution, also promoted the solubilization of soluble salts in simple lead and
zinc
oxides to a concentration that satisfies the governing standards of the TCLP
test,
and the rules governing dangerous materials. In other words, the leachate of
the
dust did not exceed the TCLP (Table 3) standard and thus is neither considered
as contaminated, nor held under the rules of dangerous materials.
The role of agitation in the first treatment
Agitation tests were performed under variable times from 15 to 60 minutes,
using
a hydrofoil impeller. The resulting granulometry of the solid fraction of the
slurry,
was obtained by a granulometer able to measure to the scale of a nanometer,
according to the settings of number, surface and volume (Figure 7). The
corresponding granulometric variation after 60 minutes indicated an acceptable
size, with a median of roughly 0,6pm for the solid. This diameter was further
reduced during the leaching of the second treatment. With other impellers,
which
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
had higher shear levels, the resulting granulometry was too fine for
optimizing the
first treatment. Other agitation tests, in which the surpernatant liquid was
analyzed
after filtration for lead and calcium content, were performed and the results
are
presented in Table 6, and in Figure 9. The chemical concentrations resulting
from
5 the test with the hydrofoil impeller indicated a stable concentration for an
agitation
time of 60 min. This agitation time represented a maximum for the extraction
of
calcium, and a plateau of saturation for the value of lead. For the other
impellers,
the elemental concentrations were too high, and thus not optimized.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
M r N
M (IR ti ti
N N N CV
e-r~r
~
w U) ~ Q 00 ~ ~ ~ ~ ti ~M
= w N Q, ~r Mti ~ do cp ~ M9rI*
F-
C7 ~_
z
z cfl
CO J r~ Q~M M~~orO.
Q Q Q V M MMMN ~'6 4 'etd'
< z
w w
o a
cu C C rro M tt NtGt-
O vr-~ pp0 MMNti
Q- r r r~ M N r
w
J
~ Q N t~C ti ti ti ti ti Cp eco0
O O a) a)
E a r M 'd ~ ~ M d~ ~
p 0 -1~ E _
~
N ~- ~ U)
N N ~
~'a D~ Q
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
27
After the first treatment which is performed in the tank (10) of figures 1 to
6, the
slurry (16) is either sent to the magnetic separation (20) to separate the
magnetite
particles and the ferrite particles, as in figures 1 to 5, which show the
first to sixth
variants; or it is sent to screening (30) and thereafter to the second
treatment (40),
as in figure 6 which shows the seventh variant, to ultimately produce a
pigment of
ferrite and magnetite suitable for use as a colorant for concrete.
The first to the sixth variants, which concern the production of ferrite
pigments
(figures 1 to 4) and the production of magnetite pigments (figure 5), will now
be
described in further detail while referring to figures 1 to 5. For each of
these
variants, as broadly described, the slurry (16) from the first treatment was
subjected to a magnetic separation (20) to obtain a ferrite fraction (24) and
a
magnetite fraction (26). Both these fractions (24 and 26) were respectively
subjected to a screening (30 or 32).
Referring to figures 1 to 4, the refined ferrite fraction (34) from the
screener (30)
was further subjected to a second treatment (40) depending on the grade of
ferrite
pigments produced. In the case of the third and fourth variants (figs 3 and
4), the
second treatment was preceded by at least one of the following steps:
decantation
(60), grinding (50 or 55), and magnetic separation (200). After the second
treatment (40), the slurry (46) obtained was subjected to filtration (70), and
thereafter to the typical process steps used in the field of pigment
production, as
for example drying (90), coating (80) and micronization (100).
The filtration step (70) produces water to be recycled (72).
It is also worth mentioning that in the first and the third process variants,
the
second treatment was preferably followed by a second magnetic separation (200,
220) used to separate the magnetite fraction (202, 222) that remained in the
slurry
(46) from the ferrite fraction (206, 226). The ferrite fraction (206, 226) was
sent
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
28
back to the ferrite production line for producing the ferrite pigments,
whereas the
magnetite fraction (202, 222) was sent to the magnetite production line.
Referring to figure 5, the magnetic fraction (26) from the magnetic separation
(20)
was sent, preferably with magnetic particles (202, 212, 222) from other steps
of
the process, to a first screening (30) at 150 pm. The fraction (38) of less
than 150
pm was sent to a ball mill (500) and then to a second screening (32) to obtain
a
first finer fraction (304) with particles having a grain size of 6 pm or less;
and a
coarser fraction (306) with particles having a grain size greater than 6 pm.
The
coarser fraction (306) was then milled and screened at 40 pm (these steps are
not
shown on figure 5) to finally obtain a coarser fraction containing particles
having a
grain size between 40 and 6 pm.
The coarser fraction (306) was wet grinded by attrition (50) to attain a mean
grain
size of approximately 0,3 pm. It was thereafter subjected to the typical
process
steps used in the field of pigment production, as for example drying (90),
coating
(80) and micronization (100).
The finer fractions (304) were purified by suspending (600) residual
contaminants
contained therein with an anionic surfactant (802), to obtain a purified
magnetic
fraction (602).
MAGNETIC SEPARATION (20)
The magnetic separation step (20) yields the first fraction (24) containing in
a
major portion ferrite particles and the second fraction (26) containing in a
major
portion magnetite particles.
In the raw EAF dust, the black magnetite is never apparent or visible to the
naked
eye, even though the magnetite is large and rough compared to the other
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
29
components of the dust. This phenomenon is explained by the adsorption of the,
ferrites to the surface of the magnetites. In the raw dust, the ferrites are
positive
and the magnetite is negative, which causes an electrostatic attraction
between
these two chemical phases. This charge can be measured with an apparatus
called " Electroacoustic Sonic Amplitude (ESA)", which enables the calculation
of
the zeta potential of the particles in aqueous medium, and the indirect and
qualitative evaluation of the surface charge of the particles. The results
indicate
that ferrites have a positive charge with a zeta of +27 mV, whereas the
magnetites
are lightly negative and have a zeta of -3 mV, which corresponds to the charge
values for naturally occurring magnetites. Also, given that the ferrites have
a
granulometry under 1 pm, they will coat the large rough surface of the
magnetite.
This rough texture of the magnetite surfaces seems to be produced by the
deposition of phases of calcium and other composites which can be removed by
attrition. These factors render it difficult to separate ferrites from
magnetites.
Laboratory experience teaches us that without a surfactant, it is possible to
obtain
a fraction concentrated in magnetite, but this fraction is brown and not
black, and
has a large proportion of ferrites trapped with the concentrated magnetite.
In the process according to the invention, by adding an anionic surfactant
(preferably sodium metaphosphate), the positive charge of the ferrites is
neutralized and can be inverted to attain negative charges with an intensity
of -40
to -160 mV, and lower. The addition of surfactant increases the surface
charges of
the fine ferrites, decreases the cohesion or the attraction between the
ferrites and
magnetites, causes a stronger repulsion between the particles of ferrites and
maintains these ferrites in suspension. The coarse magnetic fraction, which
has a
very small specific surface, is not greatly affected by the addition of
surfactant.
The granulometry and the mass of the magnetites enable the decantation of the
magnetite with the ferrite in suspension. This procedure substantially
improves the
results of the magnetic separation and the screening. The condition at the
isoelectric point is preferable in order to optimize the magnetic separation
and the
screening (see next section), while controlling the concentration of lead in
the
solid.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
Evaluation of the results
Magnetic separation in aqueous medium was performed with a drum for which a
magnetic field was generated by an electro-magnet with a maximum power of
about 1200 gauss. The slurry (16), which had a concentration of solids of 16%
5 and a mass concentration of surfactant varying from 0,1% to 1,3%, was used
in
the separation. Magnetic separators are well known and do not need further
description. The slurry (16) was fed with a flow rate of 1 I/min. To unstick
the
magnetic fraction from the drum, an additional'flow of water (22) of 1,4 I/min
was
added, totaling 150 liters of liquid (to recycle) with a concentration of 3%
solids to
10 be recuperated by decantation (60) and screening (30).
The maximum fraction of magnetite recuperated in the pulp varied from one
company to another according to its production. However, the maximum fraction
recuperated was on the order of 15 to 20% for the producer using a pre-reduced
hematite mineral and between 8 to 10% for the producer using scrap iron only.
15 The quality of separation was qualitatively evaluated under the microscope
by
observing the colour, which distinguishes magnetite from coal. Colour is also
used
to evaluate the quality of magnetic separation. Table 7 compares the three
components of colour, according to the HunterLab color scale, for the raw dust
for
separation, and for the separated and screened fractions of ferrites and
20 magnetites. The parameter "L" of 0,00 corresponds to a black standard used
to
calibrate the apparatus whereas the value 100,00 is associated with the white
standard. The parameter "L" indicated a paler shade for the fractions obtained
without the addition of surface active, and which, in consequence, only
contained
a concentration of magnetite still coated with brown ferrites. On the
contrary, with
25 the addition of surface active, the magnetic fraction was of a blacker
shade
according to the optical apparatus and also according to the naked eye.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
31
TABLE 7
COLOR COMPARISON FOR THE EAF DUST, FERRITE AND MAGNETITE,
SEPARATED BY MAGNETIC SEPARATION (MSP)
Color
Samples L a b
Raw Dust 29.09 2.52 8.60
from mill 2
Sample before MS 28.63 2.05 8.01
with 0. 4 % NaMP
D0~
Sample after 28.30 1.75 7.67
20 pm Screening
Sample of Raw Magnetite 25.73 -0.23 3.08
< 38 lum
The efficiency of the magnetic separation is supported by the mass values of
the
quantity of ferrite trapped by the magnetite. The weights of the fractions
indicate
that without the addition of surfactant, the ferrite trapped by the magnetite
reached
a maximum. On the other hand, with the addition of a surfactant, the quantity
of
ferrite decreased (Table 8). The adsorption of the surfactant occurred
preferentially on the fine fraction of the solid and thus in this case, on the
ferrites.
The magnetites, being rougher, experienced a change in charge that is less
significant and thus there less of an effect on the mobility of this phase.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
41
:3
0
'C o
-~ ~
.~ o o
=3 N M
j O ~
0 0
Ln
Z
~
WL
F ~
W ~
Z
V
> 0)
_
~ ~ ~
L) 0)
c6 ~
m W
W a ~
a n
N J ~ cn E
M m N 0 (0 M O 0) O N I' CY) I-- Z V ~) d ) a~0 ~ f' cfl
O U)
~
~ Z
U.
O U.
H ~
o o õ- 4.1 o ~
z
= z
O
a o 0
(/) tiW tiW
~ ~ ~~ ~~
C14 p, ~
~ 00
C.0
co ~ rn rn rn rn ~
m m m m w m
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
33
Another indication of the efficiency of the separation is provided by the
results of
the tests of recuperation of magnetite obtained from the rough fraction ?20pm
after screening the non magnetic fraction. This ferrite fraction comprised-
rough
contaminants (i.e. coal) and magnetite, with a smaller amount of fine silica
and
carbonates or calcium phases. The magnetite was not separated in the first
magnetic separation as it was coated with silica and phases of calcium. The
trapped quantity varied with the quantity and concentration of the added
surfactant. For a separation without surface active, 197 g of rough magnetite
was
recovered. The same fraction after having added the surface active resulted in
a
recuperation of 221 g, or 11 % more magnetite recovered. This result is
explained
by the fact that the surface active is more efficient in dispersing fine
particles, and
thus the finer contaminants from the larger spheroids of magnetite; coal does
not
influence the separation.
For the process according to the invention, it is preferable to use the
surfactant
according to a specific dosage in order to produce two fractions (24 and 26)
that
are adequate for realizing products suitable for commercial applications, as
will be
expiained in more details further below.
SCREENING (30 or 32)
Screening of the ferrite fraction (24) or the magnetic fraction (26) is
essential to
produce ferrite pigments or magnetic pigments having a commercial value,
because it allows the physical separation of larger agglomerates and certain
contaminants accompanying the ferrites and magnetites. All particles or
agglomerated substances of more than 20pm with or without magnetic
susceptibility, can be separated. Coal and even partially fused scrap metal
fragments are separated by screening.
In addition to improving the separation of the ferrites and magnetites in the
first
treatment and the magnetic separation, the addition of surfactant prevents the
clogging of the screens and enables screening with openings of 20 to 6 pm. The
clogging is caused by portiandite, a calcium hydroxide Ca(OH)2, which is
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
34
produced from lime in the raw EAF dust. Portlandite in solution and in
suspension
is deposited on the walls of containers and, in particular, on the mesh of the
screens, thus sealing the latter. By using an appropriate surface active
(sodium
metaphosphate), the calcium in solution is precipitated in the form of calcium
phosphate. This precipitation is associated with the decrease in conductivity
observed during the addition of surfactant and this decrease continues after
reaching the isoelectric point, attaining, in certain cases, a minimum of
conductivity (Figure 9).
The screening tests demonstrated that the more the surface active
concentration
is increased, the more the solution approaches a minimum of conductivity and
the
less clogging of the screens is observed. Also, the inner walls of the tanks,
screens and other equipment can be easily cleaned by simply rinsing with
water.
If no addition of a surfactant is used, the portlandite which adheres to
surfaces
and screen mesh, must be cleaned with an acidic aqueous solution. The
, concentration of surfactant giving the minimum of conductivity is not
preferred
because such a high concentration of sodium metaphosphate interferes with the
leaching of lead in the pulp.
The addition of surface active to give the isoelectric point was sufficient to
double
the slurry flow rate into the screens from 4 I/min to 7 or 3(/min and thus
increase
the capacity of filtration. The addition of surface active decreased the
number of
required cleanings for a tank of 10 kg using a screen of 20 pm by a factor of
three.
In addition to the slurry, a flow of water for screening (32) is used to
facilitate the
screening.
In the first to third variants, the rough screened fraction (36) issued from
the first
screening (30) was subjected to a magnetite separation (210) used to separate
the magnetite fraction (212) that remained in the ferrite fraction (24). The
magnetite fraction (212) was sent to the magnetite production line, as shown
in
figure 5.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
WET GRINDING or grinding by attrition (50)
This wet grinding can be accomplished with silica sand, zirconium balls or
other
materials with a spherical morphology and sufficient hardness to resist
abrasion.
The results provided were obtained with the zirconium beads with a range of
5 granulometry of 0,4 to 0,6 mm in a horizontal grinder, with horizontal type
disks.
The grinding conditions and results are presented in Table 9.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
0 0
W ~ 00 ~
H
W
U.
w
~~
0
(0 (D
o 0
'i' 'r
0
/A V+LJ,I N N
ro
Z 00 t-
C.0 J a ~ M M
CY) U) Q
Z
0 ~ a 0 n L) U) o d
Q y LL LL V Q ~ ~~
z (1) h I~ M
O N >
U
Z
p ~ - - a,
E Q N t~ h
z M
O O .2 C '" Lo M
M M ~ U O O CO
V o E
W
.2 O
~ C C ~ Q
3 E E CD a~ uNi r
O cJ C CV CV
O O O
N LQ O
O O U
U~ ~ E
L O
0
~
N -~t N O
IA CV d 0 ~ N: rn
~ Q 0) '~' * *k N Q N m
dG a O O ~S'~' O O ~ 7 E
= i- U o oaa o O O LL
LII m I CVC~~'Ll. U 0 fl. ~ ~w
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
37
The goal of this grinding is to break the large aggregates of more than 5 to
20 pm
in order to give the ferrite pigment particles a restricted range of
granulometry,
more specifically, a bell curve distribution with a median around 0,3 pm. The
granulometric distribution after wet grinding assures that the fraction of
rough
aggregates of the dust is eliminated and transferred into the range of fine
granulometry. The obtained diameter (in surface) is from 0,25 to 0,28 pm, with
a
bell curve distribution desired for the pigments. The results are illustrated
in
figures 10, 11, 12 and 13. Figures 11 and 12 illustrate the granulometric
distributions for slurries after one and two passes in the grinder. For more
aggressive leaching processes, as for the second grade ferrite pigment, the
slurry
does not require grinding, the granulometric median being already close to or
just
under 0,8 pm. Normally, the first grade ferrite pigment requires grinding in
order
to obtain an adequate dispersion. Also, some dusts may contain enough
aggregates around 20pm as to require the use of a wet grinder. For cement
additives, wet grinding is necessary, because it~ decreases the granulometry,
increases the surface contact between the particles, and generates new
surfaces
for a more efficient leaching at the second treatment (40).
The ferrite pigment particles, even after grinding, are still aggregates of
fine
nanometric particles. Figure 14 (AFM microscope) confirms this state of
agglomeration and the fine size of the constituent beads or fragments.
SECOND TREATMENT (40) OF THE FERRITE FRACTION
The goal of the second treatment (40) is to leach the heavy metals still in
the
slurry, to eliminate the less stable ferrites and give certain required
surface
characteristics to the pigments (sign and zeta potential intensity), in order
to
improve the pigment compatibility in paints, plastics and concrete.
The chemical composition of the pigmentary spinels resulting from the second
treatment (40) is represented by the chemical compositions given in Table 10.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
38
These pigments represent various slightly differing ferrites or spinels rich
in iron,
zinc, magnesium and manganese and contain the elements Al, Si, Pb, Ni, Cr etc,
as minority components. All minority components are stabilized in the
structure of
the spinels and the lead adheres to the leachate criteria of the TCLP and to
the
norms and expectations used by paint manufacturers of which the most stringent
imposes a maximum concentration of 500 ppm of lead in paint.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
39
TABLE 10
VARIATION OF CHEMICAL COMPOSITION OF THE
PIGMENTS FERRITE IN FUNCTION OF pH
SAMPLES Elements Code Units Fm# 1226 Fm# 1217 Fm# 1314 Fm# 1491
pH 3,0 pH 2,0 pH 1,5 pH 0,5
AL ICP90 ppm 4500 4000 4100 3400
Ba ICP90 ppm 70 51 45 n.d.
C CHM118 ppm 3700 3700 n.d. n.d.
Ca ICP90 ppm 8800 5900 7200 6700
Cd ICP90 ppm 107 101 112 90
Co ICP90 ppm 11 <10 47 n.d.
Cr ICP90 ppm 1580 1710 1920 1745
Cu ICP90 ppm 2560 2510 2600 2645
Fe ICP95 ppm >30 >30 >30 528100
K ICP90 ppm 600 400 500 n.d.
Mg ICP90 ppm 24600 26800 28700 30100
Mn ICP90 ppm 24450 27090 28260 25900
Mo ICP90 ppm <10 <10 11 n.d.
Na ICP95 ppm 2700 2700 n.d. n.d.
Ni ICP90 ppm 187 187 219 n.d.
P ICP90 ppm 11400 400 600 n.d.
Pb ICP90 ppm 10870 3780 3030 1685
S CHM12 ppm 100 100 n.d. n.d.
Si ICP95 ppm 12900 8800 n.d. n.d.
Ti ICP90 ppm 600 600 600 n.d.
V ICP90 ppm 108 110 102 n.d.
Zn ICP90 ppm 89140 91470 117300 100600
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
As an example, the effect of the second treatment is illustrated in Table 10
by the
variation of lead for the different third grade pigment leached at different
pHs with
nitric acid. The most important variations are the lead concentrations and the
zeta
for the different pigments. The sign of the relative charge represented by the
zeta
5 potential in aqueous medium is particularly important, the latter changing
from
+40mV for the first grade to-9 to 11 mV for the leached pigment at a pH of 1,5
to
0,5. This parameter is important for the behavior of the pigment and also
influences the pigmentary properties and the coating mechanism, or even the
type
of coating it can accept, if required.
10 Conditions for the second treatment (40)
A pulp of 8 to 10% solids in 55 liters of water was acidified with nitric acid
6 N to
the desired pH by continuous addition of acid for a period of 30 min. The pH
was
maintained for 60 min. by sporadically adding the acid while agitating the
pulp.
Decantation was preferred and the surpernatant liquid was removed.
15 In the first variant, simply water is used as the leaching agent. In the
second
variant, sulfuric acid (42) is used, and in the third variant, nitric acid
(43) is used
as the leaching agent.
PRODUCTION OF FERRITE/MAGNETITE PIGMENTS (SEVENTH VARIANT)
Referring to figure 6, and in accordance with the seventh variant used to
produce
20 ferrite/magnetite pigment, the slurry (16) from the first treatment (10)
was not
subjected to magnetite separation. The slurry was rather subjected to a
screening
at the 60 pm or less. The finer fraction, hereinafter referred as to the
refined slurry
(33) was subjected to the second leaching treatment (40) with nitric acid (43)
at a
pH of about 3, to obtain a leached slurry (48) with no or a controlled amount
of
25 ZnO which retards the setting of concrete. The leached slurry (48) was
separated
into a solid fraction (74) containing a mixture of ferrite and magnetite
pigments
and a liquid fraction (72) containing constituents soluble in nitric acid. The
solid
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
41
fraction (74) was then dried (90) to obtain dry pigments containing a mixture
of
ferrite and magnetite.
SPECIFIC CHARACTERISTICS OF THE FERRITE PIGMENT OF THE THIRD
GRADE
The pigmentary properties for the ferrite pigments of the third grade are
shown in
Table 11 along with the commercial pigments recognized as ferrites. These
commercial ferrites are obtained by mixing oxides according to a company-
specific formulation and then calcining at high temperature. The table shows
different important quantitative pigmentary properties such as:
= pH;
= humidity;
= "long oil" absorption ;
= dry colour of pigment;
= paint colour;
= gloss;
= dispersion on the Hegman gage;
0 resin incorporation time
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
z
o LO
L = ~ o
E N
~ O O
G
Z N a M L
w r m 8) ~ u~ ~ U)
C~
w
~
o
w
r U- ~ Q v Un
r 0 1' = t~ a ~ Z
1 N 0 L o
N~ m W r m~ Co
~-- w
a
0
- Ln 0 S o ~ Un
ro a =a., z
~
M =t L= t~o '- ~
M
~,. r m.'''..0)0.0 Z C7... tno (fl
z
w
c!)
a
z
t' m d r- ~ Z
O LO
O M
r r m fn c0 o LL
N z
G1 OO ti
o ~ s
a. p 2 \ \\
r m r (A 'C U) o r- c0 ~
LL V z ~ 0
I
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
N N N O M M
N MCO o0 ID NN
C)Mct, O OMN
MCO ONO NN
~
Z o ~rlt) 1~ ~00
w p n N N M O Oo 00
N 0 Cr)tC) c0 C) V-
a
w
H
Otiti
L(J ~ r ML6 M C)
LL
r LL t6 O
r 0
ce) J W o ~OCfl ctN CV 1O 0)
m F, O O~ MN 00'7 T7
N ML6 I'N 0)C-4 N
~- w
O 0)Cr) MN 00)
(L O NLo LnM 6)W q
r C') (+)L6 f-- N O" C~ ~
CD O
Z c .4 o i
w N Nll~N d~o~0
N N
a
\
O d N
O
o (ON (OM
I' N
N 001' OOOOm)
0
O 00 O
fC 'y
C
~ ~
u. O. a n'. Q.
LO
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
M dM C~O tiN0
N O ~ O O 0) CV 00
O N
~
~
z
W
IL
LLI
~ O M UOC) M O C0M0
N N O o0 N 4 OO d'
r- O O O CV N I~
L1J
Ll.
T LI.,
~ 0
Nt J W
m ~
H
W 0 CYi ouo ce)
n. N q ticfl0
Q O N N 00
w
a
~
~
z
w
m 'IT ~ w~~
00 '- CR O N
O O ch N
N (O
N T O ~ O ~
ti
0 ) O O N O) I~
o d
O = ~_
Z i
O O N.a ~ C O ~
N 6-6 Cq O N O d iL
O R f0 0 ME im a 9100 n _
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
Another advantage of ferrite pigment of the third grade is its colour
stability at
temperatures exceeding 300. C. Table 12 shows the colour parameters for a
ferrite before and after heating to 300oC.
5
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
~ ~
Z f N
tfl
0
U.
W 0 ~ ~
o J
~ M N N
6L 0 O
tn (~ V
= z
O w
O I-= o CD
T u-
0 I- a O
W ~ (~
W O
a 0
~ w
a
0
O oC Lc)
v = ~ ~
H
H =
z ,
w CY)
o'
a
tn
C14
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
47
Salt mist tests for the pigments for which the properties were presented in
the
preceding section, are given in Table 13 for exposure times of 500, 1000 and
1500 hours, in a chamber designed for accelerated corrosion testing.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
I- <O M N ~
ca c0 c6 (B c6
A A =D N
=
~ <O t N N N
c"i n N
E o co
C fn c~-
_O L I~
R
O O O C) C)
E=-~r-
~ O
d O_
O V M
N YR..v0o 0 0 0 0 0
O ")
w cn
Q
7x v
w
U. ~ (O trO M
0
LO
FW- y o (.0
Z o i.c~ Ln to Lq
~ o 06 ti o rn
O y a
41
r N ~ V Q
0 p
OC) LU w
~ ~ It
I- ~ c :
W v - ~ oo Ln o u~ In
C* co co
W ~ Q
J
W ~
a c v,
N ao a - 0_ M a a, o
0
io o~ ti o 0
Q
cn
c LO
o co
U) p o m LO ~ ~
00 eo 0o
o
U
Q
y m m m y
O a C ~.
E
cV M R q LR ~ R et
~ V O O) h G) d 81 t~ ~ <O
W 0 N
v) v' r V ~- L ~- L r s r
0)2 ~k v ~k v v ~k 0
N o " U. a u. a a u2,. c
0 ' U.
U 00 00 GO N
>
O
IL~
U.)
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
LO
~
=3
~
.~
M CM N ~
~ d = ~
0 0
0
0 0 ~
co
0 0
0
0) LO r
06 oo Ila
~
O
T-
U~
00 oo Co
ti
p.. :2 LO ~
r ~ N ~ r O
~
~ ~ aa
ti
4+ ~ ~ a LO
U
'C 'O y- y- U Z~ Z
E
~ ~ ~ 0 0 ~
O CM N
v M ~ r M v c c N z W 2 ~~
E ~ o co ~~Z cZ
~ r, ~ ~+ fn L N C7 ~ (B M~~
Q. O. O N'd m ~- m mCV Cri v- Coco
U. (1~ LL fn 0 Oa~ x~ Cfl~~~ct N~ (0
O +-~ U z O NO ir- NN M C')
_, E ~- ~
N p
V) V)
fl) V ~ ~
~k ~k o~k o
a oz ~~z cnz z M
LLfqL. Op LL ILULL U LL O LL O
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
SPECIFIC CHARACTERISTICS OF THE MAGNETITE PIGMENTS
Magnetite production uses the same treatment units with the exception of an
impact grinder and a 6 pm screen. Normally, magnetite does not require
leaching
5 with acid and its surface characteristics are more constant.
Two magnetites undergo wet grinding: (1) the magnetite fraction after impact
grinding, between 38 and 6 pm and (2) the fraction of <_6pm after the
purification
with the surfactants. In both cases, the particles are too coarse or large in
diameter to be classified as pigments and require attrition. Zirconium beads
of 0,4
10 to 0,6 or 0,8 mm were used to attain a median particle size of 0,3 pm. The
initial
concentration of the pulp was 350 g/I and the grinding was performed
continuously until the desired granulometry was obtained.
The magnetite requires purification by putting ferrites and other contaminants
such as calcium and silica into suspension. This suspension is accomplished
with
15 the aid of an anionic surfactant such as sodium metaphosphate or saratan.
The
required dosage, in order to optimize the suspension, is obtained after
titrating the
pulp with the surfactant.
The results for the magnetite pigmentary properties of the present invention
and
the competitors' pigment properties are shown in Table 14.
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
p o
L
L r U
~
Z N ~O d o
w r~ M fn o M o0
w
F-
P: 0 N
L
w ~
Z -~Y ~
N~m ;~ ~ ~
~
fn m M ~ o d - co
r LL
w 0
LO m W
C*4 N
n, ec N
w
O ~''y cn " ~- ~ z
w r 00=r c~o ~
a
~--
z
w
o
C~ Ul) NN :2
M wn ~ . z
r m 0.~~ N J
N
Rf O C o0 00
O. E .-; E O d
vO dO Z O O
L ~ ~ ~ ~ = yL. =
L
~
C N
~ t~ z o oI
L()
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
0
L
~ L T- V
~
00 M f- ~
z W N m M fA o 00
w
o
w
Z
~ Q,t~ c z
Q M 0 Rf a,
rm m M (n o -'r co
r LL
N w 0
"' w f" o
O M ~ v~ c~ "'= - z
m2~r- u)o
a
F-
z
w
~ r O
C~ ~ .. N
w~~ t- z
ma u N N
o
~ .. o..... Eo ~r
~ o E- dU) o 0
3 E =?w~
U.
L /
~
.'y_ C
u. U z ~ ~)
LO
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
00 0) Ih M CD
z N O 0) M oi N
w ~ O CO O 1- ~ O
a
w
~
w
Z ~ =-
c~~ ry 'O
(D ~ o
~ o
'ct
U.
W 0
LO - ~ U)
aw.
~ ~ o v'Y' i Morn
0
N O O O O N M
a
~
z
w
LO
o cMO ~ooC q
N O O O N O M
a
4)
o. ~ .-.
.~ ... .. ~
c ~
C J cC .Q J af .tZ
Q,
.C a Y N
U) LO 4) C.
~ CO C~ ~I c~ ~ _
O as 0 N ui cN E
CA 02549070 2006-12-21
WO 2005/059038 PCT/CA2004/002147
54
The salt mist tests are also represented in this table for the magnetites.
Magnetite has morphologic and magnetic properties that enable it to be used in
inks (Toner) of photocopiers.
Although preferred embodiments for carrying out the invention were described
in
detail above and illustrated in the annexed drawing, the invention is not
limited to
these preferred embodiments, and many changes and modifications can be made
by a person skilled in the art, without leaving the framework or the spirit of
the
invention.
