Gravity separation method using iron powder

A gravity separation method using iron powder is employed for subjecting a metal or ore to sink-float separation using a specific gravity liquid in which the iron powder is mixed and suspended. This gravity separation method comprises mixing and suspending the iron powder composed of fine particles having a size of 40 microns or less to form a specific gravity liquid having specific gravity within the range of 2.6 to 3.5, depending upon the intended use, and pouring various raw materials such as metals and ores into the specific gravity liquid so as to subject the raw materials to sink-float separation.

FIELD OF THE INVENTION 
The present invention relates to a gravity separation method using iron 
powder for performing sink-float separation of metals, ores and the like 
by using a specific gravity liquid in which iron powder is mixed and 
suspended. 
DESCRIPTION OF THE PRIOR ART 
In conventional methods of separating various raw materials by using a 
given specific gravity, the chemicals described below are generally used 
in laboratories. 
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Maximum 
Molecular Specific Viscosity 
Reagents Formula Gravity (20.degree. C.) 
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Zinc chloride ZnCl.sub.2 
1.95 
Carbon tetrachloride 
CCl.sub.4 1.60 0.98 
Benzene C.sub.6 H.sub.6 
0.88 0.65 
Toluene C.sub.7 H.sub.8 
0.88 0.59 
Bromoform CHBr.sub.3 
2.90 
Tetrabromoethane 
C.sub.2 H.sub.2 Br.sub.4 
2.96 
Methyl iodide CH.sub.3 I 
2.29 0.50 
Acetylene tetrabromide 
(CHBr.sub.2) 
2.96 
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However, all these chemicals are expensive, and some of them have high 
degrees of toxicity and are thus not usable by industry. 
Gravity separation methods have been industrially used in which suspensions 
of fine particles of solids in water, listed below, which are relatively 
inexpensive, easily available and have substantially no toxicity are 
formed. These are adjusted to have a given specific gravity so as to be 
used in gravity separation, solids as ores being placed in these liquids 
and used for sink-float separation therein. 
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Fine Solid Particle 
True Specific Gravity 
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Barytes (BaSO.sub.4) 
about 4.6 
Pyrite (FeSO.sub.4) 
about 4.6 
Magnetite sand (Fe.sub.3 O.sub.4) 
about 4.7 
Ferrosilicon (Fe + Si) 
about 5.5 
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However, although the upper limit of the specific gravity of a liquid which 
can be formed by this method depends upon the specific gravity of the fine 
solid particles serving as a medium and the ratio of water mixed 
therewith, any increase in the ratio of the fine particles mixed with the 
water causes the viscosity of the liquid to be increased. Thus, precise 
sink-float separation even of particles having sizes of 5 to 6 mm is 
difficult, and in practice the upper limit of the ratio of the fine 
particles mixed with the water is 40% by volume. Therefore, the upper 
limit for the specific gravity of a gravity liquid which can be formed by 
a medium of the type that generally used is 2.6 to 2.8 at most, and it is 
difficult to form a liquid having a specific gravity higher than this 
limit and yet having a low viscosity. 
The treatment of scrap of automobiles and domestic appliances has recently 
become an important social problem, and the separation and recovery of the 
aluminium contained in this scrap has become a particularly important 
social demand. 
Among these items of scrap, the engine blocks of automobiles contain 
portions made of aluminum alloy having a specific gravity reaching 3.15, 
while the true specific gravity of pure aluminium itself is 2.6. Thus, the 
specific gravity liquid formed by using a medium of the type generally 
used is unsatisfactory as a specific gravity liquid for use in sink-float 
separation of aluminium alloy, and such a specific gravity liquid cannot 
be easily formed. 
SUMMARY OF THE INVENTION 
The present invention has been achieved with a view to solving the 
above-described problem, and it is an object of the present invention to 
provide a gravity separation method which uses iron powder and which is 
capable of precise sink-float separation of aluminium alloy or the like 
using a specific gravity liquid having high specific gravity and yet low 
viscosity. 
To achieve the above-described object, a gravity separation method using 
iron powder of the present invention is characterized by mixing and 
suspending the iron powder composed of fine particles having a size of 40 
microns or less in water to form a specific gravity liquid with a specific 
gravity of at least 2.6 up to 3.5 depending upon the intended use, and by 
pouring the various raw materials to be treated such as metals, ores and 
the like into the specific gravity liquid formed so that the raw materials 
are subjected to sink-float separation. 
In the aforementioned gravity separation method, iron powder which is 
produced by steel works and which is composed of fine particles having a 
size of 40 microns or less is mixed and suspended in water contained in a 
water bath for the purpose of separating and recovering aluminum or an 
alloy thereof from scrap derived from automobiles, domestic appliances or 
the like, or an ore, to form a specific gravity liquid with, for example, 
a specific gravity of about 2.6 to be used for recovering aluminium or a 
specific gravity liquid with a specific gravity of 3.15 or more and low 
viscosity to be used for recovering aluminium alloy. The scrap of 
automobiles etc. or ore is poured into the specific gravity liquid formed 
so that the aluminium alloy with a specific gravity of about 3.15 or other 
non-ferrous metals with specific gravities lower than this value can be 
separated and recovered as floated product. 
As described above, in the present invention, the iron powder composed of 
fine particles having a size of 40 microns or less is used to form a 
specific gravity liquid with a specific gravity of 2.6 or more, depending 
upon the intended use, and various raw materials such as metals or ores 
are poured into the specific gravity liquid formed so as to subject these 
raw materials to sink-float separation. Therefore, it is possible to 
highly precisely separate aluminium or an alloy thereof which has a higher 
specific gravity from the shredded scrap of automobiles or domestic 
appliances, and to separate out substances which cannot be generally 
separated by conventional methods. In addition, since the use of iron 
powder in forming a specific gravity liquid with low viscosity enables 
separation of particles having sizes down to about 3 mm which is smaller 
than that which is feasible with conventional methods, the invention 
offers the remarkable effect that sink-float separation can be effected 
precisely.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An example of the present invention uses an iron powder, which is composed 
of carbon steel and which has the following physical properties, as the 
medium for forming a liquid having a high specific gravity and low 
viscosity: 
True specific gravity: 6.5 to 7.0 
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True specific gravity: 
6.5 to 7.0 
Particle size: +100 mesh . . . 10% or less 
-325 mesh . . . 80 to 90% 
Surface property: 
The surfaces have films of iron 
oxide thereon so that no red 
rust occurs in water (for 
example, Fe.sub.3 O.sub.4 film). 
Magnetic property: 
The iron powder has strong 
magnetism so as to be suitable 
for recovering them in the 
water. 
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Content of non-magnetic substances 2% or less 
Content of magnetic substances 98% or more 
Settling property: The height of the clear water produced in 5 minutes is 
10% or less of the height of a specific gravity liquid, and the settling 
speed of the iron powder in water is not so high. 
FIG. 1 shows a production process for producing Fe.sub.3 O.sub.4 coated 
steel powder. The main raw material used in this process is mill scale. 
The mill scale is provided at 102 in FIG. 1 and dried at 106. Coke powder, 
which serves as the reducing material is provided at 104 and dried at 108. 
The dried mill scale and coke is provided into an apparatus 110 which is 
used to load these materials into a sagger 112. The mill scale and coke 
powder are vertically arrange in layers and inserted into the sagger, as 
shown in the drawing. The sagger is placed in a tunnel kiln 114 having a 
reducing environment and a temperature of approximately 1000.degree. C. 
The temperature of the tunnel kiln should be less than the melting point 
of the scale. The mill scale is reduced in the tunnel kiln in a few hours. 
The sagger is taken from the furnace after the reduction is complete at 
which time the temperature of the powder is approximately 800.degree. C. 
The powder is cooled to a temperature of approximately 400.degree. C. to 
600.degree. C. outside of the furnace at 116. Since the outside of the 
furnace is subjected to outside air, i.e. an oxidate environment, the 
surface of the iron powder is oxidized and a coating film of Fe.sub.3 
O.sub.4 is formed thereon. The powder is sequentially crushed and 
classified by blowing at 118 and separated magnetically at 120 to produce 
a high quality powder which can be utilized as a heavy liquid separating 
medium having optimum grain size and magnetic properties. The powder 
produced by the curing step can alternatively be passed through the 
belt-type finish reduction furnace 124 to produce a reduced iron powder at 
126 which is suitable for powder metallurgy. 
FIG. 2 illustrates an X-ray analysis of the powder produced at 122. This 
X-ray analysis confirms this reoxidation. 
A liquid with a high specific gravity of 2.6 or more is formed by using 
iron powder having such physical properties, depending upon the intended 
use. The formation of a liquid having a high specific gravity of 3.2 is 
described below. In this case, the ratio of the iron powder mixed with 
water is as follows: 
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Weight (Kg) 
Volume (m.sup.3) 
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Iron powder 2600 0.40 
Water 600 0.60 
Total 3200 1.00 
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Concentration by volume = 40% 
Concentration by weight = 83% 
This specific gravity liquid has a concentration by volume of 40% and a 
sufficiently low viscosity, while a specific gravity as high as 3.2 can be 
obtained. Thus, the aluminium alloy contained in an engine block can be 
easily recovered by using a sink-float separation method. In addition, 
since the content of magnetic substances is as high as 98%, the iron 
powder can be recovered by means of a wet-type magnetic separator with 
substantially no loss if the product obtained by sink-float separation is 
washed with fresh water. 
As described above, the iron powder liquid with high specific gravity has 
low viscosity and thus enables raw materials to rapidly settle or float 
and gravity separation can be achieved with little error occurring due to 
undesired movement of the materials. 
When non-ferrous metal pieces obtained from shredded automobile scrap were 
subjected to gravity separation using the liquid with a high specific 
gravity of 3.2 having the above-described physical properties, the results 
obtained were as follows: 
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Conventional 
Example 
Example 
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Float yield of recovered aluminium 
40% 40% 
Sink yield of non-ferrous metal 
60% 60% 
alloy exclusive of aluminium 
Aluminium recovery efficiency 
98% 95% 
Contents of impurities 
2.0% or 5% or more 
in recovered aluminium 
less 
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The precision of this separation is extremely high compared with 
conventional separation methods using other media and liquids with high 
specific gravities. The above-described aluminium recovery efficiency and 
contents of impurities in the recovered aluminium are much better than the 
above-described values for the Conventional Example which cannot be easily 
obtained by conventional methods. The value of recovered aluminium depends 
to a significant extent upon the amount of impurities contained therein, 
i.e., the purity of aluminium. The example of the present invention shows 
a reduction in the amount of impurities to a value one half or less that 
obtainable with conventional methods. 
In addition, in the sink-float separation of the above-mentioned example 
using the high-specific gravity liquid composed of iron powder, the 
specific gravity liquid has low viscosity and thus enables gravity 
separation of fine particles and separation of particles having a size 
down to 3 mm with high precision. In contrast, the high-specific gravity 
liquid obtained from a medium (the above-described fine solid particles) 
which is generally used has high viscosity and thus makes precise 
sink-float separation even of particles having a size of 5 to 6 mm 
difficult. 
Therefore, the separation method using the high-specific gravity liquid 
obtained from the above-described medium can be applied to almost all 
sink-float separators such as rotary drum-type, vertical wheel-type and 
screw sweeping-type separators regardless of the classes thereof. Although 
this example concerns a liquid with a specific gravity of 3.2, the use of 
iron powder having a true specific gravity of up to 7.0 is feasible and 
liquids having specific gravities within the range of 2.6 to 3.5 can be 
formed by changing the ratio of iron powder mixed in. Aluminium alloys as 
well as certain types of ore can be subjected to sink-float separation 
using a high-specific gravity liquid having a specific gravity of 3.5. 
It is also effective to add fine particles (slime) of some clay minerals 
for the purpose of maintaining the stability of the above-described 
specific gravity liquid of iron powder. 
Since there is no industrial example in which various raw materials are 
subjected to sink-float separation using the above-described specific 
gravity liquid obtained by using iron powder as a medium, this invention 
will allow the development of a new industrial field in which iron powder 
is used as a new heavy media material. 
As described above, in the present invention, a liquid having a specific 
gravity of 2.6 or more is formed by using iron powder composed of fine 
particles having a size of 40 microns or less, depending upon the intended 
use, and various raw materials such as metals or ores are poured into the 
specific gravity liquid so as to be subjected to sink-float separation. 
Therefore, aluminium or an alloy thereof having a high specific gravity 
can be separated and concentrated with high precision from shredded 
automobile scrap or scrap derived from domestic appliances, and substances 
which cannot be separated by conventional methods can thus be separated. 
In addition, since the specific gravity liquid using iron powder has low 
viscosity, the present invention enables separation and concentration of 
fine particles having a size down to about 3 mm, which is smaller than 
what can be separated by conventional methods, and offers the excellent 
effect that precise sink-float separation is possible.