Method and apparatus for retrieving metallic vapor in the liquid phase using pool of molten retrieving metal

A mixture gas containing metallic vapor with oxidizing gas produced by reducing of the oxide of the metal at high temperature is led, at a high enough temperature and a low enough pressure for the reverse oxidization reaction between them to not substantially take place, into a convergent-divergent nozzle, and squirts out from the nozzle, as cooled down rapidly by adiabatic expansion in the nozzle to a low enough temperature for the oxidization reaction between them to not substantially take place, to be led to the surface of a pool of molten retrieving metal, either directly or via deceleration. The retrieving pool metal may be the same kind as the metallic vapor to be retrieved, or may be different. When the metallic vapor to be retrieved is magnesium vapor, the retrieving metal of the different kind may be lead, bismuth, tin, antimony, or a mixture thereof.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for retrieving metallic vapor 
from a mixture gas which contains said metallic vapor, and to a device for 
practicing said method; and more particularly relates to a method for 
retrieving, from a mixture gas which has been produced by a reduction 
reaction of an oxide of a metal and which contains vapor of said metal and 
oxidizing gas also produced as a result of said reduction reaction, said 
metallic vapor in a liquid state, and to a device for practicing said 
method. 
A known method of preparing a metal in the pure state is to reduce an oxide 
of the metal by heating this oxide to a high temperature along with a 
reducing material which then preferentially combines with the oxygen in 
said oxide, thus abstracting said oxygen from the oxide and leaving the 
metal in pure form. At such a high temperature the metal is left in the 
form of metallic gas or vapor, and this vapor is mixed with the other 
products of the reduction reaction, i.e. with a compound or compounds of 
the oxygen and the reducing material. Thus, the question arises as to how 
the metallic vapor can be cooled down and separated from the product of 
the reduction reaction, without the reverse or oxidizing reaction 
occurring, i.e., without the metallic vapor recombining with the reduction 
reaction product. This reverse reaction can easily occur, especially in 
the case of certain metals such as for example magnesium. 
In the case of metals which have a relatively low tendency to undergo the 
reverse or oxidizing reaction, and which have a low melting point, such as 
for example zinc, there has been practiced a prior art retrieval method in 
which the high temperature mixture gas consisting of the gaseous products 
of the reduction reaction including zinc vapor has been introduced into a 
condenser containing a mass of molten metal having a fairly low 
temperature which is lower than that of the mixture gas, and in which the 
metallic vapor in the mixture gas has been condensed into liquid by the 
molten metal being contacted intimately with the mixture gas by being 
splashed with a stirrer or paddle or impeller or the like. Thereby, the 
metallic vapor is rapidly cooled and is picked up by the molten metal. As 
a variation of this prior art method, it has been known for the condenser 
to be shaped as a U-shaped tube, with the molten metal for retrieval 
contained in the bend of the tube, and for the mixture gas consisting of 
the gaseous products of the reduction reaction including the metallic 
vapor to be blown around this U-shaped tube, being bubbled through the 
molten metal for retrieval. 
This prior art method is effective for retrieving the vapor of a metal such 
as zinc which has a relatively low tendency to undergo the reverse or 
oxidizing reaction and which has a low melting point, but it does not work 
well in the case of retrieving the vapor of a metal such as magnesium or 
calcium which has a relatively high tendency to undergo the reverse or 
oxidizing reaction and which has a high melting point. In such a case, 
when this method is applied to retrieving the vapor of (for example) 
magnesium or calcium, the reverse or oxidizing reaction occurs to such an 
extent that both the purity of the retrieved metal and also the efficiency 
of retrieval are unacceptably low. Therefore, as far as these metals are 
concerned, this method is not of practical use for retrieving their 
vapors. 
Another prior art method for retrieving metallic vapor from the gaseous 
products of a reduction reaction including said metal vapor has been the 
so called gas cooling method, in which a large volume of natural gas or 
hydrogen gas has been blown into and mixed with said gaseous products of 
the reduction reaction which are at a high temprature, so as rapidly to 
cool them. However, with such a retrieval method, it is very difficult 
completely to prevent the reverse reaction occurring, and according to 
this the purity of the retrieved metal is low, about 50% or so in the case 
of a continuous process. Further, this method has the additional 
disadvantage of having a high cost, since a large volume of gas for 
cooling is required. 
SUMMARY OF THE INVENTION 
Accordingly, in view of the above problems, it is the primary object of the 
method aspect of the present invention to provide a method of retrieving 
metallic vapor from a mixture gas, consisting of the gaseous products of a 
reduction reaction including the metallic vapor, which effectively 
performs such retrieval. 
It is a further object of the present invention to provide such a method of 
retrieving metallic vapor from a mixture gas, which provides retrieved 
metal of high purity. 
It is a further object of the present invention to provide such a method of 
retrieving metallic vapor from a mixture gas, which retrieves a high 
proportion or ratio of the metallic vapor. 
It is a further object of the present invention to provide such a method of 
retrieving metallic vapor from a mixture gas, which retrieves the metal in 
the liquid phase. 
It is a further object of the present invention to provide such a method of 
retrieving metallic vapor from a mixture gas, which is suitable for 
retrieving the vapor of a metal which has a high tendency to undergo the 
reverse or oxidization reaction. 
It is a yet further object of the present invention to provide such a 
method of retrieving metallic vapor from a mixture gas, which is suitable 
for retrieving the vapor of a metal which has a high melting point. 
It is a yet further object of the present invention to provide such a 
method of retrieving metallic vapor from a mixture gas, which does not 
require any large volume of cooling gas. 
It is a yet further object of the present invention to provide such a 
method of retrieving metallic vapor from a mixture gas, which is of 
acceptably low cost. 
According to the most general method aspect of the present invention, these 
and other objects relating to a method are accomplished by a method of 
retrieving metallic vapor from a mixture gas containing said metallic 
vapor together with oxidizing gas, wherein: said mixture gas is led, at a 
high energy temperature and a low enough pressure for the oxidization 
reaction between the metallic vapor and the oxidizing gas to not 
substantially take place, into the upstream end of a convergent-divergent 
nozzle; and the jet emitted from the downstream end of the 
convergent-divergent nozzle, which has been cooled rapidly by adiabatic 
expansion in said convergent-divergent nozzle to a low enough temperature 
for the oxidization reaction between the metallic vapor and the oxidizing 
gas to not substantially take place, is led to the surface of a pool of 
molten retrieving metal. 
Further, according to the present invention, these and other objects 
relating to an apparatus are accomplished by an apparatus for retrieving 
metallic vapor from a mixture gas containing said metallic vapor together 
with oxidizing gas, comprising: a gas tight housing means which defines a 
mixture gas supplying chamber for supplying said mixture gas at a high 
enough temperature and a low enough pressure for the oxidization reaction 
between the metallic vapor and the oxidizing gas to not substantially take 
place, and a retrieving chamber for accomodating a pool of molten 
retrieval metal; a convergent-divergent nozzle leading from said mixture 
gas supplying chamber to said retrieving chamber; means for heating said 
mixture gas supplying chamber to said high enough temperature and for 
heating said retrieving chamber to a sufficient temperature to keep said 
pool of molten retrieval metal in the molten state; and means for 
depressurizing the interior of said housing means, so that the interior of 
said mixture gas supplying chamber is kept at said low enough pressure. 
Basically, the present invention is based upon the well known principle 
developed by F. J. Hansgirg towards the end of the 1920's: that the 
reaction of equation (1) below proceeds to the right, for thermodynamical 
reasons, at temperatures over 1860.degree. C. 
EQU MgO+C=Mg+CO (1) 
According to the present invention as described above, in the case of 
retrieving metallic magnesium vapor from the mixture gas as described 
above consisting of magnesium vapor and carbon monoxide which has been 
made in the reducing furnace at high temperature by squirting it through a 
convergent-divergent nozzle (thus rapidly cooling it at a high rate such 
as 10.sup.6 .degree. C. or greater) and by using magnesium as the molten 
retrieving metal to receive the jet flow from the nozzle, as will be 
understood from results obtained in the second, third, and fourth 
preferred embodiments of the present invention, which will be detailed 
later in this specification, a much improved performance, over 
conventional methods, of retrieving magnesium vapor can be obtained. In 
fact, as will be seen later, a retrieval ratio of 90% or more can be 
realized, and the purity of the magnesium end product can be as high as 
90% or so (vide infra). Further, the product is directly usable in its 
molten state. 
However, since the molten magnesium retrieving metal pool needs to be kept 
in the molten state at all times, its temperature needs to be kept at 
650.degree. C. (which is the melting point of magnesium) or higher; and 
for instance if the temperature of this molten magnesium retrieving metal 
pool is kept at around 700.degree. C. then since at this temperature 
magnesium has a vapor pressure of 6.7 torr a certain amount of magnesium 
vapor, corresponding to this vapor pressure, is ejected from the metallic 
vapor retrieval chamber without being retrieved, as a vaporization loss. 
Hence even in an experimental furnace the retrieval ratio of magnesium 
cannot be brought to exceed 96% (94.1% in lot average). Further, although 
the molten magnesium retrieving metal pool is in the liquid state, the 
magnesium vapor in the jet flow from the convergent-divergent nozzle and 
the carbon monoxide in said jet flow mutually react together to a certain 
extent as they plunge together into the molten retrieving magnesium metal 
pool, and further on the boundary surfaces of the carbon monoxide bubbles 
in the molten magnesium some of the molten magnesium is undesirably 
oxidized. Hence according to operation in an experimental furnace it is 
difficult to increase the purity of the retrieved magnesium metal to 93.3% 
(92% in lot average) or higher. 
Therefore, according to a particular feature of the present invention, it 
is proposed to practice a method as described above, in which said 
retrieving metal is a different metal from said metallic vapor. 
By suitably choosing the retrieving metal in accordance with the metallic 
vapor which is desired to be retrieved, as will be seen hereinafter an 
improved performance of retrieving metallic vapor can be obtained. In 
particular, by choosing a type of retrieval metal which has a lower 
melting point than the metallic vapor which is desired to be retrieved, 
the temperature of the pool of molten retrieving metal can be kept lower 
than if it were composed of the same type of metal as the metallic vapor, 
and accordingly the occurrence of the reverse or oxidization reaction can 
be reduced. Thereby the efficiency of the retrieval of the metallic vapor 
can be increased, and the purity of the final product can also be 
improved. 
In particular, the particular case wherein said metallic vapor is 
magnesium, and said retrieving metal is selected from the group composed 
of lead, bismuth, tin, antimony, and mixtures thereof, is of particular 
interest. 
In this particular case, when this method is applied to a refining system 
for magnesium in which magnesium oxide and carbon are heated together in a 
reduction furnace, so as to produce a mixture gas consisting of metallic 
magnesium vapor and carbon monoxide gas, which is as stated above 
retrieved by being squirted through the convergent-divergent nozzle and by 
being led into a pool of molten retrieving metal which is either lead, 
bismuth, tin, antimony, or a mixture thereof, then since the temperature 
and pressure conditions in the reduction furnace may be chosen so as best 
to promote the reduction reaction of magnesium oxide with carbon, while 
the size and other parameters of the convengent-divergent nozzle may be 
selected as proper in order to provide the desired pressure drop and the 
desired temperature drop therethrough, thereby the retrieving metal pool 
may be kept at a temperature sufficient to keep it molten, and the 
efficiency of the magnesium reduction system as a whole may be improved. 
When the rapidly cooled and condensed magnesium vapor is absorbed by the 
molten retrieval metal pool, the magnesium forms a eutectic solution with 
the material (lead, bismuth, tin, antimony, or a mixture thereof) of said 
molten retrieving metal pool. The following consequences will ensure. 
First, upon this eutectic dissolution the chemical activity of the 
magnesium drops, as compared with the case of only magnesium. In FIG. 1 of 
the accompanying drawings, there is given a graph, in which partial mol 
ratio of magnesium is shown along the horizontal axis, and the activity 
coefficient (activity/mol ratio) of the magnesium is shown logarithmically 
along the vertical axis. The four lines show the variation of activity 
coefficient of magnesium with respect to its partial mol ratio, when the 
magnesium is in a eutectic solution with, respectively, lead, bismuth, 
tin, and antimony, at a temperature of 850.degree. C. From this figure, it 
can be seen that in the region of partial mol ratio equal to about 0.4 the 
activity coefficient of magnesium (and the activity) drops suddenly with a 
decrease in the mol partial ratio. 
Now, when the activity of magnesium drops suddenly, the reverse or 
oxidization reaction between magnesium metal vapor and carbon monoxide 
becomes difficult to occur suddenly. In other words, metallic magnesium 
and carbon monoxide change into magnesium oxide and carbon according to 
the following equation (2): 
EQU Mg+CO=MgO+C (2) 
and this equation (2) proceeds to the right when the free energy dF 
expressed by equation (3) below of the reaction becomes negative: 
EQU dF=dF'-RTln(a.sub.Mg)-RTln(P.sub.CO) (3) 
where: 
dF is the free energy of the reaction of equation (2); 
dF' is the standard free energy of the reaction of equation (2); 
R is the gas constant; 
T is the temperature; 
a.sub.Mg is the activity of magnesium; 
and P.sub.CO is the pressure of carbon monoxide. 
For instance, when T equals 300.degree. to 900.degree. C., P.sub.CO equals 
0.1 to 200 torr, a.sub.Mg equals 1.0, then dF is negative, and the 
magnesium can return to magnesium oxide by oxidization. However, the 
activity of magnesium drops suddenly as it enters into a eutectic solution 
with lead, bismuth, tin, antimony, or a mixture thereof, as shown in FIG. 
1, and so dF becomes greater as the second term of equation (3) becomes 
smaller, and the reverse or oxidization reaction expressed by equation (2) 
becomes more difficult to occur suddenly. 
Now, as the activity of magnesium drops, its vapor pressure also becomes 
smaller. Generally, the magnesium vapor pressure P.sub.Mg in Pb of 
magnesium in a Pb-Mg bath containing x.sub.i mol of magnesium at the 
temperature of T.degree. C. may be expressed by equation (4) below: 
EQU P.sub.Mg in Pb =P.sub.Mg (pure) +a.sub.Mg in Pb ( 4) 
where: 
P.sub.Mg (pure) is the vapor pressure of pure magnesium at T.degree. C.; 
and a.sub.Mg in Pb is the activity of Mg in a Pb-Mg bath containing x.sub.i 
mol of Mg at T.degree. C. 
As can clearly be seen from equation (4), as the activity of magnesium 
drops, its vapor pressure becomes smaller. In FIG. 2, in which temperature 
in degrees centigrade is shown along the horizontal axis and vapor 
pressure is shown logarithmically along the vertical axis, the variation 
with temperature of the vapor pressure of magnesium with respect to pure 
Mg and with respect to a 0.5 mol eutectic solution of Mg in Pb are shown 
by the solid lines, and for comparison the variations with respect to 
temperature of the vapor pressures of pure Sb, pure Bi, and pure Pb are 
shown by the dashed lines. From this figure, as shown by the exemplary 
ordinates and abscissae, it will be understood that the vapor pressure of 
the magnesium in the 0.5 mol eutectic solution of Mg in Pb at 700.degree. 
C. is 0.77 torr, which is about one ninth of the vapor pressure of pure Mg 
at that temperature, which is about 6.7 torr. Also, in the case that the 
magnesium is in a state of eutectic solution in bismuth, tin, antimony, or 
a mixture of these various materials, likewise the vapor pressure of the 
magnesium drops as the activity drops, although this is not shown in FIG. 
2. 
In FIG. 3, in which weight percentage of Pb in a Mg-Pb mixture is shown 
along the horizontal axis (at the lower side of the figure), and melting 
point in .degree.C. is shown along the vertical axis, the variation of the 
melting point of this Mg-Pb mixture is shown as the proportions vary. From 
this it will be understood that when the percentage by weight of lead is 
0% (i.e., in the case of pure magnesium) the melting point is 650.degree. 
C., but as the content of lead increases and the content of magnesium 
decreases the melting point of the eutectic solution drops, and for 
example when the mol partial ratio of magnesium is 0.5 the melting point 
is 480.degree. C. Therefore, as compared with the previously described 
case wherein the retrievel metal is pure magnesium (i.e. as in the case in 
embodiments two, three, and four of the present invention), the 
temperature of the retrieval metal pool, when this is such a 50% mixture 
of lead and retrieved magnesium, can be set substantially lower; and this 
not only confers advantages in handling and in saving energy, but also 
keeps the vaporization loss of magnesium and the occurrence of the reverse 
or oxidization reaction low. FIG. 4 is a diagram similar to FIG. 3 showing 
the melting performance of Mg-Sn mixture, from which it will be understood 
that the same effect is available by using a Mg-Sn mixture as the 
retrieving mixture. 
For instance, when magnesium is to be retrieved by using a retrieving 
molten metal bath of lead, and the mol ratio of the retrieved magnesium 
and lead in this retrieving metal bath is kept between zero and 0.5, then 
the melting point of the eutectic solution will be 480.degree. C. at the 
maximum. If therefore the temperature of this molten retrieving metal bath 
is kept at 580.degree. C., taking a margin of 100.degree. C. over the 
maximum melting point for safety, then as seen from FIG. 2 the vapor 
pressure of the magnesium will be equal to 0.06 torr (with x.sub.i equal 
to 0.5 mol) or less, and a vaporization loss of one hundredth or less will 
occur, as compared with the case in which pure magnesium is used as the 
retrievel metal, in which case the vapor pressure of magnesium is 0.7 
torr. 
The elements which make up the molten retrieving metal pool, as described 
above, may be lead, bismuth, tin, antimony, or a mixture thereof, all of 
which can form a eutectic solution with the retrieved magnesium, and have 
effects as described above or similar. However, when the molten retrieving 
metal pool is composed of tin, the following reactions occur: 
EQU Sn+2CO=SnO.sub.2 +2C (5) 
EQU SnO.sub.2 +2Mg=2MgO+Sn (6) 
According to the computation of the free energy of equation (5), tin turns 
into tin oxide by reacting with carbon monoxide at a temperature of 
500.degree. C. or lower, at an operating pressure of 6 torr, and at a 
temperature of 600.degree. C. or less at atmospheric pressure, and 
magnesium is oxidized according to equation (6), with the result that if 
the molten retrieving metal pool is composed of tin then the lower limit 
of temperature allowable for operation is relatively high, as compared 
with the case of lead, bismuth, or a combination thereof. As for antimony, 
as shown by the curves of FIG. 2, its vapor pressure is relatively higher 
than those of lead, bismuth, or tin, and hence a greater vaporization loss 
will occur than in the case of those other elements. Further, since the 
melting point of antimony is relatively high, as at 630.degree. C., it is 
more difficult to be used as the retrieving metal, than the three other 
elements. 
Therefore, as material for the retrieving molten metal pool, lead, bismuth, 
or a combination thereof is preferred. When these materials are used, the 
temperature of this molten retrieving metal pool is desired to be set in a 
range in which the properties of the drop in activity and drop in melting 
point due to the eutectic dissolution of the retrieved magnesium can be 
effectively utilized, i.e. a relatively low temperature range below the 
temperature at which the vaporization loss and the reverse or oxidization 
reaction become unacceptable but above the melting point of the alloy 
formed with the retrieved magnesium. Specifically, this temperature should 
be 250.degree. to 850.degree. C. in the case of a lead retrieving metal 
bath, 260.degree. to 1000.degree. C. in the case of a bismuth 
retrievingmetal bath, and 120.degree. to 1200.degree. C. in the case of a 
retrieving metal bath which is a combination of lead and bismuth. 
One of the specific advantages of the method according to the present 
invention for retrieving metallic vapor is that the temperature and 
pressure conditions which are most appropriate for the operation of the 
reduction furnace for producing the metallic vapor can be set up 
substantially independently from the conditions in the retrieving chamber, 
which can be set up as being most appropriate for the retrieving of the 
metallic vapor, since the configuration of the convergent-divergent nozzle 
can be suitably adjusted. If as earlier suggested the convergent-divergent 
nozzle is used under the proper expansion condition, for example by 
additional injection of inert gas into the mixture gas upstream of the 
nozzle, then the density of the mixture gas as it squirts out from the 
nozzle, just before it collides with the molten retrieval metal, is kept 
high, since this jet flow is in a highly converged state, in terms of 
density. In this case, the density of the jet flow as it collides with the 
molten retrieval metal pool is desired to be 1.5 gm/m.sup.3 or greater. In 
this case, the impact of the jet on the surface of the molten retrieving 
metal pool to agitate and mix it may well be sufficient, and then no 
mechanical stirring means for keeping the mixture well agitated will be 
necessary. Hence the volume of the retrieving metal pool can be kept 
small. On the other hand, when the convergent-divergent nozzle is being 
used under the insufficient expansion condition, then the jet flow 
continues to expand and cool after it has left the nozzle, and in this 
case although the speed with which the jet flow collides with the molten 
retrieval metal in fact increases the problem arises that its density 
becomes less. However, in this case, if an auxiliary device such as a vane 
wheel or reflecting plate is provided in the path of the jet flow, so as 
to absorb some of the kinetic energy of the jet flow and so as smoothly to 
lead the jet flow into the molten retrieval metal pool, no problems need 
arise. Additionally, it may be required to provide a stirrer for helping 
with the mixing of the retrieval metal pool, which requires this pool to 
be not very small, but this again need not cause any particular problem. 
Next, a discussion will be made as to the most desirable values for the 
temperature and the pressure of the jet flow from the convergent-divergent 
nozzle, just before it collides with the surface of the molten retrieving 
metal pool. 
In FIG. 5, in which temperature in degrees Centigrade is shown along the 
horizontal axis and pressure in torr is shown along the vertical axis 
logarithmically, there is shown a state diagram of magnesium. In this 
diagram, the solid lines denote the boundary between the solid, the 
liquid, and the gaseous states. When magnesium vapor is rapidly cooled by 
the convergent-divergent nozzle, it is supercooled into such states as 
shown by the dashed line in the figure. In order effectively to retrieve 
the magnesium into the molten retrieving metal in the liquid state, it is 
desired that the temperature and pressure of the jet flow from the 
convergent-divergent nozzle just as this jet flow enters the molten 
retrieving metal should be such that the magnesium vapor in said jet flow 
in the supercooled condition due to rapid cooling is easy to liquefy, and 
therefore the temperature of the jet flow at this point is preferred to be 
above 400.degree. C. and more preferably between 490.degree. and 
650.degree. C., and substantially equal to the temperature of the molten 
retrieval metal pool; while the pressure of the jet flow at this point is 
preferred to be greater than or equal to 3 torr, and more preferably is 
between 5 and 30 torr. The temperature and pressure of the jet flow may be 
adjusted to be within these ranges by suitably configuring the 
convergent-divergent nozzle, and by suitably adjusting the pressures 
upstream and downstream thereof, possibly also by introducing inert gas 
such as argon gas into the mixture gas upstream of the nozzle, as 
previously described.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention will now be described with reference to six preferred 
embodiments each of the apparatus and of the method thereof, and with 
reference to the appended drawings. 
THE CONSTRUCTION OF THE FIRST APATUS EMBODIMENT 
In FIG. 6 there is shown a schematic structural view of an apparatus for 
retrieving metal in the liquid phase from a gas containing vapor of the 
metal, according to the first preferred apparatus embodiment of the 
present invention, which is particularly applied to the reduction of zinc 
oxide by carbon as will be seen hereinafter, and which is used for 
practicing the first preferred embodiment of the method for retrieving 
metal in the liquid phase according to the present invention. In this 
figure, the reference numeral 1 generally denotes a reduction furnace 
which is substantially formed as a closed container, which has a furnace 
body 3 provided with a layer 2 of insulating material; and a furnace 
chamber 4 is defined as a cavity within this reduction furnace 1. A first 
heater 5 is embedded in the wall of the furnace chamber 4, generally 
around said furnace chamber 4 and within the layer 2 of insulating 
material, so as to heat up the furnace body 3 and said furnace chamber 4 
defined therein with said layer 2 of insulating material providing an 
insulation function. 
In the upper end wall 6 of the furnace chamber 4 there is provided a 
reaction material charging port 7, to which is connected the lower end of 
a lower charging chamber 12b of a reaction material charging hopper 8, the 
upper end of an upper charging chamber 12a of which is connected to a 
charging intake 11. Two control valves 9 and 10 are provided, respectively 
between the lower end of the upper charging chamber 12a and the upper end 
of the lower charging chamber 12b and between the lower end of the lower 
charging chamber 12b and the charging port 7, so that by opening and 
closing these control valves 9 and 10 in an alternating fashion as will be 
easily understood by one of ordinary skill in the art material for 
reaction may be charged into the reaction furnace chamber 4 through the 
charging port 7 without substantially deteriorating the gas tight 
condition of the reaction furnace chamber 4. In the lower end wall or 
bottom 13 of the furnace chamber 4 there is provided a reaction residue 
discharge port 14 which is controlled by a valve; in fact, again, a 
similar double valve arrangement is provided for discharging reaction 
residues produced in the chamber 4 of the furnace 1 by reduction (as will 
be explained later) through this reaction residue discharge port 14 
without deteriorating the gas tight condition of the reaction furnace 
chamber 4, although this is not shown in the figure. 
The side wall 15 of the furnace chamber 4 has a mixture gas discharge port 
16 formed therein, and a mixture gas conduit 18 leads from this gas 
discharge port 16, with the interposition of a perforated filter tube 17, 
so as to communicate the furnace chamber 4 with a metallic vapor 
retrieving chamber 22 provided below and to the left as seen in the figure 
of the furnace chamber 4 within the furnace body 23 of a metallic vapor 
retrieving furnace 21. Particularly according to an important principle of 
the present invention, the downstream end of this conduit 18 is formed as 
a convergent-divergent nozzle or Laval nozzle 19 of the above described 
sort. 
Within the lower part of the metallic vapor retrieving chamber 22, below 
and opposed to the lower end of the convergent-divergent nozzle 19, there 
is present during operation of the apparatus a pool 20 to molten 
retrieving metal. The lower part of the metallic vapor retrieving chamber 
22 is communicated, via a molten metal take out port 30 and via a molten 
metal take out conduit 32 which is controlled by a control valve 31, to a 
ladle 33 for removing molten metal. A slag take out port not shown in the 
figure is also provided for removing slag from the surface of the pool 20 
of molten retrieving metal in the retrieving chamber 22. Vacuum ports 25 
and 26 are provided in the upper part of the retrieving chamber 22 and are 
connected, via vacuum conduits 27 and 28 respectively, to a vacuum pump 
29, for evacuating the interior parts of the apparatus as a whole to 
appropriate vacuum levels, as described later. A second heater 24 is 
embedded in the wall of the furnace body 23 of the metallic vapor 
retrieving chamber 22, generally around said retrieving chamber 22, so as 
to heat up the body 23 of the retrieving furnace 21 and said retrieving 
chamber 22 defined therein. 
Particularly according to a particular feature of this first apparatus 
embodiment of the present invention, the central axial line 34 of the 
convergent-divergent nozzle 19 extends in the metallic vapor retrieving 
chamber 22 substantially vertically, so that as explained later during 
operation of the nozzle 19 the spray or jet flow 35 of mixture gas 
including metal vapor from said nozzle 19 should impact substantially at 
right angles onto the surface of the pool 20 of molten retrieving metal in 
the lower part of the retrieving chamber 22. 
The General Operation of the First Apparatus Embodiment 
The shown apparatus according to the first preferred embodiment of the 
apparatus of the present invention is generally used as follows. First, 
material for reduction of an appropriate sort for producing gas vapor of a 
metal which is required to be recovered or retrieved as will be understood 
in detail later is charged into the furnace chamber 4 of the reduction 
furnace 1, by charging this material into the upper charging chamber 12a 
of the charging hopper 8 through the charging intake 11, and by then 
opening and closing the control valves 9 and 10 in an alternating fashion 
as outlined above so as to transfer this reduction material through the 
lower charging chamber 12b into the furance chamber 4 without allowing gas 
from the outside to enter the furnace chamber 4 in substantial amount. 
Then the first heater 5 is operated so as to heat up the furnace chamber 4 
and the reaction material charged therein to a predetermined temperature 
T.sub.1, so as to cause this reduction material to be reduced into a gas 
mixture containing vapor of the desired metal which is to be recovered or 
retrieved, said gas mixture being at a pressure P.sub.1. This mixture gas 
then passes in the heated state through the opening 16 in the side wall 15 
of the reduction furnace 1 and is then ejected from the furnace chamber 4, 
according to the difference of pressures between the interior of the 
furnace chamber 4 which is at said pressure P.sub.1 and the interior of 
the metallic vapor retrieving chamber 22 which is kept at a pressure 
P.sub.2 substantially lower than the pressure P.sub.1, through the conduit 
18 and through the convergent-divergent nozzle 19 at the downstream end of 
said conduit 18, into the metallic vapor retrieving chamber 22, and sprays 
out of the convergent-divergent nozzle 19 as a jet 35 which impinges 
against the surface of the pool 20 of molten retrieving metal in the 
bottom of said retrieving chamber 22. As this mixture gas passes through 
the convergent-divergent nozzle 19, it reaches a supersonic speed and 
expands adiabatically very quickly, and thus the metal vapor is very 
quickly cooled down by this adiabatic expansion to a second temperature 
T.sub.2, and may be at least partly condensed into fine metal droplets or 
particles. This cooling down is so quick that it occurs without said metal 
vapor having a chance to recombine with other constituents of said mixture 
gas (i.e., to be again oxidized thereby), due to the very quick cooling of 
said mixture gas, and the final second temperature T.sub.2 down to which 
the mixture gas is cooled by the adiabatic expansion in the 
convergent-divergent nozzle 19 is so low as to be below the temperature at 
which the recombination or reoxidization reaction can substantially take 
place. 
The jet 35 including cooled metallic vapor and possibly fine particles of 
liquid or solid metal thus produced impinges on the surface of the pool 20 
of molten retrieving metal in the bottom of said retrieving chamber 22, in 
this first preferred embodiment substantially perpendicularly, and the 
metal in said jet 35 becomes mixed with and entrained into the molten 
retrieving metal. Bubbles 36 of gas from the jet may become temporarily 
entrained below the surface of the pool 20 of molten retrieving metal, but 
this need not cause any substantial problem. The retrieving chamber 22 is 
maintained at its pressure P.sub.2 by the remainder gas from the jet 35 
being sucked out of said retrieving chamber 22, via the ports 25 and 26 
and the conduits 27 and 28, by the operation of the vacuum pump 29. The 
sucking rate of the pump 29 thus is controlled so as to maintain the 
pressures in the furnace chamber 4 and in the metallic vapor retrieving 
chamber 22 at substantially their respective desired values P.sub.1 and 
P.sub.2, according of course also to various other parameters of the 
apparatus and its operation. 
From time to time, some of the retrieving molten metal pool 20 in the 
bottom portion of the metallic vapor retrieving chamber 22, with retrieved 
metal from the jet 35 entrained therein, is removed via the port 30 and 
the conduit 32 by operation of the valve 31 into the ladle 33, without 
disturbing the depressurized state of the apparatus. Further, from time to 
time, some of the slag in the bottom portion of the furnace chamber 4 is 
removed via the port 14 by operation of the valve, again without 
disturbing the depressurized state of the apparatus. 
Description of the First Method Embodiment 
The first preferred apparatus embodiment of the present invention described 
above was operated by charging a mixture of zinc oxide powder (which in 
fact was made by oxidizing zinc sulphide and refining it) and carbon 
formed into lumps as a raw material for reduction into the furnace chamber 
4 of the reduction furnace 1, by operating the vacuum pump 29, by 
operating the first heater 5, by charging zinc metal into the metallic 
vapor retrieving chamber 22, and by melting said zinc metal into a pool 20 
of retrieving molten metal for retrieving the zinc produced by reduction 
in the reduction furnace 1. Thus, in this embodiment, the retrieving metal 
(zinc) used for the retrieving metal pool 20 was the same metal as the 
metal (zinc) which was to be retrieved. The temperature T.sub.1 to which 
the furnace chamber 4 and the reduction material charged thereinto were 
heated was 950.degree. to 1050.degree. C., and the rate of suction of the 
vacuum pump 29 was controlled so as to keep the pressure P.sub.1 within 
the furnace chamber 4 at approximately 450 to 550 torr and so as to keep 
the pressure P.sub.2 within the metallic vapor retrieving chamber 22 at 
approximately 50 to 90 torr. The second heater 24 was so operated as to 
keep the temperature within the metallic vapor retrieving chamber 22 at 
about 500.degree. C., so as to keep the retrieving metal pool 20 of zinc 
metal therein in the molten state. 
As explained above, the zinc oxide in the reaction chamber 4 of the 
reduction furnace 1 was reduced by the carbon, so as to produce metallic 
zinc in vapor form and oxidizing gas such as carbon monoxide and carbon 
dioxide, and this mixture of metallic zinc vapor and oxidizing gas then 
flowed out through the conduit 18 and through the convergent-divergent 
nozzle 19 into the metallic vapor retrieving chamber 22, attaining a 
supersonic speed as it passed through the convergent-divergent nozzle 19. 
In fact, in this first embodiment, the nozzle 19 was functioning under the 
insufficient expansion condition. The jet flow 35 thus produced was 
quickly cooled down by adiabatic expansion in the nozzle 19 to below the 
temperature at which the reverse reaction of the oxidizing gas oxidizing 
the zinc vapor could occur, and impinged against the surface of the molten 
retrieving zinc metal pool 20 within the metallic vapor retrieving chamber 
22, and the zinc vapor (which in fact was partially liquefied and/or 
solidified) in said jet flow was entrained into and mixed with the molten 
zinc metal pool 20. 
The entrained zinc was then of course brought to the liquefied state by 
this entrainment into the retrieving metal pool, and remained therein; and 
the oxidizing gas in the mixture then, after plunging into the molten zinc 
pool 20 and temporarily formed bubbles such as the shown bubbles 36 in the 
molten zinc pool 20, rose to the surface and was sucked away by the vacuum 
pump 29. The retrieved zinc was removed from the apparatus from time to 
time as explained above. The depression of the liquid surface of the pool 
20 of molten retrieving zinc metal was about 50 mm. The throat diameter of 
the convergent-divergent nozzle 19 was 25 mm. The physical condition of 
the raw material charged into the reduction furnace chamber 4 was lump 
briquette. The retrieval ratio was 99.3%. The average purity of the 
retrieved zinc was 98.0%. 
The results described above of operating the first embodiment of the 
apparatus of the present invention according to the first preferred 
embodiment of the method of the present invention show that in the case of 
a metal such as zinc, which has a relatively low melting point, and which 
has a relatively low tendency to become reoxidized, a good result of 
retrieving metallic vapor from the gas products of a reduction reaction 
can be obtained, with a purity and a retrieval ratio both close to 100%, 
even without the use of any device such as a collision plate or the like 
for slowing down the speed of the jet flow from the convergent-divergent 
nozzle. 
The Construction of the Second Apparatus Embodiment 
FIG. 7 is a schematic skeleton structural view of an apparatus for 
retrieving metal in the liquid phase which is a second preferred 
embodiment of the apparatus according to the present invention. In this 
figure, parts of the second preferred apparatus embodiment shown, which 
correspond to parts of the first preferred apparatus embodiment shown in 
FIG. 6, and which have the same functions, are designated by the same 
reference numerals and symbols as in that figure. 
In this second preferred embodiment, the construction of the reduction 
furnace 1, and of the charging hopper 8 and so on, is quite the same, as 
in the first preferred embodiment shown in FIG. 6. Further, the lower part 
of the metallic vapor retrieving chamber 22, and the arrangements 
including the conduit 32 for removing molten metal therefrom, are also 
quite the same as in the first embodiment. However, according to a 
particular feature of this second apparatus embodiment of the present 
invention the convergent-divergent nozzle 19 extends into the upper part 
of the metallic vapor retrieving chamber 22 and opens therein in such an 
orientation that its central axial line 34 extends, not vertically as in 
the case of the first preferred embodiment, but horizontally, so that as 
explained later during operation of the nozzle 19 the spray or jet flow 35 
of mixture gas including metal vapor from said nozzle 19 is squirted 
substantially parallel to the surface of the pool 20 of molten retrieving 
metal in the lower part of the retrieving chamber 22. Further, directly 
opposed to said nozzle 19 there is provided in the upper part of the 
metallic vapor retrieving chamber 22 a deflection plate 37, angled with 
respect to the central axial line 35 of the nozzle 19, with said 
inclination angle being adjustable between about 45.degree. and about 
60.degree.. Further, the front surface or the right surface in the figure 
of the deflection plate 37 is formed in a concaved shape, and a cooling 
water conduit 38 is provided for supplying cooling water to the rear side 
of said deflection plate 37. Thus, when a jet flow 35 of gas is squirting 
out of the nozzle 19, this deflection plate is able to deflect this jet 
flow, as schematically shown in the figure, through an angle of 
approximately 90.degree., so as to direct it down with a flow of 
substantially reduced force against the surface of the molten retrieving 
metal pool 20 in the retrieving chamber 22, with the concave surface of 
the deflection plate 37 performing a focusing action on said deflected jet 
flow so as to keep it together and prevent it from dispersing. 
The General Operation of the Second Apparatus Embodiment 
The shown apparatus according to the second preferred embodiment of the 
apparatus of the present invention is generally used as follows, in a 
manner basically similar to the operation of the first apparatus 
embodiment. First, material for reduction of an appropriate sort for 
producing gas vapor of a metal which is required to be recovered or 
retrieved as will be understood in detail later is charged into the 
furnace chamber 4 of the reduction furnace 1, as before. Then the first 
heater 5 is operated so as to heat up the furnace chamber 4 and the 
reaction material charged therein to a predetermined temperature T.sub.1, 
so as to cause this reduction material to be reduced into a gas mixture 
containing vapor of the desired metal which is to be recovered or 
retrieved, said gas mixture being at a pressure P.sub.1, again as before. 
This mixture gas then passes in the heated state through the opening 16 in 
the side wall 15 of the reduction furnace 1 and is then ejected from the 
furnace chamber 4, according to the difference of pressures between the 
interior of the furnace chamber 4 which is at said pressure P.sub.1 and 
the interior of the metallic vapor retrieving chamber 22 which is kept at 
a pressure P.sub.2 substantially lower than the pressure P.sub.1, through 
the conduit 18 and through the convergent-divergent nozzle 19 at the 
downstream end of said conduit 18, into the metallic vapor retrieving 
chamber 22, and sprays out of the convergent-divergent nozzle 19 as a jet 
35 which passes substantially horizontally, this time, to impinge against 
the right side surface in the figure of the deflection plate 37, and to be 
reflected thereof, being deflected through an angle of approximately 
90.degree. as described above, so as then to impact substantially in the 
vertical direction on the surface of the pool 20 of molten retrieving 
metal in the bottom of said retrieving chamber 22, with the speed of said 
jet being substantially diminished by said reflection action. As before, 
as the mixture gas passes through the convergent-divergent nozzle 19, it 
reaches a supersonic speed and expands adiabatically very quickly, and 
thus the metal vapor is very quickly cooled down by this adiabatic 
expansion to a second temperature T.sub.2, and may be at least partly 
condensed into fine metal droplets or particles. This cooling down is so 
quick that it occurs without said metal vapor having a chance to recombine 
with other constituents of said mixture gas (i.e., to be again oxidized 
thereby), due to the very quick cooling of said mixture gas, and the final 
second temperature T.sub.2 down to which the mixture gas is cooled by the 
adiabatic expansion in the convergent-divergent nozzle 19 is so low as to 
be below the temperature at which the recombination or reoxidization 
reaction can substantially take place. 
Again, when the deflected jet 35 including cooled metallic vapor and 
possibly fine particles of liquid or solid metal thus produced impinges on 
the surface of the pool 20 of molten retrieving metal in the bottom of 
said retrieving chamber 22, now substantially perpendicularly, again the 
metal in said jet 35 becomes mixed with and entrained into the molten 
retreiving metal. Again, bubbles 36 of gas from the jet may become 
temporarily entrained below the surface of the pool 20 of molten 
retreiving metal, but this need not cause any substantial problem. The 
retrieving chamber 22 is maintained at its pressure P.sub.2 by the 
remainder gas from the jet 35 being sucked out of said retrieving chamber 
22, via the port 25 and the conduit 27, by the operation of the vacuum 
pump 29. The sucking rate of the pump 29 thus is again controlled so as to 
maintain the pressures in the furnace chamber 4 and in the metallic vapor 
retrieving chamber 22 at substantially their respective desired values 
P.sub.1 and P.sub.2, according of course also to various other parameters 
of the apparatus and its operation. 
Similarly to the operation of the first preferred embodiment, from time to 
time, some of the retrieving molten metal pool 20 in the bottom portion of 
the metallic vapor retrieving chamber 22, with retrieved metal from the 
jet 35 entrained therein, is removed via the port 30 and the conduit 32, 
as before. 
Description of the Second Method Embodiment 
The second preferred apparatus embodiment of the present invention 
described above was operated by charging a mixture of magnesium oxide 
powder and carbon formed into lumps as a raw material for reduction into 
the furnace chamber 4 of the reduction furnace 1, by operating the vacuum 
pump 29, by operating the first heater 5, by charging magnesium metal into 
the metallic vapor retrieving chamber 22 as a retrieving metal, and by 
melting said magnesium metal into a pool 20 of retrieving molten metal for 
retrieving the magnesium produced by reduction in the reduction furnace 1. 
Thus, in this second preferred embodiment, the retrieving metal 
(magnesium) used for the retrieving metal pool 20 was again the same metal 
as the metal (magnesium) which was to be retrieved. The temperature 
T.sub.1 to which the furnace chamber 4 and the reduction material charged 
thereinto were heated was 1750.degree. to 1850.degree. C., and the rate of 
suction of the vacuum pump 29 was controlled so as to keep the pressure 
P.sub.1 within the furnace chamber 4 at approximately 50 to 70 torr and so 
as to keep the pressure P.sub.2 within the metallic vapor retrieving 
chamber 22 at approximately 10 to 70 torr. The second heater 24 was so 
operated as to keep the temperature within the metallic vapor retrieving 
chamber 22 at about 700.degree. C., so as to keep the retrieving metal 
pool 20 of magnesium metal therein in the molten state. 
As explained above, the magnesium oxide in the reaction chamber 4 of the 
reduction furnace 1 was reduced by the carbon, so as to produce metallic 
magnesium in vapor form and oxidizing gas such as carbon monoxide, and 
this mixture of metallic magnesium vapor and oxidizing gas then flowed out 
through the conduit 18 and through the convergent-divergent nozzle 19 into 
the metallic vapor retrieving chamber 22, attaining a supersonic speed as 
it passed through the convergent-divergent nozzle 19. The jet flow 35 
produced was thus quickly cooled down by adiabatic expansion in the nozzle 
19 to below the temperature at which the reverse reaction of the oxidizing 
gas oxidizing the magnesium vapor could occur, and first impinged against 
the face of the deflection plate 37, to be reflected or deflected at an 
angle of approximately 90.degree. off this deflection plate 37 to then 
impact at reduced speed against the surface of the molten retrieving 
magnesium metal pool 20 within the metallic vapor retrieving chamber 22, 
and the magnesium vapor in said jet flow was entrained into and mixed with 
the molten magnesium metal pool 20. 
The entrained magnesium was of course brought to the liquefied state by 
this entrainment into the retrieving molten magnesium metal pool, and 
remained therein; and the oxidizing gas in the mixture then, after 
plunging into the molten magnesium pool 20 and temporarily forming bubbles 
such as the shown bubbles 36 in the molten magnesium pool 20, rose to the 
surface and was sucked away by the vacuum pump 29. The reduction of the 
speed of the jet flow 35 including the magnesium vapor, caused by the 
deflection plate 37, ensured that the surface of the molten magnesium 
retrieving metal pool 20 was not too severely splashed about by too 
violent an impact of said jet flow thereagainst, and also that the 
magnesium vapor in the jet was not dispersed sideways upon impact with the 
molten magnesium surface. The retrieved magnesium was again removed from 
the apparatus from time as explained above. In detail, the depression of 
the liquid surface of the pool 20 of molten retrieving magnesium metal was 
about 30 to 50 mm, and substantially no splash of molten metal from the 
surface of the molten magnesium pool 20 occurred. The throat diameter of 
the convergent-divergent nozzle 19 was 25 mm, the physical condition of 
the raw material charged into the reduction furnace 1 was again lump 
briquette. The angle of the deflection plate 37 was 55.degree.. The 
retrieval ratio was 90 to 95%. The average purity of the retrieved 
magnesium was 92.3%. 
The results described above of operating the second preferred embodiment of 
the apparatus of the present invention according to the second preferred 
embodiment of the method of the present invention show that even in the 
case of a metal such as magnesium, which has a relatively high melting 
point, and which has a relatively high tendency to become reoxidized, a 
good result of retrieving metallic vapor from the gas products of a 
reduction reaction can be obtained, with a purity and a retrieval ratio 
both better than in the case of any conventionally known method, by the 
use of the shown collision plate for slowing down the speed of the jet 
flow from the convergent-divergent nozzle. 
In FIG. 8, there are shown the values of the pressure, the temperature, and 
the speed of the mixture gas as it flows along through an exemplary 
convergent-divergent nozzle 19 used in the above described second 
embodiment (illustrated at the top of FIG. 8) the diameter of whose inlet 
opening is 50 mm, the diameter of whose throat is 25 mm, the diameter of 
whose outlet opening is 28 mm, and the length of which from the inlet 
opening to the outlet opening is 60 mm. The figure is a combination of 
three graphs, in all of which distance along the central axial line of the 
nozzle is shown along the horizontal axis, and in which respectively 
pressure in torr, temperature in degrees centigrade, and speed in meters 
per second are shown along the vertical axis. Further, FIGS. 9a and 9b are 
schematic graphs showing the changes in the values of the pressure in the 
reduction furnace 1 and the retrieval ratio (i.e., retrieved molten metal 
weight divided by theoretical retrieval amount) with time, in a batch test 
of a theoretical retrieval amount of 6 kg of magnesium conducted in the 
manner described above according to the second preferred embodiment of the 
method of the present invention, using the above described 
convergent-divergent nozzle. By comparing the above described experiment 
of retrieving magnesium vapor and this bath test, it can be seen that the 
method and the device for retrieving metallic vapor according to the 
second embodiment of the present invention can effectively retrieve 
magnesium vapor at high retrieval ratio even when operated in batch mode, 
although continuous operation is to be preferred. Conceivably, the reason 
for the fact that the method and the device for retrieving metallic vapor 
according to the second embodiment of the present invention showed a lower 
retrieval ratio when operated in the batch mode than when operated in the 
continuous mode is that part of the magnesium vapor adhered in solid form 
to the face of the deflection plate 37, and that this solidified magnesium 
was not measured as part of the retrieved magnesium metal. 
The Construction of the Third Apparatus Embodiment 
FIG. 10 is a schematic skeleton structural view of an apparatus for 
retrieving metal in the liquid phase which is a third preferred embodiment 
of the apparatus according to the present invention. In this figure, parts 
of the third preferred apparatus embodiment shown, which correspond to 
parts of the first and second preferred apparatus embodiments shown in 
FIGS. 6 and 7, and which have the same functions, are designated by the 
same reference numerals and symbols as in those figures. 
In this third preferred embodiment, the construction of the reduction 
furnace 1, and of the charging hopper 8 and so on, and of the metallic 
vapor retrieving chamber 22 as a whole, is the same, as in the first 
preferred embodiment shown in FIG. 6; and as in the first preferred 
apparatus embodiment the convergent-divergent nozzle 19 extends into the 
upper part of the metallic vapor retrieving chamber 22 and opens therein 
in such an orientation that its central axial line 34 extends vertically. 
The only difference is that, directly opposed to said nozzle 19, there is 
provided in the central part of the metallic vapor retrieving chamber 22, 
a vane wheel 39, which is structured with a horizontally rotatably mounted 
hub 40 and a plurality of vanes 41 projecting therefrom. The vane wheel 39 
is rotatably mounted with the vanes 41 on its lower part at least 
partially submerged under the surface of the pool 20 of molten retrieving 
metal in the metallic vapor retrieving chamber 22, and with those of its 
vanes 41 on its left part in FIG. 10 directly opposed to the 
convergent-divergent nozzle 19, in its axial line. Thus, when a jet flow 
35 of gas is squirting out of the nozzle 19, a major part of the metallic 
vapor in this jet flow impinges against these vanes 41 of the vane wheel 
39 and sticks thereto in liquid form, as schematically shown in the 
figure, so as to cause the vane wheel 39 as a whole to rotate in the 
counterclockwise direction in the figure. Thus this rotation of the vane 
wheel 39 gently brings this molten metal under the surface of the molten 
retrieving metal pool 20 in the retrieving chamber 22, so that the metal 
is retrieved by the metal pool 20 in a relatively gentle manner. 
Description of the Third Method Embodiment 
The third preferred apparatus embodiment of the present invention described 
above was operated, substantially in the same way as in the case of the 
second preferred embodiment, by charging a mixture of magnesium oxide 
powder and carbon formed into lumps as a raw material for reduction into 
the furnace chamber 4 of the reduction furnace 1, by operating the vacuum 
pump 29, by operating the first heater 5, by charging magnesium metal into 
the metallic vapor retrieving chamber 22 as a retrieving metal, and by 
melting said magnesium metal into a pool 20 of retrieving molten metal for 
retrieving the magnesium produced by reduction in the reduction furnace 1. 
Thus, in this third preferred embodiment, the retrieving metal (magnesium) 
used for the retrieving metal pool 20 was again the same metal as the 
metal (magnesium) which was to be retrieved. The temperature T.sub.1 to 
which the furnace chamber 4 and the reduction material charged thereinto 
were heated was again 1750.degree. to 1850.degree. C., and the rate of 
suction of the vacuum pump 29 was controlled so as to keep the pressure 
P.sub.1 within the furnace chamber 4 at approximately 50 to 70 torr and so 
as to keep the pressure P.sub.2 within the metallic vapor retrieving 
chamber 22 at approximately 5 to 10 torr, in this case. 
The second heater 24 was again so operated as to keep the temperature 
within the metallic vapor retrieving chamber 22 at about 700.degree. C., 
so as to keep the retrieving metal pool 20 of magnesium metal therein in 
the molten state. 
As before, the magnesium oxide in the reaction chamber 4 of the reduction 
furnace 1 was replaced by the carbon, so as to produce metallic magnesium 
in vapor form and oxidizing gas such as carbon monoxide, and this mixture 
of metallic magnesium vapor and oxidizing gas then flowed out through the 
conduit 18 and through the convergent-divergent nozzle 19 into the 
metallic vapor retrieving chamber 22, attaining a supersonic speed as it 
passed through the convergent-divergent nozzle 19. The jet flow 35 
produced was thus quickly cooled down by adiabatic expansion in the nozzle 
19 to below the temperature at which the reverse reaction of the oxidizing 
gas oxidizing the magnesium vapor could occur, and first impinged against 
the vanes 41 of the vane wheel 39, so as to be collected thereon in the 
liquid state, thereafter to be brought relatively smoothly and gently 
under the surface of the molten retrieving magnesium metal pool 20 within 
the metallic vapor retrieving chamber 22, and thus the magnesium vapor in 
said jet flow was entrained into and mixed with the molten magnesium metal 
pool 20, and remained therein; and the oxidizing gas in the mixture, after 
plunging into the molten magnesium pool 20 and temporarily forming bubbles 
such as the shown bubbles 36 in the molten magnesium pool 20, rose to the 
surface and was sucked away by the vacuum pump 29. The reduction of the 
speed of the jet flow 35 including the magnesium vapor caused by the vane 
wheel 39, again ensured that the surface of the molten magnesium 
retrieving metal pool 20 was not too severely splashed about by too 
violent an impact of said jet flow 35 thereagainst, and also that the 
magnesium vapor in the jet was not disperesed sideways upon impact with 
the molten magnesium surface. The retrieved magnesium was again removed 
from the apparatus from time to time as explained above. In fact, the 
results described above the operating the third preferred embodiment of 
the apparatus of the present invention according to the third preferred 
embodiment of the method of the present invention were substantially the 
same as in the case of the second preferred embodiments of the device and 
the method of the present invention, described above. 
The Construction of the Fourth Apparatus Embodiment 
FIG. 11 is a schematic skeleton structual view of an apparatus for 
retrieving metal in the liquid phase which is a fourth preferred 
embodiment of the apparatus according to the present invention. In this 
figure, parts of the fourth preferred apparatus embodiment shown, which 
correspond to parts of the first through third preferred apparatus 
embodiments shown in FIGS. 6, 7, and 10, and which have the same 
functions, are designated by the same reference numerals and symbols as in 
those figures. 
In this fourth preferred embodiment, the construction of the reduction 
furnace 1, and of the charging hopper 8 and so on, and of the metallic 
vapor retrieving chamber 22 as a whole, is the same, as in the second 
preferred embodiment shown in FIG. 7; and as in the second preferred 
apparatus embodiment the covergent-divergent nozzle 19 extends into the 
upper part of the metallic vapor retrieving chamber 22 and opens therein 
in such an orientation that its central axial line 34 extends 
horizontally, so that the jet flow from said nozzle 19 impacts against a 
deflection plate 37. However, in this fourth preferred embodiment, the 
difference is that further a vane wheel 39 of the same construction as in 
the case of the third preferred embodiment is additionally provided, as 
directly opposed to the deflected jet flow from said deflection plate 37. 
Again, the vane wheel 39 is structured with a horizontally rotatably 
mounted hub 40 and a plurality of vanes 41 projecting therefrom, and is 
rotatably mounted with the vanes 41 on its lower part at least partially 
submerged under the surface of the pool 20 of molten retrieving metal in 
the metallic vapor retrieving chamber 22, and with those of its vanes 41 
on its left part in FIG. 11 directly opposed to the deflected jet flow 
from the deflection plate 37. Thus, when a jet flow 35 of gas is squirting 
out of the nozzle 19, first this jet flow is deflected by the deflection 
plate 37, and then a major part of the metallic vapor in this deflected 
and slowed down jet flow impinges against these vanes 41 of the vane wheel 
39 and sticks thereto in liquid form, as schematically shown in the 
figure, so as to cause the vane wheel 39 as a whole to rotate in the 
counterclockwise direction in the figure. Thus this rotation of the vane 
wheel 39 gently brings this molten metal under the surface of the molten 
retrieving metal pool 20 in the retrieving chamber 22, so that the metal 
is retrieved by the metal pool 20 in a relatively gentle manner. Thus this 
fourth preferred apparatus embodiment is, conceptually, the combination of 
the second and the third preferred embodiments. 
Description of the Fourth Method Embodiment 
The fourth preferred apparatus embodiment of the present invention 
described above was operated, substantially in the same way as in the case 
of the third preferred embodiment, by charging a mixture of magnesium 
oxide powder and carbon formed into lumps as a raw material for reduction 
into the furnace chamber 4 of the reduction furnace 1, by operating the 
vacuum pump 29, by operating the first heater 5, by charging magnesium 
metal into the metallic vapor retrieving chamber 22 as a retrieving metal, 
and by melting said magnesium metal into a pool 20 of retrieving molten 
metal for retrieving the magnesium produced by reduction in the reduction 
furnace 1. Thus, in this fourth preferred embodiment, the retrieving metal 
(magnesium) used for the retrieving metal pool 20 was again the same metal 
as the metal (magnesium) which was to be retrieved. The temperature 
T.sub.1 to which the furnace chamber 4 and the reduction material charged 
thereinto were heated was again 1750.degree. to 1850.degree. C., and the 
rate of suction of the vacuum pump 29 was controlled so as to keep the 
pressure P.sub.1 within the furnace chamber 4 at approximately 30 to 50 
torr and so as to keep the pressure P.sub.2 within the metallic vapor 
retrieving chamber 22 at approximately 5 to 10 torr. The second heater 24 
was again so operated as to keep the temperature within the metallic vapor 
retrieving chamber 22 at about 700.degree. C., as to keep the retrieving 
metal pool 20 of magnesium metal therein in the molten state. 
As before, the magnesium oxide in the reaction chamber 4 of the reduction 
furnace 1 was reduced by the carbon, so as to produce metallic magnesium 
in vapor form and oxidizing gas such as carbon monoxide, and this mixture 
of metallic magnesium vapor and oxidizing gas then flowed out through the 
conduit 18 and through the convergent-divergent nozzle 19 into the 
metallic vapor retrieving chamber 22, attaining a supersonic speed as it 
passed through the convergent-divergent nozzle 19. The jet flow 35 
produced was thus quickly cooled down by adiabatic expansion in the nozzle 
19 to below the temperature at which the reverse reaction of the oxidizing 
gas oxidizing the magnesium vapor could occur, and first impinged against 
the deflection plate 37, so as to be deflected and slowed thereby, and 
then impinged against the vanes 41 of the vane wheel 39, so as to be 
collected thereon in the liquid state, thereafter to be brought relatively 
smoothly and gently under the surface of the molten retrieving magnesium 
metal pool 20 within the metallic vapor retrieving chamber 22, and thus 
the magnesium vapor in said jet flow was entrained into and mixed with the 
molten magnesium metal pool 20, and remained therein; and the oxidizing 
gas in the mixture, after plunging into the molten magnesium pool 20 and 
temporarily forming bubbles such as the shown bubbles 36 in the molten 
magnesium pool 20, rose to the surface and was sucked away by the vacuum 
pump 29. The two phase reduction of the speed of the jet flow 35 including 
the magnesium vapor, first caused by the deflection plate 37 and then 
secondarily caused by the vane wheel 39, very positively ensured that the 
surface of the molten magnesium retrieving metal pool 20 was not too 
severely splashed about by too violent an impact of said jet flow 35 
thereagainst, and also that the magnesium vapor in the jet was not 
dispersed sideways upon impact with the molten magnesium surface. The 
retrieved magnesium was again removed from the apparatus from time to time 
as explained above. 
The throat diameter of the convergent-divergent nozzle 19 was 28 mm. The 
physical condition of the raw material charged into the reduction furnace 
1 was again lump briquette. The angle of the deflection plate 37 was 
55.degree.. The retrieval ratio was 93 to 96%. The average purity of the 
retrieved magnesium was 93.3%. 
The results described above the operating the fourth preferred embodiment 
of the apparatus of the present invention according to the fourth 
preferred embodiment of the method of the present invention are better 
than the results obtained in the cases of the second and the third 
preferred embodiments, and thus show that, in the case of a metal such as 
magnesium, which has a relatively high melting point, and which has a 
relatively high tendency to become reoxidized, the best results of 
retrieving metallic vapor from the gas products of a reduction reaction 
can be obtained, with a purity and a retrieval ratio both better than in 
the case of any conventionally known method, by the use of both a 
collision plate for slowing down the speed of the jet flow from the 
convergent-divergent nozzle and also a vane wheel for gently bringing the 
metal vapor into the molten retrieving metal pool. 
Remarks Relative to the First Through the Fourth Embodiments 
With regard to the above described first through fourth preferred 
embodiments of the method according to the present invention, in which the 
molten metal pool 20 used for retrieving the metallic vapor from the 
mixture gas squirted out from the convergent-divergent nozzle 19 is 
composed of the same metal as said metallic vapor, as an operational 
procedure this pool of molten retrieving metal may be prepared in the 
earlier stages of metal retrieval by either (a) capturing and storing the 
metallic vapor in the mixture gas which has flowed into the metallic vapor 
retrieving chamber 22 at the bottom of said chamber 22; or (b) charging 
metal prepared separately beforehand. 
The Construction of the Fifth Apparatus Embodiment 
In FIG. 12 there is shown a schematic structural view of an apparatus for 
retrieving metal in the liquid phase from a gas containing vapor of the 
metal, according to the fifth preferred apparatus embodiment of the 
present invention, which is particularly applied to the reduction of 
magnesium oxide by carbon as will be seen hereinafter, and which is used 
for practicing the fifth preferred embodiment of the method for retrieving 
metal in the liquid phase according to the present invention. This fifth 
preferred apparatus embodiment will be described in detail because it is 
much different from the four previously described embodiments. In this 
figure, parts of the fifth preferred apparatus embodiment shown, which 
correspond to parts of the first through fourth preferred apparatus 
embodiments shown in FIGS. 6, 7, 10, and 11, and which have the same 
functions, are designated by the same reference numerals and symbols as in 
those figures. 
In FIG. 12, the reference numeral 1 generally denotes a reduction furnace 
which is substantially formed as a closed container, and which is 
constructed substantially in the same manner as the reduction furnace of 
the four previously described embodiments, having a furnace chamber 4 
defined as a cavity within it, around which a heater (not particularly 
shown) is provided, so as to heat up the reduction furnace body and said 
furnace chamber 4. As before, in the upper end wall of the furnace chamber 
4 there is provided a reaction material charging port, to which is coupled 
a reaction material charging hopper 8, and in a similar way to that 
described previously with respect to the first four embodiments of the 
present invention raw material for reaction (i.e., reduction) can be 
charged into the reaction furnace chamber 4 from the hopper 8 through the 
charging port without substantially deteriorating the gas tight condition 
of the reaction furnace chamber 4. In the lower end wall or bottom of the 
furnace chamber 4 there is provided a reaction residue discharge port for 
discharging reaction residues produced in the chamber 4 of the reaction 
furnace 1 by reduction (as will be explained later), although this is not 
shown in the figure. 
The side wall of the furnace chamber 4 has a mixture gas discharge port 16 
formed therein, and a mixture gas conduit 18 leads from this gas discharge 
port so as to communicate the furnace chamber 4 with a metallic vapor 
retrieving chamber 22 provided below and to the left as seen in the figure 
of the furnace chamber 4. Particularly according to an important principle 
of the present invention, the downstream end of this conduit is formed as 
a convergent-divergent nozzle or Laval nozzle 19 of the above described 
sort. 
Within the lower part of the metallic vapor retrieving chamber 22, below 
and opposed to the lower end of the convergent-divergent nozzle 19, there 
is present during operation of the apparatus a pool 20 of molten 
retrieving metal. A slag take out port arrangement not shown in the figure 
is also provided for removing slag from the surface of the pool 20 of 
molten retrieving metal in the retrieving chamber 22. A vacuum port 25 is 
provided in the upper part of the retrieving chamber 22 and is connected, 
via a vacuum conduit, to a vacuum pump 29, for evacuating the interior 
parts of the furnace chamber 4 and the metallic vapor retrieving chamber 
22 to appropriate vacuum levels, as will be described later. In this fifth 
preferred embodiment, two stirrers 116 are provided for agitating the 
molten pool 20 of retrieving metal in the metallic vapor retrieving 
chamber 22. As in the third preferred embodiment of the present invention, 
previously described, there is provided in the central part of the 
metallic vapor retrieving chamber 22 a vane wheel 39, which is structured 
with a horizontally rotatably mounted hub 40 and a plurality of vanes 41 
projecting therefrom. The vane wheel 39 is rotatably mounted with the 
vanes 41 on its lower part at least partially submerged under the surface 
of the pool 20 of molten retrieving metal in the metallic vapor retrieving 
chamber 22, and with those of its vanes 41 on its left part as seen in 
FIG. 12 directly opposed to the convergent-divergent nozzle 19 in its 
axial line 34. Thus, when a jet flow 35 of reaction product gas is 
squirting out of the convergent-divergent nozzle 19, a major part of the 
metallic vapor in this jet flow impinges against these vanes 41 of the 
vane wheel 39 and sticks thereto in liquid form, so as to cause the vane 
wheel 39 as a whole to rotate in the counterclockwise direction as seen in 
the figure. Thus this rotation of the vane wheel 39 relatively gently 
brings this molten retrieved metal under the surface of the molten 
retrieving metal pool 20 in the retrieving chamber 22, so that the metal 
is retrieved by the metal pool 20 in a quite gentle manner. A heater 119 
is provided around the retrieving chamber 22, for keeping the molten metal 
pool 20 therein in the melted state, as will be more particularly 
described later. 
The bottommost part of the metallic vapor retrieving chamber 22 is 
communicated via a molten metal take out conduit 117 to a not quite 
bottommost part of an vaporation chamber 105, which is incorporated in a 
distillation apparatus, generally denoted by the reference numeral 104, 
which is provided below and to the left as seen in the figure of the 
furnace chamber 4. Further, the not quite bottommost part of the metallic 
vapor retrieving chamber 22 is communicated via a molten metal returning 
conduit 118 to the bottommost part of said evaporation chamber 105 of said 
distillation apparatus 104. Above the evaporation chamber 105 in the 
distillation apparatus 104 there is provided a condensation chamber 106. 
The heater 119 also surrounds the evaporation chamber 105 and the 
condensation chamber 106, and also the molten metal take out conduit 117 
and the molten metal returning conduit 118, as well as the metallic vapor 
retrieval chamber 22 as previously explained, so as appropriately to heat 
up all these chambers and conduits and so as to keep the molten metal in 
them at appropriate temperatures, as will be explained in detail later. 
There is provided another vacuum pump 111, communicated to an upper part 
of the condensation chamber 106, for evacuating the interior parts of the 
distillation apparatus 104 to appropriate vacuum levels, as described 
later. 
A pump or impeller mechanism 127 is provided in the molten metal returning 
conduit 118, in this embodiment, for providing an appropriate molten metal 
circulation in the apparatus, i.e. for urging the molten metal in the 
molten metal take out conduit 117 and the molten metal in the molten metal 
returning conduit 118 in the directions shown by the arrows in FIG. 12. A 
metal vapor passage 129 is provided as substantially vertically extending 
from the upper part of the evaporation chamber 105 to an upper part of the 
condensation chamber 106, and a conduit 121 is provided for taking out 
molten retrieved metal from the lower part of the condensation chamber 106 
to a heated ladle 122; this conduit 121 is controlled by a valve which is 
not shown, so as to enable the operator to remove molten retrieved metal 
from the condensation chamber 106 without disturbing the depressurized 
state of the apparatus. 
The General Operation of the Fifth Apparatus Embodiment 
The shown apparatus according to the fifth preferred embodiment of the 
apparatus of the present invention is particularly suited for realizing a 
metal retrieval process as described above in which the pool 20 of molten 
metal used for retrieval is of a different type of metal from the metallic 
vapor which is to be retrieved, and is generally used as follows. First, 
material for reduction of an appropriate sort for producing gas or vapor 
of a metal which is required to be recovered or retrieved as will be 
understood in detail later is charged into the furnace chamber 4 of the 
reduction furnace 1, by charging this material into the charging hopper 8 
and by then opening and closing the control valves associated therewith so 
as to transfer this reduction material into the furnace chamber 4 without 
allowing gas from the outside to enter the furnace chamber 4 in 
substantial amount. Then the heater is operated so as to heat up the 
furnace chamber 4 and the reaction material charged therein to a 
predetermined temperature T.sub.1, so as to cause this reduction material 
to be reduced into a gas mixture containing vapor of the desired metal 
which is to be recovered or retrieved, said gas mixture being at a 
pressure P.sub.1. This mixture gas then passes in the heated state through 
the opening in the side wall of the reduction furnace 1 and is then 
ejected from the furnace chamber 4, according to the difference of 
pressures between the interior of the furnace chamber 4 which is at said 
pressure P.sub.1 and the interior of the metallic vapor retrieving chamber 
22 which is kept at a pressure P.sub.2 substantially lower than the 
pressure P.sub.1, through the conduit which leads to the 
convergent-divergent nozzle 19 at its downstream end, into the metallic 
vapor retrieving chamber 22, and sprays out of the convergent-divergent 
nozzle 19 as a jet 35 which impinges against the surface of the pool 20 of 
molten retrieving metal in the bottom of said retrieving chamber 22. As 
this mixture gas passes through the convergent-detergent nozzle 19, as in 
the previous embodiments described above it reaches a supersonic speed and 
expands adiabatically very quickly, and thus the metal vapor in said 
mixture gas is very quickly cooled down by this adiabatic expansion to a 
second temperature T.sub.2, and in fact may be at least partly condensed 
into fine metal droplets or particles. This cooling down is so quick that 
it occurs without said metal vapor having a chance to recombine with other 
constituents of said mixture gas (i.e., to be again oxidized thereby), due 
to the very quick cooling of said mixture gas, and the final second 
temperature T.sub.2 down to which the mixture gas is cooled by the 
adiabatic expansion in the convergent-divergent nozzle 19 is so low as to 
be below the temperature at which the recombination or reoxidization 
reaction can substantially take place. 
The jet 35 including cooled metallic vapor and possibly fine particles of 
liquid or solid metal thus produced impinges on the vanes 41 of the vane 
wheel 39, and is as described above thereby brought relatively gently 
beneath the surface of the pool 20 of molten retrieving metal in the 
bottom of said retrieving chamber 22, and thus the metal in said jet 35 
becomes mixed with and entrained into the molten retrieving metal, which 
is envisaged as being, as explained above, of a different sort from said 
metal to be retrieved. Bubbles 36 of gas from the jet may become 
temporarily entrained below the surface of the pool 20 of molten 
retrieving metal, but this need not cause any substantial problem. The 
mixture pool 20 of the molten retrieving metal and the retrieved metal in 
the metallic vapor retrieving chamber 22 is kept agitated and thus well 
mixed together by the two stirrers 116. The retrieving chamber 22 is 
maintained at its pressure P.sub.2 by the remainder gas from the jet 35 
being sucked out of said retrieving chamber 22, via the port 25 and the 
conduit provided therefor, by the operation of the vacuum pump 29. The 
sucking rate of the pump 29 thus is controlled so as to maintain the 
pressures in the furnace chamber 4 and in the metallic vapor retrieving 
chamber 22 at substantially their respective desired values P.sub.1 and 
P.sub.2, according of course also to various other parameters of the 
apparatus and its operation. From time to time, some of the slag in the 
bottom portion of the furnace chamber 4 is removed via the port provided 
therefor (not shown), without disturbing the depressurized state of the 
apparatus, and similarly slag on the pool 20 of metal mixture in the 
retrieving chamber 22 is removed. 
Thereby, the molten retrieval metal pool 20 in the retrieval chamber 22 
becomes more and more charged with retrieved metal from the metallic vapor 
which has squirted through the convergent-divergent nozzle 19. Now, the 
operation of the pump or impeller 127 maintains a steady circulation of 
this molten metal pool 20 in the directions as shown by the arrows in FIG. 
12 to take this molten metal including retrieved metal out from the 
retrieval chamber 22, through the molten metal take out conduit 117, into 
the evaporation chamber 105 wherein it is heated up by the action of the 
heater 119 to a temperature substantially higher than the boiling point of 
the retrieved metal (i.e. the metal whose vapor was produced by reaction 
in the reaction furnace 1) but substantially lower than the boiling point 
of the metal for retrieval which was originally charged into the retrieval 
chamber 22, which is a different metal from and which has a higher boiling 
point, than the metal which is to be retrieved. Thus, at this time, all or 
at least a substantial amount of the retrieved metal is boiled off from 
the surface of the molten metal in the evaporation chamber 105 as a gas or 
vapor, leaving behind a molten metal mass which is at least substantially 
depleted of the lower boiling point retrieved metal, and is thus 
substantially proportionally enriched with the higher boiling point 
retrieval metal. From this evaporation chamber 105, this molten metal is 
then returned via the molten material returning conduit 118 to the 
retrieval chamber 22, therein to again receive metal vapor to be 
retrieved; while the vapor crossing substantially only of retrieved metal 
which is being evaporated from the surface of the molten metal mass 
contained in said evaporation chamber 105 passes through the conduit 129 
and into the condensation chamber 106, to be therein condensed according 
to the temperature maintained therein which is substantially below the 
boiling point of said metal which is to be retrieved. Subsequently, this 
substantially pure molten retrieved metal in said condensation chamber 104 
is removed therefrom via the conduit 121 into the ladle 122. 
Description of the Fifth Method Embodiment 
The fifth preferred apparatus embodiment of the present invention described 
above was operated by charging a mixture of magnesium oxide powder (which 
in fact was made by oxidizing magnesium sulphide and refining it) and 
carbon, in equal mol amounts, formed into lumps as a raw material for 
reduction, into the furnace chamber 4 of the reduction furnace 1, by 
operating the vacuum pump 29, by operating the heaters, by charging a 
substantially pure mass of lead metal as a metal for retrieval into the 
metallic vapor retrieving chamber 22, and by melting said lead metal into 
a pool 20 of retrieving molten metal for retrieving the magnesium vapor 
produced by reduction in the reduction furnace 1. Thus, in this 
embodiment, the retrieving metal (lead) used for the retrieving metal pool 
20 was a different metal from the metal (magnesium) which was to be 
retrieved. The temperature T.sub.1 to which the furnace chamber 4 and the 
reduction material charged thereinto were heated was 1800.degree. C., and 
the rate of suction of the vacuum pump 29 was controlled so as to keep the 
pressure P.sub.1 within the furnace chamber 4 at approximately 100 torr 
and so as to keep the pressure P.sub.2 within the metallic vapor 
retrieving chamber 22 at approximately 5 to 6 torr. The heater 119 was so 
operated as to keep the temperature within the metallic vapor retrieving 
chamber 22 at about 580.degree. to 600.degree. C., so as to keep the 
retrieving metal pool 20 of lead metal therein in the molten state. 
As explained above, the magnesium oxide in the reaction chamber 4 of the 
reduction furnace 1 was reduced by the carbon, so as to produce metallic 
magnesium in vapor form and oxidizing gas such as carbon monoxide, and 
this mixture of metallic magnesium vapor and oxidizing gas then flowed out 
through the conduit 18 and through the convergent-divergent nozzle 19 into 
the metallic vapor retrieving chamber 22, attaining a supersonic speed as 
it passed through the convergent-divergent nozzle 19. In fact, in this 
fifth embodiment, the nozzle 19 was again functioning under the 
insufficient expansion condition. The jet flow 35 thus produced was 
quickly cooled down by adiabatic expansion in the nozzle 19 below the 
temperature at which the reverse reaction of the oxidizing gas oxidizing 
the magnesium vapor could occur, and impinged against the vanes 41 of the 
vane wheel 39 so as to be slowed thereby and to lose some of its kinetic 
energy, molten magnesium which collected on said vanes and also the jet 
flow 35 as a whole then impinging relatively gently on and plunging under 
the surface of the molten retrieving lead metal pool 20 within the 
metallic vapor retrieving chamber 22, and the magnesium vapor (which in 
fact was partially liquefied and/or solidified) in said jet flow was 
entrained into and mixed with the molten lead metal pool 20. 
The entrained magnesium was then of course brought to the liquefied state 
by this entrainment into the retrieving lead metal pool, and remained 
therein; and the oxidizing gas (including the carbon monoxide) in the 
mixture then, after plunging into the molten lead pool 20 and temporarily 
forming bubbles such as the shown bubbles 36 in the molten lead pool 20, 
rose to the surface and was sucked away from the vacuum pump 29. The 
magnesium and the lead which thus were together molten in the pool 20 were 
kept well mixed together by the stirrers 116. Thereby, the molten lead 
retrieval metal pool 20 in the retrieval chamber 22 became more and more 
charged with retrieved magnesium metal from the magnesium vapor which had 
squirted through the convergent-divergent nozzle 19. 
As described above, the operation of the pump or impeller 127 maintained a 
steady circulation of this molten mixture of lead and magnesium metals, in 
the directions as shown by the arrows in FIG. 12, between the retrieval 
chamber 22 and the evaporation chamber 105, through the molten metal take 
out conduit 117 and the molten metal returning conduit 118. In the 
evaporation chamber 105, this metal mixture was heated up by the action of 
the heater 119 to a temperature of about 850.degree. to 900.degree. C., 
which was a temperature substantially higher than the boiling point of the 
retrieved magnesium metal but substantially lower than the boiling point 
of the lead metal for retrieval which was originally charged into the 
retrieval chamber 22. Thus, at this time, all or at least a substantial 
amount of the retrieved magnesium metal was boiled off from the surface of 
the molten metal mixture in the evaporation chamber 105 as a gas or vapor, 
leaving behind a molten metal mass which was at least substantialy 
depleted of the lower boiling point retrieved magnesium metal, and was 
thus substantially proportionally enriched with the higher boiling point 
lead retrieval metal. From this evaporation chamber 105, this molten metal 
was then returned via the molten metal returning conduit 118 to the 
retrieval chamber 22, therein to again receive magnesium metal vapor to be 
retrieved; while the vapor consisting substantially only of retrieved 
magnesium metal which was being evaporated from the surface of the molten 
mixture metal mass contained in said evaporation chamber 105 passed 
through the conduit 129 and into the condensation chamber 106, to be 
therein condensed according to the temperature maintained therein which 
was approximately 680.degree. to 700.degree. C., i.e. substantially below 
the boiling point of said magnesium metal which was to be retrieved. By 
the way, the condensation chamber 106 was maintained at a pressure of 
approximately 6 to 10 torr by the vacuum pump 111. Subsequently, this 
substantially pure molten retrieved magnesium metal in said condensation 
chamber 106 was removed therefrom via the conduit 121 into the ladle 122. 
In fact, this process operated continuously at such a rate that the mol 
ratio of retrieved molten magnesium in the molten metal pool 20 in the 
metallic vapor retrieving chamber 22 was kept at about 50%. The retrieval 
ratio of magnesium, in this fifth preferred embodiment, was 97.8%. The 
average purity of the retrieved magnesium was 97.9%. 
The results described above of operating the fifth embodiment of the 
apparatus of the present invention according to the fifth preferred 
embodiment of the method of the present invention show that in the case of 
a metal such as magnesium, which has a relatively high melting point, and 
which has a relatively high tendency to become reoxidized, a result of 
retrieving metallic vapor from the gas products of a reduction reaction 
which is better both with regard to retrieval ratio and with regard to 
purity of final product can be obtained, when the retrieval metal is 
different from the magnesium metal which is being retrieved, and in 
particular is lead. 
The Construction of the Sixth Apparatus Embodiment 
In FIG. 13 there is shown a schematic structural view of an apparatus for 
retrieving metal in the liquid phase from a gas containing vapor of the 
metal, according to the sixth and last preferred apparatus embodiment of 
the present invention, which is again particularly applied to the 
reduction of magnesium oxide by carbon as will be seen hereinafter, and 
which is used for practicing the sixth preferred embodiment of the method 
for retrieving metal in the liquid phase according to the present 
invention. In this figure, parts of the sixth preferred apparatus 
embodiment shown, which corresponds to parts of the first through fifth 
preferred apparatus embodiments shown in FIGS. 8 through 12, and which 
have the same functions, are designated by the same reference numerals and 
symbols as in those figures. 
In this sixth preferred embodiment, the construction of the reduction 
furnace 1 and the furnace chamber 4 therein is substantially the same as 
in the fifth preferred embodiment, except that a cylinder 222 suitable for 
containing an inert gas such as argon gas is connected via a conduit 223 
and a valve 224 so as to supply a controllable amount of inert gas such as 
argon gas to the interior of said furnace chamber 4. Again, the products 
of the reduction reaction in the furnace chamber 4, augmented by this 
controllable amount of inert gas fed from the cylinder 222, pass out 
therefrom down the conduit to the convergent-divergent nozzle or Laval 
nozzle 19 of the previously described sort. 
The metallic vapor retrieving chamber 22 is structured similarly to that of 
the fifth preferred embodiment, except for the following points. No vane 
wheel such as the vane wheel 39 of the fifth preferred embodiment is 
provided for slowing down the speed of the jet 35 of reaction gases and 
metal vapor which is being squirted out from the nozzle 19, and in line 
with this structural feature the metallic vapor retrieving chamber 22 is 
shaped as somewhat thinner and taller than the retrieving chamber 22 of 
the fifth preferred embodiment shown in FIG. 12. Further, since the jet 35 
will thus hit the surface of the molten retrieving metal pool 20 in this 
retrieving chamber 22 much harder and quicker, no stirrers such as the 
stirrers 116 of the fifth preferred embodiment are provided, in this sixth 
preferred embodiment, since the force of this jet 35 is sufficient for 
agitating the molten metal pool 20 and keeping it well mixed (i.e., for 
keeping the retrieved metal well mixed with the retrieving metal which is 
intended to be different from said retrieved metal, as in the fifth 
preferred embodiment). Further, a shield member 230 is provided for 
preventing splashes of molten metal from being splashed up by the jet 35 
to pass into the conduit leading to the vacuum pump 29. 
As in the fifth preferred embodiment, the lower parts of the metallic vapor 
retrieving chamber 22 are communicated via the molten metal take out 
conduit 117 and the molten metal returning conduit 118 to the evaporation 
chamber 105, which is incorporated in the distillation apparatus 104, 
which is provided below and to the left as seen in the figure of the 
furnace chamber 4, and which is substantially the same in construction as 
the distillation apparatus 104 of the fifth preferred embodiment shown in 
FIG. 12. 
The General Operation of the Sixth Apparatus Embodiment 
The shown apparatus according to the sixth preferred embodiment of the 
apparatus of the present invention is again particularly suited for 
realizing a metal retrieval process as described above in which the pool 
20 of molten metal used for retrieval is of a different type of metal from 
the metallic vapor which is to be retrieved, and is generally used in a 
manner similar to that in which the fifth preferred embodiment is used; 
except for the following points. First, an inert gas such as argon gas is 
continuously injected at a controlled flow rate from the cylinder 222 into 
the furnace chamber 4, while the material for reduction of an appropriate 
sort for producing gas or vapor of the metal which is required to be 
recovered or retrieved is being reduced into a gas mixture containing 
vapor of said desired metal to be retrieved, thus augmenting the pressure 
of said gas mixture, which is brought to be at a pressure P.sub.1, which 
of course can be freely adjusted within limits by control of the amount of 
supplemented inert gas. This mixture gas containing gas (such as argon 
gas) then passes in the heated state through the opening in the side wall 
of the reduction furnace 1 and is then ejected from the furnace chamber 4, 
as before, according to the difference of pressures between the interior 
of the furnace chamber 4 which is at said pressure P.sub.1 and the 
interior of the metallic vapor retrieving chamber 22 which is kept at a 
pressure P.sub.2 substantially lower than the pressure P.sub.1, through 
the conduit 18 which leads to the convergent-divergent nozzle 19 at its 
downstream end, into the metallic vapor retrieving chamber 22, and sprays 
out of the convergent-divergent nozzle 19 as a jet 35 which impinges 
against the surface of the pool 20 of molten retrieving metal in the 
bottom of said retrieving chamber 22. As this mixture gas passes through 
the convergent-divergent nozzle 19, as in the previous embodiments 
described above it reaches a supersonic speed and expands adiabatically 
very quickly, and thus the metal vapor in said mixture gas is very quickly 
cooled down by this adiabatic expansion to a second temperature T.sub.2, 
and again in fact may be at least partly condensed into fine metal 
droplets or particles. This cooling down is again so quick that it occurs 
without said metal vapor having a chance to recombine with other 
constituents of said mixture gas (i.e., to be again oxidized thereby), due 
to the very quick cooling of said mixture gas, and the final second 
temperature T.sub.2 down to which the mixture gas is cooled by the 
adiabatic expansion in the convergent-divergent nozzle 19 is so low as to 
be below the temperature at which the recombination or reoxidization 
reaction can substantially take place. It is particularly planned, in this 
operation of the convergent-divergent nozzle 19 of the sixth preferred 
embodiment of the present invention, according to the supplementation of 
the volume of the reaction gases produced in the reaction chamber 4 by the 
injected inert gas such as argon gas from the cylinder 222, that said 
nozzle 19 should be operated under the proper expansion condition. The jet 
35 from the convergent-divergent nozzle 19 impinges quite violently on the 
surface of pool 20 of molten retrieving metal in the bottom of the 
retrieving chamber 22, and thus the metal in said jet 35 becomes mixed 
with and entrained into the molten retrieving metal, which is envisaged as 
being, as explained above, of a different sort from said metal to be 
retrieved. Bubbles of gas from the jet 35 may become temporarily entrained 
below the surface of the pool 20 of molten retrieving metal, but this need 
not cause any substantial problem. The mixture pool 20 of the molten 
retrieving metal and the retrieved metal in the metallic vapor retrieving 
chamber 22 is kept agitated and thus well mixed together by the violence 
of the uncushioned impact of the jet 35, without need for any stirrers 
like the stirrers 116 of the fifth preferred embodiment. As before, the 
retrieving chamber 22 is maintained at its pressure P.sub.2 by the 
remainder gas from the jet 35 (including the supplemental inert gas) being 
sucked out of said retrieving chamber 22, via the port and the conduit 
provided therefor, by the operation of the vacuum pump 29, said conduit 
being as mentioned above shielded by the shield 230. The sucking rate of 
the pump 29 again is controlled so as to maintain the pressures in the 
furnace chamber 4 and in the metallic vapor retrieving chamber 22 at 
substantially their respective desired values P.sub.1 and P.sub. 2, 
according of course also to various other parameters of the apparatus and 
its operation. 
Thereby, the molten retrieval metal pool 20 in the retrieval chamber 22 
becomes more and more charged with retrieved metal from the metallic vapor 
which has squirted through the convergent-divergent nozzle 19. The 
operation of the distillation apparatus 104 for separating out the desired 
metal to be retrieved (which was reduced in the reduction furnace 4) is 
quite the same as in the fifth preferred embodiment described above, and 
hence will not be particularly discussed herein. 
Description of the Sixth Method Embodiment 
The sixth preferred apparatus embodiment of the present invention described 
above was operated, in a fashion similar to the fifth preferred method 
embodiment described above, by charging a mixture of magnesium oxide 
powder and carbon, in equal mol amounts, formed into lumps as a raw 
material for reduction, into the furnace chamber 4 of the reduction 
furnace 1, by operating the vacuum pump 29, by operating the heaters, by 
charging a substantially pure mass of lead metal as a metal for retrieval 
into the metallic vapor retrieving chamber 22, and by melting said lead 
metal into a pool 20 of retrieving molten metal for retrieving the 
magnesium vapor produced by reduction in the reduction furnace 1. Thus, 
again, in this sixth preferred embodiment, the retrieving metal (lead) 
used for the retrieving metal pool 20 was a different metal from the metal 
(magnesium) which was to be retrieved. The temperature T.sub.1 to which 
the furnace chamber 4 and the reduction material charged thereinto were 
heated was 1800.degree. C., and the rate of suction of the vacuum pump 29 
and the rate of injection of supplemental inert gas (which was argon gas) 
were controlled so as to keep the pressure P.sub.1 within the furnace 
chamber 4, this time, at approximately 150 torr, and so as to keep the 
pressure P.sub.2 within the metallic vapor retrieving chamber 22 at 
approximately 12 to 14 torr. The heater 119 was so operated as to keep the 
temperature within the metallic vapor retrieving chamber 22 at about 
580.degree. to 600.degree. C., so as to keep the retrieving metal pool 20 
of lead metal therein in the molten state. 
The magnesium oxide in the reaction chamber 4 of the reduction furnace 1 
was reduced by the carbon, so as to produce metallic magnesium in vapor 
form and oxidizing gas such as carbon monoxide, and this mixture of 
metallic magnesium vapor and oxidizing gas, mixed with the supplemental 
argon gas, then flowed out through the conduit 18 and through the 
convergent-divergent nozzle 19 into the metallic vapor retrieving chamber 
22, attaining a supersonic speed as it passed through the 
convergent-divergent nozzle 19. In fact, in this sixth embodiment, the 
nozzle 19 this time functioned under the proper expansion condition. The 
jet flow 35 thus produced was quickly cooled down by adiabatic expansion 
in the nozzle 19 to below the temperature at which the reverse reaction of 
the oxidizing gas oxidizing the magnesium vapor could occur, in fact to a 
temperature of about 500.degree. to 550.degree. C., and impinged against 
the surface of the molten retrieving lead metal pool 20 within the 
metallic vapor retrieving chamber 22, and the magnesium vapor (which in 
fact was partially liquefied and/or solidified) in said jet flow 35 was 
entrained into and mixed with the molten lead metal pool 20. The entrained 
magnesium was then of course brought to the liquefied state by this 
entrainment into the retrieving lead metal pool, and remained therein; and 
the oxidizing gas (including the carbon monoxide) and the argon gas in the 
gas mixture then, after plunging into the molten lead pool 20 and 
temporarily forming bubbles therein, rose to the surface and was sucked 
away by the vacuum pump 29. The magnesium and the lead which thus were 
together molten in the pool 20 were kept well mixed together by the force 
of the jet 35. Thereby, the molten lead retrieval metal pool 20 in the 
retrieval chamber 22 became more and more charged with retrieved magnesium 
metal from the magnesium vapor which had squirted through the 
convergent-divergent nozzle 19. Subsequently, the retrieved magnesium 
metal was separated out from the lead retrieving metal by the distillation 
apparatus 104, as in the operation of the fifth preferred embodiment 
described above. 
The retrieval ratio of magnesium, in this sixth preferred embodiment, was 
98.2%. The average purity of the retrieved magnesium was 98.9%. 
The results described above of operating the sixth embodiment of the 
apparatus of the present invention according to the sixth preferred 
embodiment of the method of the present invention show that by the 
addition of sufficient argon gas to keep the convergent-divergent nozzle 
19 functioning in the proper expansion condition the result of retrieving 
metallic vapor from the gas products of a reduction reaction can be 
superlative, both with regard to retrieval ratio and with regard to purity 
of the final product. 
Although the present invention has been shown and described with reference 
to several preferred embodiments thereof, and in terms of the illustrative 
drawings, it should not be considered as limited thereby. Various possible 
modifications, omissions, and alterations could be conceived of by one 
skilled in the art to the form and the content of any particular 
embodiment, without departing from the scope of the present invention. 
Therefore it is desired that the scope of the present invention, and of 
the protection sought to be granted by Letters Patent, should be defined 
not by any of the perhaps purely fortuitous details of the shown 
embodiments, or of the drawings, but solely by the scope of the appended 
claims, which follow.