Process for the recovery of lead from a lead-bearing sulfide concentrate

Lead is recovered from a lead-bearing sulfidic concentrate by heating the concentrate in such a manner that lead and its compounds pass into the gas phase. The oxygen pressure in the gas phase is adjusted by oxidation or reduction in order to cause the compounds of lead to react with each other to form lead, and the gas phase is cooled in order to condense the metallic lead out from the gas.

BACKGROUND OF THE INVENTION 
The present invention relates to a method for the recovery of lead from a 
lead-bearing sulfide concentrate by heating the concentrate so that the 
compounds of lead pass into the gas phase. 
Most of the world's lead is produced from lead-bearing sulfide concentrates 
by a sintering-shaft-furnace process. In the sintering machine the 
concentrate is oxidized in order to remove the sulfur and it is brought 
into a particle form suitable for shaft-furnace reduction. 
The greatest disadvantage of the process is its large quantities of waste 
gas, which are produced during both the sintering and the shaft-furnace 
process. It has been estimated that process and ventilation gases which 
contain sulfur dioxide and dusts are produced at a rate of about 670 kmol 
(15 000 Nm.sup.3) per one tonne of concentrate. The purification of the 
waste gases to correspond to the current requirements of environmental 
protection causes a considerable increase in the costs of lead production. 
The aim of recent research has been to create a process in which the sulfur 
dioxide is obtained in a concentrated form and the quantity of 
dust-bearing waste gases is minimal. In principle, a single-stage process 
is possible for pure concentrates which contain only very little quarz. 
Sulfidic lead concentrate is oxidized directly to metal in one process 
stage. As a sub-reaction, lead sulfide sulfidizes first to oxide according 
to the reaction below 
EQU PbS+1/2O.sub.2 =PbO+SO.sub.2 
Thereafter, the excess lead sulfide reduces the oxide to metal according to 
the following reaction 
EQU 2PbO+PbS=3Pb+SO.sub.2 
At a low operating temperature of the process, lead sulfate and oxysulfates 
are obtained instead of oxide. Metallic lead is produced when these 
compounds react with lead sulfide. 
The single-stage lead production process is best applicable to pure 
concentrates. Owing to the great mutual affinity of lead oxide and silica, 
the concentration of lead in the slag increases and the yield of metallic 
lead decreases as the concentration of quartz in the concentrate 
increases. Releasing lead from the silicate requires so low an oxygen 
pressure that, in the presence of sulfur dioxide, lead sulfide is obtained 
instead of metallic lead. 
At those temperatures and oxygen pressures which are used in direct 
production of lead, the zinc present in the concentrate oxidizes and 
passes into the slag. In order to maintain the melting point of the slag 
sufficiently low, the slag has to be fluxed, which for its part increases 
the losses of lead into the slag. 
Processes of several stages have been applied to the treatment of impure 
concentrates. It has been possible to eliminate the disadvantages of the 
sintering process, i.e. dilute sulfur dioxide gas and passing of lead 
oxide dust into the environment, the formation of sulfates and 
difficulties in temperature control, by shifting to closed reactors, the 
product of which is a melt containing the lead oxide. Such is, for 
example, the Kivcet process (FI Lay-Open Print 56028). 
The vapor pressure of lead sulfide especially, but also of lead oxide, is 
high at the operating temperatures of the lead production process. This is 
the reason for the large quantities of fly dusts, which are typical of the 
process and highly detrimental. Both in a multi-stage and in a 
single-stage process there occurs volatilization of both lead sulfide and 
oxide. The boiling point of lead sulfide is about 1610 K. and that of lead 
oxide about 1810 K., and so at the processing temperatures the gas may 
contain large quantities of the said compounds. Volatilized lead compounds 
leave the processing apparatus along with the sulfur-dioxide bearing gas. 
Depending on the sulfur dioxide pressure, only lead sulfide, sulfate and 
various oxysulfates are stable below 1050-1150 K. For this reason, the 
dust separated from cooled gas, the dust possibly representing a very high 
proportion of the lead amount fed into the process, mainly consists of 
these compounds. The amount of lead oxide is less. 
Feeding the fly dust to the oxide reduction stage is not possible because 
of its sulfur content. During the reduction stage the sulfur would be 
reduced and would leave along with the gas in the form of lead sulfide. 
Likewise, the concentration of sulfur in the lead produced would be high. 
The most common method of treating the dust is to feed it back to the 
oxidation stage together with fresh concentrate. However, there is the 
disadvantage in the amount of energy required by the endothermal 
decomposition reactions of the sulfates and the increase in the gas 
quantity in the process owing to the high rate of recycling of dust. 
One of the main objectives in the development of lead processes has been to 
reduce the amounts of dust. One method to achieve this has been to cool 
the gas in the outlet section of the oxidation reactor so that the lead 
compounds condense and fall back into the hot melt. This procedure is used 
in the Kivcet process. However, the return of cooled dust, which possibly 
contains sulfates, results in excessive consumption of heat. 
Furthermore, U.S. Pat. No. 4,169,725 discloses a process for the suspension 
smelting of sulfidic complex or mixed ores or concentrates in order to 
separate the impurities present in them, a process in which the 
non-volatile impurities are subjected to a reducing or sulfidizing 
treatment in the lower section of the reaction zone in order to return 
them to the gas phase before the solid is separated and impinges against 
the melt. By this procedure it is ensured that the impurities will not 
substantially pass into the melt but remain in the gas phase. In this 
patent it is noted that a considerable amount of lead oxide can be made to 
remain in the gas phase in spite of the reduction and that the lead 
sulfides can be evaporated to low concentrations in the gas phase without 
the oxidation of the sulfide. It is also noted that the reduction and 
sulfidization of lead from molten silicates is difficult. 
Another method, applied in several processes, for decreasing the amount of 
dust is to inject the sulfide concentrate either to the melt surface or 
below the surface of the melt in the furnace. Thus a rapid dissolving of 
the sulfide in the molten lead or a reaction with the lead oxide present 
in the slag is effected, and thereby the activity of the lead sulfide 
decreases and its volatilization decreases. 
None of the methods described above entirely eliminates the dust problem 
involved in lead production processes. A large proportion of the lead 
content of the concentrate continues to be removed along with the gas and 
is sulfated or sulfidized during the cooling of the gas. 
The object of the present invention is thus to eliminate the entire dust 
problem involved in prior known lead production processes and to provide a 
process for the recovery of lead from a lead-bearing sulfide concentrate 
by heating the concentrate in such a manner that the compounds of lead 
pass into the gas phase. 
SUMMARY OF THE INVENTION 
The present invention is based on the observation that it is possible to 
exploit the dependence of the concentration of lead in a gas which 
contains lead, sulfur and oxygen on both the oxygen pressure and the 
temperature of the gas in such a manner that substantially all the 
compounds of lead can be caused to remain in the gas phase and react in it 
to form metallic lead, which is thereafter separable from the gas phase. 
At a low oxygen pressure, the lead present in a gas is mainly in the form 
of lead sulfide, the vapor pressure of which is higher than that of lead 
oxide and metallic lead. At a high oxygen pressure, the lead is mainly 
present in the form of oxide, the temperature of which at the smelting 
temperatures is also higher than that of metallic lead. Within the range 
between the extreme oxygen pressures mentioned above, there appears in the 
gas, in addition to the two compounds mentioned above, metallic lead in a 
thermodynamic equilibrium corresponding to the oxygen pressure in the gas 
and to the temperature of the gas. 
The process according to the invention can be carried out advantageously by 
first heating the sulfide concentrate either at a low oxygen pressure or 
at a high oxygen pressure, so that a maximal quantity of the lead 
compounds passes into the gas phase, whereafter the gas phase is oxidized 
or respectively reduced in order to control its oxygen pressure. The 
sulfide concentrate is heated preferably to so high a temperature that it 
melts, for example to a temperature which is 1373 K. at minimum and 
preferably 1773 K. at maximum, and the oxygen pressure is adjusted 
respectively to approximately 2.multidot.10.sup.-7 atm at maximum and 
respectively preferably to approximately 2.multidot.10.sup.-4 atm at 
maximum. If the sulfide concentrate is first heated at a high oxygen 
pressure, the heating is carried out to 1373 K. at minimum and preferably 
to 1873 K. at maximum and the oxygen pressure is adjusted respectively to 
5.multidot.10.sup.-10 atm at minimum and to 6.multidot.10.sup.-6 atm at 
maximum. 
When the metallic lead has been formed in the gas phase, the gas phase is 
cooled to a temperature which is 1073 K. at minimum and at which the 
oxygen pressure is (0.1-1).multidot.10.sup.-10 atm at minimum, and most of 
the lead is condensed at a temperature which is 1272 K. at minimum and at 
which the oxygen pressure is 10.sup.-10 -10.sup.-7 atm, the remainder 
being condensed at a temperature lower than the above. 
The gas phase can be cooled by feeding into the gas phase a cooling agent 
such as water, cold gas or advantageously lead, in which case the control 
of the oxygen pressure and the cooling are advantageously carried out in 
the same stage by feeding to this stage a cold oxidizing agent or reducing 
agent while cooling.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
If the oxygen pressure is low and the operation is carried out at a 
temperature at which the slag composed of the secondary constituents of 
the concentrate is molten, the gas can usually contain all the lead of the 
concentrate without being saturated with lead sulfide. At a high oxygen 
pressure, the same applies regarding lead oxide. If, on the other hand, 
the operation is carried out at a suitable oxygen pressure between the 
extreme oxygen pressures described above, the low vapor pressure of 
metallic lead, compared with the vapor pressures of sulfide and oxide, 
limits the amount of lead present in the gas. 
As an illustration, FIG. 1 shows the composition of a gas which contains 
sulfur, oxygen, nitrogen and lead, at a constant temperature, 1373 K., as 
a function of the oxygen pressure in equilibrium with metallic lead. 
When the oxygen pressure in the gas at 1373 K. is adjusted towards the 
optimum, about 6.multidot.10.sup.-7, the concentration of either PbS or 
PbO, depending on the direction from which the optimum is approached, 
begins to decrease. When the oxygen pressure is adjusted further towards 
the optimum after the point of saturation of metallic lead has been 
reached, the metallic lead begins to condense as a liquid. The 
condensation of metallic lead causes a total reaction of sulfide and 
oxide: 
EQU PbS(g)+2PbO(g).fwdarw.3Pb(l)+SO.sub.2 (g) (1) 
At the optimum oxygen pressure, the sum of the gaseous substances PbS(g), 
PbO(g) and Pb(g) is at its minimum. 
At a sufficiently high temperature, the vapor pressure of metallic lead is 
also so high that, regardless of the oxygen pressure, in an extreme case 
all of the lead treated in the process can be taken up by the gas phase 
and the gas is still undersaturated with lead. FIG. 2 shows the 
composition of a gas the oxygen pressure of which has been controlled 
optimally, i.e. as a function of the temperature. The gas has been 
obtained from the smelting of lead concentrate by means of almost only 
oxygen. 
The dew point of the gas with regard to metallic lead is about 1680 K. When 
the gas is cooled to below its dew point, metallic lead condenses and the 
PbS and PbO of the gas react with each other, the final product being 
liquid lead. In certain process conditions, 97% of the lead content of the 
gas is condensed to metallic lead already at 1373 K. At 1173 K. the gas is 
practically free of lead. 
It is seen from FIG. 3 that at a sulfur dioxide pressure of 1 atm metallic 
lead is stable only above approximately 1173 K. At this temperature, 
however, the sulfur content of the lead is high. When the oxygen pressure 
of the gas at 1373 K. is adjusted to its correct value, 97% of the lead 
content of the gas described above can be condensed in such a manner that 
the sulfur content of the lead is only about 0.1%. Sulfur contents even 
lower than this have been achieved in laboratory experiments. 
In the process according to U.S. Pat. No. 4,169,725 no attempt is made to 
adjust the oxygen pressure to the stability range of metallic lead and, 
furthermore, the aim is to retain an operating temperature at which the 
vapor pressure of metallic lead is also high, and lead and its compounds 
remain in the gas phase when the solid in suspension is being separated. 
Essential parts of the process can be improved by applying to lead 
production processes the thermodynamic behavior of the gas described 
above, which contains among other things sulfur, oxygen and lead. The 
oxygen pressure of the gases coming from the oxidation stages of the 
process is usually so high that the lead present in them is in oxidic 
form. Such a gas is directed at a high temperature to a reduction zone, to 
which some reductant such as carbon or a hydrocarbon is fed in addition to 
the gas at such a rate that the oxygen pressure of the gas reaches its 
optimum value, taking the temperature into account. 
By thereafter cooling the gas to a temperature of 1000-1500 K., depending 
on the sulfur dioxide pressure in the gas, the lead content of the gas is 
caused to condense to metal. The metal mist can be removed from the gas by 
known methods. The small amount of lead and compounds of lead remaining in 
the gas condenses during a subsequent cooling of the gas and can be 
recovered in the form of lead sulfide and sulfates. This dust can be 
returned to the smelting process. 
The gas leaving the reduction zone of a two-stage lead process may contain 
lead not only in the form of metallic vapor but also in the form of a 
sulfide, owing to the incomplete oxidation during the oxidation stage. It 
is advisable to direct such a gas not to the reduction zone but instead to 
the oxidation zone, in which the oxygen pressure of the gas is adjusted by 
means of technical oxygen, air, a mixture of these, or some other oxidant, 
to the same value as it was adjusted in the reduction zone in the case of 
an oxygen-rich gas. In order to condense the lead, the gas is treated in 
the same manner. 
In order to obtain optimal results, not only the pressure of oxygen but 
also its temperature in the condensation zone must be controlled with 
precision. If the condensation is carried out at too high a temperature, 
the quantity of lead and compounds of lead remaining in the gas phase is 
high. If, on the other hand, the temperature during condensation is too 
low, the sulfur content of the condensing lead is high or the product may 
comprise, instead of metallic lead, varying amounts of lead sulfide, lead 
sulfate or lead oxysulfates, depending on the pressures of sulfur dioxide 
and oxygen. 
The gas can be cooled to the condensation temperature by known methods, for 
example most advantageously by so-called direct cooling, in which a 
suitable amount of water, liquid lead or a cold gas which does not cause 
harmful reactions in the process gas is injected into the gas. In indirect 
cooling, in order to produce an adequate cooling bath, the heat transfer 
surfaces must be at a temperature lower than that to which the process gas 
must be cooled, possibly even below the stability range of lead. In this 
case, the sulfur content of the lead accumulating on the heat transfer 
surfaces is high or lead sulfates and sulfide are formed on them. 
After the adjustment of the oxygen pressure, before the cooling of the gas, 
a large proportion of its lead content is in the form of sulfide and 
oxide. During the cooling and thereafter, these react with each other, 
forming metallic lead, which condenses. In order to produce as complete a 
reaction as possible, it may be necessary to arrange retention time for 
the gas before the separation of liquid lead. It might also be necessary 
to carry out the cooling in several stages and to allow the gas to react 
in between or to carry out the cooling in accordance with a certain 
time-dependent function. 
In order to control the sulfur content in the lead and the distribution of 
impurities, it may be necessary to carry out a condensation of most of the 
lead at a higher temperature, for example 1473 K., and a second 
condensation at a lower temperature, for example 1173 K., in which case 
the sulfur content of the lead condensed during the latter stage is 
higher. At a lower temperature the vapor pressure of lead is very low, 
only about 0.004 bar, so that the rate of recovery of lead is very high. 
In this case, dusts which would have to be returned to the previous stage 
of the process are not produced. 
In pilot-scale experiments, the oxidation of lead concentrate was carried 
out in the reaction shaft of a flash smelting furnace in a suspension of 
gas and solid. Thereby it was observed that the volatilizations of lead 
and compounds of lead are greatly dependent not only on the temperature of 
the suspension but also on the degree of oxidation of the concentrate i.e. 
the oxygen pressure of the gas. At a high temperature (1700-1750 K.) and 
using a slight oxidation of the concentrate, the volatilization of the 
lead was at its best over 97%. At the same time about 97% of the silver 
fed into the reactor also volatilized. The reaction shaft of a flash 
smelting furnace is very advantageous for volatilization. Owing to rapid 
heating, the sulfides evaporate out of the concentrate, in which their 
activity is high, before the metals have time to combine with slag-forming 
compounds. By further decreasing the degree of oxidation, the 
corresponding volatilizations may be achieved at a lower temperature. 
By applying the control of the gas phase oxygen pressure and temperature in 
a lead process described above to a flash smelting process or to some 
corresponding oxidation process, a process is obtained in which the lead 
content of the lead concentrate can be separated directly in the form of 
metallic lead in one furnace and lead recovery apparatus. 
Oxygen, air or a mixture of these two is fed, either cold or pre-heated, to 
the volatilization stage of the process, for example into the reaction 
shaft of a flash smelting furnace, and possibly fuel is also fed in order 
to increase the temperature. In addition to the oxidation of the fuel, the 
oxygen to be used for burning the concentrate is controlled optimally in 
such a manner that the volatilization of the volatile valuable elements 
present in the concentrate, such as lead and copper, is maximal but that 
at the same time fuel is used at a rate suitable in terms of the 
economical result of the process and its thermal balance. 
During the next stage of the process, the solid fed into the gas separates 
from the gas flow and passes onto the floor of the furnace. The compounds 
of the non-volatile metals, for example copper and iron sulfides, form a 
matte on the floor of the furnace. A slag is formed on top of the matte by 
the oxides of the same metals and by slagging substances. The matte and 
the slag are discharged from the furnace and treated further by known 
methods. 
During the separation stage the gas is directed to the oxidation or 
reduction stage described above and thereafter to the condensation of 
lead. 
The process has great advantages in comparison with prior known processes. 
If the furnace is constructed so that the finely-divided dust traveling 
along with the gas during the oxidation stage is removed effectively from 
the gas phase during the oxidation stage, an effective separation is 
achieved between the non-volatile substances, such as copper, iron and 
slagging components, and on the other hand volatile substances, such as 
lead, silver, zinc, antimony and arsenic. The removal of non-volatile 
constituents from the gas can be made more effective by directing the gas 
to the process stage described above, in which the oxygen pressure is 
adjusted either by oxidation or by reduction. 
Another effective place for separating the secondary constituents of the 
concentrate in the process is the lead condensation stage. Arsenic, 
bismuth and other compounds having a high vapor pressure dissolve in the 
lead only to a slight degree during the condensation stage. When the gas 
is cooled to the lead condensation temperature, only part of the zinc 
remains in metallic form in the gas phase, part is dissolved in the 
produced lead or in the lead used for cooling. If the concentrate has a 
high zinc content, most of the zinc is oxidized during the condensation 
and is obtained as a dross from top of the lead. 
The invention is described below in greater detail by way of an example. 
EXAMPLE 1 
The process according to the invention is used for treating a lead 
concentrate with the following composition: 
Pb--72%, 
Fe--5%, 
S--14%, 
SiO.sub.2 --3%, 
CaO--3%, 
Al.sub.2 O.sub.3 --3%. 
The concentrate is heated to a temperature of 1400 K. by means of flue 
gases almost devoid of free oxygen, the gases having been obtained by 
burning a fossil fuel with air, whereby 97% of the lead sulfide content of 
the concentrate volatilizes. The composition of the gas obtained from the 
volatilization in our example is as follows: 
CO.sub.2 --9.5%, 
Co--1.0%, 
H.sub.2 O--12.5%, 
H.sub.2 --0.6%, 
SO.sub.2 --0.8%, 
Na--64.4%, 
H.sub.2 S--0.07%, 
S.sub.2 --0.04%, 
PbS--10.1%, 
PbO--0.03%, 
Pb--0.84%, 
pO.sub.2 --0.28.multidot.10.sup.-11 atm. 
Next, oxygen is added at a rate of about 0.11 kmol per 1 kmol of gas to the 
gas obtained from the volatilization stage. Part of the lead sulfide 
present in the gas oxides to oxide and metal, part remains in sulfidic 
form. 
The composition of the gas after the oxidation stage at 1400 K. is as 
follows: 
CO.sub.2 --10.4%, 
CO--0.05%, 
H.sub.2 O--13.1%, 
H.sub.2 --0.03%, 
SO.sub.2 --10.8%, 
N.sub.2 --64.0%, 
Pb--0.84%, 
PbS--0.24%, 
PbO--0.52%, 
pO.sub.2 --0.44.multidot.10.sup.-7 atm. 
86% of the lead of the gas coming from volatilization has condensed. 
The oxidized gas is cooled to a temperature of 1273 K. Lead vapor continues 
to condense, and lead sulfide and lead oxide react with each other, 
forming metal. The composition of the cooled gas is as follows: 
CO.sub.2 --10.6%, 
CO--0.01%, 
H.sub.2 O--13.2%, 
H.sub.2 --0.01%, 
SO.sub.2 --11.1%, 
N.sub.2 --64.7%, 
Pb--0.18%, 
PbS--0.07%, 
PbO--0.13%, 
pO.sub.2 --0.53.multidot.10.sup.-9 atm. 
97% of the lead of the gas has condensed as metal. The remainder condenses 
in the form of oxide, sulfide, sulfate and oxysulfates of lead during the 
after-cooling of the gas. This dust is recovered and fed to the 
volatilization stage or, advantageously, to the oxidation stage of the 
process. 
EXAMPLE 2 
At a pilot plant experiment lead concentrate with the following composition 
was treated by a method according to the invention: 
Pb--45.0%, 
Fe--6.4%, 
Cu--1.8%, 
S--14.6%, 
SiO.sub.2 --14.4%, 
CaO--2.7%, 
MgO--4.6. 
In the reaction shaft of the flash smelting furnace concentrate was melted 
at a rate of about 1000 kg/h at a temperature of 1720 K. For a partial 
oxidation of the concentrate about 57 kg/h of technical oxygen was fed. 
For the creation of the necessary additional heat butane was, moreover, 
burnt in the reaction shaft by using a stoichiometric amount of technical 
oxygen. 
In addition to gas it was received from the reaction shaft as a product 
slag, matte and metal. The lead content of the slag was about 0.5%. The 
matte contained lead about 10% and copper about 28% i.e. about 1% and 
nearly 100% of the lead and copper content of the concentrate, 
respectively. 
Of the lead content of the concentrate about 85% was volatilized into the 
gas. The composition of the gas after the reaction shaft was the 
following: 
Pb--1.7%, 
PbS--12.1%, 
PbO--0.1%, 
S.sub.2 --1.5%, 
SO.sub.2 --18.4%, 
CO.sub.2 --24.0%, 
CO--7.0%, 
H.sub.2 O--28.0%, 
H.sub.2 --2.4%, 
Oxygen pressure--1.4.multidot.10.sup.-7. 
For oxidation of lead sulfide and other combustible compounds oxygen was 
fed to the rising shaft of the flash smelting furnace at a rate of about 
68 kg/h, whereby the following gas composition was received: 
Pb--6.6%, 
Pb--1.5%, 
PbO--4.3%, 
SO.sub.2 --28.7%, 
CO.sub.2 --26.7%, 
CO--1.0%, 
Oxygen pressure--5.8.multidot.10.sup.-6. 
The oxidized gas was conducted to the first cooling stage, where the 
temperature was lowered to about 1000 K. The temperature was chosen so as 
not to pass below the dew point of PbO. During the cooling the dew point 
of the metallic lead is gone below and a part of the lead is condensed. 
In the next stage reaction time was given to the gas, whereby PbO and PbS 
were reacted with each other to metallic lead, and the next cooling was 
carried out on the same grounds as the previous to a temperature of 1440 
K. 
Periodic coolings were carried out until the temperature was about 1173 K. 
Hereby the concentration of the gas was the following: 
Pb--0.04%, 
PbS--0.02%, 
PbO--0.04%, 
SO.sub.2 --33.8%, 
CO.sub.2 --31.0%, 
Oxygen pressure--1.6.multidot.10.sup.-9. 
Of the lead content of the gas about 99% was condensed as metal. 
EXAMPLE 3 
Lead concentrate with the following concentration is treated by the method 
according to the invention: 
Pb--45.0%, 
Fe--7.6%, 
S--15.7%, 
SiO.sub.2 --12.1%, 
CaO--2.4%, 
Al.sub.2 O.sub.3 --1.6%. 
The concentrate is fed together with the necessary flux to the reaction 
shaft of the flash smelting furnace, where it is oxidized by the aid of 
technical oxygen. As a result a sulfur-free lead oxyde containing slag as 
well as a gas with the following composition is received. 
O.sub.2 +Ar--3%, 
N.sub.2 --5%, 
SO.sub.2 --77%, 
PbO--15%. 
The gas received from the melting is conducted to the rising shaft of the 
flash smelting furnace, where butane gas is mixed with it. After the 
reduction the composition of the gas is the following: 
Pb--6.7%, 
PbS--2.4%, 
PbO--5.1%, 
S.sub.2 --0.005%, 
SO.sub.2 --70.5%, 
N.sub.2 --4.7%, 
CO.sub.2 --4.5%, 
CO--0.2%, 
H.sub.2 --5.8%, 
H.sub.2 --0.06%, 
H.sub.2 S--0.005%, 
Oxygen pressure--1.4.multidot.10.sup.-5. 
The gas leaving the rising shaft is cooled and lead recovery from the gas 
is carried out. At a temperature of 1273 K. the composition of the gas is 
the following: 
Pb--0.18%, 
PbS--0.13%, 
PbO--0.25%, 
S.sub.2 --1.8.multidot.10.sup.-5, 
SO.sub.2 --82.0%, 
N.sub.2 --5.3%, 
CO.sub.2 --5.3%, 
CO--0.003%, 
H.sub.2 O--6.6%, 
H.sub.2 --0.003%, 
H.sub.2 S--1.4.multidot.10.sup.-5, 
Oxygen pressure--1.8.multidot.10.sup.-8. 
In our experiment 56% of the lead content of the concentrate has been 
slagged and can be recovered by the aid of a reduction process. 44% of the 
lead content of the concentrate has been volatilized into the gas, of 
which 96.5% has been recovered as metal by the aid of reduction and 
condensing processes of lead.