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Dec. 31, 1946.
2 Sheets-Shee't 1
Filed March 15, 1944
I f?it’li/IS
Yam 63 [Made/f
James A’. franda/Z'
Dec. 31, 1946.
‘Filed March 15, 1944
2 Sheets-Sheet 2
Patented Dec. 31, 1946
Albert J. Phillips, Plain?cld, and Yurii E.
Lebedeif and James R.. Crandall, Metuchen,
N. J., assignors to American smelting and Re
?ning Company, New York, N. Y., a corpora
tion of New Jersey
Application March 15, 1944, Serial No. 526,630
8 Claims. (Cl. 23-209)
This invention relates to a process for treating
selenium bearing material to recover selenium as
release the selenium. The receptacle containing
the charge is then placed in a closed retort and
elemental selenium. The invention has been
utilized advantageously in the treatment of ?ue
or baghouse dust containing selenium collected
during the roasting and doré furnace processing
heated to react and drive off the selenium as gas
eous selenium and selenium dioxide. The closed
retort is provided at one end with a compartment
or section which, during operation, is ?lled with
of copper re?nery slimes. However, the inven
tion is not limited to the treatment of baghouse
ducing reagent. A condenser is connected to this
section of the retort to condense the reduced
10 metal vapors. Volatilized SeOz and Se vapors
dust but may be employed in the processing of
raw sludges, slimes and the like material con
taining selenium.
In treating copper re?nery slimes which con
tain gold, silver, copper, selenium and tellurium,
it has been the general practice in most re?neries
to subject the slimes to an oxidizing roast to as
sist in the subsequent removal of copper by leach
ing with acid. During roasting some of the se
heated coke, charcoal or like carbonaceous re
which are released from the roasted charge are
drawn through or over this heated coke whereby
the SeOz vapor is reduced to selenium metal va
por. The latter is recovered as liquid selenium by
passing the vapors into a suitable condenser.
Moisture and excess H2804 vapor which are in
termiXed with the selenium vapor are not con
densed and pass from the selenium vapor con
denser into an outer condenser where these va
lenium and tellurium present is oxidized and
passes into the ?ue system where it is collected
in the baghouse along with other metal values. 20 pors of sulphuric acid and steam are condensed
and collected, the waste gases, largely carbon
Most of the selenium, however, is not volatilized
dioxide, being discharged therefrom through a
and remains in the slimes possibly as doré metal
water sealed exit. '
selenides and tellurides. In the conventional
In carrying out the process no preliminary di
practice, selenium is separated from the roasted
gesting of the selenium bearing material is re
slimes as sodium selenite by establishing 2. mol
quired and the amount of H2804 added usually
ten bath of the slimes and adding sodium car
is only about 5% by weight of the charge depend
bonate and nitre in suflicient amounts to react
ing, of course, on the content of selenium in the
with the gold and silver selenides present to slag
off the selenium in the form of sodium selenite. 30 material being treated. Preferably the required
amount of sulphuric acid is vmixed with the
This sodium selenium slag is subsequently leached
charge before it is placed in the retort and no
with water and neutralized to precipitate tellu
or stirring of the charge during roast
rium which is recovered as tellurium oxide. After
as the preliminary mixing is suf
?ltering the solution the selenium is then pre
?cient to adequately disperse the acid throughout
cipitated from the ?ltrate by acidifying the solu
tion and treating it with sulphur dioxide gas in I'‘~. . til the charge whereby the selenium is caused to
react with the acid and is driven off as either
the conventional manner whereby the selenium
oxide or elemental Se vapor when heated in the
is recovered as red amorphous selenium.
retort. By utilizing the novel heating and re
The present invention provides a relatively
ducing arrangement of our invention the digest
simple process which permits the selective recov
ery of selenium from selenium bearing baghouse 40 ing and roasting of the charge to release the
selenium as gaseous S802 and the reduction of
dust without involving the treatment of aqueous
this gaseous selenium dioxide to Se prior to con- ,
solutions of selenium dioxide and acid. The pro
densing is carried out concurrently and in a single
cess of this invention results in the direct re
retort. The apparatus is easy to operate and the
covery of elemental selenium from selenium bear
ing material by a single pyrometallurgical opera
process results in high recoveries of selenium with
tion and eliminates the necessity of employing
a minimum loss of values.
solution handling means, centrifuges, stills, and
Although the novel features which are believed _
?lter press equipment, which is expensive, in or
to be characteristic of this invention will be par
der to recover selenium in a commercially valua
ble form.
According to our process selenium bearing ma
terial which may contain 1% or more moisture
ticularly pointed out in the claims appended
hereto, the invention itself, as to its objects and
advantages, and the manner in which it may be
carried out, may be better understood by refer
ring to the following description in connection
is placed in a receptacle and su?icient sulphuric
acid is added in excess of that required to react
With the accompanying drawings forming a part
with the selenium compounds in the charge and 55
thereof in which a typical commercial installa
tion embodying our invention is illustrated.
Fig. 1 is a plan view of one type of apparatus
for practicing our invention, the arrangement
showing a battery of retorts connected to a con
denser, the retorts being shown partly broken
An over?ow spout 4| is provided near the top of
the receptacle 40 whereby condensate collected
in the receptacle 4!] over?ows into a receiving
vessel 42. Liquid condensate in the receptacle
40 provides a liquid seal for the condenser 36
and is arranged to maintain the entire furnace at
away and in section to more clearly illustrate the
a pressure of about one inch of water during the
Fig. 2 is a vertical sectional view of’ the appa~
ratus shown in Fig. 1 and taken substantially
on line 2-—2 of Fig. 1 and looking in the direc
tion of the arrows;
Fig. 3 is a sectional view in elevation taken
substantially on the line 3-3 of Fig.‘ 1.. i
Referring to the drawings in detail In desig
nates a retort in which the charge is roasted. A
number of these retorts forming a battery'may'
be used, as shown in Fig. 1, where the. quantity
.The retorts H] are preferably made of cast
iron inasmuch as it is resistant to attack. For
our commercial installation we have used a
- standard 10" cast iron pipe 8' and 6" long with
?anged end portions 45 and 46. The charging
end of‘ the retort: is?tted with a removable plate
15 48 which ‘is machined so that it can be bolted
tightly in place. The opposite end of the re
tort is. ?tted. to.the condenser pipe or tube I2 at
its ?anged end 5|, the contacting surfaces be
of material to be treated warrants such an in
ing machined so as tov ?t closely together to
stallation. The retorts are each connected to a 20 provide a sealed connection as illustrated in Fig.
condenser l2 which in turn is connected to a
2. Inasmuch as we have found that cast iron
common condenser and storage receptacle I3
is more. resistant to- attack‘ by selenium than
from which liquid selenium is tapped as indi
ordinary iron or steel we prefer to make the re~
cated at I4. The condenser I2, as illustrated in
tort l0 and forepart' of the selenium condenser
Fig. 2, is arranged to slope downwardly from 25 t2 of‘ cast iron. The remaining portion of the
the retort to the storage condenser receptacle l3
so that as the selenium condenses on the walls
of the condenser l2 it will flow away from the
condenser l2‘ and larger condenser receptacle 13
may be made of ordinary iron or steel since
these parts are subjected to lower temperatures
retort end and into the large condenser recep
than the: retort and forepart of the condenser l2‘.
tacle l3.
For‘ retaining the charge during roasting
For convenience in making‘ a tightly sealed
boats 55 are utilized. These boats, which may
joint between the retort and condenser the re
be made of iron, are of suitable length- and size
tort i0’ is also arranged to slope downwardly
so that they can be ?lled with selenium bearing
from the front to the rear in conformity with
material and inserted inside the retort ID as
the'slope-of the attached'condenser l2. To pro
illustrated in Figs. 2-- and‘ 3- The boats may be
vide for controlled heating of the retort and con
made by'slitting a length of 8“ pipe and spread
denser arrangement they are disposed in tem
ing it' so asv to fit the 10" diameter retort and
perature regulated'compartments of a furnace
welding en'ds onto the‘ pipe sections. The size of
as illustrated in Fig. 2; To accomplish this‘ the
the boats are preferably such as can be readily
retort‘ H1‘ is suitably mounted over the‘ furnace 40 loaded and manually" handled.
combustionv chamber l5 by supporting it at its
Using our process in the treatment of ?ue
opposite ends in. the furnace walls’ Hi and H.
dust, the. boats are loaded with selenium bear
A ba?le wall l8 extends along beneath the retort
ing baghouse dust mixed with approximately 5%
and is. provided with ?ue openings I'S- near the
by weight of the dry chargeof 60° Bé. sulphuric
rear wall I‘! of. the furnace‘.
45 acid. The boats containing this mixture are
Hot gasesof combustion produced by the burn
placed in the retort which. has been. previously
er 2]‘ pass upwardly through the ?ue openings
heatedto about1350'° F. Each boat ordinarily
l9, as. indicated by arrows in Figs. 2' and 3, and
contains. approximately 70- pounds of material
circulate about." the retort'throughout its length
and is operated. on a twelve hour cycle.‘ That is,
heating it uniformly, the waste gases being ? 50 the. complete cycle for each retort, including
nally discharged .into the. stack opening 22; at
charging and unloading, is 12 hours. When the
the front‘of the; furnace- Each retort is'con
retort is heatedto the proper temperature, ordi
tained in a separate compartment 23 utilizing
nary lump charcoal or coke isplaced in the rear
common: partitioning walls 24; A wall or pier
most section of: the retort as illustrated-at 80 in
25 extends upward from the ground?ll 26 beneath 55 Fig. 2. before: the charge boats 55 are inserted.
the resort chamber providing a ?rm" support for
Sufficient charcoal is- introduced to reduce all
the retort and furnace structure as illustrated
the S602 vapor given off by the charge to Se
in Fig. 3. '
vapor before it passes tov the condenser I2.
In order to maintain the chambers 30 and. 3|
In carrying out the process the temperature of
of'thefurnaoe in which the condensers I2 and I 3 60 the retort and. charcoal is kept above the boiling
are mounted at the temperature required for
point of selenium (1272° F.) , otherwise selenium
proper operation, auxiliary burners 32. may be
may condense in the‘ charge or retort before it
utilized. Similar auxiliary burners, not shown,
maybe utilized to raise. the, temperature of the
reaches the selenium condenser l2. This, of
course, should‘ be avoided. The temperature in
the! furnace combustion chamber I5 is prefer
ably maintained‘ at about 1350°'F. which is some
what. above-theb'oiling point of selenium and as
chamber‘. 30 where necessary. for. proper opera
tion of the condenser [2‘. Waste combustion
gases. from these burners‘ may be discharged
through a separate stack opening not’ shown.
sures a. temperature ofatleast 1-272° F. in the
Steam and sulphuric acid vapors which are not
center ofjthe charge- In view of the very low
allowed to condense in the condenser l3- are 70 thermal conductivity of selenium bearing’ bag
passed out through the discharge conduit 35 and
house. dusta longer. timeand higher roasting’ tem~
into the air cooled~ condenser 3.6. This latter
perature isirequired than: Would'otherwise‘b'e the
condenser is closed at the top while the lower
case toremove: the selenium; from the‘dust par.
end is sealed by water and condensate 38‘ re‘~
ticles forming thev charge. ,
tained in the receptacle 40 as shown in Fig. 2.
The chamber around: the. selenium condenser
l2 and condenser storage [3 is maintained at
about 450° F. At this temperature liquid selenium
collects on the inside of the condenser pipe 52 and
?ows by gravity down into the larger condenser
tlal charge contained about ‘ 7.44 pounds ‘of
selenium of which 6.5 pounds or 87.5% was re
covered as'vitreous selenium. A small amount
of selenium, usually less than 1% under optimum
Hi. In order to cause the liquid selenium to 5 conditions, escapes to the outer condenser and
is found in the condensate along with sulphuric
readily flow out of the tap hole [4 the condenser
acid and water. This selenim, however, is not
l3 should be kept at a temperature of about
lost being returned for treatment with the next
450° F. Should it fall below this temperature the
auxiliary burners 32 are operated to raise the
In the speci?c method described selenium‘ is
temperature so that the selenium ?ows freely 10
recovered as liquid selenium which we refer to
from the condenser 13 which is tapped inter
as elemental selenium. When this liquid ele
mittently. After tapping the selenium from the
mental selenium is tapped from the condenser and
condenser IS the auxiliary burners may be turned
cooled quickly, as by casting in shallow or water
Where the selenium bearing .material contains 15 chilled molds, a vitreous form of selenium is pro—
duced. Where the more stable so-‘called metallic
too much moisture it may be subjected to a pre
form vis desired the liquid selenium is cooled slowly
liminary de-watering and drying treatment prior
or the vitreous modi?cation is heated for some
to adding sulphuric acid and roasting. The
time above about 180° F. to cause it to pass over
selenium bearing dust which we have treated as
described ordinarily contains upwards of 1% 20 into the metallic form. The several allotropic
forms of selenium are well known and it will be
moisture. This moisture is driven off as water
obvious that the method of this invention may
vapor along with excess sulphuric acid during the
be utilized to recover selenium in any desired
process and is recovered as condensate in the con
form. Such changes as required to produce the
denser 36. The recovered sulphuric acid may if
desired be used over again in a new charge.
In 25 desired form of Se is contemplated to come within
addition to the sulphuric acid and water vapor
the scope of this inventionas de?ned by the
collected in the condenser 36 a small amount,
appended claims.
It will be apparent from the foregoing descrip
usually less than 1%, of colloidal red selenium
tion that the method of this invention may be
escapes from condenser I3 and is deposited on
the walls of the outer condenser. This is, how- .
modi?ed to suit the varying conditions incident
to using the invention, and while certain novel
features of the invention have been disclosedand
ever, not lost as it is recharged into the retort
and recycled. The residue remaining in the
roasted charge at the end of the heating cycle
contains about 0.5% selenium.
are pointed out in the annexed claims it will be
understood that various omissions, substitutions
and changes may be made by those skilled in the
art without departing from the spirit and scope
of the invention.
As a typical example of how our process is car
ried out, the following is illustrative:
To a charge comprising selenium baghouse dust
What is claimed is:
l. A process for treating selenium bearing ma
pounds of 60° Bé. H2SO4 was added and after
thoroughly intermixing the acid with the dust at 40 terial to recover selenium as elemental selenium
which comprises intermixing said selenium bear
ordinary room temperature conditions the mix
ing material with sulphuric acid and subjecting
ture, which was relatively dry, was placed in an
the mixture to a roasting temperature of approx
iron boat and inserted into the cast-iron retort
imately 1350° F. while shielded from contact with
of the furnace. The retort was tightly sealed
and heated to 1350° F. Roasting of the charge " air to react the acid with said material and drive
o? substantially all the selenium as volatile se
was conducted for approximately eight hours.
lenium and selenium dioxide, passing said vola
At a temperature of 600° F. SeOz was volatilized
tile vapors through heated carbonaceous mate
and around 1300° F. Se was vaporized. Both
rial to cause the reduction of the selenium dioxide
S602 and Se vapors were passed through the
heated charcoal, the temperature of the charcoal 50 to selenium vapor, and condensing the selenium
vapor to recover the selenium as elemental se- '
being maintained at around 1300° F. whereby all
lenium substantially free from sulphuric acid and
SeOz was reduced to Se while in the vapor phase.
weighing 40 pounds and assaying 18.6% Se, 2.2
The selenium vapor was passed into the con~
2. A process for treating selenium bearing ma
denser I2 which was kept at a temperature such
that the Sc vapor condensed and flowed into the 55 terial to recover selenium as elemental selenium
which comprises intermixing said selenium bear
large condenser and storage receptacle [3 con
ing material with sulphuric acid, said acid being
nected thereto as shown in the drawings. Mois
introduced in an amount up to about 5% by
ture and excess I-I2S04 vapor was carried through
weight of the charge, heating the mixture sub
the selenium condenser to the outer condenser
60 stantially out of contact with air to a tempera
where it was condensed and collected.
ture above the boiling point of selenium and se
Liquid selenium tapped from the condenser
lenium dioxide to react the charge with said acid
weighed 6.5 pounds. This liquid selenium was
and bring about volatilization of substantially
cooled quickly in a mold forming vitreous selenium
having a black glassy appearance but when viewed _ all the selenium in said material, conducting the
through relatively thin sheets appeared dark red. G” selenium vapors over a bed of hot carbonaceous
material to cause the reduction of selenium diox
Selenium in the amount of about 1% collected
ide vapor to selenium vapor, and then condensing
in the condensate along with excess H2804 and
was returned to the retort with a new charge.
After roasting for eight hours the residue was re
moved and charged into a cupel furnace for re—
said selenium vapors to recover selenium as ele
covery of remaining metal values. The residue
taken from the retort was found to contain 0.8%
selenium. This material was charged into a cupel
furnace for treatment to recover other values.
In the example it will be observed that the ini 75
mental selenium.
3. A process for treating selenium bearing ma
terial to recover selenium as elemental selenium
which comprises intermixing said selenium bear
ing material with sulphuric acid, said acid being
introduced in an amount up to about 5% by
weight of the charge, heating the mixture while
excluding air therefrom to a temperature above
the boiling point of selenium and selenium diox
ide to react the chargev with said acid and bring
about volatilization of substantially all the se
lenium in said material, conducting the vapors
phuric acid to approximately 1350° F. with sub
stantial exclusion of air and‘ for a time sui?cient
to cause the selenium compounds to react with
the acid and the selenium to be released as SeOz
4 and Se vapors, conducting said SeOz and Se va
evolved during heating over a bed of hot car
bonaceous material to cause the reduction of se
pors along with excess sulphuric acid vapor and
water vapor through heated carbonaceous mate
lenium dioxide vapor to selenium vapor, then
rial whereby all the SeOz vapor is reduced to Sc
cooling the vapors which comprise selenium va
vapor, selectively condensing the ‘Sc vapor from
por, sulphuric acid and water vapor to a tem 10 the mixture of sulphuric acid vapor and water va
perature which will cause the selenium vapor to
Dor to recover said selenium as elemental sele
condense but above that at which sulphuric acid
nium, and condensing the mixture of sulphuric
and water vapor condense whereby elemental se
lenium is recovered, and thereafter condensing
the sulphuric'acid and water vapor.
4. A process for treating selenium bearing bag~
house dust recovered from metallurgical furnace
operations which comprises intermixing a charge
of said selenium bearing material with sulphuric
acid in excess of the amount required to react
with the selenium compounds present in said
charge, heating said charge substantially out of
acid and Water vapors which has been substan
tially depleted of selenium whereby said excess
sulphuric acid and water vapors are collected as
a condensate for recycling.
7. A process for treating selenium bearing bag~
house dust recovered from metallurgical furnace
operations which comprises intermixing sulphuric
acid therewith in excess of the amount required
to react with the selenium compounds present
in the resulting charge, heating said charge sub
contact with air to react the acid with the se
stantially out of contact with air toreact the acid
lenium of the charge whereby the selenium of
with the selenium of the charge whereby the sele
the‘ charge is volatilized as SeOz and Se vapors,
nium of the charge is released as S802 and Se
subjecting said vapors: to a reducing action to
vapors, passing said vapors through a reducing
bring about the reduction of S602 to Se while in
atmosphere to bring about the reduction of SeOz
the vapor phase, and conducting the resulting
to Se while in the vapor phase, conducting the
stream of selenium vapors, water vapor and sul
selenium vapors along with water vapor and sul
phuric acid vapor along a course while cooling it 30 phuric acid vapor into a condenser and condens
to selectively condense the Se vapor in the form
ing the Se vapor in the form of elemental sele
of elemental selenium without condensing the
nium without condensing the sulphuric acid and
sulphuric acid and water vapor present.
water vapors present, maintaining the condensed
5. A process for recovering selenium as e1e~
selenium heated to a temperature su?icient to
mental selenium from selenium bearing baghouse
maintain the condensed selenium vapor in a liq
dust comprising preparing a charge by intermix
uid state, drawing 01? said liquid selenium into
ing approximately 5% by weight of sulphuric acid
a receptacle and quickly cooling the liquid sele
with a portion of said selenium. bearing material,
nium to form vitreous selenium.
the quantity of acid introducedrbeing based on
8. A process for treating selenium bearing ma
the amount .of seleniumpresent in the portion
terial such as slimes from copper re?neries to
making up the charge, heating the resultant mix
recover selenium which comprises intermixing
ture of selenium bearing material and sulphuric
selenium bearing material with sulphuric
acid to approximately 1350° F. while precluding
acid, roasting the mixture substantially out of
any substantial access of- air to the mixture,hold
contact with air to react the selenium bearing
ing said charge at this temperature fora time
material and sulphuric acid and cause the sele
su?icient to cause the selenium compounds to
nium to be released as gaseous selenium dioxide
react with the acid and the selenium to be re
and selenium metal vapor, the selenium contain
leased as S802 and Se vapors, conducting said
ing vapors being intermixed with evolved sul
SeOs and Se vapors along with excess sulphuric
acid and water vapor, subjecting the gase
acid vapor and Water vapor through a reducing 50
ous mixture to reducing conditions whereby the
_ atmosphere comprising heated carbonaceous ma
gaseous selenium dioxide present is converted to
terial whereby all the SeOz is reduced toSe vapor,
selenium meta-l vapor, cooling the resultant gase
and selectively condensing the Se vapors from
ous mixture of selenium metal vapor, sulphuric
said gaseous mixture of sulphuric acid vapor and
acid and water vapor to selectively condense the
water vapor to recover said selenium as elemental
selenium metal vapor to liquid selenium, the cool
ing temperature to which the vapor mixture is
6. A process for recovering selenium as ele
subjected being controlled to cause the selenium
mental selenium from selenium Ibearing bag
metal vapor to condense to liquid elemental sele
house dust comprising preparing a charge by in
nium while preventing the condensation of sul
termixing approximately 5% by weight of sul 60 phuric acid and water vapor, and withdrawing
phuric acid with a portion of said selenium bear~
the resulting liquid elemental selenium.
ing material, the quantity of acid introduced be
ing based .on the amount of selenium present in
the portion making up the charge,_heating ‘said
mixture of selenium bearing material and sul-' 65
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