Note: Descriptions are shown in the official language in which they were submitted.
109103~i
This invention relates to the treatment of slimes from
the electrolytic refining of copper.
It is already known to digest slimes from copper electrol-
ysis using concentrated sulphuric acid and air at atmospheric
pressure. The digested slimes may then be roasted to drive off
the selenium as volatile selenium dioxide or may be treated with
diluted acids or alkali to dissolve oxidized copper, selenium
and tellurium which must then be separated. The main disadvan-
tages of this method include a substantial emission of SO2
during the digesting operation as well as the length of time of
such digesting operation which lasts usually between 4 and 6
hours. There are also difficulties involved in obtaining proper
separation of copper, selenium and tellurium from one another.
It has also been recently suggested in German patent
No. 1,948,300 of Norddeutsche Affinerie to treat slimes in an
autoclave at a pressure of over 5 atmospheres and a temperature
above the boiling point of the solution present in the autoclave
in order to remove copper and nickel from the solution while
leaving selenium, tellurium, arsenic and the noble metals in the -~
solid residue. This method has the disadvantage of operating at
very high pressures, leading to engineering difficulties and
excessive capital and maintenance costs for autoclaves, and also
leaves the problem of separating various substances in the residue,
such as selenium and tellurium, from one another.
It is accordingly the object of the present invention to
devise an improved method which provides the treatment of copper
refinery slimes in a simple and efficient operation leading to
ready separation of the various constituents of the slimes.
It is a further object of the invention to provide an
economical method for treating copper refinery slimes employing
readily available equipment or equipment which may be easily
manufactured, using pressures below 5 atmospheres.
--1--
1091035
Other objects and advantages of the novel slimes treat-
ment process will be apparent from the further more detailed
description thereof.
The method of this invention basically comprises leaching
the slimes with dilute sulphuric acid under an oxygen partial
pressure of up to about 50 psi, preferably between about 20 and
~ 50 psi, and an elevated temperature of between about 18~ and
¦ 320F (8~ and 160C), preferably between about 200and 30~ F,
until copper and tellurium present in the slimes are substan-
10 tially dissolved, and effecting a liquid-solid separation of the
leached slurry so as to separate the leach liquor from the leach
slimes, then the leach liquor is treated with metallic copper to
!~ cement the tellurium as copper telluride and said copper telluride
; cement is separated from the remaining solution which is suitable
for the production of copper sulphate. According to another
embodiment of the process, the separated leach slimes containing
mainly selenium, lead, silver, gold and remaining impurities are
dried, mixed with a binder and pelletized, the pellets are then
roasted to remove selenium as selenium dioxide and the roasted
20 pellets are smelted to remove the remaining impurities leaving a
doré metal containing essentially silve~ and gold.
The leaching takes place in an autoclave under normal
agitation using diluted sulphuric acid preferably having a
sulphuric acid concentration of between about 20 and 40%. The
most preferrred acid concentration has been found to be between
250 gpl and 300 gpl. Within two or three hours, depending on the
ultimate leaching conditions, the leaching operation will normally
lead to the dissolution of substantially all copper and of at
least 75% of tellurium. The leach liquor containing these metals
30 is then filtered from the leach slimes which are then usually
washed with warm water. This leach liquor is then treated with
metallic copper, preferably in the form of copper shot or the
like, to cement the tellurium as copper telluride which can then
--2--
10~103~
be treated in a conventional manner to obtain pure tellurium or
its desired compounds. The remaining solution is suitable for
the production of copper sulphate (CuSO4.5H2O) also in
conventional manner.
The treatment of the leach liquor with metallic copper
can be performed in any suitable manner but it is preferred to
carry it out in a cementation reactor which has a form of gener-
ally horizontally disposed cylindrical vessel with inwardly pro-
jecting baffles provided along its internal wall to achieve
adequate intermixing of the copper shot with the leach liquor.
The reactor is rotatable about its horizontal axis and is normal-
ly slightly inclined towards its feeding end. In operation it is
provided with copper shot or similar metallic copper material in
sufficient amount to cement the tellurium of the leach liquor
which is introduced into the reactor so that it is about half to
three quarters full. The reactor is then rotated while maintain-
ing the temperature of the material in the range of 150 to 200F,
thereby providing good intermixing of the copper shot with the
liquor contained in the reactor This leads to effective cemen-
tation of the tellurium present in the reactor to copper telluride
within a period of about one to two hours. Obviously, the di-
mensions of such cementation reactor can vary depending on the
quantities of liquor to be treated. The amounts of copper shot
necessary as well as of liquor to be introduced into the reactor
will be readily determined by a man familiar with the art depending
on the quantity of tellurium present in the liquor which is to be
cemented as copper telluride. The specific temperature and time
of operation can also be readily adjusted to achieve optimum
results.
The leached slimes from the leaching operation are nor-
mally unsuitable for pelletization as such because they are too
wet and the amount of moisture in the slimes is a very important
factor to achieve proper pelletization. The slimes also cannot
10~103S
be roasted directly to remove selenium dioxide because they are
not in the form which is most suitable for such operation. The
oxidizing medium, such as air, will not readily pass through
unpelletized slimes during roasting and they will agglomerate
into large roasted chun~s which would be difficult to treat
further and from which the reco~ery of selenium is poor.
It is already known from U.S. patent No. 2,948,591,
issued on August 9, 1960 to E. C. Handwerk et al., to roast slimes
admixed with a binder and pelletized into suitable pellets or
1~ other similar agglomerates in order to separate oxidized selenium
therefrom. Such an operation is quite advantageous and, for this
reason, the wet slimes coming from the leaching operation according
to this invention must be adapted for pelletization and then
roasting of the obtained pellets. This has been achieved by dry-
ing the wet unleached slimes, then admixing them with a binder
such as bentonite and pelletizing the same into suitable pellets
having a diameter of between about 1/4 and about 3/4 inch.
The drying operation is preferably carried out in one
step by passing the wet slimes between a pair of heated rolls
which dry and pulverize the slimes.
The rolls are preferably heated with steam which is
injected inside of said rolls. When the wet slimes are intro-
duced between these rolls, they are heated and squeezed, thereby
reducing their moisture content from about 25% to about 8% or
less. It should also be noted that the rolls of the drier are
preferably chromium plated in order to prevent sticking of the
leached slimes thereonto.
Once the wet slimes have been so dried, they are admixed
with bentonite or another suitable binder to provide a consistency
suitable for pelletization and the mixture is then pelletized in-
to pellets of desired size. Preferably a disc pelletizer is used
onto which this mixture is fed together with some water to pro-
duce the desired pellets. Thereafter, these pellets are roasted
10S'103S
at a temperature of betweon about 1,200~ and 1,500F for a
period of one to two hours, preferably with an air flow of about
30 to 60 cfm to remove selenium dioxide, which can then be
scrubbed with water to produce selenious acid. Selenious acid
may then be transformed in conventional manner into elemental -~
selenium by precipitation with sulphur dioxide.
Finally, the roasted pellets are smelted in a dore furnace
in conventional manner to remove the remaining impurities leaving
a doré metal containing about 96~ silver and about 4% gold. The
smelting operation in the doré furnace takes place at a temper-
ature in the range of 1,800F to 2,500F with addition of soda
ash as flux. This, of course, is well known in the art.
The invention will now further be described in greater
detail with reference to the appended drawing which diagram-
matically illustrates a preferred embodiment of the method ac-
cording to the present invention.
As shown in the drawing, the slimes from a copper refin-
ery are mixed with predetermined quantities of water and H2SO4
in a make-up tank from which the mixture is introduced into
autoclave 2 where the leaching operation is performed under oxygen
pressure, heat and agitation. Oxygen cannot be replaced by air
because if air under pressure is used, a great deal of foam will
be formed and the leaching operation will not proceed success-
fully. Once the leaching operation is terminated, the leached
slime slurry is transferred into a holding tank 3 from which it
is introduced into a filter press 4. After initial liquid-solid
separation in the filter press 4, warm water is introduced into
this filter press to wash the solids. This warm water may then
be returned into make-up tank 1 replacing fresh water, for the
preparation of a new batch.
The leached liquor from the filter press 4 is forwarded
to a leach liquor storage tank 5 from which it is introduced in-
to a cementation reactor 6 together with metallic copper, to
10~103~
effect cementation of tellurium as coppcr telluride. The copper
telluride cement is then separated from the remaining solution
by filter pr-ss 7 and sent for further conventional treatment to
produce pure tellurium while the solution is sent to a copper
sulphate plant for production of CuSOg.5H2O.
The wet slimes from filter press 4 are forwarded through
a feeder 8 to a steam roller drier 9. The wet slimes are intro-
duced into the nip of a pair of steel rollers and are dried and
pulverized through heat and pressure between said rollers. To
avoid sticking of the slimes to the rollers, the latter are pref-
erably chromium plated. Then, the dried slimes are admixed with
a binder, such as bentonite, in mixer 10, and fed through a feed-
bin 11 and belt feeder 12 onto a pelletizer 13 where they are
pelletized into pellets of suitable size of between about 1/4 and
3/4 inch in diameter. The binder is preferably used in a pro-
portion of between 5 and 10%. The obtained raw pellets are
introduced into a storage tank 14 from which they are conveyed
into a roaster 15 where they are roasted using heat and air to
form selenium dioxide which can then be scrubbed in scrubber 16
with water to form selenious acid that can be stored in the
storage tank 17 from which it will be forwarded to selenium
precipitation.
The roasted pellets coming out of roaster 15 are smelted
in a doré furnace 18 to remove remaining impurities and to
produce the dore metal consisting essentially of silver and gold.
The following non-limitative example will further illus-
trate the invention:
EXAMPLE
_ _~
4,700 lbs of slimes, on dry basis, from the copper
refinery of Canadian Copper Refiners Limited, in Montreal East,
Canada, having approximately the following composition:
--6--
10~103S
Cu 21 - 26%
Ag 20 - 27~
, Au 0.30 - 0.45%
; Se 12 - 15%
Te 1.5 - 2.2%
i Pb 5 - 10%
SO4~ 10 - 14%
As 1.5 - 2.0%
Sb 1 - 1.5%
Bi ~0.5%
SiO2 ~4.0%
Sn ~0.5%
Zn ~0.3%
were introduced into a make-up tank together with 1,550 gal. of
water and 280 gal. of 93% H2SO4 and mixed therein to obtain a --
10 slurry having a specific gravity of about 1.3. The slurry was --
then charged into a stainless steel baffled autoclave having a -
capacity of 2,400 gallons and provided with a 6 blade 25 HP turbine
capable of running at 175 rpm. The autoclave was heated through
an outer steam jacket until the temperature of the slurry therein
~I reached 240F.
;~ An outer cooling jacket,which alternated with the steam
.ll jacket, was also provided to maintain the temperature at the
desired level. The autoclave was pressurized with oxygen to a
total pressure of 50 psig with the oxygen partial pressure being
20 about 30 psi. 5,700 cubic feet of oxygen were used during the
leaching operation which lasted three hours and the leached slime
slurry was then discharged into a holding tank.
The slurry was then filtered to separate the leach liquor
from the solid slimes which were further washed with warm water.
~, The filter press used for this operation was of a plate and frame
type having a filtering volume of 30 cubic feet.
A~out 1,600 gallons of leached liquor were produced having
:;
85 gpl Cu, 60 gpl Te and 150 gpl H2SO4. Also, about 4,300 lbs of
wet leached slime with a moisture content of about 25% were
;¦ 30 produced having 1% Cu, 1% Te, 19% Se, as well as lead, silver,
gold and the remaining impurities.
The leached liquor was then treated in a horizontal
cylindrical reactor (27 ft. long x 2 1/2 ft. diameter) having
_ 7 _
1(1~103S
inwardly projecting radial baffles provided alon~ its internal
wall, said reactor rotating at 15 rpm and being loaded with
7,500 lbs of copper shot. The feed rate of solution to the
reactor was 10 gallons per minute and the temperature was 200F.
The reactor was made of 316 stainless steel. The cementation
slurry was then filter-pressed giving about 140 lbs of copper
telluride and aboNt 1,600 gallons of leach liquor for copper
sulphate production. The leach liquor contained about 90 gpl Cu,
1 gpl Te and about 110 gpl H25O4. At least 85~ Te was removed
during this operation. The filter press used was identical to
the leached slime filter press already described above.
The wet slime from the leach slime filter press contain-
ing about 25% moisture was dried by passage through a chromium
plated stainless steel roller drier heated with steam. The
moisture content of dry slime was about 8~. The dry slime was
then mixed with bentonite in a proportion of 100 lbs of bentonite
for 1,500 lbs of slime and the mixture was charged onto a 54 inch
diameter disc pelletizer capable of producing 1,500 lbs of raw
pellets per hour. A little water in the form of water jets was
also directed onto the pelletizer to help produce the desired
pellets. The preferred pellet diameter was found to be 3/8 of an
inch .
The obtained raw pellets were then roasted in a roaster,
which can be of continuous or batch type, having an operating
temperature of about 1,500F. Air flow through the pellets was
about 30 cfm. An adequate flue system for removing about 300 lbs
of SeO2 per hour was also provided.
The selenium dioxide from the roaster was treated in a
scrubber system which is capable of scrubbing 300 lbs of SeO2
per hour using water. Water (as selenious acid: H2SeO3) was
recirculated to produce H2SeO3 solution containing about 100 gpl
Se, which is suitable for selenium precipitation. 1,500 lbs per
hour of raw pellets were normally introduced into the roaster
--8--
109103S
containing about 19% Se and resulting in about 300 lbs per hour
of SeO2 which were sent to scrubber and about 1,215 lbs per
hour of roasted pellets which were ~ansferred to a doré furnace
for smelting and production of the doré metal.
In the doré furnace, the roasted pellets were smelted
with soda ash at temperatures between 1,800F and 2,500F to
remove remaining impurities leaving a doré metal containing about
96% silver and 4% gold. This doré metal was finally treated in
a parting plant to separate silver from gold.
