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Jàn. 7, 1947.
F‘íle‘d Jan. 23, 1943
2 Sheets-Sheet’ 1
Jan; 7, 1947.
Filed Jan. 23, 1945
2 Sheets-Sheet 2
Patented Jan. 7, 1947
Gregoire Gutzeit and Elliott J. Roberts, Westport,
and. Robert B. Thompson, Wilton, Conn, as
signors to The Dorr Company, New York, N. Y.,
‘a corporation of Delaware
Application J anuary 23, 1943, Serial No. 473,406
6 Claims.
(01. 23-53)
This invention relates to the recovery of tin
and metals of the same class Írom ores and mill
It renders specìally possible the ex
traction of tin trom refractory ores (complex
cassìterite-sulphide ores and ores containing so
called colloîdal tin) as well as from the tail
ings of tin concentrators, although it is not ap
plicable to ores with a carbonate gangue.
Tin occurs principally as the mineral cassit
ing conditions, and the third stage comprises a
leaching operation whereby a tin-hearing solu
tion is selectively obtained that can be separated
from the gangue residue.
Another stage com
prises precipitating the tin out of its mother
liquor under criti'cal conditions.
Since it is the tin that is the value to be
‚recovered and since the proportion thereof in
the ore or other material is ‘small, a high per
centage of extraction of the tin is a feature of
erite, S1102. As is well known to mining en
advantage of this invention. Since tin ore is
gineers, there are two main types of tin ores:
normally Íound only in out of the way places in
the ?rst one is the so’called stream tin, i. e., an
the world, where freight rates are high, the
alluvial deposi‘t where the cassiterite particles are
availability of chernical reagents is very impor
generally tree; the other type is the 10de tin, in
tant. Another feature of advantage in this in
which the tìn oxide is mcstly associated with
vention is the possibility of regeneration of the
stannite (tin copper sulphide), pyrites, arseno
reagent for reuse.
pyrites, bismuth, antimony, and arsenic sulphides,
As the roasting stage: If one attempts to re
and often with wolframite. A rarer occurrence
duce the cassiterite of a tin ore which has a sub
is the eluvial tin (French Indo-China, Belgian
Congo). The ores of the ?rst types generally 20 stantial content of iron compounds as well as
other base metals in some proportion, the dif?
yield clean concentrates and fairly good tailings.
culty is faced in that in the process of reduc
These are principally found in the Malaya Pen
ing the tin, iron and/or certain other elements
insula and in the Netherland Indies (Banka and
are likely to be reduced to the metallic state. A1
Billiton). The second type is more scattered
loys of the tin and these metals then form and
over the world, and is found mainly in Bolivia,
no economicai method has yet been found Íor
Nigeria, Belgian Congo, Cornwall (E’ngland),
leaching out tin so alloyed. Therefore, the ?rst
Brittany (‘France) , China, and Indo-China. This
object of the roast of this ínvention is to reduce
type of ore is dif?cult to concentrate. The l0sses
the tin compound while not reducing the iron,
in the concentration tailings are alWays very high,
230 so that the reduced tin compound is made avail
especially in the slime fraction where grades of
2.5% Sn and. over are not rare.’ The sulphîdes
are often ?oated out of the crude ore, but even
so the tailings and concentrates stil1 contain
more or less base-metal sulphides. In the smelt
ing plant, the concentrates have to be roasted, “
sometimes recleaned by‘ gravity methods, and
leached with hydroc‘nloric acid in order to remove
the impurities (excess of iron) prior to the smelt
ing operation proper.
The object of this invention is to recover the
tin lost in these concentrator tailíngs, or even to
treat directly the refractory ores as well as any
suitable mill product.
Many attempts have been made to leach the
tin directly from its ores or Írom concentrates
but these have all failed due to the fact that
cassiterite is completely insoluble in all aqueous
solutions. (Mantel’l, “Tin” (1929) A. C. S. Mono
graph Series, pp. 131-138.) 'I'his invention pro
poses to make use of severa1 important and. con
joint stages of treatment of which the ?rst is a
reducing sulphidizing raast which results, under
cr‘itical conditions, in the formation of a solu
ble tin compound. The secohd stage comprises
cooli‘ng the roasted material under non‘oxidiz- ‘
able Íor subsequent leaching. T0 that end this
invention proposes to use a sulphidizing atmos
phere whereby the tin oxide of the ore or ore ma
terìa1 is converted Írom tin oxide principally to
stannous sulphide (SnS) which is soluble in a
subsequent leaching process. What is perhaps of
eq1lal importance, is that the iron and certain
other elements are held as, or are convertedto,
sulphides, trom which combination they do not
so readily reduce to the metallic state.
The requirements of this suiphidizing roast are
that ?rst it must be carried out in an atmosphere
of reducing gas such as hydrogen and enough
sulphur should be present to convert the tin and
possible interfering elements to their sulphides.
The sulphur needed is preferably evolved in situ,
although it may be added as a gas if desired.
‘The temperature of the Toast is important, be
cause if too 10W, the requisite ‘reactions do not
take place, while if too high, tin may be lost
through volatilization. Suiî1cient time must be
allowed to convert the major part of the tin into
the sulphidcè, but too long a reaction time should
be avoided due to the danger of Íormation of
metallic iron or other metal which would alloy
with any metallic tin which may be formed dur
ing the process. This is especially true when the
sulphur supply is marginal or inadequate. It is
as tailings, is submitted, properly subdivided as‘
to particle size, to the treatment as summarized
above, and if the roasted products are leached in
practically impcssible and is also unnecessary to
entirely prevent the r‘ormation of metallic tin
a waak sodium hydroxide solution, the curve of
recovered ‚tin plotted as a function of the roast
as long as the alloying metals are prevented Írom
ing temperature for a speci?c time interval wil]
show a maximum indicating a critical tempera
ture range, which curve falls away and also shows
that undesirable reactions result if the tempera
ture is too high.
As already stated, the tin-hearing 10de ores al
ways contain sulphides, and mainly pyrite.
Thus the requirements of the roast include the
presence of a proper amount of sulphur and a
reducing gas as well as temperatures within a
critical range and a certain control of the time
interval of heating. The ore or mi1l product
to be so roasted should be properly sub-divided
Pyrite (FeS2) decomposes into pyr1‘hotìte (FeSw)
‘as to particle size, which should preferably not
at a temperature a'oove 575° C. The reaction is
be in excess of 65 mesh and in general the smaller 15 very rapid at 665° C. In the presence of hydro«
the particle size the better if the process is to be
gen, .however, the decomposition of pyrite starts
at a lower temperature. Thus, the sulphur for
The temperature range should be a‘oove 55€)“
the reaction is furnished in Bolivian tin ore by
C. and below 900° C.‚ with optimum between 650°
the alteration of pyrite to pyrrhotite which pyrite
C. and 830° 0. The amount of sulphur present 20 or its sulphur-hearing equivalent is added to the
should be substantially over the theoretical chem
ore to supply any lack of natural constituent
ical requirements thereof to accomplish the re
. frorn which sulphur vvill evo1ve in situ, and the
action and the amount of hydrogen or other
series of reactions involved may be represented
strongly reducing gas should always be su?î
by the follovving equations:
cient to assure the reducing action.
As to the cooling stage, the roasted, treated
and converted. tin-hearing material should be
cooled under nomoxidizing conditions. A variety
of cooling methods can be used so long as the
reduced constituents of the ore are not permitted 30
to have any substantial reversion due to oxida
As to the leaching stage, the essential charac
teristic of this treatment is that the cooled, re
duced and sulphidized ore material is subjected
to the tin sulphicle leaching action of a caustic
alkali such as caustic soda (NaOH) .
If the reduction is performed with hydrogen in
the presence of pyrite or other sulphur evolving
constituent from which sulphur is volatilized at a
temperature lower than the temperature of the
main reaction, the equation may be written in
summarized form as Íollows:
The reason
for this is that the tin sulphide and metallic tin
The use of a large excess of pyrite is objectiona
bie, so its use must be carefully controlled.
rials, including the iron and copper compounds, 40
These reactions occur only abov_e 550° C. Above
arenot. So the purpose of the leaching stage is
900° C. the tin sulphide volatilizes badly. Stan
to dissolve selectively the tin compound out of the
nous sulphide, as already stated, is soluble in
ore material, whereupon the tin compounds in
alkalis provided some oxidizing compound such
solution are readily separable from the solid
as air be present. Stannous su1phide is further
gangue residue.
45 slowly reduced by the hydrogen to metallic tin
As to the precipitation stage, the tin solution is
SIIS’+H2=S?+H2S. Pure metallic tin is also
subjectecl to the action of a precipitation agent
soluble in sodium hydroxide in the presence of an
such as calcium, barium, strontium or magne
oxidizing agent. Hovvever, in the presence of re’
are soluble in alkali whereas the gangue mate
sium sa1t but preferably lime. Here, however, a
requisite is that precipitation shall take place in
a relatively high concentration of already pre
cipitated soiid phase of calcium-tin compounds,
probabiy calcium orthostannate. Uniess this
precaution is used, a much larger amount of 1ime
is needed, indeeol as much as 30€) percent of theo
duced metals (Cu, Bi, Fe, etc.) the metallic tin
wil] form al1oys which are insoluble in alkalis.
These reactiong are not separate as in the sys
tematic description above, but take place simul
taneously at different rates. In fact, just above
the reaction temperature, SnSz is possibly formed
besides SnS and some Sn. Moreover, the condi
retical and then the precipitate yielded is 10W in
tions in the furnace are also a function of the
grade, very ?nely divided ancl dif?cult of separa
time. At the beginning, there is an excess of
tion. On the other hand, if the precipitation is
sulphur present, and the sulphidizing reaction is
carried out in the presence of a high concentra
at its maximum; but when most of the sulphur
tion or pulp blanket of already precipitated stan 60 has been evolved and has reacted or escaped as
nate, the precipitated particles are coarse crys
hydrogen sulphide, this atmosphere becomes
tals with a rapid settling rate and the solution is
more and more reducing.
cornpletely stripped of tin with only the theoret
If the sulphur available is marginal or inade
ical quantity of lîme. 'I‘hîs means that they not
quate, it is still possible to obtain fair results by
only wil1 settle quickly in the mother liquor, but
are readily ?iterable therefrom. The separated
mother liquor or ?ltrate which is a harren solu
tion, is then available for recirculation and reuse
as a solvent in the leaching stage.
After ?ltration ancl drying the stannate is pref
erably calcined to drive out the combined water,
forming anhydrous calcium orthostannate, since
in this form the product may be stripped more
If a tin ore or a tin-hearing mill product such_
carefully controlling the degree of reductîon more
particularly as exempli?ed by the time. By hold
ing the time of contact at the reaction tempera
ture to a minimum which may be as 10W as 10
minutes or so, a reasonable recovery may often
be obtained, whereas langer times of 30 minutes
may result in drastic lowering of the extraction
olctainable with the NaOH solution.
A possible explanation of this behavior is as
follows; At 650° or 700° pyrite readily breaks
down into pyrrhotite, FeSm, with the rest of the
sulphur being liberated as S2 or converted into
I-I2S. These compounds carry out the other re
actions indicated and the rest is carried away. If
then all of the íron is in the form of pyrrhotite
and the tin in the form of 5118, we have an ideal
setup. IÎ more reducing gas is passed over the
charge metallic tin may form, bui; metallic íron
is prevented from Íorming for a long period be
cause the FeS1.2 must be substantially converted
to FeS
tains in the plant, but in special cases intentîonal
temperature adjustment may be indicated by
simple tests.
The best means of recovering the tin is a‘ pre
cipitation procedure which makes use of the ad.
dition of lime. The tin is precipitated as hy—
drated calcium orthostannate, containing alu
mina and calcium carbonate as the principal im
purities. The precipitation of the Sn should
preferably be carried out in the presence of pre
viously precipitated Sn, i. e.‚ of a precipitate of
calcium stannate produced in a Íormer cycle, for
before any l5'eS is reduceol to metallic íron. It
otherwise a large excess of lime would be neces
takes a large excess of H2 to so reduce the FeSr.z
sary, in order to strip the solutionof its Sn. If
the theoretical amount of linie be added to the
solution. it has been found that not more than
2Û% of the Sn is recovered, and it was neces
sary to go to 300% of theoretical to e?îectively
to FeS: of the order of 106-1000 mols of H2 per
atom of sulphur removed, depencling on the tem
perature. If only a small amount of this buffer
ing pyrrhotite is present, practical considerations
may cause enough hydrogen to be used to over
come the margin of safety which the pyrrhotite
affords and cause metallic íron to be iormed:
precipitate the tin. But, iÍ the lime loe added
to the solution in the presence of previously pre
cipitated Sn, the calculated amount on the basis
of CaSnO3 reduces the tin content of the solution
which will then quickly alloy with any tin it
to a very 10W value. As NazC0z builds up in the
solutions through excess of CO2, a certain amount
comes in contact with and tie this tin up as an
of lime is used in precipitatìng,r CaC0s.
alkali insoluble particle.
Ïore, a slight excess of lime over tin is actually
If a hydrocarbon gas is ’used to provide the re
used in practice.
clucing atmosphere, the presence of steam as a
Effecting the precipitation in the presence of a
catalyst for the cracking of the hydrocarbon is
2%;% suspension of previous precipitates from a
alrnost a requirement in order to yie1d high re 30 concentration of 10 to 12 grams of tin per liter of
coveries. From the roasting furnace there es
solution has given excellent results. Such a step
capes volatilized S, H2S, ASH3, SìoSs, etc. In some
seems to scrub the solution of its supersaturation
cases it may be advantageous to remove the stan
and lorings the solution into equilibrium. The
nite prior to the reducing treatment, by flotation,
stannate precipitate is sandy, it settles to a 10W
acid leaching, or chlorine leach, as this mineral
density of say 64% solids, anci ?lters easily,
directly Íorms an alkali-insoluble compound.
Since no excess lirne is used, the mother liquor
The next step is the cooling, Which should be
can be re-used without carbonation as it is al
done to a temperature below the melting point of
reacly substantially free of lime. However, if re
tin (230° C.) and under careful control so that
g‘eneration is necessary, it can be done by the use
the ore is cooled and passed into the leaching so« 40 of sodium carbonate or carbon dioxide.
lution in such a way as to prevent re-oxidation of
A very satisfactory apparatus fcr accomplish
the reduced ore. The leaching solution is best an
‚ing this precipitation step, is a machine made
alkali, like sodium sulphide, potassium sulphide,
and sold by The Dorr Company, In’c., of New
potassium hydroxide, or sodium hydroxide, and
York, as shown in United States of America Pat
should not contain calcium ions (soft’water). ‚‚~ ent No. 2,259,221‚ to Darìoy, Roberts and Weber.
From an econornical point of view, NaO-ï-I seems
in this apparatus, the precipitant is added to the
to be the best suited dissolvent. The ore is agi
lower part of the machine wherein flocculation
tatecl With a weak solution of sodium hydroxide
takes place in a zone contaìning‘ a sludge blanket.
(containing‘ an excess of reagent, say about ?ve
The sludge bianket rises to a level above a sludge
times the amount of tin to be leached)_ for a pe .5 o collecting pocket frorn which the precipitate is
riod of time up to the order of 25 hours. A coun
drawn oí’f, while clari?ed effluent overlies the
ter-ourrent decantation system is advantageous.
sludge blanket and over?ows from the upper sec
The dissolution of tin compouncls in the caus
tion of the machine. ‘The hydrated calcium or
tic solution requires the presence of oxygen to
thostannate precipitate, which runs about 41%
convert the tin to the stannic condition in which (u) Sn, is then dewatered such as by ?ltering. It
state it is soluble in caustic. This oxygen can be
contains 5 molecules of crystallization water,
’ supplied by contacting the solution with atmos
which are expelled at about 5Gil° C. or below
pheric air. I-Iowever, if air loe also used for agi«
yielding a calcined product with more than 50%
tation purposes, care should be exereised to pre
Sn. The latter may be direc-tiy smelted to re
vent the formation of appreciable amounts of so
cover the tin, or may be treated in various ways
to arrive at the ?nal metallic tin.
dium carbonate.
O-ther methods of recovering the dissolVed tin
The chemical reactions of the dissolution are as
values from the alkaline leaching medium are
possible and in certain cases may be economically
6:3 more desirable. One of these is to carbonate the
alkaline solution with a CÜ2 containing gas in the
presence of an electrolyte such as NaCl if the
Solutì0ns are rather dilute. In this case the" tin
The strength of sodium hydroxide to be used
is precipitated as hydrated stai1nio oxide which
is not important, but the total amount of NaOI-I
may be separated, dried and calcined to yield a
present should be high enough to provide oom‘
high-grande product. »01’’ 892 may be used asÌ-a
plete dissolu-tion in a reasonalole time. Seven to
precipitating agent. — The remaining solution'is
eight per cent by weight of NaOI-I on the basis of
’ regenerated with a controllecl amountoi lime.
the calcined ore (containing 2% Sn) gave excel
Direct ele‘ctrolysis of the solution is alsoa possi-ï
lent results. The dissolution wil1 ordinarily be
conducted atpwhatever temperature normally ob
bility with the’productioh of electrolyti‘c‘ï metal‚l
which may be then melted down and cast into
The tin may also be precipitated from so
lution in the metallic state by means of zinc dust,
preferably after deaerating. In this case, zinc
hydroxide will also be separate and may be recov
ered separately.
Example 1
Fine s1ime tailings from the 'I'elamayu (Ara
mayo C‘ompany, Bolivia), containing 2.49% Sn
(of which 10% as stannite and. the rest as cassi
terite) as well as pyrites and other metallic sul
phides, were heated in a rotary kiln to 799° C.
The heating perìod was 22 minutes in an atmos
sho‘wn in the diagram inéludes an agitator. It is
contemplated that this leaching station will con
tain suitable agitators, together with a succession
of thickeners for practicing what is commonly
known as counter-current decantation or coun
ter-current leaching and decantation. The reac
tion product is subjectecl in the leaching station
l9 ‘to action thereon by an alkaline leaching sol
vent, such as sodium hydroxide, and in the leach
10 ing station the tin goes into solution. The solu
tion pregnant with the dissolved tin passes as ef
fluent from the leaching station I9 through pipe
20 into a, precîpitation station 2I which is housed
a machine to which there is also supplied
phere of hydrogen and water vapor, provided by 15
through pipe 22 a precipitating agent, such as the
saturation of the reducing gas in water heated to
hydroxides, oxides or salts of calcium, barium,
51° C. The kiln was rapidly cooled and the ore
magnesium, or the like.
ieached at a dilution of 5:1 with an 0.8% sodium
station or machine 2I, in the
hydroxide solution. After 20 hours, 70.04% of
the tin contained in the ore was extracted. A 20 preferrecl form is described in the aiorementioned
patent, and includes within its tank an assembly
second leach with a fresh solution containing
23 of rotatable ?occulating paddles or blades, and
0.8% NaOH gave an additional recovery of 8.5%.
a sludge receiving and collecting pocket 24 from
Thus, the total recovery was 78.54 % .
which sludge is withdrawn through a pipe 25 and
Example 2
conducted to a ?lter 26 or other dewatering appa
Composite taílings from the Telamayo Mine 25 ratus. The precip‘itating agent precipítates or
strips the tin out from the pregnant solution that
(Aramayo Company, Bolivia), containing 1.86%
enters the machine or tank 2I, and this solid pre
Sn and 4.5% S, prìncipally as pyrite, was batch
cipitate is removed from the tank in the form of
roasted in a rotary kiln to 7 99° C_ for 25 minutes in
sludge that is dewatered on the ?lter 25. Filter
a current of hydrogen, and cooled in the same gas.
The calcine containing 1.94 Sn, was leached with 30 cake from ?lter 26 passes to a, calciner station 21
from which calcium stannate 28 emerges suitable
20 gpl. NaOI-I solutions in a. cyclic test procedure
smelting or other treatment for recovering its
simulating counter-current leaching and decanta
tin content.
tion, The pregnant solutions were precipitated
So‘ much for the direct steps. But the process
with lime in the presence of previously precipi 35
this invention can be carried out continuously
tated material and the harren solutions reused.
and cyclically. 'I‘o that end. the mud or pulp that
The test was continued for 10 cycles and an aver
forms a sediment in the leaehing station or thick
age extraction of 83% and 9, tin recovery as
ener 19 is raked to discharge whereupon it is con
CaSn0s of around 80% was obtained. The ?nal
ducted through pipe 29 to a, dewatering and wash
product aiter calcíning containea 51.4% Sn. 40
ing or ?lter station 312. From thîs ?lter, there are
Smelting tests on the latter product with the ad
two discharges, namely, one by which the ?lter
dition of SÌO2 and F8203 gave high reco-veries of ‚
cake of mud or pulp from which the solution has
metallic tin.
been substantially removed passes to discard or
Drawings acco-mpany thîs speci?catio-n for aid
waste as at 31, and the other is the alkali solu
ing in an understanding of the invention, in which
tion ?ltrate or leaching liquor containing some
Fig. 1 shows a graph based upon tests showing
tin which passes through pipe 32 on its way back
the critical temperature factor for two different
into the leaching station I9. Supernatant e?‘lu
time intervals (combined of course with the
ent from the precipitation station 2| over?ows
proper reducing and sulphidizing conditions) ‚
from the upper section thereof in the form of an
while Fig. 2 is a. diagrammatic ?owsheet to indi 50 alkali solution substantially harren of tin in solu
cate in general the sequence of machines or appa
tion, and is conducted through pipe 33 back to
ratus usable to p1‘actice the invention on a com—.
the leaching station IS].
mercial scale.
Assuming now that an operator has a plant
In Fig. 2 of the drawings, I I indicates a furnace
ready to start up and he wants to determine the
or kiln in which the ore is subjected to a reducing 55
quantities of materials to use; the non-carbonate
sulphidizing roast, to which furnace the ore 12 is
tin ore or material is analyzed to determine the
fed together with a suitable reducing gas l3. The
amount of volatilizable sulphur needed in the
furnace may also have fed to it pyrite 15 or other
kiln. The ore usually comprises tin compounds,
source of sulphur, but ìf pyrite be used, an ex
divided into a major portion of tin oxide and a
cess of pyrite is detrimental in the leaching, so 60 minor portion of tin-sulphide complex. Other
the quantity used should be carefully controlled.
constituents are iron oxides and sulphides as well
In the event that a tin ore to be treated has a
as silicates of various kinds. The tin, sulphur
su?îcient sulphur content naturally in it‚ of course
pyrite need not be added. From the furnace H,
gaseous products E6 of the reaction are emitted
in the form mainly of sulphur and hydrogen-sul
phide but these will also contain other products
such as ASH3, SbS3, and the iike. The hot solid
reaction products are discharged from the fur
nace | I into a cooling apparatus or station i'l' so
that they will be cooled quickly in a manner to
prevent or minìmize their re-oxidation. From the
cooling apparatus 11 the solid reaction product
passes through pipe Iâ and is subjected to a leach
ing treatment in a leaching station ’i9‚ which as
and reactible iron content is determined analyti
cally. Then there is calcuiated the quantity of
sulphur needed chemically to be equivalent to the
tin and iron. In such a calculation it is best to
?gure the tin as SnS and the iron as FGS1.2. IÍ
insu?icient S is shown by the calculation, pyrite
is added to make up the difference. It is appar
ent that there is available for tin and oxide iron
compounds 0.8 atom of sulphur per mol of FeS2.
some excess of sulphur above that so calculated
makes the reduction less critical as to timing but
too much is undesirable. This then comprises
the burden of the kiln, and hydrogen or hydrogen
containing reducing gas is continually passed
through the kîln during the heat treatment stage
when the tin oxide is converted to stannous sul
phide while the sulphur minimizes reduction of
iron compounds to metallic iron. As the resulting
tin compounds are soluble in alkalis while the iron
compounds are insoluble, an alkali leach causes
the dissolving of the tin compounds, leaving the
iron compounds as solid residue. Therefore, con
joint requirements for the practice of this inven
tion‚are exempli?ed, for instance, in the sulphidiz
ing reducing roast treated at a reaction tempera
ture within a speci?c range followed by alkali
leaching, followed by a special precipitation stage
2. The process according to claim 1, character
ized in that the period during which said ore ma
terial is heated and the temperature at which it
is heated are such that the formation of other
metals adapted to alloy with tin is rninimizecl.
3. The process accordìng to claim 1, character
ized in that the solution pregnant with tin is
reacted with a metal oxide selected from the group
consisting of calcium oxide and barium oxide to
precipitate a tîï1 cümpollnd
4. The process according to claim 1, in that the
solution pregnant with tin is reacted with a metal
oxide selected from the group consisting of cal
cium oxide and barium oxide to precipitate a tin
compound, regenerating‘ at the Same time the
if unusual ef?ciency is to be realized therein, and 15 alkaline metal hydroxide solution, separating the
then calcination of the separate precipitated tin
precipitate and the solution, and re-using the said
compound or other tin recovery step, with the‘
solution to leach the cooled reduced ore.
leaching operation being cyclic.
5. The process according to claim 1, character
We claim:
ized in that the solution pregnant with tin is
1. The process of treating tin ore, which com
reacted with calcium oxide te precipitate calcium
príses heating the ore during a controlled period
stannate, the precipitation step being conducted
of time above 550° and below 800° C. in a strongly
in the presence of an eXcess of previously precipi
reducing atmosphere and in the presence of
calcium stannate.
enough sulphur so that stannous sulphide and
6. The process according to claim 1, character
metallic tin are Íormed and so that the iron in
ized in that the solution pregnant with tin is sub
the ?nal product is in the ‚form of its sulphide
jected to neutralization by an acid reagent chosen
stable at the reaction temperature, and under
from the group consisting of CO2 ‘and S02 f0î‘
such conditions to insure that tin sulphide is not
precipitating a tin ccmpound out of the pregnant
volatilized; cooling said‘treated material under.
separating the precipitate and solutîon,
non-oxidizing conditions; leaching out; the treat 30 solution,
and regeneratìng the solution with a controlled
ed material with a solution of an alkaline metal
hydroxide in the presence of enough oxygen to
transform (1) substantially completely metallic
tin into an alkali metal stannate salt, and (2)
stannous sulphide into an alkali metal stannate 35
salt and. a salt of alkali metal, tin and sulphur;
and precipitating a tin compound Írom tl_1_is solu
amount of lime.
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