Note: Descriptions are shown in the official language in which they were submitted.
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THIS invention relates to the recoYery of tungsten values from tungsten
bearing ores or concentrates.
Tungsten is generally found in nature in scheelite type ores and
wolframite type ores. These two ores differ substantially in their
chemical composition being a calcium tungsta~e and an iron-manganese
tungstate, respectively. Consequently, di~ferent processes have
generally been used to recover the tungsten values from each type of
ore. In the case of scheelite ores, the classical prior art process
is to treat the ore with hydrochloric acid to produce insoluble
tungst;c ac;d. The tungstic ac;d ;s taken up in an amnlonia solution
to produce ultimately ammoniuln paratungstate (APT). Wolframite on the
other hand is usually decomposed by fusing the ore with sodium hydrox;de/
sodium carbonate which extracts the tungsten as sod;um tungstate. The
cooled fused product is leached with water to extract the soluble sod;um~
tungstate. Similarly, this may be treated with hydrochloric acid to
precipitate tungstic acid wh;ch is taken up in an ammonia solution to
produce APT.
British patent specification No. 1,089,913 describes a process for
recovering tungsten values from both scheelite and wolframite type ores
or concentrates. This process comprises fusing powdered scheelite
and/or wolframite type ores or concentrates with a fluxing mixture of
sodium carbonate, sodium chloride and sod;um nitrate (wh;ch mixture also
contains, in the case of the starting material containing calcium, a~
least sufficient siliceous material to form calcium silicate therewith), ~`~
leaching the cooled, fused material with water ar,d separating a tungsten-
bearing alkalin2 leacri liquor rrom water-insolub'e impurities, acidifying
the separated leach liquor and adding thereto sufficient of a fluoride or
hydrofluoric acid to form~ with any silicon and phosphorus present,
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compounds which are substantially insoluble in
organic media, extracting the thus-treated material with an organic
solution comprising an organic amine capable of forming a water-insoluble
organic amine tungsten complex to transfer tungsten from the aqueous to
the organic phase, separating the phases, treating the separated organic
phase, with aqueous ammonia to form a water-soluble ammonium tungstate, and
separating the aqueous phase containing a~nonium tungstate from the
organic phase. This process involves, as an essential step, the fusion
of powdered scheelite and/or wolframite type ores or concentrates with
a mixture of sodium carbonate and sodium chloride. Indeed, ;t is stated
in the specification that a fluid melt should be produced. Typical
temperatures at which the fusion take place are 69BC to 825C.
Fox U.S. Patent Specification No. 3,800,025 describes a process of
extracting tungsten values from low grade tungsten ores which includes
the steps of roasting a particulated tungsten-containing ore in a water
containing atmosphere in the presence of sodium chloride and at least
one of the reagents selected from sodium carbonate and sodium phosphate
at a temperature in the range of about 600C to about 900C for about 1
to 3 hours, water leaching the resulting calcines to dissolve soluble
tungsten values and filtering. This process is restricted in appli-
cation to low grade tungsten ores and requires a water containing
atmosphere for its operation. Mcreover, r;elatively high roast tempera-
; tures and relatively low amounts of sodium reactant are generally used.
According to the present inventlonl there is provided a process for
~ recovering tungsten values from a high grade tungsten-bearing ore or`
-~ concentrate including the steps of roasting without fusion the ore or
concentrate in the presence of a reactive composition selected from an
alkali metal chloride, an alkali metal carbonate and mixtures thereof,
; 30 and extracting water-soluble tungsten values from the ro~sted product. It is
essential to the process that~roasting takes place without ~eneral fusion,
that is the mix of material and flux must not form a fluid melt during
roasting. The fact that a melt is not produced confers a much greater
flexibility in process design and can result in energy savings. The
roasted product is an easily handleable material.
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The tungsten values in the roasted product will be in the
form of water-soluble alkali metal tungstate. This product -
may thereafter be treated in known manner to recover the
tungsten values as tungsten metal. For example, the tung-
sten values may be water leached from the roasted mixture
and the leach liquor then treated in the manner described ,
in British Patent Specification No. 1,089,913. These
treatment steps are essentially an application of chemistry
known in the art.
The alkali metal for both the chloride and the carbonate
will invariably be sodium.
The tungsten-bearing ore or concentrate is a high grade one,
i.e. one containing at least 20 percent by weight tungsten
as tungsten oxide (WO3). Such materials~will generally be
of the scheelite or wolfra~mite type and may contain up to
80.5 percent tungsten as tungsten oxide.
The reactive composition may be an alkali metal chloride,
an alkali metal carbonate or a mixture thereof. It is a
particularly preferred eature of the process that the re-
active composition con8ists solely of an~alkali metal car-
bonate such as sodium carbonate. It has surprisingly been
"ound that excellent tungsten recoveries, at relatively
mild temperatures can be'achieved using sodium carbonate
alone.
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The roasting temperatuxe will vary according to the nature
of the ore or aoncentrate being treated and th~ type and
~; quantity of reactive compo8ition present. ~he important
point is that a temperature must be chosen whiah will not
~ result in fusion of the ore or aoncentrate taking place
`~; 30 but will yet be~high enough for the desired reaction to
take place in a reasonable time. As a general rule tem-
peratures in the rangq 600 to 800C will be used. For
wolframite ores, lower temperatures down to 500C can be
used and good extractions still obtained. When the
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recoveries are low then the roasted product, after filtra-
tion, can be dried and remixed with reactive reagent and
then re-roasted. This can be continued until as much of
the tungsten as desired has been extracted from the ore.
The re-roasting of ore to increase the tungsten extraction
may be used particularly with scheelite ores.
The amount of reactive composition present during roasting
will also vary according to the nature of the ore or con-
centrate. There should be at .....
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least sufficient sodium oresent to combirle with all the tun~sten to ~orn;
sodiunl tuTIgstate. It has been found, however, that a stoichiometric excess
of sodium is generally necessary when the ore being treated is a wolframite
ore.
The roasting must take place for a sufficient time to convert as much as
possible of the tungsten to sodium tungstate. The roasting time is
typically up to 120 minutes, although for many ores no particular
advantage has been found by heating for a period of longer than 60
minutes.
Where necessary, depending on the ore composition and/or type of heating
equipment being used, the reactive composition may also contain a
suitable oxidising agent such as sodium nitrate. Such an oxidising
agent is particularly useful where wolframite ores or concentrates are
being treated. Where the tungsten-bearing ore or concentrate also con-
tains a substantial quantity of calcium it may be desirable in some cases
to include finely divided silica in the reactive composition. The silica
reacts with the calcium to form tricalcium silicate which is subse-
quently readily separable from the sodium tungstate.
. `
The tungsten-bearing ore or concentrate and the reactive composition will
generally both be provided in finely divided state and~will be intimately
mixed prior to roasting. After roasting, the product may be leached with
water. It has been found experimentally that one leach and a replace-
ment wash under appropriate conditions are generally sufficient. The
fact that there is no fusion during roasting means that leaching may
take place on the roasted product as such without subjecting that product
to a crushing or like step. Moreover, leaching may take place while the
roasted product is still hot.
After leaching, the leach liquor is treated by commonly known m~thods to
remove impurities such as alumlnium, magnesium, phosphorous, silicon,
antimony, arsenic and molybdenum.
After the first purification step, the filtrate may be further purified
by treatment with a fluoride or hydrofluoric acid. The adequately
purified solution is then subjected to a conventional solvent extraction
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procedure. The tungsten contained in the organic phase may be
extracted with ammoniuln hydroxide to provide an aqueous ammonium
tungstate solution.
Tungsten metal powder may be produced from the ammonium tungstate by
known methods.
Various scheelite ~.d wolframite ores and mixtures thereof were treated
by the process of the invention using various reactive compositions,
ratios of ore to reactive composition and at different roasting
temperatures. In all these experiments the ore and reactive com-
position was in finely divided or particulate form and was roasted as
a mixture. After roasting, the sodium tungstate was leached with
water, the residue separated from the leach liquor by filtration and
washing and the leach liquor treated in the manner generally described
above to recover the tungsten values. The results of the experiments
are given in the Tables~ below.
.
Exper ments 1 to_4: The ore used was a wolframite ore containing
68,1% tungstic oxide; the reactive composition was sodium carbonate
and the roast temperature was 650C.
TABLE
20 : Experiment Ore Na2C03 Nature;of Roasted % Tungsten
(9)~ (9) Product Extraction
1 25 25 Powdery ~99 ~`
: 2 40 20 ~ ~ 9~
3 40 l o ~ 88 :
2s 4 50 ~ 8 ~ 62 ~ .
The stoichiometr~c ratio of tungstic oxide (W03) content to the reactive
composition is about 2,2. -
These experiments illustrate the importance of having a stoichiometric
excess of sodium present and the excellent recoveries which can be
achieved using sodium carbonate above. The roasted product, of a
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powdery nature, was easily handleable and could be subjected directly to
leachin~, and while still hot.
Experiments 5 to 8: The orc used was a scheelite ore containing 74,8%
tungstic oxide, the reactivc composition was sodium c'arbonate; and the
roast temperature was 650C for experiments 5 and 6 and 800C for
experiments 7 and 8.
TABLE II
Experiment Ore Na2C03 Nature of Roasted % Tungsten
(9) r ~ Product Extract~on
Powdery ~ 16
6 50 8 " ~15
; 7 300 48 " 23
8 300 53 " 25
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It will be noted that the tun~sten extractions are rèlatively low. The
reason for this is that a less than the stoichiometric quantity of sodium ~'~
carbonate was required to pr~vent fusion taking place. The roasted
product was powdery and~could be dire~ctly leached,;`and while still hot.
The leached residue, after~drYing. can~again be roasted in the presence
of~sodlum~carbonate~and~leached to increase; the tungsten extraction.
;20 `~ Thls~cin be repeated as often as desired to extract~as`much of the
tungsten as pqss1ble.;~
Experirnent~9~
p~ 0res~'were roasted at various temperatures usin~ var~ous ratlos of reactive
compositions to ore~ The roactivq compQs~t~on in each case conta~ned
l part sodlum carbonate to 0.fi7 parts sod~um~chlor~de, The results of
t~ese exper1ments~are set out~ln Table 111~
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rABLE III
Ore/Flux Roast Nature of % Tun~sten
Weight Basis Temperature Roasted Product Recovery
-
Wolframite (68,7% W03)
.
1/1,67 500 Powder 71
1/1,25 500 " 76
1/1,0 500 Sticky Powder 64
1/1,0 550 Lum~y 81
1/0,75 550 " 61
1/0,50 550 " 60
1/0,25 550 " 48
Scheelite ~71,4% W03) (SiO2 present)
1/1,67 500 Powder 32
1/1,25 500 " 24
1/1,0 500 " 36
1/0,5 500 " 19
1/0,75 550 Sticky Powder 22
In all the above experiments the roasted product could be subjected
direct1y to leaching with water, and while hot. The powdery roasted
;~ 20 product was easily hand1eab1e.
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g.
Experiment 10.
In this experiment a scheelite concentrate containing 74,8% of W03 and a
wolframite concentrate containing 68,1% W03 were mixed 1:1 by weight
~ and the mixture was mixed Wittl sodium carbonate in th,e proportion of
S 1 part of sodium carbonate to four parts of the mixture. Roasting was
conducted at 650C for four hours.
Thus 300 9 of scheelite, 300 9 of wolframite and 150 9 of sodium car-
bonate were mixed and roasted. The theoretical stoichiometric amount
of sodium carbonate was 98 g. The percentage extraction of tungsten
was 58%.
'Experiment 11
.
The residue from experiment 10 was again mixed with sodium carbonate
and roasted at 650C and two tests conducted with different amounts of
sodium carbonate. The results are given in table IV.
TABLE IV
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Residue (g) Na2C03(g) Theoretical Percentage Overallpercentage
Stoichiometric Extraction extraction
Na2CO of W
14,4 ' 71 , 90
, 30 ~2,1 ; 86 ~ 95
The overall tungsten extraction is 90 and 9S percent at residue:
Na2C03 ratios of 7:3 and 1:3.~ The~particular ratio chosen will depend t
on the particular economic circumstances under which any process operates
at any given time.
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As far as the applicant is aware, this is the first process which has
been found to be suitable for treating mixtures of scheelite and
, wolframite. The latter acts to reduce the tendency of scheelite to
form a sticky product.
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