CA1136422A

CA1136422A - Recovery of tungsten values from tungsten- bearing materials

Info

Publication number: CA1136422A
Application number: CA000340128A
Authority: CA
Inventors: George S. James; Alfred M. Harris; Gwilym J. Rees
Original assignee: Anglo American Corp of South Africa Pty Ltd
Current assignee: Anglo American Corp of South Africa Pty Ltd
Priority date: 1978-11-17
Filing date: 1979-11-19
Publication date: 1982-11-30
Also published as: EP0011475A1; TR21615A; AU525137B2; PT70465A; AR224633A1; AU5291879A; JPS5589446A; JPS595657B2; ATE1681T1; BR7907441A; EP0011475B1; ES486063A1; DE2963902D1; ZA786478B

Abstract

ABSTRACT OF DISCLOSURE

A method of recovering tungsten values from a high grade tungsten bearing ore or concentrate such as scheelite or wolframite includes the steps of roasting, without fusion, the ore or concentrate in the presence of a reactive composition selected from the group of an alkali metal chloride, an alkali metal carbonate and mixtures thereof and extracting the water-soluble tungsten values from the roasted product, e.g. by water leaching. The reactive composition is preferably an alkali metal carbonate on its own.

Description

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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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-4a-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.
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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.
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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 :
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.;~

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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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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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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of 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 the group of an alkali metal chloride, an alkali metal carbonate and mixtures thereof and extracting water-soluble tungsten values from the roasted product.

2. A method according to Claim 1, in which fusion is prevented by controlling the amount of reactive composi-tion used.

3. A method according to Claim 1 or Claim 2, wherein the reactive composition is a mixture of an alkali metal chloride and an alkali metal carbonate.

4. A method according to Claim 1 or Claim 2, wherein the reactive composition consists soley of an alkali metal carbonate.

5. A method according to Claim 1, wherein the alkali metal is sodium.

6. A method according to Claim 1, wherein the roasting takes place at a temperature in the range 500°C to 800°C.

7. A method according to Claim 1, wherein the water-soluble tungsten values are extracted from the roasted product by leaching with water.

8. A method of Claim 7, wherein the roasted product is leached while it is hot.

9. A method according to Claim 1, wherein the ore is a scheelite ore and the roast temperature is in the range 600°C to 800°C.

10. A method according to Claim 9, wherein the roasted product is, after extraction of water-soluble tungsten values therefrom, roasted in the presence of the reactive composition and further water-soluble tungsten values then extracted therefrom.

11. A method according to Claim 1, wherein the ore is a wolframite ore and the roast temperature is in the range 500°C to 800°C.

12. A method according to Claim 11, wherein the amount of reactive composition used is such that a stoichiometric excess of sodium is present in relation to the tungsten oxide in the ore.

13. A method according to Claim 1, wherein the ore is a mixture of wolframite and scheelite.

14. A method according to Claim 13, wherein the roasted product is, after extraction of water-soluble values therefrom, roasted in the presence of a reactive composi-tion and further water-soluble values are extracted from the thus roasted product.