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Studies on the recovery of tungsten from a composite wolframite–scheelite concentrate
Hydrometallurgy 58 Ž2000. 43–50 www.elsevier.nlrlocaterhydromet
Studies on the recovery of tungsten from a composite wolframite–scheelite concentrate K. Srinivas, T. Sreenivas, R. Natarajan, N.P.H. Padmanabhan) Ore Dressing Section, Bhabha Atomic Research Centre, A.M.D.Complex, Begumpet, Hyderabad 500016, India Received 11 January 2000; received in revised form 2 June 2000; accepted 3 June 2000
Abstract Studies on the recovery of tungsten from a multi-metal tin–tungsten ore from Kreghystan were carried out by a combination of physical beneficiation and soda ash roast–aqueous leach technique. Cassiterite, wolframite and scheelite are the main valuable minerals in this ore. However, a significant amount of wolframite occurs finely disseminated in scheelite. This composite nature of mineralisation has limited the scope of using physical separation methods in generating individual concentrates of either wolframite or scheelite with economical recovery. In view of this, a combined tungsten minerals concentrate which is free of majority of other heavy mineral — cassiterite was first obtained by physical up-gradation methods and was later subjected to tungsten extraction by soda ash roast–aqueous leach technique. The effect of process variables such as: roasting time, temperature and feed-to-alkali ratio were studied. At optimum roasting and leaching conditions, about 95% of WO 3 values were extracted. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Tungsten; Physical beneficiation; Soda ash roast y aqueous leaching
1. Introduction The chief economic minerals of tungsten are wolframite ŽŽFe, Mn. WO4 . and scheelite ŽCaWO4 .. Tungsten ores are generally subjected to physical beneficiation techniques such as gravity, flotation, magnetic and electrostatic separation to obtain marketable grade mineral concentrates Ž60–70% WO 3 .. However, physical beneficiation of low-grade tungsten ores having the mineralisation in finely disseminated form, invariably yields marketable grade concentrates only at sub-optimal recovery. A techno-
)
Corresponding author. E-mail address: [email protected] ŽN.P.H. Padmanabhan..
logical solution for maximising recovery from such low grade ores is as follows: Ža. pre-concentrate the ore to a reasonable grade, say 5–40% WO 3 in the case of tungsten ores, with maximum recovery by physical beneficiation and Žb. subject the pre-concentrate to suitable hydro- or pyro-metallurgical techniques of upgradation, where recoveries are generally high, to produce a value-added marketable intermediate grade product w1x. This intermediate product can be further purified by normal methods Žsolvent extraction, electrowinning etc.. to obtain very high purity end products. This procedure was successfully implemented on both low grade tin w2x and tungsten w3,4x ores. This paper presents application of similar methodology for recovering tungsten values from a multi-metal tin–tungsten ore from Kreghystan.
0169-4332r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 3 8 6 X Ž 0 0 . 0 0 1 2 6 - 2
44
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
The major minerals Žweight-wise. in the primary gravity pre-concentrate of the Kreghystan ore are cassiterite Ž38%., wolframite q scheelite Ž22%., tourmaline Ž37%. and quartz Ž3%.. A unique feature of tungsten mineralisation here is the presence of considerable amount of wolframite finely disseminated in scheelite ŽFig. 1.. This composite nature of tungsten mineralisation has limited the scope of using physical beneficiation techniques in generating individual concentrates of either wolframite or scheelite with economical recovery. In view of this, physical separation techniques Žmagnetic and high tension separation. were used to separate out the majority of the cassiterite values from the primary gravity pre-concentrate to obtain a predominantly wolframite–scheelite concentrate. The combined tungsten minerals concentrate thus generated was later subjected to tungsten extraction by soda ash roast–aqueous leaching method. The soda ash roast–aqueous leach process was successfully tested on a low grade wolframite concentrate Ž7% and 24% WO 3 . by Subramanian et al. w3x and on a scheelite concentrate Ž65% WO 3 . by Paramguru et al. w4x. However, no studies have been reported on the applicability of this method for recovering tungsten values from combined tungsten minerals Žwolframiteq scheelite. concentrate. Investigations on this line are imperative as deposits having combined mineralisation of wolframite and
scheelite are not uncommon w5x as found in the Kreghystan ore.
2. Chemical reactions The soda ash roast–aqueous leach extraction process consists of roasting of the mineral concentrate with a mixture of soda ash and sodium nitrate Žoxidizing agent for converting Wq4 Wq6 . at appropriate temperature. Roasting converts tungsten minerals into water-soluble Na 2WO4 compound.
™
Na 2 CO 3 q CaWO4
™ Na WO q CaCO 2
4
3
Ž 1.
Na 2 CO 3 q Ž Fe,Mn . WO4
™ Na WO q Ž Fe,Mn. CO 2
4
3
Ž 2.
It is evident from Eq. Ž1. that calcium carbonate is one of the reaction product formed during the roasting of scheelite. Depending on the temperature of roasting calcium carbonate may undergo further dissociation yielding calcium oxide as shown in Eq. Ž3.. CaCO 3
™ CaO q CO
2
Ž 3.
Studies by Paramguru et al. w4,6x and Shamsuddin and Sohn w7x have indicated that presence of CaO or CaCO 3 in the leach liquor would back precipitate some of the tungsten values in the form of CaWO4
Fig. 1. Incident light photograph indicating nature of tungsten mineralisation in Kreghystan multi-metal tin–tungsten ore. Wolframite occurs as fine inclusions in scheelite Žmagnification: 330 = ..
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50 Table 1 Particle size analysis of feed for roasting experiments Size Žmm.
Weight%
q500 y500q212 y212q100 y100q74 y74
0.76 22.45 57.20 11.26 8.33
during aqueous leaching of roasted mass. Paramguru et al. w6x have also observed that presence of Na 2 CO 3 in the leach liquor would eliminate back precipitation of CaWO4 .
3. Experimental The mineralogical composition Žby weight. of the wolframite–scheelite concentrate used in the roasting studies is as follows: wolframiteq scheelite 34%, cassiterite 5.6% and tourmaline 60.4%. The partial
45
chemical analysis of the sample is: WO 3 21.21%, CaO 3.64% and Sn 5.0%. About 90% by weight of the feed used for the roasting experiments are in the size range of 500–74 mm ŽTable 1.. All the roasting experiments were carried out in a muffle furnace at a 5-g scale. The feed was mixed with a pre-determined quantity of sodium carbonate ŽLR grade. and fixed quantity Žone third weight of sodium carbonate. of sodium nitrate ŽLR grade. and loaded in the furnace in a mild steel boat. The charge was allowed to react at desired temperature for a given time duration with intermittent mixing. After the reaction period, the roasted mass was air-cooled and the tungsten values were brought into solution by agitation leaching in 100 ml of hot water Ž353 K. for 30 min. The impeller to vessel diameter ratio is 0.6 and the stirring rate was 600 miny1 . The pH of the suspension after the addition of roasted mass to hot water was 12.2 " 0.2. The residue obtained after the first stage of leaching was agitated again for 30 min with 50 ml of hot water Ž353 K. to recover additional tungsten values, if any. In the second stage of leaching the pH of the suspension was about
Fig. 2. Extraction of tungsten values by soda ash roasting–aqueous leaching: effect of roasting temperature. feed-to-Na 2 CO 3 ratios 1:1.5.
46
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
Fig. 3. Extraction of tungsten values by soda ash roasting–aqueous leaching: effect of roasting time. feed-to-Na 2 CO 3 ratios 1:1.5.
Fig. 4. Extraction of tungsten values by soda ash roasting–aqueous leaching: effect of roasting feed-to-Na 2 CO 3 ratio.
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
10.3 " 0.3. A small quantity of alkali was added during the second stage of leaching when the pH of the suspension was on the lower limit of the abovementioned range, mainly to prevent back-precipitation of scheelite. The effect of roasting temperature, time and feedto-carbonate ratio on the extraction of tungsten values was studied. The efficiency of the overall process was estimated by the amount of tungsten values extracted into solution. The WO 3 content of the leach liquors and residues was estimated using a spectrophotometer by the dithiol method w8x.
47
3.1. Results and discussion
3.1.1. Effect of roasting temperature Fig. 2 illustrates the effect of roasting temperature on extraction of tungsten values from the combined wolframite–scheelite concentrate. The temperature was varied between 673 and 873 K and a roasting duration of 5 h was maintained throughout. The weight ratio of feed-to-sodium carbonate was 1:1.5 in all the experiments. Maximum extraction, about 95%, of WO 3 values was obtained in a roasting
Fig. 5. Material balance for tungsten extraction from wolframite–scheelite composite concentrate by soda ash roast–aqueous leach technique.
48
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
temperature range of 823–873 K. Microscopic observation of the roasted mass obtained at temperatures - 773 K have indicated presence of feed unreacted with Na 2 CO 3 . 3.1.2. Effect of roasting time Optimisation studies on the roasting time were carried out by maintaining the roasting temperature at 823 K and feed-to-Na 2 CO 3 ratio at 1:1.5. Results of these experiments are given in Fig. 3. As seen from the WO 3 values extracted, it is evident that the reaction is complete in 2 h of roasting period. About 97% of WO 3 values were extracted from a feed roasted for 2 h. Further increase in roasting duration has given only 1–2% increase in the overall recovery.
3.1.3. Effect of sodium carbonate addition The effect of feed-to-sodium carbonate ratio on roasting characteristics of tungsten were carried out at constant temperature and time of 823 K and 2 h, respectively. Results are presented in Fig. 4. Progressive increase in amount of WO 3 values extracted was observed with increase in the ratio up to 1:1.5. At this ratio about 97% of WO 3 values were taken into the aqueous phase. 3.1.4. Characteristics of leach liquor and roast residue The material balance for the roasting experiment carried out at optimum conditions — time duration 2 h, temperature 823 K and feed-to-sodium carbonate
Fig. 6. Ža. XRD pattern of feed for roasting experiments. Scheelite ŽS., Wolframite ŽW., Cassiterite ŽC., Quartz ŽQ. and Tourmaline ŽT.. Žb. XRD pattern of leach residue obtained after aqueous extraction of roasted mass. Scheelite ŽS., Cassiterite ŽC., Quartz ŽQ. and Tourmaline ŽT..
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
49
Fig. 6 Ž continued ..
ratio of 1:1.5, is given in Fig. 5. Totally about 96% of the tungsten values were extracted during two stages of leaching with the first stage alone yielding about 94% recovery. The leach liquors obtained at first and second stages of leaching were mixed and analysed for major noxious elements. The liquors contained Fe, Mn and Bi - 5 mgrl, Si - 34 mgrl, P - 10 mgrl and no Sn content. XRD analysis ŽFig. 6. of the leach residue showed peaks corresponding to cassiterite, scheelite, quartz and tourmaline mineral phases. The presence of scheelite in the leach residue could be either unreacted material or that which was back precipitated during the leaching process. The results clearly indicates selective roast-
ing of tungsten minerals as compared to the other major heavy mineral–cassiterite.
4. Conclusions A study on the multi-metal tin–tungsten ore of Kreghystan indicated the applicability of an approach comprising of physical beneficiation and soda ash roast–aqueous leach for recovering tungsten values from a composite concentrate of wolframite and scheelite. Processing of the physically-beneficiated tungsten mineral concentrate Ž21.21% WO 3 , 3.64% CaO and 5% Sn. by roasting Žtemperature 823 K,
50
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
time 2 h and feed-to-Na 2 CO 3 ratio of 1:1.5. followed by aqueous leaching gave about 95% recovery of WO 3 values. The W-laden leach liquor is completely free of Sn.
w3x
w4x
Acknowledgements The authors express sincere thanks to Mrs Jagson International, New Delhi for providing the ore sample and to Dr.C.K.Gupta, Director, Materials Group, BARC, Mumbai for the continued encouragement and keen interest in these investigations. They also express gratitude to their colleagues for chemical and petromineralogical charaterisation.
w5x
w6x
w7x
References w1x P. Borchers, Processing of tungsten, Tungsten, 1st International Tungsten Symposium, Stockholm, Mining Journal Books ŽLondon. 1979, pp. 64–77. w2x W.T. Denholm, K.A. Foo, N.J. Pocock, Tin volatilization:
w8x
smaller plants for mines and smelters, Miner. Process. Ext. Metall., in: M.J. Jones, P. Gill ŽEds.., Inst. Min. Met. ŽLondon. 1984, pp. 275–290. C. Subramanian, A.K. Suri, C.K. Gupta, Processing of low grade tungsten concentrates of Degana, Trans. Indian Inst. Met. 45 Ž4. Ž1992. 207–213. R.K. Paramguru, K.N. Jena, P.K. Sahoo, Extraction of tungsten from scheelite concentrate by soda ash roast–leach method, Trans. Inst. Min. Metall. 99 Ž1990. C67–C70. R.F. Horsnail, The geology of tungsten, Tungsten, 1st International Tungsten Symposium, Stockholm, Mining Journal Books ŽLondon. 1979, pp. 18–63. R.K. Paramguru, K.N. Jena, P.K. Sahoo, Extraction of tungsten from low-grade wolframite and scheelite concentrates by soda ash roast–leach method, Tungsten resources development, National Workshop on Tungsten Resources Development, Regional Research Laboratory, Council of Scientific and Industrial Research, Bhubaneswar, India, 1987, pp. 117– 121. M. Shamsuddin, H.Y. Sohn, in: H.Y. Sohn, O. Norman Carlsor, J. Thomas Smith ŽEds.., Proceedings Symp. TMSAIME, Refractory Metals Committee and the Physical Chemistry of Extractive Metallurgy Committee at the 110th AIME Annual Meeting, Chicago, IL, Feb. 22–26, 1981. S.C. Srivatsava, S.R. Bhaisare, D.N. Wagh, C.S.P. Iyer, Analysis of tungsten in low grade ores and geological samples, Bull. Mater. Sci. 19 Ž2. Ž1996. 331–343.
Studies on the recovery of tungsten from a composite wolframite–scheelite concentrate K. Srinivas, T. Sreenivas, R. Natarajan, N.P.H. Padmanabhan) Ore Dressing Section, Bhabha Atomic Research Centre, A.M.D.Complex, Begumpet, Hyderabad 500016, India Received 11 January 2000; received in revised form 2 June 2000; accepted 3 June 2000
Abstract Studies on the recovery of tungsten from a multi-metal tin–tungsten ore from Kreghystan were carried out by a combination of physical beneficiation and soda ash roast–aqueous leach technique. Cassiterite, wolframite and scheelite are the main valuable minerals in this ore. However, a significant amount of wolframite occurs finely disseminated in scheelite. This composite nature of mineralisation has limited the scope of using physical separation methods in generating individual concentrates of either wolframite or scheelite with economical recovery. In view of this, a combined tungsten minerals concentrate which is free of majority of other heavy mineral — cassiterite was first obtained by physical up-gradation methods and was later subjected to tungsten extraction by soda ash roast–aqueous leach technique. The effect of process variables such as: roasting time, temperature and feed-to-alkali ratio were studied. At optimum roasting and leaching conditions, about 95% of WO 3 values were extracted. q 2000 Elsevier Science B.V. All rights reserved. Keywords: Tungsten; Physical beneficiation; Soda ash roast y aqueous leaching
1. Introduction The chief economic minerals of tungsten are wolframite ŽŽFe, Mn. WO4 . and scheelite ŽCaWO4 .. Tungsten ores are generally subjected to physical beneficiation techniques such as gravity, flotation, magnetic and electrostatic separation to obtain marketable grade mineral concentrates Ž60–70% WO 3 .. However, physical beneficiation of low-grade tungsten ores having the mineralisation in finely disseminated form, invariably yields marketable grade concentrates only at sub-optimal recovery. A techno-
)
Corresponding author. E-mail address: [email protected] ŽN.P.H. Padmanabhan..
logical solution for maximising recovery from such low grade ores is as follows: Ža. pre-concentrate the ore to a reasonable grade, say 5–40% WO 3 in the case of tungsten ores, with maximum recovery by physical beneficiation and Žb. subject the pre-concentrate to suitable hydro- or pyro-metallurgical techniques of upgradation, where recoveries are generally high, to produce a value-added marketable intermediate grade product w1x. This intermediate product can be further purified by normal methods Žsolvent extraction, electrowinning etc.. to obtain very high purity end products. This procedure was successfully implemented on both low grade tin w2x and tungsten w3,4x ores. This paper presents application of similar methodology for recovering tungsten values from a multi-metal tin–tungsten ore from Kreghystan.
0169-4332r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 3 8 6 X Ž 0 0 . 0 0 1 2 6 - 2
44
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
The major minerals Žweight-wise. in the primary gravity pre-concentrate of the Kreghystan ore are cassiterite Ž38%., wolframite q scheelite Ž22%., tourmaline Ž37%. and quartz Ž3%.. A unique feature of tungsten mineralisation here is the presence of considerable amount of wolframite finely disseminated in scheelite ŽFig. 1.. This composite nature of tungsten mineralisation has limited the scope of using physical beneficiation techniques in generating individual concentrates of either wolframite or scheelite with economical recovery. In view of this, physical separation techniques Žmagnetic and high tension separation. were used to separate out the majority of the cassiterite values from the primary gravity pre-concentrate to obtain a predominantly wolframite–scheelite concentrate. The combined tungsten minerals concentrate thus generated was later subjected to tungsten extraction by soda ash roast–aqueous leaching method. The soda ash roast–aqueous leach process was successfully tested on a low grade wolframite concentrate Ž7% and 24% WO 3 . by Subramanian et al. w3x and on a scheelite concentrate Ž65% WO 3 . by Paramguru et al. w4x. However, no studies have been reported on the applicability of this method for recovering tungsten values from combined tungsten minerals Žwolframiteq scheelite. concentrate. Investigations on this line are imperative as deposits having combined mineralisation of wolframite and
scheelite are not uncommon w5x as found in the Kreghystan ore.
2. Chemical reactions The soda ash roast–aqueous leach extraction process consists of roasting of the mineral concentrate with a mixture of soda ash and sodium nitrate Žoxidizing agent for converting Wq4 Wq6 . at appropriate temperature. Roasting converts tungsten minerals into water-soluble Na 2WO4 compound.
™
Na 2 CO 3 q CaWO4
™ Na WO q CaCO 2
4
3
Ž 1.
Na 2 CO 3 q Ž Fe,Mn . WO4
™ Na WO q Ž Fe,Mn. CO 2
4
3
Ž 2.
It is evident from Eq. Ž1. that calcium carbonate is one of the reaction product formed during the roasting of scheelite. Depending on the temperature of roasting calcium carbonate may undergo further dissociation yielding calcium oxide as shown in Eq. Ž3.. CaCO 3
™ CaO q CO
2
Ž 3.
Studies by Paramguru et al. w4,6x and Shamsuddin and Sohn w7x have indicated that presence of CaO or CaCO 3 in the leach liquor would back precipitate some of the tungsten values in the form of CaWO4
Fig. 1. Incident light photograph indicating nature of tungsten mineralisation in Kreghystan multi-metal tin–tungsten ore. Wolframite occurs as fine inclusions in scheelite Žmagnification: 330 = ..
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50 Table 1 Particle size analysis of feed for roasting experiments Size Žmm.
Weight%
q500 y500q212 y212q100 y100q74 y74
0.76 22.45 57.20 11.26 8.33
during aqueous leaching of roasted mass. Paramguru et al. w6x have also observed that presence of Na 2 CO 3 in the leach liquor would eliminate back precipitation of CaWO4 .
3. Experimental The mineralogical composition Žby weight. of the wolframite–scheelite concentrate used in the roasting studies is as follows: wolframiteq scheelite 34%, cassiterite 5.6% and tourmaline 60.4%. The partial
45
chemical analysis of the sample is: WO 3 21.21%, CaO 3.64% and Sn 5.0%. About 90% by weight of the feed used for the roasting experiments are in the size range of 500–74 mm ŽTable 1.. All the roasting experiments were carried out in a muffle furnace at a 5-g scale. The feed was mixed with a pre-determined quantity of sodium carbonate ŽLR grade. and fixed quantity Žone third weight of sodium carbonate. of sodium nitrate ŽLR grade. and loaded in the furnace in a mild steel boat. The charge was allowed to react at desired temperature for a given time duration with intermittent mixing. After the reaction period, the roasted mass was air-cooled and the tungsten values were brought into solution by agitation leaching in 100 ml of hot water Ž353 K. for 30 min. The impeller to vessel diameter ratio is 0.6 and the stirring rate was 600 miny1 . The pH of the suspension after the addition of roasted mass to hot water was 12.2 " 0.2. The residue obtained after the first stage of leaching was agitated again for 30 min with 50 ml of hot water Ž353 K. to recover additional tungsten values, if any. In the second stage of leaching the pH of the suspension was about
Fig. 2. Extraction of tungsten values by soda ash roasting–aqueous leaching: effect of roasting temperature. feed-to-Na 2 CO 3 ratios 1:1.5.
46
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
Fig. 3. Extraction of tungsten values by soda ash roasting–aqueous leaching: effect of roasting time. feed-to-Na 2 CO 3 ratios 1:1.5.
Fig. 4. Extraction of tungsten values by soda ash roasting–aqueous leaching: effect of roasting feed-to-Na 2 CO 3 ratio.
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
10.3 " 0.3. A small quantity of alkali was added during the second stage of leaching when the pH of the suspension was on the lower limit of the abovementioned range, mainly to prevent back-precipitation of scheelite. The effect of roasting temperature, time and feedto-carbonate ratio on the extraction of tungsten values was studied. The efficiency of the overall process was estimated by the amount of tungsten values extracted into solution. The WO 3 content of the leach liquors and residues was estimated using a spectrophotometer by the dithiol method w8x.
47
3.1. Results and discussion
3.1.1. Effect of roasting temperature Fig. 2 illustrates the effect of roasting temperature on extraction of tungsten values from the combined wolframite–scheelite concentrate. The temperature was varied between 673 and 873 K and a roasting duration of 5 h was maintained throughout. The weight ratio of feed-to-sodium carbonate was 1:1.5 in all the experiments. Maximum extraction, about 95%, of WO 3 values was obtained in a roasting
Fig. 5. Material balance for tungsten extraction from wolframite–scheelite composite concentrate by soda ash roast–aqueous leach technique.
48
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
temperature range of 823–873 K. Microscopic observation of the roasted mass obtained at temperatures - 773 K have indicated presence of feed unreacted with Na 2 CO 3 . 3.1.2. Effect of roasting time Optimisation studies on the roasting time were carried out by maintaining the roasting temperature at 823 K and feed-to-Na 2 CO 3 ratio at 1:1.5. Results of these experiments are given in Fig. 3. As seen from the WO 3 values extracted, it is evident that the reaction is complete in 2 h of roasting period. About 97% of WO 3 values were extracted from a feed roasted for 2 h. Further increase in roasting duration has given only 1–2% increase in the overall recovery.
3.1.3. Effect of sodium carbonate addition The effect of feed-to-sodium carbonate ratio on roasting characteristics of tungsten were carried out at constant temperature and time of 823 K and 2 h, respectively. Results are presented in Fig. 4. Progressive increase in amount of WO 3 values extracted was observed with increase in the ratio up to 1:1.5. At this ratio about 97% of WO 3 values were taken into the aqueous phase. 3.1.4. Characteristics of leach liquor and roast residue The material balance for the roasting experiment carried out at optimum conditions — time duration 2 h, temperature 823 K and feed-to-sodium carbonate
Fig. 6. Ža. XRD pattern of feed for roasting experiments. Scheelite ŽS., Wolframite ŽW., Cassiterite ŽC., Quartz ŽQ. and Tourmaline ŽT.. Žb. XRD pattern of leach residue obtained after aqueous extraction of roasted mass. Scheelite ŽS., Cassiterite ŽC., Quartz ŽQ. and Tourmaline ŽT..
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
49
Fig. 6 Ž continued ..
ratio of 1:1.5, is given in Fig. 5. Totally about 96% of the tungsten values were extracted during two stages of leaching with the first stage alone yielding about 94% recovery. The leach liquors obtained at first and second stages of leaching were mixed and analysed for major noxious elements. The liquors contained Fe, Mn and Bi - 5 mgrl, Si - 34 mgrl, P - 10 mgrl and no Sn content. XRD analysis ŽFig. 6. of the leach residue showed peaks corresponding to cassiterite, scheelite, quartz and tourmaline mineral phases. The presence of scheelite in the leach residue could be either unreacted material or that which was back precipitated during the leaching process. The results clearly indicates selective roast-
ing of tungsten minerals as compared to the other major heavy mineral–cassiterite.
4. Conclusions A study on the multi-metal tin–tungsten ore of Kreghystan indicated the applicability of an approach comprising of physical beneficiation and soda ash roast–aqueous leach for recovering tungsten values from a composite concentrate of wolframite and scheelite. Processing of the physically-beneficiated tungsten mineral concentrate Ž21.21% WO 3 , 3.64% CaO and 5% Sn. by roasting Žtemperature 823 K,
50
K. SriniÕas et al.r Hydrometallurgy 58 (2000) 43–50
time 2 h and feed-to-Na 2 CO 3 ratio of 1:1.5. followed by aqueous leaching gave about 95% recovery of WO 3 values. The W-laden leach liquor is completely free of Sn.
w3x
w4x
Acknowledgements The authors express sincere thanks to Mrs Jagson International, New Delhi for providing the ore sample and to Dr.C.K.Gupta, Director, Materials Group, BARC, Mumbai for the continued encouragement and keen interest in these investigations. They also express gratitude to their colleagues for chemical and petromineralogical charaterisation.
w5x
w6x
w7x
References w1x P. Borchers, Processing of tungsten, Tungsten, 1st International Tungsten Symposium, Stockholm, Mining Journal Books ŽLondon. 1979, pp. 64–77. w2x W.T. Denholm, K.A. Foo, N.J. Pocock, Tin volatilization:
w8x
smaller plants for mines and smelters, Miner. Process. Ext. Metall., in: M.J. Jones, P. Gill ŽEds.., Inst. Min. Met. ŽLondon. 1984, pp. 275–290. C. Subramanian, A.K. Suri, C.K. Gupta, Processing of low grade tungsten concentrates of Degana, Trans. Indian Inst. Met. 45 Ž4. Ž1992. 207–213. R.K. Paramguru, K.N. Jena, P.K. Sahoo, Extraction of tungsten from scheelite concentrate by soda ash roast–leach method, Trans. Inst. Min. Metall. 99 Ž1990. C67–C70. R.F. Horsnail, The geology of tungsten, Tungsten, 1st International Tungsten Symposium, Stockholm, Mining Journal Books ŽLondon. 1979, pp. 18–63. R.K. Paramguru, K.N. Jena, P.K. Sahoo, Extraction of tungsten from low-grade wolframite and scheelite concentrates by soda ash roast–leach method, Tungsten resources development, National Workshop on Tungsten Resources Development, Regional Research Laboratory, Council of Scientific and Industrial Research, Bhubaneswar, India, 1987, pp. 117– 121. M. Shamsuddin, H.Y. Sohn, in: H.Y. Sohn, O. Norman Carlsor, J. Thomas Smith ŽEds.., Proceedings Symp. TMSAIME, Refractory Metals Committee and the Physical Chemistry of Extractive Metallurgy Committee at the 110th AIME Annual Meeting, Chicago, IL, Feb. 22–26, 1981. S.C. Srivatsava, S.R. Bhaisare, D.N. Wagh, C.S.P. Iyer, Analysis of tungsten in low grade ores and geological samples, Bull. Mater. Sci. 19 Ž2. Ž1996. 331–343.