Düşük tenörlü şelit konsantrelerinden tungsten metal tozu üretimi

Abstract

Bu tez çalışmasında, % 35 UD_ vs % 5.2 S içeren Uludağ şelit konsantresinden tungsten üretimine yönelik, deneysel çalışmalar yapılmıştır. İzlenen deneysel pro sedür kavurma, alkali füzyon, suda liç, çözelti temizle me, Tungstik asit-Amonyum Paratungstat çöktürme ve re- düksiyon kademelerinden oluşmaktadır. Elde edilen deneysel sonuçlara göre, konsantredeki piritik kükürdün, bir döner fırında 75D C'da, 2 saat sü re ile ve teorik miktarın iki katı hava üflenerek, % 0.7 değerine kadar düşürülmesi mümkün olmuştur, Grijinal numunenin doğrudan alkali füzyanunda, Na.,FeS, ile göste rilen mat fazı oluşmakta ve bu faz Lü çözünme veriminin % 78'e kadar düşmesine yol açmaktadır. Kükürdü giderilmiş numunede % 99'un üzerinde bir tungsten verimi elde etmek için, 900 C'da 1 saat süreyle ve gerekli miktarın 2 katı NanC0" ilâvesi ile alkali füzyon yapmak yeterli olmaktadır. Bu ekstraksıyon oranı için, alkali füzyon sonrası 60 C'daki su ile 1/5 K/5 ora nında 1 saat süreyle çözümlendirme yapmak gerekmektedir. Kirli Na"lü0, çözeltisinin MgCl?.6H"0 ve Na_S ile temiz lenmesinden sonra, litresinde Î7.6 mg Mo, B.6 mg Al, 0.B mg Fe ve eser miktarda Si bulunan temiz bir çözelti elde edilmiştir. Bu çözeltiden önce HC1 + HN0_ ilâve siyle H"UD, ve daha sonra da NH, ile APT çöktürülmüştür. APT'ın Ralsinasyonu ile U0_ üretilmiştir. UJO'in W? gazı altında 70aaC'da bir saat ve 1050aC da 3 saat tutulmasıyla % 99.8 safiyette, 0.22 mz/g BET değerinde ve 1-5 mikron tane boyutunda, karbür kalite sinde toz üJ metali üretilmiştir. Tüm bu işlemler sonun da, % 9B!lik bir tungsten üretim verimi mümkün olmakta dır.

Tungsten, located at the VI. group of the periodic table, has a melting point uf 3410 C and finds uide range of applicatians as a refractory metal due ta high strength/ujsight ratia. Its high melting paint and IDUJ vapor pressure makas it an ideal candidate far engineering applicatians such as electric discharge machining, x-ray and transmission tubes, lamp filament supparts, heating alements far high temperature furnaces and fluorescent lamps, electronic heaters and emitters, lamp filaments supparts, glass-ta-metal seals, electrical cantacts, electrodes for arc lamp, and in uelding» Allaying the tungsten uith elements such as niabium, tantalum, molybdenum and rhenium increases high tempera¬ ture strength, toughness and creep resistance so that it can be used in severe enviranments such as gas türbine vanes, rocket nozzles, flame shields, containers in very corrosive environments and nuclear applicatians. in the carbide form, tungsten is highly demanded material ta be used as cutting taals and drilling tips. The most important tungsten ores ara uolframite ((Fe5Mn)klD, ) and scheelite (CatdO^K Other tungsten ares are as follaus: Reinite F6^, (tetraganal) Ferritungstite (Fe-O.,. UCU. fih^O ) Tungstite ar Tungsten (lilD,.H,0 ar H9lıJO, ) Ochre J ^ ^ ^ Tharatungstite [2üJ03. H2D+(Th02, C102, ZrOg).Hgü] Meymacite(Tunstite) UO-.H.G Cammerical processes far tungsten praductian generally use uolframite ar scheelite cancentrates. Main steps being the Ammanitım Paratungstate (APT) praductian, UD_ praductian and tunnnten metal pauıder productian; different methods employ different rautes depending an the üJD- content of the rau material. in Turkey, a plant uas established by ETİBANK in Uludağ-Bursa ta praduce scheallte cancentrate containing 6G-65 % UJD, by utilizing the örs cantaining 0.52 % UCU. Hatjever,/orily 30--40 % üJCU cantaining concentrate produc- tian uas economically feasible due ta th.e high sulphur cantent af.the reserve. Therefare, this facility mas shut douın in 1989. it is the aim of this research ta determine the optimum conditians far the praductian of tungsten metal pauder by using the lau grade scheelite cancentrate cantaining 35 % UO., and 5.2 % 5 of Etibank, Uludağ plant via roasting alkali fusian, aqueaus leaching, salution stripping, tungstic acid precipitatian, APT precipitation and thus tungstic oxide (LüO_) synthesis, and tungsten metal pouder productian by reduction. The general flou chart far the production af tungs¬ ten metal pauder is given in the follauıing figüre.1« in tungsten praduction the first intermediate aim is the production of sodium tungstate (Na-lılD,). in the case of scheelite cancentrate containing 6G-B5 % UCU, the HC1 digestion, falloujed by a filtration yields ta THE PRODUCTION OF TUNGSTEN METAL POWDER BY UTILIZING LOU GRADE SCHEELITE CONCENTRATE SUMHARY Tungsten, located at the VI. group of the periodic table, has a melting point of 3410 C and finds wide range of applications as a refractory metal due to high strength/ujeight ratio. Its high melting point and low vapor pressure makes it an ideal candidate for engineering applications such as electric discharge machining, x-ray and transmission tubes, lamp filament supports, heating elements for high temperature furnaces and fluorescent lamps, electronic heaters and emitters, lamp filaments supports, glass-to-metal seals, electrical contacts, electrodes for arc lamp, and in welding. Allaying the tungsten with elements such as niobium, tantalum, molybdenum and rhenium increases high tempera ture strength, toughness and creep resistance so that it can be used in severe environments such as gas turbine vanes, rocket nozzles, flame shields, containers in very corrosive environments and nuclear applications. In the carbide form, tungsten is highly demanded material to be used as cutting tools and drilling tips, The most important tungsten ores are wolframite ( (Fe,Mn)klD, ) and scheelite (CatdO, ). Other tungsten ores are as follows: Reinite FBW0, (tetragonal) Ferritungstite (Fe O^.UOj.?h^O) Tungstite or Tungsten (UQ-.H^O or H9W0, ) Ochre 3 d d * Thorotungstite [2QJ03. H20+(Th02, C102, ZrOg).HgO] Meymacite(Tunstite) lilQ-.H-O Vll an impure Na_UO,. Houever, since ETİBANK "Uludağ, concent- rate contains sulphur as given in the fallouing tatile.1- a mare camplicated route is emplayed. TABLE: 1. Chemical Campaunds af ETİBANK-Uludağ Scheelite Concentrate Element ör Compounds Ueight, % lı)03 35-° Fe 27.0 SiU2. 10"ü 02(asFe30^ ör Fe^) 9.3 CaQ 9-D S 5.2 A1203 2-2 Mn 1 -2 Zn a-6 MqO °-3 MÜ Ü 3 Q.2 A roasting process at 7DO-85DDC and uith different air flou rates uas employed to eliminata the sulphur. The roasting product uas fused in the presence af Na2CÜ3 at aOD-10QQDC. This uas folloued by the optimiza- tian of leaching ta abtain the impure Na^LJO, solution. Tıi.'.a impure salution uas cleaned by using MgCl_.6H_G from impurities such aa Si,Fe and Al at 8D°C and pH = 10. The effact af MgCl,,, 6H,,G ueight Qn the impurity behaviour uas '. in\/gstigated at tnis step. The molibden um impurity uas claaned by using sodium sulfide at 80 C and pH=2.5. Finally, the clean Na_LJD, salution uas used to obtain H,-,ljJO/ and then APT via standart methods. The final steps cansisted af lüü., synthesis by precipitatian of APT and redüction OT (jJO_ by using hydrogen gas at elevated temperatures. in the roasting experiments performed, the optimum temperature ta decrease the sulphur content from 5.2% to 0.7 % uas found ta be 750°C. The optimum air flou rate uas found ta be tuice that of thearetically calcu- lated value far the horizontal rotary furnace used. The optimum quantity of Na_CO_ ta fuse the sulphur- free CalıJG, uas found ta be tuice that af thearetically calculatea value. The temperature far an effecetive fusion uıas 9GD C and the time 1 hour. Tha excess quantity of Na2CG_ dirsctly depends on the fusion temperature. The transition from CaUO, to Na^UO, is faster at higher temperatures but the vaporization of sadium becames mare dramatic at these high temperatures. The so faund optimum temperature of 900 C is derivated from this phonemena. The aqueous leaching conditions also have an effect an the total yield. At certain conditions, if the solid lıquid ratia is less than Ü.4, the solubility yield can be as high as 99 %. Homever, the optimum ratia uas determined ta be 0.2 far easy filtering. The pregnant soiution obtained at this ratio cantains 44.22 g tungsten per liter,uhich is suitable for an effective precipitation of tungstic asid is falloiıiing steps. Purificatian af Na?WO, salutian is vital for the applications of the tungsten metal product. Impurities such as Fe,Al and Si uere cleaned by the addition af MgCl^.SHpO at BG°C and pH=10. This process decreased the 5i content ta trace quantities and the Fe to O.flmg/1 from 0.024 g/1. Houjever, the Al content could be decreased ta 25 mğ/1 fram 0.315 g/1. The resultant Al and the Ma impurities uere cleaned by the addition of Na?S at 80 C and pH= 2.5. The leaching duratian far bath steps uas 1 hour» The resultant Na?UO, solution had 17.4 mg/1 Ma and B.6 mg/1 Al. The results obtained fram the purificatian experiments are given in the falloujing tables.2. TABLE: 2. The Results of The Purif ieation Experirnents. CJuantity nf MgCl2.6H2D Fe mg/1 Al mg/1 x Staich. 3 6.k 214.4 6 5.k 189.k 9 3.8 Bk.D 12 2.2 57.0 15 0.8 20.0 duantitiy of Na_S Ma mg/1 Al mg/1 x Staich. 3 126.2 25 6 Bk,B 19.2 9 49.8 13.0 12 44.2 10.4 15 38.6 9.2 30 17.6 8.6 The tungstic acid was precipitated by same HNG_ and by k times the excess HC1 from the clean Na"U0, solution. This tungstic acid was leached by using 1 kg 28% i\IH3 per 1 kg of UD3 content at 6D C. The APT precipitation then took place during cooling to room temperature. The tungstic oxide can be obtained calci nation of tungstic acid. However, APT precipitation as a',n intermediate step has a vital remove the sodium impurity. importance to The precipitated APT was analyzed at DTA-TGA instruments. Dehydration took nlace within the temperature range of 138-150 C, whereas this tempera ture range for the release of NH_ was 242-265°C. Total weight loss during this calcination was 1 5% The reduction of ÜJD _ was performed according to the values given in the literature at a maximum tempe rature of 1050 C and k hour duration. The duration of the reduction was found to be critical since sub oxides exist in the system. The resultant tungsten metal powder had a composi tion as given below: The powder had a 8.E.T. surface area of 0.22 m2/g and a grain size of 1-5 microns. The sulphur content of the scheelite concentrate was found to have significant effect on the total tungsten yield. If the sulphur content is decreased down ta 0.7 % by roasting, the total tungsten yield can be as high as 9B %. If the sulphur-rich concent rate is used in alkali fusion, the Na-Fe mattephase (Na,FeS.,) forms. The CaUO, has a high solubility in this phase, which decreases the total tungsten yield by entrapping a significant portion of tungsten.