Kobaltın alumina içeren fayalitik curuflardaki çözünürlüğünün incelenmesi
The Salubility of cobalt in alumina containing fayalitic slags
- Tez No: 100564
- Danışmanlar: DOÇ.DR. ONURALP YÜCEL
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Alümina, Bakır, Cüruf, Kobalt, Çözünürlük, Üretim, Alumina, Copper, Slag, Cobalt, Solubility, Production
- Yıl: 1999
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: Belirtilmemiş.
Özet
KOBALTIN ALUMINA İÇEREN FAYALİTİK CURUFLARDAKİ ÇÖZÜNÜRLÜĞÜNÜN İNCELENMESİ ÖZET Metal dışı proseslerinde cüruftaki metal kayıpları günümüz metalurjistleri için ilgi odağıdır, özellikle günümüz cevherlerinin metal konsantrasyonlarının azalması ve büyük miktarlarda biriken cüruf yığınları buna nedendir. Bakır curuflanndaki kobalt kayıplarının üretim aşamasında azaltılması, ayrıca üretim sonrası oluşan cüruflardan kobaltm kazanımı için bu metalin özelliklerinin ve yapısının, fayalitik cüruflarla olan davranışlarının bilinmesi gereklidir. Özellikle kobaltın Fe-Co-Cu-S alaşımı ile alumina içeren fayalitik cüruf arasındaki dağılımına etki eden parametreler ne ulusal ne de uluslararası alanda yeterli değildir. Bu çalışmada bilimsel araştırmalara temel oluşturabilmek için farklı miktarlarda kobalt içeren bakır alaşımlarının alumina içeren fayalitik cüruflarla belli atmosfer ve sıcaklık koşullarında dengeye getirilerek kobalt oksidin cürufta çözünme mekanizması araştırılmıştır. Bu çözünme mekanizması kobaltın hem alaşımdaki hem de curufdaki aktivite katsayıları ve aktivite değerlerinin ölçünmesiyle belirlenmiştir. Deneysel çalışmalara öncelikle saf malzemelerden hareketle Cu-Co alaşımları ve FeO-Si02-Aİ203 cürufları hazırlamadan başlanmıştır. Dengeye ulaşmak için gerekli süreyi belirlemek amacıyla % 3.2 Co içeren bakır alaşımları cürufla 1673 K sıcaklık 1.125xl0“8 atm. ve 4.536xl0”10 atm. kısmi oksijen basınçlarında 240 dakikaya kadar reaksiyona sokulmuştur. Optimum süre 120 dak. olarak belirlendikten sonra değişik miktarlarda kobalt içeren bakır alaşımları (% 0.5 - 7 Co) fayalitik cürufla 1673 K sıcaklık ve 1. 125x1ü“8 atm., 2.396xl0”9 ve 4.536xl0"10 atm. kısmi oksijen basınçlarında 120 dak. reaksiyona tutulmuşlardır. Dengeleme deney sonuçlarından faydalanılarak kobalt oksidin cüruftaki aktivite ve aktivite katsayıları hesaplanmış ve cüruftaki kobalt oksit mol oranının aktivite katsayısına karşılık, ycoo = -12.277 Xcoo + 3. 1137 (1) şeklinde ifade edilebileceği saptanmıştır. Bu eşitlikte, çarpan durumundaki mol oranı kobalt oksit aktivite katsayısı üzerinde değer olarak ihmal edilebilir seviyelerde olduğundan (% 4.28 CoO'e kadar) aktivite katsayısı mol oranından bağımsız olarak YcoO = 2.83 ±0.283 (2) şeklinde ifade edilmiş ve sabit değer olarak gösterilmiştir. Elde edilen kobalt oksit aktivite katsayısı literatürdeki daha düşük sıcaklarda yapılan çalışmalarla kıyaslanmıştır. Bu çalışmadaki sonuçlardan yola çıkılarak kobaltın cüruftaki çözünürlük artışının ortamdaki oksijen basıncının ve/veya alaşımdaki kobaltın vııaktivitesinin artışına bağlı olduğu gösterilerek (%Co) = 0. 1 167xP021/2.aco x 106 (3) eşitliği elde edilmiştir. Bu çalışma 1573 K'de yapılmış bir başka çalışmasıyla karşılaştırılarak, kobaltın cüruftaki çözünme artışının kobaltın aktivite ve/veya oksijen basıncıyla arttmakta olduğu fakat sıcaklıkla azaldığı ispat edilmiştir. vııı
Özet (Çeviri)
SOLUBILITY OF COBALT IN ALUMINA CONTAINING FAYALITTC SLAGS SUMMARY Cobalt is the 30th most abundant element on earth and comprises approximately 0.0025% of the earth's crust. Cobalt, a transition series metal with atomic number 27, is a metallic element that is similar to silver in appearance. It occurs in mineral form as arsenides, sulphides, and oxides; trace amounts are also found in other minerals of nickel and iron as substitute ions. Cobalt minerals are commonly associated with ores of nickel, iron, silver, bismuth, copper, manganese, antimony, and zinc. The world's largest cobalt reserves are Zaire, Zambia, Morocco, Canada, and Australia. Together the ores of these countries contain well over one-half of the world cobalt supply. The richest deposits are in Zaire and Zambia. The reserves of Canada and Australia comprise approximately one-fourth of the world supply. Smaller but commercially practical ore bodies also exist in the Russia, Finland, Uganda, and the Philippines. Cobalt is a strategic metal and is a key component in products that require high levels of strength and resistance to heat and corrosion. The largest use for cobalt is superalloys used, for example, to make jet engine parts and gas turbines for pipeline compressors. Consumption of cobalt in the rechargeable battery sector has increased dramatically with the boom in notebook computers and cellular phones. Another large consumer is the chemical industry which uses cobalt for numerous applications such as catalysts for petroleum and chemical processing; drying agents in paints and inks; ground coats for porcelain and enamel; and pigments for ceramics, paints, and plastics. Magnetic alloys require cobalt as do cutting and wear resistant materials such as cemented carbides. The non-ferrous smelting industry is undergoing dramatic changes in order to offset increased production costs and as a result of increasingly stringent regulations governing emission to the atmosphere and the working environment. This has resulted in the development of new processes for the smelting of copper, nickel and lead concentrates, which in the majority of cases require some form of slag cleaning. Process development has been most active in the copper and nickel industry however, significant changes can he expected in the lead industry over the next few years in response to environmental concerns. Metal losses in slags during non-ferrous extractive metallurgical process are of great concern to the metallurgist, especially today as the ores relatively rich in metals are diminishing and large volumes of slags are involved each day in smelting practice. In our country copper extractive slags have a quantity of cobalt depends on ore and/or extractive techniques. IXThe behaviour of cobalt is of economic importance during copper smelting and refining because cobalt enters the smelting circuit and represents a potentially valuable by product. However, the recovery of cobalt can be as low as 45 pet and rarely exceed 60 pet. The recovery depends on the distribution of cobalt between matte and discard slag in the smelting stage and an important factor affecting this distribution is the activity coefficient of cobalt oxide in slag. The cobalt distribution can be used also as a practical indicator of the extent of oxidation within a smelting furnace. A significant proportion of cobalt usually reports in primary matte from a copper or nickel-smelting furnace but is extensively slagged off during the subsequent converting operation, cobalt being more easily oxidised and slagged than nickel and particularly copper. Consequently, cobalt tends to concentrate in converter slag, particularly in slag formed towards the end of the converter cycle, due to the oxidation and slagging (silicate formation) of the metals present in the matte. The standard free energy curves and starts with oxidation of Fe show the sequence of oxide formation clearly, then Co, Ni and finally Cu. Converter slag can be reduced in electric furnaces with coke or coke breeze, to give an alloy or low sulphur matte containing Cu, Ni, Co, Fe and S. Sulphide addition in the form of nickel or copper concentrates, or as pyrrhotite or pyrite assists in collecting the byproduct metal values and also helps form a matte with higher sulphur content which has a lower melting point and is therefore more easily tapped from the electric slag treatment furnace. Typically cobalt may be present in converter slag at levels ranging from 0.3 to 3 %, Co. depending on the ore smelted and on whether all or only the final converter slag is treated, and is reduced to less than 0.2 %, Co in the waste slag. Cobalt recovery increases with the amount of reductant added and with the reduction time in the electric furnace, but iron reduction increases at the same time so that high cobalt recovery is usually combined with high Fe content in the matte or alloy tapped from the electric furnace. This matte or alloy must then the treated usually hydrometallurgically to recover the cobalt. In order to minimize the loss of cobalt at production stage or recycle the cobalt from slag, it is necessary to determine its form and origin. There has been a wide divergence of opinion on the subject of the form of copper slags and there is little data about behaviour of cobalt at copper slags. Aim of this study is to satisfy the lack of data about the solubility of cobalt oxide in slags. Not only this, but also these experiments will be useful for recovery of cobalt from copper smelting slags in our country. The distribution of cobalt between slag and alloy has been previously studied. Smith and Masson equilibrated cobalt silicate melts with Pt-Rh-Co alloys at controlled oxygen pressures and reported an average cobalt oxide activity coefficient of 1.2 relative to the solid, for melts containing around 0.6 mole fraction of CoO at both 1723 and 1773 K. Wang et al equilibrated silica-saturated iron silicate slags with liquid Co-Au and Co-Cu alloys, respectively, and reported the cobalt content of contiguous alloys and slags for temperatures of 1523, 1573, and 1623 K and oxygen pressures of between 10 and 10“10 atm. Activity coefficients for cobalt oxide were calculated from these data by Grimsey and Toguri and summarized by the followingrelationship: Ycoo=l,94 + 0. 123 x (wt per Co) (1) Reddy, equilibrated alumina-saturated iron silicate slags (Fe/SiC<2 of 1.34) with liquid Co-Cu alloys at temperatures of 1473 to 1573 K and reported the infinite dilution activity coefficient of cobalt oxide (relative to the pure liquid) as In ycoO= 19.63-1.298 x 10”2T (2) Reddy and Healy equilibrated liquid Cu-Co alloys with iron-free cobalt silicate slag at 1523 K while Fontana et al reported the solubilities of cobalt in iron silicate slags containing lime that were equilibrated with Cu-Co by levitation at 1623 K and at oxygen pressures of between 10“7 and 10”10 atm. However, the lack of any oxygen pressure measurements in the former case, or alloy compositions in the latter, mistake these data difficult to assess. Katyal and Jeffes determined the activity coefficient of cobalt oxide in iron silicate and ferrite slags through equilibration with liquid Co-Cu alloys at temperatures between 1523 and 1623 K. The levitation melting technique was used and oxygen potentials were controlled by the mixture of CO and CO2 gases for iron silicate slags relatively close to silica saturation (with around 35 wt per silica), the average activity coefficient of cobalt oxide was reported as 1 relative to the pure liquid standard state and independent of the cobalt content of slag up to the maximum of 19 %. In the work of Grimsey and Liu, the solubility of cobalt oxide in silica-saturated iron silicate slags (1.16 to 10.00 wt per) in equilibrium with cobalt-gold-iron alloys (1.10 to 6.52 wt per cobalt) and oxygen pressures of 10'9 and 10“10 atm has been investigated at 1573 K. The activity coefficient of cobalt oxide, yc0o has been calculated relative to pure solid cobalt oxide as stantdard. namely, Ycoo = 0.91 ±0.09 (3) and a relationship derived between weight percent cobalt in slag, Co (wt per), oxygen pressure, P02, and activity of cobalt relative to liquid cobalt, ac0, namely, Co (wt per )=1.32xl06PO21/2aco ± % 10 (4) In this study, the solubility of cobalt in alumina containing iron silicate slags (10 wt per alumina, 47 wt per total iron, 26 wt per silica) were equilibrated with cobalt- copper alloys (0.5 to 7 wt per cobalt) and oxygen pressures of 1.125xl0”8, 2.396xl0“9 and 4.536xl0”10atm. has been investigated at 1673 K. When equilibrium is reached between a liquid Co-Cu alloy an iron silicate slag containing cobalt oxide, and a CO2/CO gas that sets a specific oxygen pressure, the relevant equilibria are [Cokey + C02 = (CoO)sIag + CO (5) CO + l/202= C02 (6) where the brackets represent the metal and the parentheses represent the slag phase, respectively. Iron is also transferred from slag to alloy. xiCo-Cu alloys and alumina containing fayalitic slags were prepared in an Tammann furnace at argon atmosphere, 1673 K about 1 hour. After that, 5 gr alloy and 5 gr slag were put into the alumina crucibles and held at 1673 K in a horizantal, MoSi2 tube furnace and under a stream of purified and dried CO2 -CO gas, controlled at set ratios by flow meters and at a total flow of 600 cm3/min. The temperature was measured by an alumina-sheathed PtRh30/PtRh6 thermocouple placed directly beside the sample, while the oxygen pressure was monitored by a stabilized zirconium oxide solid electrolyte cell placed just beside the sample. After equilibration time (2 hours determined), the samples were quenched into water. Solidified slags were analyzed for Co, Fe, Cu, SİO2 and A1203 and alloys were analyzed for Co, Fe, Cu. The activity coefficient of cobalt oxide in the slag was calculated from the equilibrium Co(i)+ l/202=CoO (S) (7) where the equilibrium constant K\s 4.570 x 103 at 1673 K for the metal-slag-gas equilibrium, Ycoo=(4.57 x 103xPo21/2 x aco)/Xc0o (8) where yc0o is the activity coefficient of cobalt oxide in slag relative to pure solid CoO, Xcoo is the mole fraction of cobalt oxide in slag, P02 is the oxygen pressure in atmospheres, and aco is the activity of cobalt in the alloy relative to pure liquid cobalt. The oxygen pressure was calculated from the C02/CO ratio in the gas through the equilibrium constant was taken as at 4.250x 10+8at 1673 K The calculation of cobalt activity for Co-Cu was calculated from lnYco(cu-co)=(4221/T)Xcu2 (1383-1768 K) (9) Where ya, (Cu-co), activity coefficient of cobalt, T, temparature, Xcu mol fraction of copper. If cobalt metal was present in slag in addition to oxide, then a plot of Co (pct)/ac0 vs PC02/PCO will not pass through the origin. In this work, there were an agreement with previous studies that cobalt at slag was totally as CoO form. In this study, the activity coefficient of cobalt oxide relative to pure solid cobalt oxide was calculated and listed along with data associated with the calculation. The activity coefficient is plotted against mole fraction of cobalt oxide. The activity coefficient appears to decrease slightly with an increase in mole fraction of cobalt oxide, ycoo=-12.277Xcoo+3.11 (10) but the effect was not significant statistically, and the data were described by the mean value: ycoo = 2.83 ± 0.283 (11) XIIwhere the error was calculated at the 90 pet confidence level. Since Co (wt pet) in slag is approximately proportional to Xc0o, a substitution of previous equations with rearrangement shows that a plot of Co (wt pet) vs P02 should be linear through the origin. The plot is shown that the line drawn on the diagram was obtained by regression; namely, (%Co) = 0.1167xPO21/2.acoX 106 (12) This equation quantifies the increase in solubility of cobalt that occurs in slag with either an increase in oxygen pressure or cobalt activity in the system. A study of the solubility of cobalt in alumina containing iron silicate slags at J 673 K in contact with liquid Cu-Co alloys at oxygen pressures of 1.125xl0“8, 2.396xl0”9 and 4.536xl0"10 atm. showed that: (I) The activity coefficient of cobalt oxide was constant and independent of cobalt oxide content up to 4.28 pet in slag. (II) The activity coefficient for cobalt oxide as measured here is significantly higher than as calculated from other studies because of higher temparature. (DT) The solubility of cobalt increased in slag with both an increase in the oxygen pressure and/or activity of cobalt in the system but decreased with increase in temperature. XIII
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