Zonguldak (Kokaksu) bölgesi boksitlerinden alümina üretim parametrelerinin saptanması ve ekonomik değerlendirilmesi

Abstract

Ill ÖZET Alumina ve alüminyum üretiminin cna hammaddesi hidrate - Al^ü^ minerali olan boksit cevheridir. Boksit cevherlerinin ana komponentleri, A1~0~, SiÖ~, Fe~CL, TiO? ve rLÖ şeklindedir. Ay rıca az miktarda organik maddeler, Mn, P, V, Cr, Mi, Ga, Ca, F v.b. de içerirler. Bugün dünya alümina üretiminin % 90'ından fazlası Bayer Teknolojisi ile gerçekleştirilmektedir. Ülkemizde, 1973 yılında işleve geçen Seydişehir Alüminyum Tesislerinde, boehmitik karak terdeki Mortaş, Değirmenlik ve Doğankuzu yatakları boksitleri Bayer Prosesi ile işlenmektedir. Yurdumuzda bu bölgenin dışında, 1960'tan sonra Ki. T. A. ta rafından ağırlık verilen tarama çalışmaları ile saptanmış, çe şitli boksit yataklarımız bulunmaktadır. Her boksit cevherinin kimyasal ve mineralojik yapısı farklı olduğundan, bu farklılık lara bağlı olarak, alümina üretimleri de farklı proses paramet relerinde gerçekleştirilir. Bu parametrelerin saptanması için de laboratuvar araştırmalarına gereksinim vardır. Araştırma konusu olarak saptanan, Türkiye'de işlenmeyen Zonguldak (Kokaksu) bölgesi boksitleri kimyasal ve mineralojik yönden incelenmiş, x-ray faz analizi ile cevherin tipi diaspo- rik olarak saptanmıştır. Araştırma konusu cevherin mineralojik tipinin diasporik oluşu çalışmaya ayrı bir özellik vermiştir. Zira diasporik cevherler, bugün dünyada, endüstriyel ölçüde, Çin, Vietnam, Romanya ve Sovyetler Birliğinde işlenmektedir. A1203 (%53,20) ve Si02 (%3,<S5) içeriği yönünden Bayer Pro sesine uygun olan cevherin modül değeri 14,57, Baz eşdeğeri 47,32IV şeklinde saptanmıştır. Çeşitli kostik molar oranlarında clürrinot çözeltileri ile çeşitli temperatür, basınç ve sürelerde yürütülen deneysel ça- 3 lışmalar, 500 an kapasiteli, mekanik karıştırıcılı, elektrikle ısıtılan, 300 C kontakt termometre, 50 ctü manometresi olan pas lanmaz çelikten reaktörde gerçekleştirilmiştir. Her çalışmada boksit ağırlığının %4'ü kadar CaO ilave edilmiştir. Her deneyde elde edilen kırmızı çamur örneklerinin kimyasal analizleri yapılmış ve faz oluşumlarını izlemek için x-ray diff- raktogramları çekilmiştir. Farklı parametrelerde gerçekleştiri len tüm deneylerde, deneysel alümina verici, boksit tüketimi (t/t alümina) kırmızı çamur üretimi (t/t alümina), NaOH ve Al-C-, kayıpları (kg/t alümina) tayin edilmiştir. Deneysel çalışmalar sonucunda, en ekonomik koşullar; 220 - 5°C'de, 21-33 atü basınç aralığında, 30 dakika sürede, 300 gr/lt Na~0 (a = 3,7 ; a = 1,6) konsantrasyonunda çözelti ile gerçekleştirilen proseste elde edilmiştir. Bu parametrelerde yürütülen çalışmada, teorik alümina veri mi aşılmış (%95, 30), %96,48'lik deneysel verime ulaşılmıştır. Boksit tüketimi 1,928 t/t alümina; kırmızı çamur üretimi, 0,831 t/t alümina, NaOH kaybı, 42,879 kg/t alümina; Al20- kaybı 36,065 kg/t alümina olarak saptanmıştır. Bu parametrelerde elde edilen kırmızı çamurun x-ray faz analizi sonucunda, diaspor fazının tamamen çözünürleştiği, az miktarda Bayer it (4,39 A°), Nordstrandit (2,347 A°), Natrodaun (3,23 ; 2,264 A°), Hidrograssularit (3^1 ; 5,1 A°) ve Bicchulit (2,77 A°) fazlarının oluştuğu görülmüştür. 4,9 ve 2,^2 A dede Portlandit fazı görülmüştür.

SUMMARY THE DETERMINATION OF THE PARAMETERS OF ALUMINA PRODUCTION FROM THE BAUXITE OF ZONGULDAK (KOKAK S U REGION) AND THE' ECONOMIC EVALUATION Bauxite is a nixed rock of aluminium hydroxide minerals with varying amounts of hematite, goethite, kaolinite, anatcse, rutile, ilmenite etc. contaminants. Based on the results of the exploration and that of the investigations of the last few decades one of the most up-to- date definitions was made by Bardossy (1976). According to his definition `bauxite is a sedimentary rock in which the total amount of the Al, Fe ant Ti-oxides and hydroxides is more than 50% with the dominance of Al-minerals. ` On the basis of their mineral composition, bauxites can be listed into the following five types : - Pure gibbsitic bauxites - Gibbsitic bauxites containing quartz - Mixed bauxites (Gibbsitic+Boehmitic) - Boehmitic bauxites - Diasporic bauxites With respect to the selection of the process technology, the mineral composition is of vital importance. Geologically defined bauxites can be industrial or ore- grade types, if they are suitable for economic alumina producing by any actually used technology. The widespread sy stem-commonly used in the USSR is the classification of bauxites on the basis of their `module` define as the ratio of the Al_0, and SiO~ content of bauxite.VI A1?0- % M=-Si02 % « According to the value of the module, bauxite can be classified as follows : Is class bauxite, if the value is : M > 10 II class bauxite, if the value is : M= 7-10 IIIr class bauxite, if the value is : M= 4-7 XL IV class bauxite, if the value is : U = 2.6-4 th V class bauxite, if the value is : M< 2.6 Generally the bauxites are ore-grade for the Bayer-techno logy with a module 7 or more and with 40% of Al-O^-content or more. Based on the experiences of the alumina plants some parts of the chemically analysed Al-0, content can never be recovered. This Al-O-, content is two times (in some cases three times) higher than that of the reactive SiO- content. Based on these, the formula of the Basic Equivalent or Bev can be worked as follows : Bev = Al20gt - 2Si02% or : AljOg*. - 3Si02% It is the Bayer-technology that is used worldwide in the industrial processing of the bauxites. More than 90% of the world's total alumina is produced by this technology. This technology involves great demands on the investigation and analy sis. The composition of bauxite to be processed, the efficiency of digestion, moreover the getting injto solution of the conta minants should be known.VII The most important operations in the Bayer Process are as follows : crushing the bauxite (wet grinding in the presence of the digesting liquor is the usual modern practice) ; digestion (at a pressure of 1 to 40 atmospheres and temperatures of 100 to 250 C or even higher) in continuous digesting lines that generally consist of autoclaves and in sometimes of simple tanks ; dilution of slurry obtained after digestion; separation of the non-digested residue (red mud) by settling and washing in counter flow decan- tation ; followed by filtration ; further purification of the saturated sodium-aluminate solution by filtration, cooling and crystallization (decomposition) in presence of seed alumina ; filtration and washing of the product ; calcination at 1,100 to 1,200 C ; and recirculation of the spent liquor to the wet grindinc or to the digestion stages after evaporation and making up with fresh caustic soda to compensate for any losses. The total ore reserve in Turkey is determined by M.T.A. as 430 million tons. In our country the alumina production is only made in Seydişehir Alumina Plant with Bayer Process. In the mentioned plant, the alumina production is made with boehmitic bauxites from the regions of Mcrtaş, Doğankuzu and De ğirmenlik. Since each baxite reserve has different chemical and mine- ralogical composition, the economical investigation must be made according to characteristics of the ores. The other bauxite reserves in Turkey apart from the region of Seydişehir are not investigated from the point of chemical, mineralogical composition and production of alumina.VIII The aim of this study is the evaluation bauxite reserve of Zonguldak (Kokaksu region) in respect of alumina production end the determination of technological parameters depending on the quality of bauxite. The representative samples arriving from the mines of Kokak su region has been crushed, ground and sieved according to ASIM E- 11 in order to extract its Al-O, content with high efficiency. According to the results of the chemical and qualitative phase analysis, the type of bauxite which is investigated has been determined as diasporic. Since the ore is diasporic, 4% CaO has been added to each digestion test. The digestion tests for determining the optimum parameters 3 have been carried out in steel autoclave of 500 cm capacity, equipped with mechanic stirrer, and by direct electric heating. The digestion tests have been made with sodium-alurninate solu tions at different caustic molar ratios to get A1?0~ content of bauxite into solution at contant temperature and pressure. At the end of each digestion test, aluminate liquor has been separated from the red mud by the aid of centrifuge. After filtrating and washing, red mud samples have been dried on 110°C for a night and ground minus 100 y for chemical analysis and minus 63 y for x-ray investigation. The following chemical components have been determined in the red mud samples : '; L.0.1. Si02 Fe203IX Al2°3 Ti02 CoO No20 c X-Ray diffractograms have been taken by x-ray instrument- DPOH-1. From the results of chemical analysis of bauxite and red muds, the actual recovery of alumina, specific bauxite consump tion, specific red mud production and the bound Na^O and Al^O^ losses have been determined for each of parameter. According to the results of chemical and mineralogical phase anolysis of the red muds, in experiment 19 we investi gated that the actual alumina recovery has been exceeded to the theoretical one. As shown from the x-ray diffractogram of the red mud pro duced from this experiment, the diaspor phase has been entirely got into solution. ' From the point of economy, the optimum parameters have been gained in this experiment. The above mentioned experiment has been carried out at the parameters which are pointed out below : Temperature 220 * 5 C Pressure 21-33 atm. Digestion time 30 minutes Caustic molar ratio of digestion liquor 3.7Required molar ratio of aluminate liquor 1.6 Caustic Na~0 content of digestion liquor 300 g/1 In this experiment the values that influence the economy f the process, have been determined as, the experimental A190~ recovery, 96.48% ; bauxite^consumption, 1.928 t/t alumina ; red iud production, 0.831 t/t alumina ; the bound Na-O and Al?0_ losses, 42.879 and 36.065 kg/t alumina, respectively. o m