Etibank Üçköprü krom zenginleştirme tesisi artıklarından küçük boyutlu kromitin zenginleştirilmesi
Concentration of fine chromite tailings from Etibank Üçköprü gravity concentration plant
Yazar: ALİ GÜNEY
Danışman: PROF.DR. GÜVEN ÖNAL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü
Derece: Doktora, 1990
Konu: Maden Mühendisliği ve Madencilik = Mining Engineering and Mining
Dizin: Cevher zenginleştirme = Ore dressing ; Flotasyon = Flotation ; Kromit = Chromite

Özet:
ÖZET Etibank üçköprü Kron İşletmesi Karagedik Krom Zenginleştirme Tesisinin 100 yıla yakın bir süredir stoklanan artıklarını değerlendirmek amacıyla, stoklardan karelaj yapılarak belli aralıklarla sondaj numuneleri alınmış ve yapılan analizler sonucunda da stokların ortalama Cr içeriğinin % 12 olduğu, toplam stok miktarının da yaklaşık 800 bin ton olduğu tesbit edilmiştir. Zenginleştirme deneylerine esas olan numune üzerinde yapılan mineralojik incelemeler sonucunda, Kromit, Serpantin grubu mineraller (Krizotil, Antigorit), Olivin, Piroksen, Manyezit mineralleri izlenmiştir. Numune üzerinde yapılan boyut analizleri sonucunda da 0.1 mm üzerinde % 43.8 oranında, % 7.95.Cr203 içerikli malzemenin % 22.5 krom dağılımına sahip olduğu, 0.1 mm boyutu altında ise % 56.2 oranında, % 21.23 Cr203 içerikli malzemenin, % 77.5 krom dağılımına sahip oldu ğu tesbit edilmiştir. Zenginleştirme deneyleri 0.1 mm altındaki boyut grubu malzeme ile yapılmıştır. Deneylerde Sarsıntılı Masa, Yüksek Alan Şiddetli Yaş Manyetik Ayırma ve Flotasyon ile zenginleştirme yöntemleri kullanılmış tır. Yaş Manyetik Ayırma ve Sarsıntılı Masa deneyleri sonucunda, % 39 ve % 52 Cr203 konsantreler, % 23 ve % 30 krom verimi ile elde edilmiş, % 7 ve % 15 Cr203 içerikli malzeme ise artık olarak atılmıştır. Flotasyonla zenginleştirme deneyleri, klasik flotasyon yöntemi nin yanı sıra ince boyuttaki cevherlerin zenginleştirilmesinde yeni teknikler olan Kolon ve Jet Flotasyon yöntemleri kullanılarak yapılmış, ve her üç flotasyon sisteminin karşılaştırılması Dünya'da ilk kez bu tez kapsamında yer almıştır. Her üç flotasyon yönteminin laboratuvar ölçeğindeki modelleri üzerinde saptanan optimum flotasyon koşulları, daha sonra pilot ölçek teki sistemler üzerinde denenerek, zenginleştirme özellikleri tesbit edilmiştir. Pilot ölçekli klasik, Kolon ve Jet Flotasyon devreleri ile yapı lan deneyler sonucunda, Klasik Flotasyon deneyinde; % 32.8 oranında, % 41.56 Cr203 konsantre, % 61.6 krom kazanma verimi ile elde edilmiş- Kolon Flotasyonunda % 1 8.5 oranında, % 46.18 Cr2 03 içerikli konsantre, % 40 krom kazanma verimi ile Jet Flotasyonunda ise, % 29.6 oranında, % 43.09 Cr2 03 içerikli konsantre, % 64.2 krom kazanma verimi ile elde edilmiştir. Yapılan pilot ölçekli flotasyon deneyleri sonucunda, Jet Flotas yon yönteminin, Klasik ve Kolon Flotasyon yöntemine oranla, gerek flo tasyon kapasitesi, gerek verim açısından üstün olduğu, Kolon Flotasyon yönteminin ise, diğer iki yönteme oranla daha selektif olduğu saptan mıştır.

Abstract:
SUMMARY CONCENTRATION OF FINE CHROMİTE TAILINGS FROM ETÎBANK ÜÇKÖPRÜ GRAVITY CONCENTRATION PLANT Chromium was discovered in 1797 by Louis Vauguelin, a French che mist. Although it occurs in many minerals, it can be only be extracted economically from chromite, which belongs to the spinel group of mine rals. Chromite deposits occur as stratiform and podiform (Alpine). Stratiform deposits have a homogeneous structure and uniform chemical composition compared with podiforjn. The Cr203 content is low (30 to 40 %) and iron oxide content is high (25 to 30 %). Alpine chromite deposits are observed as lenticular disseminated ore with transitions to banded ore. They contain a lot of Cr203 (55 % ) and little iron oxide (15 to 20 %). Chromite is used in four different fields based on their differ ing properties; as metallurgic chromite: Cr203 min 46%, Cr/Fe ratio min.2, as chemical chromite: Cr203 up to 46 %, Cr/Fe ratio min. 1.5 to 2.1, as refractory chromite: Cr203 + A1203 min. 60 %, A1203 min. 20 % and as casting sand: Cr,0, min. 14 %, Fe 0 max. 26 %, SiO, max. 4 %, CaO max. 0.5 %. Turkey is one of the leading countries in the world in the pro duction of chromite, also in chromite reserve with a total of 137.1 million tonnes. Turkey occupies the 5 th place in the world. Chromite deposits in Turkey are of Alpine (Podiform) type and generally occur in the shape of lenses. Mineralization can be observed as disseminated, banded leopard and massive forms. The production in Turkey was 960.000 tonnes in 1988, the distribution being 786.000 tonnes of lump ore with a grade of 36 % Cr203 and further 180.000 tonnes of chromite concentrate. In addition to 48 % of Cr20,, 60.000 tonnes of ferrochrome, and 50.000 tonnes of chrome chemicals were produced 80 % of the ore production was exported and the remaining quantity was consumed domestically. In three years time, the lump ore production is planned to reach a figure of 1 million tonnes per annum, 350.000 tonnes for concentrate and " 150.000 tonnes for ferrochrome. In Turkey there are 19 chromite concentration plants where gravity concentration methods are applied (Stripa), Jig, Humpreys, Spirals, Shaking Tables andMagnetic Separations. The coarse ore processing in chromite plants is accomplished through hand picking, stripa or jigs, In the fine sizes of minus 1 mm, shaking tables, spirals or magnetic separation are used, whereas VIfractions finer than 0.1 mm are treated by flotation and wet magnetic separation. The tailings in Etibank üçköprü Chromite Concentration plant in Karagedik have been stockpiled for 100 years. These stockpiles are drilled at certain intervals and samples have been taken to determine the Cr203 grade. The Cr203 content in the first stockpile was found tobe 9.47 % while the second stockpile assayed 13.11 %. The amount of chromite in the stockpiles is about 1 millions tonnes. The samples used in to investigate the possibility of upgrading chromite samples from the second stockpile assayed as 15.15 % Cr203, 7.50 % FeO, 6.05 % A1203, 28.30 % SiQ,, 31.50 MgO and 0.3 % CaO. X-ray diffraction and X-ray fluoresence methods were applied to determine mineral composition of concentrate, middlings, tailings. The mineralogical characterization conducted on samples revealed that chro mite occurs in serpentinite group- minerals (chrysotile, antigorite), olivine, pyroxene, magçıesite, tremolite, talc and opal. The results of the screen analysis on the second stockpile samp les, showed thats the amount of chromite on plus 0.1 mm size range was found to be 43.8 % by weight with 22.5 % Cr203 distribution and assayed 7.95 % Cr203. On the other hand, the amount, Cr203 distribution and content on minus 0.1 mm were found to be 56.2 %, 77.5 % and 21.23 % respectively. In the minus 0.1 mm particle size range, the sub-sieve material (-0.038 mm) amounted to 55.7 % with 24.25 % Cr203 content. High intensity wet magnetic separation and slime shaking table were used on minus 0.1 mm size range. The concentrates assayed 39 % and 52 % Cr203 with 23 % and 30 % Cr2 03 recoveries respectively. The tailings were determined as 7 % and 15 % Cr203 with recoveries of 10 % 36 % respectively. As the treatment of fines below 0.1 mm creates problems in gravity concentration processes, preliminary flotation tests were conducted to see the possibility of utilizing the flotation process in the fine size range. Various collectors and modifiers as a function of pH were tested to achieve the optimum conditions. The best results were obtained when a mixture of collectors, F-3635 + SM-15, F-443 + Unitol-1090, OMC-377 + SM-15 was used in flota tion. The performance data in terms of reagent consumption and selec tivity demonstrated that the collector mixture, such as 0MC-377 + SM-15 yielded the optimum result, both being modified fatty acids. Zeta potential measurement on pure chromite samples in the absence and presence at various cations were performed in order to identify the mechanisms involved in the flotation of chromite. The effect of Ca*2, Mg2, A!*3, Cr3 cations on the zero point of charge of chromite was determined at different concentrations. The adsorption density of 0MC-377 and SM-15 collectors used in the flotation test were determined by means of infrared spectroscopy. VIIThe conventional flotation tests with OMC-377 + SM-15 mixture were performed as a function of pH, collector and Na2Si03 concentrations and conditioning time. The systematic flotation tests on the chromite showed that pulp density; 20 %, pH: 10.3 - 11.0, Na2Si03 : 4000 gr/t, OMC-377 + SM-15: 1200 gr/t and 0MC-377/SM-15: 0.7: were optimum. The conventional flotation tests carried out at the optimum con ditions produced a concentrate containing 41.58 % Cr203 with 20.5 % weight and 42 % Cr203 recovery and the tailings with 13.11 % Cr203 content and 27.5 % recovery. Middlings with 16.09 % Cr203 content were also obtained at the amount of 38.5 %. Conventional flotation cells are sometimes not ideal for separa tion of valuable minerals from gangues because of turbulance and a lack of bubble size control, especially with ultrafine sized materials. As an alternative, column flotation has been introduced intermit tently since the early 1960's, most of the column flotation work has been done on coal, iron one, graphite, glass beads, copper-molybdenum ore. Column flotation provides quiescent separation conditions because of the lack of turbulence caused by mechanical impellers and allows for coantercurrent flow of bubbles and pulp with addition of washwater in the froth to inhibit short circuiting of feed material to the con centrate in continuous operation. Column flotation is more energy efficient, requires less space, and can be automated, thus providing tight process control. Bubble size is a known factor in flotation efficiency because as bubble size decreases, the surface area per unit volume increases. Therefore, more surface area is available for attachment at any given air volume. Bubbles cause a wake as they rise and draw unattached material with them. Thus, the larger the bubble, the faster the rise rate and the greater the amonut of material drawn up with the bubble. Bubble-particle hydro dynamics suggest that fine particles may never collide with large bubbles because the fine particles, being low in mass, cannot deviate from the stream line and are swept away as the bubble passes. Systematic column flotation experiments using laboratory type column flotation cell were performed. In these tests, OMC-377 + SM-15 collector mixture was used and the pulp density, pH, the concentration of OMC-377 and SM-15, the amount of Na2Si03 were studied. The best column flotation conditions were determined as pulp density: 10 %, pH: 10-11, Na2Si03 : 3000 gr/t, 0MC-377 + SM-15: 1200 gr/t, OMC-377/ SM-15: 0.2. At the optimum conditions, the column flotation tests produced a concentrate containing 48 % Cr203 with the amount of 16.7 % by weight and a chrome recovery of 40.5 %, tailings with the amount of 51.6 % by weight contained 8.09 % Cr203 and distribution of 20.8 %. The column flotation test resulted in middlings containing 24.50 % Cr203 with the amount of 31.7 % by weight. Flotation is commonly applied for cleaning the slurries. However, with increased proportions of particles in the size range of approxi mately -0.020 mm the selectivity of this cleaning process decreases. when the conventional flotation method is utilized. In the Institut VIIIfür Chemeingenieurtechnik of the Technical University of Berlin a new flotation apparatus has been developped based on the free jet principle and is able to produce good cleanning results in the critical range of particle sizes below 0.020 mm. Jet Flotation apparatus consists of two zones; one of the zones gives maximum turbulence. Generation of air bubles and loading same with solid particles, in the second zone is the zone of quietened flow, laminar buoyancy of loaded bubbles to the surface of the pulp. In the jet flotation, the conditioned feed pulp is pumped through the nozzle pipe. Upon iffluxing from a nozzle, the air is entrained by the feed jet and beaten into the pulp when the feed jet impringes upon the surface of the pulp. This causes a state of strong turbulence in the encasing tube, thus offering favourable conditions for contact between the air bubbles and the solid particles, which is of primary importance for attachment and adhesion of solid to air bubbles. The penetration depth of the water-air-jet into the pulp depends on the initial pressure exerted by the jet on the pulp surface. The immersion depth of the encasing tube can be so adjusted so as to' attain outside of the tube a laminer flow that allows an undisturbed buoyancy of the loaden bubbles to the pulp surface. The operating conditions of the jet flotation process are as follow: Injection pressure: 0.8-1 kg/cm, penetration depth of injec tor: 0.3 m-, immersion depth of the encasing tube: 0.2 m. Other conditions such as pulp density, proportion of the 0MC-377 and SM-15, pH, the amount of Na,Si03 were systematically studied. The optimum conditions of the jet flotation were determined as: pulp density: 10 %, pH: 11.0, Na,Si0, : 4000 gr/t, 0MC-377 + SM-15: 1200 gr/ton, OMC-377/ SM-15: 0.2. The optimum jet flotation conditions produced a concentrate con taining 43.56 % Cr20, with the amount of 8.0 % by weight and 17.3 % chrome recovery, tailings contained 9.18 % Cr203 with the amount of 34.6 % by weight and 15.8 % distribution. The jet flotation tests, yielded a middling containing 23.32 % Cr203 with the amount of 57.4 % by weight. The conventional pilot flotation tests were carried out at the optimum flotation conditions obtained from systematic conventional flotation test, a chromite concentrate containing 41.56 % Cr203 at the amount of 32.8 %, by with 61.6 % chrome recovery was obtained and tailings contained 12.62 % Cr203 at the amount of 67.2 % by weight with a distribution of 34.8 %. Three pilot plant size colums were designed and constructed using plexiglass with the dimensions of 13 x 13 cm cross-section and 2.5 m high. The colums were composed of five sections. Each Section has a length of 30 cm. The bottom sections is used for bubble generation 3 columns were connected in series. Column parameters such as feed injection, tailings removal and recirculation, air and wash water injection, column height and bubble type could also be varied. The clear plexiglass construction allowed for visual monitoring. IXThe column pilot flotation tests carried out at the optimum conditions yielded a chromite concentrate containing 46.18 % Cr203 at the amount of 18.5 % by weight with 40 % chromite recovery and tailings contained 15.75 % Cr203 with the amount of 81.5 % by weight and a dist ribution of 60 %. The jet flotation pilot tests carried out at the best flotation conditions from a series of jet flotation tests on the laboratory scale, resulted in chromite concentrate containing 43.09 % Cr203 with the amount of 29.6 % by weight and 64.2 % chromite recovery." The tailings had 10.10 % Cr203 content in the amount of 70.4 % by weight with a 35.8 % distribution. In this thesis laboratory and pilot plant scale flotation tests on fine size chromite using conventional, column and jet flotation methods have been compared:. The results have shown that the performan ce of jet flotation method is more favorable than those of conventional and column flotation from the point of recovery and capacity. Although thecolumn flotation yielded concentrates {% 46.18 % Cr,03) higher than those obtained by the other two methods. On the other hand, the reco very was slightly lower than the'ones with conventional and jet flota tion.