Kalkopirit cevherinin bakteriyel özütleme yöntemi ile değerlendirilmesi

Abstract

Bu çalışmada Yozgat-Akdağ yöresinden alınmış olan kalkopirit cevheri örneklerinin Thiobacillus- ferroxidans türü bakterilerle özütlenmesi gerçekleştirilmiş ve özüt- leme işlemlerinde çeşitli parametlerin bakır çözünürlüğü üzerine etkisi incelenmiştir. Bunlara bağlı alarak da düşük tenörlü bakır cevherlerinin, değişik parametreler gözönünde bulundurularak, değerlendirilme alanları araş tırılmıştır. Bunun için önce uygun besiyerleri hazırlanarak, Al manya'dan (DSM-Deutsche Sammlung von mikraorgnismen und Zelkulturen GmbH) aktif kültür alarak getirtilmiş alan bakteriler üretilmiş daha sonra üretilen bakterilerle kalkopirit örnekleri belli sürelerde özütleme işlemine tabii tutulmuştur. Özütleme deneyleri, çalkalamalı bu banyosunda 250ml' lik erlenmayerler de sabit sıcaklıkta gerçekleştirilmiştir, Gerçekleştirilen deneylerde, karıştırma hızı, cevherin ta necik boyutu ve karışımın pulp yoğunluğu değiştirilmiş ve bunların çözünürlük üzerine etkileri incelenmiştir.

Copper is one of the most useful metals and it has a great importance for many industries; like most other metals, copper came originally from the Earth's hot interior in the form of solutions which were thrust up through cracks in the Earth's crust uihere volcanic or other igneous distrubances shattered the rocks. As they ascended, the -hot liquids or vapours cooled and solidified, often in or close to quartz viens. Sometimes ore solutions penetrated the minute pores in adjoining rocks, or replaced other minerals there as myriads of almost microscopic grains. These are the turn most com mon forms in which copper occurs: In a vein system, as in the so-called lode mines, or disseminated through masses of rock. Mineralization of copper occurs innaturain many different forms. The most common is chalcopyrlte, or "yellow ore", which contains copper, iron and sulphur. About half of the world's known copper reserves exist in this form. The famous Rio Tinto mines of southern Spain,, which have been worked for two thousand years or more contain a great deal of chalcopyrlte and ore also one of the world's important sources of sulphur. Two other valuable copper minerals btr bornite, or "peacock ore" (because of its fine irridercent colours) and chalcocite which has a slaty-gray or sooty appearan ce. Some copper ores have become oxidized, mostlydue to weathering, and these include cuprite, malachite and azurite. All of these, together with the sulphide chalcocite, are, as we have seen, among those found at Timna and which, with the addition of a certain amount of "native copper", provided most of the metal used in ancient times. Vll Native copper, the pure metal found in its metal lic state, and not in chemical combination with other elements, was probably looked upon by early man as a sort of malleable stone and during the transitory period from the Stone Age to the Metal Age-sometimes known as the "Chalcolithic" Period, "chalco" being derived from a Greek word meaning Copper was used it in much the same way as it nad been used stone and shell. It is probable that there were three m ain stages in the development of the art of metal working. In the first stage native copper was hammered into shape; in the second it was melted and cast; and in the third it was smelted from its ores. In some parts of the wolrd there could have been as long as two thousand years between the first and third stages, or even between the second and third, but the discovery where metal could be obtained by smelting, must rank in importance with the discovery of the rneanB to produce fire artificially and undoubtedly marks one of the milestones in man's history. Copper's bright and pleasing appearance was a great attraction to primitive man; he found that it was ductile enough to put into almost any shape that he required and that in the process it became hard enough to be sharpened in to weapons or to be fashioned into other implements of lasting quality. It is not clear at what stage he first realized tha copper is vir tually indestructible but he knew that what ever he made was made to last. With copper and tin being found near to each other in many parts of the world, bronze, an alloy of these two metals, began to be produced, at first accidentally but later under some sort of scientific control which varied the constituents of the alloys to suit the pur poses for which they were required. Copper is present in the Earth's crust mainly in the form of sulphide minerals such as chalcopyrite (CuFeSz), bornite (Cu^FeS,) and chalcocite (Cu2S). The concentration of these minerals in an orebody is low, and typical copper ores contain from 1/2 % copper (open pit mines) to 1 or 2% copper (underground mines). Copper also occurs in the form of oxidized minerals (carbonates, oxides, silicates, sulphates), but to a much lesser extent. Ores containing these minerals are almost always treated by hydrometallurgical methods. Vlll Approximately 90% of the world's primary copper originates in sulphide ores. Sulphides are not readily treated by hydrometallurgical methods (i.e. they are not easily leached) so that the vast majority of the extraction is by pyrometallurgical techniques starting with copper concentrates. The extraction consists of the following four Bteps: a)- Concentration by froth flotation; b)- Roasting (an uptionslstep) ; c)- Matte smelting (in blast,, reverberatory, electric or flash furnaces) d)- Converting to blister copper. A recent development has been the combining of (b) (c) and (d) in a continous process, several configura tion of which have Just reached the commercial stage. The final product of this succession Df Bteps is impure blister copper which must be fire-and electro- refined before it is suitable for fabrication and use. Although copper is most often found in the form of sulphides it also occurs in oxidized form as carbonates oxides, silicates and sulphates, particularly in Africa. These oxide minerals, when present in sufficient quantity in the ore, can be reduced pyrometallurgically to impure copper in the blast furnace and in the past this was dune ' However, the oxide ores present! y being mined are poof in copper for direct pyrometajlurgical reduc tion. In addition, most oxide minerals cannot be effi cientlycancentrated by froth f lotation~and they are, therefore, more effectively treated by hydrometallurgi cal techniques, i.e. by leaching with sulphuric acid fo'lDwed by precipitation or electrowining of the copper from solution. The ore is prepared for leaching by breaking (and crushing and grinding if necessary) to expose a large surface for efficient extraction. It is contacted with a solvent, almost always sulphuric acid, either by gravity in large dumps or heaps of low grade, or by mechanical agitation in vast or thaks (for higher grade ares or concentrates). IX The resulting leach solutions are treated for copper recovery either by precipitation with scrap iron (cementation) or, in the case of concentrated leach solutions byfelectrouinning. The copper obtained by cementation is contaminated with iron and- it is usually retreated in the smelting furnace or converter of a convertional sulphide smelter. The copper obtained by electrowining is melted cast and sent to market for non-electrical use. In this study, the aim was to investigate dissolu bility of copper from chalcopyrite using Thiobacillus f errooxidans. bacteria were received from Deutschl^and DSM-Deutsche Sammlung von mikroorganismen und zellkul- turen GmbH and grown on 9K media so that metabolic products were produced which were capable of leaching copper from a chalcopyrite concentrate. The mechanisms of the process are not completely understood_but it is known that several autotrophic bacteria (bacteria which live in the absence of organic matter) like Thiobacillus.ferrooxidans and Thiobacillus thiooxidans accelerate the leaching reactions to some extent. The active bacteria Thiobacillus ferrooxidans derive their life energy from the reaction: Fe 2+ -»¦ Fe 3+ The bacteria assisted leaching process is believed to take place as fololws: (a) Ferrous ions enter solution by the chemical action of sulphuric acid and oxygen on iron sulphide minerals; CuFeS2 + 40 CuSO^+FeSD^ (b) Thiübacillus ferrooxidans chemically attacks the ferrous ions to form ferric ions: 2FeSQ(i + H2SD^V2D2 _^f^ F. (S", +h2D action (c) The ferric ions act as a leachant for sulphide minearls Fe2(S0i()3 + Cu2S+2D2 > 2FeS0Zt + 2CuSD^ or: 2Fe2(SDit)3+CuFeS2+3D2+2H2D ^ 5FeSD4+CuSD4+ or: 2H2S0it Fe2(SD4)3+FeS2+3D2+2H2D » 3FeS0it+2H2SG4 Reaction (b) and (c) then become cyclic. These reactions can all proceed without the presence of bacteria, but the enzymes of Thiübacillus ferrooxidans catalyse reaction and accelerate the whole leaching process. Most sulphide mine waters contain the active autotrophic bacteria, use of these mine waters for the leach solutions (with dilute H"50, ) automatically provides the initial cultures of bacteria for the leach systems. For optimum bacterial action, the leaching should be carried out under conditions in which the bacteria will flourish, and these are: (a)- a pH between 1,5 and 3,5; (b)- Temperatures between 25° and 4GDC (c)- an adequate oxygen supply (obtained by aerating the solutions or by periodically draining the are pile) XI (d)- Avoidance af exposing the solutions to sunlight, In addition, good contact of the leachant (and its bacteira) with the solids is imperative for rapid leac hing. This contact can be improved to some extent by adding a wetting agent to the leach solution. It can be noted that the cyclic nature of reactions leads to a buildup of H"SD, and ferric i ons. ^?SD4 buildup offsets in part acid losses in gangue materials and thus it is useful, However, the leach solutions tend to become saturated in ferric sulphate and this tends to precipitate as basic ferric sulphate in the leach dumps. For tests with Thiobacillus ferrooxidans, the inorganic_salts medium of Silverman and Lundren was used This medium was called 9K. Chalcopyrite.was used as a source of metal, and contained 12.065% Copper and 33.5% iron. Analyses were measured by atomic absorption spectra photometry. A series of tests were made with the variables such as pulp density, agitation and different, 'sîz¥b;;. Low grade copper sulphide ore was ground and materials passing through a -2GD and -325 mesh was used in the experiments. All the experiments were uniformly carried out in Erlenmayer flasks whish were shaken in 'a shaker with 40-80 revolutions per minute. Incubation temperature was 32 -35DC. Different amount of materials were used in 70 ml medium, the initial pH was adjusted to 2,5 with sulfuric acid, the medium was sterilized and then inoculated 5 ml of the actively grown culture. Each experiment continued 12 days and every 3 days about 1 ml sample »was withdrawn preiodically. xn Results af these experiments were given in the next pages. Microbiological processes have a several advanta ges for metal industries. The microbiological leaching process can be consi dered for the recovery of metals either from lou-grade materials as well as from high-grade sulphide bearing concentrates. This process requires low capital investment and low operating cost. It can be built near to the mining sites. It does nut required either high temperature or pressure. It is easy to operate and control. Furthermore, this process does not compromise in any way the quality of the Environment.