Oksitli Bakır Cevherlerinden Hidrometalurjik Yöntemle Bakır Sülfat Kristalleri Üretimi

Abstract

Bakır, gerek metalik halde gerekse de çeşitli bileşikleri halinde günümüzde birçok alanda yaygın olarak kullanılmaktadır. Eski çağlardan bugüne kadar bakır, dünyada en çok kullanılan metalerden biri olmuş ve önem bakımından demir ve alüminyumdan sonra üçüncü sırada yer almaktadır. Elektrik ve ısı iletkenliğinin çok iyi olması, aşınma ve korozyona karşı dayanıklılığı, soğuk ve sıcak olarak işlenebilme kolaylığı, parlak ve güzel rengi ve birçok metalle kolay alaşım yapabilmesi nedeniyle kullanım alanı çok geniştir. Özellikle elektrik ve tesisat kabloları, otomotiv sektörü, beyaz eşya sektörü ve elektronik sektöründe geniş bir kullanım alanına sahiptir. Dünyada bakır üretimi, sülfürlü ve oksitli bakır cevherlerinin madencilik yöntemleri ile çıkarılması, zenginleştirilmesi ve değerlendirilmesi ile yapılmaktadır. Genellikle pirometalurjik yöntemlerle üretilmekte olan bakır, oksitli ve tenörü düşük bir cevher söz konusu ise hidrometalurjik yöntemlerle de üretilebilmektedir. Dünya geneline bakıldığında bakır üretiminin yaklaşık %80’i pirometalurjik yöntemler ile gerçekleşmekte ve %20 civarında ise hidrometalurjik yöntemler kullanılmaktadır. Bugün hidrometalurjik yöntemlerle bakır bileşikleri üreten birçok tesis bulunmaktadır. Oksitli bakır cevherlerinden bakır üretiminde yaygın olarak kullanılan yöntemlerden birisi de sülfürik asit liçidir. Bu çalışmada bakır minerali olarak sadece malahit içeren bir oksitli bakır cevherinin sülfürik asit çözeltilerinde liç koşulları incelenmiştir. Liç deneyleri, 250ml’lik beherler içersinde, manyetik karıştırıcılar yardımı ile yapılmıştır. Katı-sıvı oranı, asit konsantrasyonu, karıştırma hızı, çözümlendirme süresi ve sıcaklık gibi parametreler göz önünde bulundurularak yapılan liç deneylerinden sonra filtrasyon işlemi ile katı-sıvı ayırımı yapılmış ve çözeltiler 250 ml’lik balon jojelere depolanmıştır. Liç kinetiği çıkarılmıştır. Çözünme kinetiğinin matematiksel metodu aşağıdaki gibi logaritmik bir fonksiyon olarak tanımlanmıştır; y = k ln(x) +b Bu proses için aktivasyon enerjisi 2,1 kJ/mol olarak hesaplanmış ve çözünme mekanizmasının difüzyon kontrollü olduğu ortaya konmuştur. Liç deneylerinden sonra, empirüte giderme işlemi yapılmış ve buharlaştırma yöntemiyle bakır sülfat iyonları bakır sülfat 5 hidrat şeklinde çöktürülmüştür. Çöktürülen bakır sülfat tuzu oda sıcaklığında bir gün boyunca kurutulduktan sonra X-Işınları difraktrometresi analizi ile %99,1 saflıkta bakır sülfat 5 hidrat elde edilmiştir.

Copper, the red metal, apart from gold the only metallic element with a color different from a gray tone, has been known since the early days of the human race. It has always been one of the significant materials, and today it is the most frequently used heavy non-ferrous metal. The utility of pure copper is based on its physical and chemical properties, above all, its electrical and thermal conductivity (exceed only by silver), its outstanding ductility and thus excellent workability, and its corrosion resistance. Copper is one of the most important base metals next to aluminum and zinc. It finds many application areas in both metallic form and also as its various components, such as metallurgy, chemistry, paint and agriculture industries etc. About %80 of the primary copper in the world comes from low-grade or poor sulfide ores, which are usually treated by pyrometallurgical methods. Pyrometallurgical methods are not normally suitable for the processing of low-grade ores. Instead, hydrometallurgical methods are usually preferred for the recovery of copper from these kinds of ores. Today, there are many plants that produce copper compounds using hydrometallurgical processes. In these plants, following hydrometallurgical treatments, ores, which contain appreciable amount of copper, emerge. About %15 of the primary copper originates from low-grade oxidized (oxide) or mixed (oxidized and sulfidic) ores. Such materials are generally treated by hydrometallurgical methods. Copper oxide minerals containing the copper in the divalent state (e.g. malachite (Cu2(OH)2CO3)), azurite (Cu3(OH)2(CO3)2, tenorite (CuO) and chrysocolla (CuSiO3.2H2O)), are completely soluble either in acid or alkaline media. Various studies have been carried out over a long period of time to recover valuable copper from copper oxide ores. Sulfuric acid is generally preferred as leaching agent for oxidized copper ore. In general, the methods reported for the recovery of copper from ores involve two steps; the first one involves dissolving the copper from the ores and the second one is the recovery of the dissolved copper by solvent extraction, cementation or precipitation as copper compounds. The first step is commonly leaching, which may be either acid media or alkaline media. Researchers have been focused on the dissolution of copper from ores using various acid and alkaline media. However, second step is more important regarding recovery of dissolved copper from solution. For these reason, the literature contains numerous studies focused on the recovery and selective separation of copper from solution. The methods capable of separating metal ions from solutions include solvent extraction, cementation, and precipitation as a compound. Both solvent extraction and cementation techniques result in high efficiencies but generally do not ensure a complete purification. Solvent extraction method allows the efficient recovery of metal ions, but the method is not cost effective and not applicable in most media. Leaching is the term applied to the process of recovering a metal from the metal source by a solvent or lixivant, and it is typically the first step of any hydrometallurgical process. In the leaching process, strong acids, such as HCl, HNO3 and H2SO4, are commonly used as the leaching reagents. Sulfuric acid is the preferred lixivant in the leaching of the oxidized copper ores, such as azurite, malachite, tenorite and chrysocolla. Sulfuric acid is the most common reagent in malachite leaching. Dissolution of copper oxide and malachite using sulfuric acid has been studied by many researcher. The dissolution experiments were performed inside a 250 mL Pyrex beaker in a temperature-controlled shaking bath to ensure uniform heat convection at the surface of the beaker. The ground malachite ore was added into the agitated sulphuric acid solution at the required temperature. Solid/liquid separation was performed immediately following each dissolution experiment. The copper content was determined using 0.1 M EDTA as the titrant and murexide as the indicator. The impurities present in the solution were determined using atomic absorption spectrometer (AAS) (Perkin Elmer AAnalyst 800). optimum recovery parameters were determined by evaluating the effects of the following factors: temperature and time, acid concentration, liquid/solid ratio and stirring speed. For each experiment, 50 mL of various sulfuric acid solutions of 0.4-2.0 M and 20 g of ore sample were employed to dissolve the copper incorporated in the malachite ore. To investigate the dissolution behavior of the copper from the malachite ore, a kinetic study was undertaken. The sample was examined by XRD and TGA analysis. The kinetic study of dissolution of copper from malachite ore was investigated. For this purpose, different mathematical model equations are proposed to represent different rate controlling steps. In order to ascertain the appropriate kinetic equation, these results were checked against recovery versus time plot. This plot of experimental data is then superimposed on kinetic models in order to determine which theoretical plot fits the experimental data (plot not shown here). However, neither chemical nor diffusion models were given linearity versus time. These models (i.e. chemical and diffusion models) are unable to explain the dissolution of malachite for the rapid initial reaction and the complete leaching period studied. For this reason “y = k*ln(x) + b” a logarithmic equation was selected as kinetic model. The following model would change linearly with time. In equation, y is the dissolution of copper percentage, x is the leaching time, k is the rate constant and b is the constant coefficient. The activation energy for copper dissolution was calculated to be 2.02 kJ/mol, which indicates that this is a diffusion-controlled process. This is supported by the significant increase in dissolution due to stirring. In the present work, a hydrometallurgical process was developed to recover copper salt from the ore sample. It was demonstrated that the copper incorporated in the ore could be dissolved more than 99%, with the use of dilute sulfuric acid solutions (0.4 M–2.0 M) even under moderate experimental conditions. The activation energy of copper dissolution was calculated to be 2.02 kJ/mol, which indicates that this is a diffusion-controlled process. These results were confirmed in the experiments used to investigate the effects of shaking rate and temperature. The proposed process avoids environmental problems and allows for the non-hazardous hydrometallurgical recovery of copper from the malachite ore.