Tuz Gölü'nden solvent ekstraksiyonuyla lityum eldesi
Solvent extraction of lithium from Tuz Lake
Yazar: MERVE ÖZTÜRK
Danışman: DOÇ. DR. MEHMET ŞEREF SÖNMEZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Elektrokimyasal olarak aktif bir metal olan lityum, yüksek redoks potansiyeli ve yüksek spesifik ısı kapasitesi özelliklerinden dolayı modern elektrik araçlarının gelişiminde anahtar bir element rolündedir. Üstün özelliklerinden dolayı önceleri gelişmiş elektronik cihazlarında güç kaynağı olarak kullanılırken ikincil lityum iyon piller olarak anılan teknolojinin geliştirilmesiyle cep telefonlarında ve diz üstü bilgisayarlarda kullanılmaya başlanmıştır. Günümüzde, dünya pazarında, şarj edilebilir pillerin yaklaşık %37'si lityum iyon pilleridir ve kullanımı sürekli artmaktadır. Lityum endüstriyel olarak, lityum karbonat, lityum hidroksit, lityum klorür ve bütil lityum bileşikleri şeklinde üretilmektedir. Enerji ve karbon ayak izi, endüstriyel gelişmeler ve çevre duyarlılığı göz önüne alındığında lityumun birincil ve ikincil kaynaklardan verimli ve hızlı bir şekilde kazanılmasını sağlayacak yöntemlerin geliştirilmesi önem arz etmektedir. Bu yüzden ülkemizde üretimi gerçekleştirilmeyen lityumun yerli kaynaklardan üretilmesi hedeflenmelidir. Bu kapsamda; lityumun kazanımına dair uygulanan yenilikçi üretim yöntemleri üzerine araştırmalar yapılarak uygun yöntemin solvent ekstraksiyonu olduğu öngörülmüştür. Bu çalışmada; Tuz Gölü'nde bulunan lityumun elde edilmesi amaçlanmıştır. Tuz Gölü'nden lityum üretilmesindeki en temel zorluk yüksek Mg/Li oranıdır. Dolayısıyla öncelikle göl suyunda bulunan empüritelerin uzaklaştırılmasına yönelik deneysel çalışmalar gerçekleştirilmiştir. Ardından, Tuz Gölü'nden lityum kazanımı için solvent ekstraksiyon yöntemi uygulanmıştır. Bu yöntemde TBP (Tri-butyl-phosphate), MIBK (Methyl-iso-butyl ketone) sistemi kullanılarak ekstraksiyon işlemi yapılmıştır. FeCl3 ise yardımcı ekstrantant ajanı olarak tercih edilmiştir. Sadece Li seçiciliği üzerine değil; Mg ayrımı için de Cyanex 272 ve D2EHPA organikleri tercih edilmiştir. Aynı zamanda yükleme verimini artırmaya yönelik iki farklı organiğin kombinasyonuyla da sinerjik SX sistemleri oluşturularak çalışmalar yapılmıştır. Aliquat 336 ve Versatic 10 organikleri de yine Li seçiciliği için kullanılarak yüksek verimle lityum karbonat eldesi üzerine çalışmalar yürütülmüştür. Yapılan çalışmalarda; empüritelerin giderilmesi amacıyla uygulanan solar buharlaştırmanın verimli olmadığı görülmüştür. TBP'nin, farklı seyrelticiler (Kerosen, MIBK) ve FeCl3 kullanılarak uygulandığı SX sistemlerinde Li seçiciliği üzerine etkin bir ayrım sağlanamamıştır. Bu nedenle Cyanex 272 ve D2EHPA ile yapılan SX sistemlerinde Mg ayrımına dair çalışmalar gerçekleştirilmiştir. Buna göre; pH 5,5 değerinde magnezyumun organiğe yüksek oranda yüklendiği; lityumun ise yok denecek kadar az yüklendiği görülmüştür.  Yapılan diğer SX sistemlerinde istenilen verime ulaşılamadığından  Cyanex 272 ve kerosen ile gerçekleştirilen SX sistemi üzerinde uygun yükleme ve sıyırma  parametrelerinin belirlenmesi için çalışmalar yürütülmektedir.

Abstract:
Lithium, an electrochemically active metal, has huge importance in terms of a lot of application areas such as ceramic products, glass products and Lithium Ion Batteries. Due to its superior properties such as high redox potential and high spesific heat capacity, it was previously used as a power source in advanced electronic devices. With the development of the so-called secondary lithium-ion batteries, it has started to be used in mobile phones and laptops. Today, in the World market, approximately 37% of rechargeable batteries are lithium-ion batteries and usage of them is constantly increasing. Besides, in the industry of nuclear and arms, lithium will be preferred because of the energy storage property. Lithium is used with other salts in the medicine, cosmetic, paint and industrial products. Because of the high reactivity of Li, production of it from mineral and clays is very difficult and it causes high energy consumption and cost. Besides, pollution issues has been observed. So, brines with high lithium content have been preferred as sources of Li. On the other hand, waste batteries are also used for production of Li as recovery process.
At present, 80 million tonnes of lithium resources have been identified globally. Brine reservoirs form the 66% of global lithium reserves. When compared the countries in terms of lithium reserves, Chile has the largest lithium reserves. Especially, in the Salar De Atacama area, 1400 ppm lithium is found. Considering the energy and carbon footprint, industrial developments and environmental sensitivity, it is important to develop methods that will enable lithium to be obtained efficiently and quickly from primary and secondary sources. So, it should be aimed to produce lithium, which is not produced in our country, from domestic sources.
In Turkey, some boron areas in Balıkesir and Bursa have the sources of lithium as by product.  Studies for the  recovery of Li from this areas have been continued. According to previous studies for salt lakes in  Turkey such as  Tuz lake, Tersakan lake, Ağgöl etc. , the highest amount of lithium was found in the Tuz lake. But, it has huge amount of Mg so, the separation of Mg and Li is very difficult in terms of both economically and production method. Therefore, there is no study for the recovery of lithium from Tuz Lake.
In this study; It is aimed to obtain lithium in Tuz Lake. The main difficulty for producing lithium from Tuz Gölü is the high Mg / Li ratio. Lithium is industrially produced in the form of lithium carbonate, lithium hydroxide, lithium chloride and butyl lithium compounds. 
According to Mg/Li ratio, production method of lithium from brines can be changed. If the Mg/Li ratio is lower than 6, conventional solar evoporation process is applied for obtaining the Li. But, if the ratio of it is higher than 6, new methods are needed.  According to literature research, there are new methods for the separation of Li from high Mg/Li ratios in brines. These latest advances are adsorpsion, membran methods, electrochemical methods, reaction-coupled separation technology and solvent extraction. 
 
Adsorption is the holding of the material in the interface. Macro transport, micro transport and sorption are the steps of adsorpsion. The most important factor is adsorption material. For lithium, aluminum salt adsorbents and magnesium-titanium based lithium ion sieve adsorbents are used. Membran methods are ultrafiltration, nanofiltration and electrodialysis. They depend on pressure and electric potential.
In the electrochemical methods, lithium ion capture system and rocking-chair type battery system are found. The parts of this method are electrolyte, anode, cathode and auxiliary membranes. Reaction coupled separation technology depends on chemical reaction and physical separation. In this method, separation of Mg is provided based on atomic lattice structure and ion selectivity. Aluminum-based double-layer hydroxide structure is used. 
When compared these methods, solvent extraction is a highly preferred method for lithium because of high selectivity, industrial applicability and economically when considering high efficiency and purity. In the lithium recovery by the extraction method, impurity ions remain in aqueous phase, lithium ions remain in the organic phase. Secondly, back-extraction of Li from organic phase are applied by using stripping tests. Additionally, recirculation of organic phase is made for reuse in the extraction. In the other step, purification of lithium-rich solution is applied to get pure lithium solution. Especially, evaporation is applied for the purification. Dissolved impurities are precipitated as solid particles. Consequently, Li2CO3 is obtained by adding of sodium carbonate as precipitating agent.
When literature research are examined for SX of lithium; TBP, TOPO, HBTA, Aliquat 336 and Versatic 10 are used as organics with different diluents such as kerosene, MIBK, chloroform. The parameters of SX are found as pH of brines, Fe/Li mol ratio, O/A ratios, temperature, concentration of organics and single or multi stages. According to literature research for high Li selectivity TBP-kerosene and FeCl3 system and TBP-MIBK and FeCl3 were applied. FeCl3 was used as co-extraction agent for TBP system. MIBK can be used as both organic and diluent for the SX of Li. However, Aliquat 336 and Versatic 10 organics were also used for Li selectivity, and studies were carried out to obtain lithium carbonate in high yield.
Not only in terms of Li selection; Cyanex 272 and D2EHPA organics were preferred for Mg separation. At the same time, studies have been carried out by creating synergistic SX systems with the combination of two different organics to increase the loading efficiency. With reference to pH and extraction graphics of Cyanex 272 and D2EHPA, there are spesific pH values are found for the separation of Mg. Besides, operating temperatures and viscosities of them are important factors for efficiency of SX. 
In the studies carried out; it has been observed that solar evaporation applied to remove impurities was not efficient. In SX systems where TBP was applied using different diluents (Kerosene, MIBK) and FeCl3. By using these systems, an effective separation on Li selectivity could not be observed. In the literature researches synthetic salt lakes were used. But in this study real samples of Tuz lake were used. So, some impurities which are not separated can be effective on behavior of this SX systems. For this reason, studies on Mg separation were carried out in SX systems made with Cyanex 272 and D2EHPA. For Cyanex 272, Sx was applied at 50-55°C for arranging of the viscosity. NaOH was used to regulate of suitable pH values for high yield. Different kinds of mol ratios for organic mixtures and O/A ratios for SX systems were calculated and applied. In the studies, it was found that magnesium at pH 5.5 is highly loaded to  
organic; Lithium was found to be loaded negligibly. Since the desired efficiency could not be achieved in other SX systems, studies are carried out to determine the appropriate loading and stripping parameters on the SX system made with Cyanex 272 and kerosene.