Potasyum feldspat cevherinden potasyum kazanımı
Potassium recovery from potassium feldspar ore
Yazar: METE TAYHAN SERDENGEÇTİ
Danışman: DOÇ. DR. MURAT OLGAÇ KANGAL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Cevher Hazırlama Mühendisliği Ana Bilim Dalı / Cevher Hazırlama Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Maden Mühendisliği ve Madencilik = Mining Engineering and Mining

Özet:
Feldspat mineralleri seramik ve cam endüstrisinin ana hammaddelerinden biridir. Oldukça geniş pazarı olmasının yanı sıra Türkiye maden ihracatı kalemlerinde kömürden sonra 2. sıradadır. Türkiye coğrafyasında feldspat mineralleri oldukça fazla bulunmaktadır. 
Bu yatakların rezerv olarak değerlendirilebilmesi için demir ve titan içeriklerinin belirli bir seviyenin altında olması gerekmektedir. Bu seviyenin altında olmadığı için kullanılamayan birçok feldspat cevheri yatağımız da mevcuttur ve potasyum feldspat olarak da adlandırılan mikroklin minerali de bunların içinde yer almaktadır. Kırşehir masifinde seramik ve cam sanayiinde kullanılacak şartları sağlayamayan kaynaklar geniş bir yer kaplamaktadır. 
Potasyum feldspat mineralinin içerisindeki potasyum varlığı, literatürde yapılan çalışmalar sonucunda, gübre sanayiinde kullanılmak üzere potas olarak üretilme imkanı ortaya konulmuştur. Potas gübresi, bitkilerin gelişirken ihtiyacı olan 3 temel elementten biri olan potasyum elementi ihtiyacını karşılamaktadır ve üretimi doğal çözünebilir tuzlardan gerçekleştirilmektedir. Tarım sanayiinde oldukça geniş bir kullanım alanına sahip olmasına rağmen, bu tip tuz gölü yatakları dünyada yaygın değildir. Tarımsal üretimi oldukça yüksek olan Türkiye sınırları içinde bu tip bir göl bulunmamakta, potas gübresi ihtiyacının tamamı yurtdışından sağlanmaktadır. Bu çalışma kapsamında Kırşehir İli'nde bulunan yüksek muskovit içerikli potasyum feldspat cevherinden potasyumun eldesi çalışılmıştır. 
Tez kapsamında öncelikle doğrudan liç deneyleri yapılmış, ardından kalsiyum klorür ilavesi ile klorlaştırıcı kavurma ve liç yöntemi ile potasyum ekstraksiyonu denenmiştir. Kavurma işlemine girecek feldspat cevheri boyutu -106 µm olarak optimize edildikten sonra 650 Co ile 950 Co sıcaklıklar arasında her birinde 30 ila 180 dakika arasında kavurma deneyleri yapılıp, 850 Co 60 dakika kavurma süresinde %100 potasyum kazanma verimine ulaşılmıştır. 
Beklenen yer değiştirme reaksiyonu 650 Co, 60 dakika kavurma süresinde başlayıp 850 Co, 60 dakika kavurma süresine kadar tamamlandığı; ardından alkalilerin buharlaşmaya başladığı görülmüştür. Sonrasında optimum feldspat:CaCl2 oranı bulunarak en uygun koşullarda XRD analizi çekilmiş ve mineral dönüşümleri ortaya konmuştur. Kavrulmuş üründe silvin oluşumu gözlemlenirken, hem kavrulmuş üründe hem liç kekinde, beslenenden farklı olarak anortit, halit ve hidrogrossular varlığına rastlanmıştır. 
Pülpte katı oranı, sıcaklık ve süre olmak üzere liç parametreleri optimize edilip en uygulanabilir koşullar %15 pülpte katı oranında (ağırlıkça), 40 Co sıcaklıkta ve 60 dakika süresinde %90 potasyum kazanma verimi ile elde edilmiştir. Son olarak kalsiyum klorüre alternatif olarak kireç, kalsit ve sodyum klorür denenmiş, yalnızca sodyum klorür tuzundan üzerine gidilebilir potasyum kazanma verimleri elde edilmiş, tuz miktarının optimizasyonu yapılmıştır. Kalsiyum klorür eklentisi ile cevherdeki potasyum içeriğinin tamamını çözeltiye alınırken, sodyum klorür kullanılarak yapılan deneylerde ancak potasyumun %60'ı kazanılmıştır.

Abstract:
Potassium is the 7th most abundant element in the world, while it has a significant function in growing plants with nitrogen and phosphorus. In agricultural areas, potassium should be analyzed at certain intervals and potassium addition should be made according to results. Potash (K2O) fertilizers are produced from soluble reserves. There are two main compounds that are used as potash source. First one is potassium chloride (KCl) and known minerals of this compound are sylvite (KCl) and carnallite (KMgCl3.6(H2O)). Second source is potassium sulphate (K2SO4) and mostly found minerals of potassium sulphate are kainite (MgSO4.KCl.3(H2O)) and leonite (K2Mg(SO4)2.4(H2O)).  All of those minerals are mostly found in salt lake deposits. In some of the fruits and vegetables, only potassium sulphate can be used because of their sensitivity to chloride but potassium sulphate is not as widespread as potassium chloride. Because of that, potassium sulphate is mostly produced from potassium chloride by reacting it with sulphuric acid. Despite having a huge agriculture industry, Turkey does not have any known potash reserves and imports all of the potash demand. 
Feldspars, as one of the potassium resource, are the most common rock forming minerals and forms 60% of the earth crust. Feldspar group has nearly 20 recognized members but only two of them are used commercially, which are sodium feldspar and potassium feldspars. General formula of feldspars is XAl(1-2)Si(3-2)O(8) where X can be sodium, potassium and calcium. 
If feldspar has more than 7% Na2O, it classifies as sodium feldspar, however, it is named as potassium feldspar with K2O content of above 10% K2O. Those feldspars are commercial products and 70% of those are used in glass industry. While there are important limitations in terms of iron and titanium contents for these industries, decreasing their contents provides an enormous economic benefit.
Furthermore, potassium feldspars can be evaluated as a source of potash and can be processed with a heat treatment followed by water leaching without being constrained. This operation can be an alternative potash production and value-added products can be produced from feldspars. Moreover, there are many studies in literature showing potash production from feldspar is possible.
Studies for producing potash from feldspars was researched intensively almost 120 years before in the USA. Despite having deep background, there is no any plant which produces potash from feldspars because most of the studies were examined the issue without an economical concern. In addition, those studies can be re-evaluated considering today's technology. In the last decade, there are several studies, which produces potash from feldspars with roasting and water leaching method.
Moreover, investigation about displacement reaction between calcium of CaCl2 and potassium of microcline with thermodynamical approach was very limited in the literature. Thus, in this study, Gibbs free energy calculation was made to prove the reaction between them. As it is known that ΔGo = ƩΔGoproducts - ƩΔGoreactants formula should be used in such that reactions. So, Gibbs free energy was found ΔGo= -74,076 kJ/mol for microcline-CaCl2 system, and ΔGo = -80,814 kJ/mol for albite-CaCl2 system for 800 Co degree. Since these values are less then zero, the reaction occurs spontaneously.
In the scope of thesis, The ore which contains microcline, albite and muscovite with 9.69% K2O, was investigated to be used as a potash for agriculture. The experimental studies showed that leaching without roasting did not extract potassium from feldspar. Thus, roasting – leaching method was investigated. Water was chosen as a solvent because it showed selectivity to salts. The optimum particle size was chosen as -106 µm because -212 µm, -106 µm, and -75 µm did not show significant extraction differences and -212 µm had powerful adhesion. After optimization of the size of the ore which is fed to roasting as -106 µm, roasting experiments was made between 650 and 850 Co and the duration of 30 to 180 minutes was investigated for each Most effective feldspar:CaCl2 ratio was found 1:1.5 and 99.8% of the potassium was extracted from potassium feldspar. 
It is showed that expected displacement reaction was started at 650 Co and 60 minutes and completed at 850 Co, 60 minutes. After that temperature and duration, alkali content of the mineral started to volatilize. Then optimum feldspar:CaCl2 ratio was found and XRD analysis was made in most efficient conditions to show mineral transformation.
The transformation of the minerals was thought to be: i) microcline was converted to sylvite and anorthite, ii) albite was converted to halite and anorthite, iii) silicate was converted to wollastonite and iv) muscovite was converted to hydrogrossular which is a family in the garnet group. Transition of microcline to anorthite and quartz was shown in the literature before. In this study, it was understood that microcline consumes CaCl2 too and converted to again garnet group but hydrogrossular family mineral with chemical formula of Ca3Al2(SiO4)3-x(OH)4x with (OH) partly replacing (SiO4) where with the degree of x it can be grossular, hibschite or katoite. From an economic point of view, consumption of CaCl2 by the muscovite increases the cost but almost 100% potassium extraction was obtained in this circumstances. Therefore, patterns showed that high portion of halite remained in the leach residue which can be result of solid liquid separation or leaching conditions. However, since the aim of the study was potash production, the transformation and extraction of K were focused.
Leaching conditions such as solid ratio, temperature and duration was optimized and most useful conditions was chosen as 15% solid ratio (wt.), 40 Co and 60 minutes. Finally, lime, calcite and sodium chloride was used instead of calcium chloride and only sodium chloride was showed improvable results. With the addition of calcium chloride, whole potassium content of the ore was solved but with the sodium chloride only 60% of the potassium was solved.
Potassium, which is a key component in agriculture and ceramic-glass industries, is expected to be produced nearly 43 million tons in all over the world in 2019. Therefore, production of high value added products from potential potassium resources has increased in importance. K-feldspar, as an alternative one, was subjected to a series of experiments in order to extract potassium with high efficiency. Based upon the results obtained in this study, the method for selective extraction of potassium was revealed, while 90% K extraction was achieved. 
Although roasting feldspar with a specific proportion of CaCl2 has been investigated in many studies previously, this study has an originality in terms of expressing the correlation of roasting duration & temperature and more particularly achievement of a high K extraction with the ore with high amount of impurity.
On the other hand, it should be noted that roasting is an energy intensive process, however, the occurrence of the substitution reaction between feldspar and the additives like CaCl2 requires relatively high temperature. As the mechanism of this reaction is revealed properly, alternative methods to initiate the reaction should be investigated in further studies. In this concept; lowering the roasting temperature, decreasing the amount of additive, using cost effective additives, and/or various techniques to apply external force on the sample can be the essential topics.