Soma termik santral uçucu küllerinden nadir toprak elementlerinin (NTE) kazanımı
Recovery of rare earth elements (REEs) from Soma thermal power plant fly ash
Yazar: GÜLŞAH GÜVEN
Danışman: PROF. DR. GÜLAY BULUT
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Cevher Hazırlama Mühendisliği Ana Bilim Dalı / Cevher Hazırlama Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2024
Konu: Maden Mühendisliği ve Madencilik = Mining Engineering and Mining

Özet:
"Nadir toprak elementleri" (NTE) terimi, periyodik tabloda Lantanitler olarak
sınıflandırılan lantan ve lutesyum elementlerinin yanı sıra itriyum ve skandiyum
elementleri arasındaki 15 elementten oluşan bir grubu ifade eder. Bu elementler
"nadir" olarak adlandırılmaktadır, çünkü zenginleştirme süreçleri yoluyla
birbirlerinden seçici olarak ayırmak ve saf halde elde etmek zordur. NTE piyasasındaki
yüksek arz talepleri ve artan fiyatlar nedeniyle birçok ülke yerel kaynaklardan
faydalanmak için ikincil kaynaklara ve geri dönüşüme odaklanarak yeni kaynaklara
yönelmiştir. Kömür ve kömür yan ürünlerinden NTE geri kazanımı potansiyel olarak
umut verici bir kaynaktır.
Bu tez çalışması kapsamında, Konya Şeker San. Tic. A.Ş. (Manisa/Soma) tarafından
işletilen Soma Termik Santrali uçucu kül numunesinden nadir toprak elementlerinin
kazanımı cevher zenginleştirme yöntemleri kullanılarak araştırılmıştır. Çalışmaların
başında uçucu külün karakterizasyon çalışmaları yapılmıştır. Fiziksel zenginleştirme
deneyleri kapsamında, özgül ağırlık farkına dayalı ayırma yapan Mozley masası ve
santrifüjlü ayırıcılar (Multi Gravite Separatör (MGS) ve Knelson) kullanılmıştır.
Fizikokimyasal zenginleştirme deneylerinde ise, Denver flotasyon cihazı kullanılarak
karbon uzaklaştırma deneyleri gerçekleştirilmiştir. Kimyasal zenginleştirme deneyleri
kapsamında ise, doğrudan asit liçi ve alkali ısıl işlem+asit liçi deneyleri yapılmıştır.
Uçucu kül elek analizi deney sonuçlarına göre; malzemenin d80 boyutu 105 mikron
olarak bulunmuştur. Temel oksit analizleri sonucu uçucu kül numunesinin başlıca
SiO2, CaO, Al2O3 ve Fe2O3 bileşiklerinden oluştuğu tespit edilmiştir. Ayrıca, ICP-MS
analizleri sonucunda uçucu kül numunesinin toplam NTE içeriği ASTM D6357
standartı ile yapılan külleme işlemine göre 197 g/t olarak elde edilmiştir.
Fiziksel zenginleştirme deneyleri sonrasında fizikokimyasal zenginleştirme deneyleri
gerçekleştirilmiştir. Flotasyon deneyleri kapsamında, karıştırma hızı 1000 dev/dk,
PKO %10, doğal pH'sı olan 13,10 gibi parametreler sabit tutularak, Span80 ve Tween
20 ile hazırlanan emülsifiye kerosen 1500 g/t ve 2500 g/t miktarlarında kullanılarak
deneyler yapılmıştır. Ayrıca, köpürtücü seçiminin flotasyon verimi üzerindeki etkisini
incelemek için 250 g/t MIBC ve İzooktanol kullanılarak deneyler gerçekleştirilmiştir.
Toplayıcı olarak Tween20 ile emülsifiye edilen kerosenin ve köpürtücü olarak
MIBC'nin kullanıldığı flotasyon deneylerinde batan üründeki en yüksek NTE
içeriğine (226 g/t) %89 NTE kazanma verimi ile ulaşılmıştır.
Doğrudan asit liçi deneylerinde ise liç süresi 2 saat, katı:sıvı oranı 1:10, karıştırma hızı
400 dev/dk olarak seçilmiştir. Bu deneylerde kullanılan asitler HCl, H2SO4 ve HNO3
(0-3 mol/L konsantrasyonları arasında) olarak tercih edilirken, uygulanan liç
sıcaklıkları 20, 50 ve 90°C'dir.
Alkali ısıl işlem deneyi 400 °C'de, 2 saat boyunca, 1:1 oranda NaOH:uçucu kül
kullanılarak gerçekleştirilmiştir. Alkali ısıl işlem ürünlerine uygulanan asit liçi
deneylerinde liç süresi 2 saat, karıştırma hızı 400 dev/dk ve katı:sıvı oranı 1:10 olarak
seçilirken, doğrudan asit liçinde kullanılan asitler benzer konsantrasyonlarda ve liç
sıcaklıklarında kullanılmıştır. Alkali ısıl işlem sonrasında uçucu kül numunesine
uygulanan asit liçi deneyleri sonucunda en yüksek ∑NTE çözündürme verimi olan
%94,7'ye 3 mol/L HCl asit konsantrasyonu ve 20 ⁰C liç sıcaklığında ulaşılmıştır. Katı
artıktaki NTE içeriği ise 114 g/t olarak tespit edilmiştir. Alkali ısıl işlem+asit liçi
sonucundaki en uygun deney koşullarının tespitinden sonra liç süresinin
belirlenmesine yönelik olan yapılan deneylerde 2 saat en uygun liç süresi olarak
belirlenmiştir.

Abstract:
The term "rare earth elements" (REE) refers to a group of 15 elements between the
elements lanthanum and lutetium, as well as the elements yttrium and scandium, which
are classified as Lanthanides in the periodic table. It is known that there are more than
250 minerals that contain REEs and that the average concentration of REEs in the
Earth's crust is around 0.015%. These elements are referred to as "rare" because it is
challenging to selectively separate them from one another through enrichment
processes and acquire them in pure form. Due to the high supply demands and
increasing prices in the REE market, many countries have focused on new resources
by focusing on secondary resources and recycling to benefit from local resources. REE
recovery from coal and coal by-products is a potentially promising resource.
With the growing strategic importance of rare earth metals, the Chinese government
designated these metals as "strategic commodities" in 2007. The fact that rare earths
play a critical role in the defense industry is one of the main reasons why these metals
are called strategic elements. They are also widely used in high-tech fields such as
renewable energy, hybrid vehicles, permanent magnets and catalysts.
Among alternative sources, coal and coal by-products, which are widely used
especially in the energy sector, are considered as potential rare earth resources.
Approximately 75% of the coal produced in Turkey is used in thermal power plants
and this coal contributes around 30% to Turkey's electricity generation. The pulverized
coal is sprayed into the combustion section of the boiler and burned at 1400 ⁰C.
Pulverized coal ashes obtained from thermal power plants after coal combustion are
used as cement additives in construction. Fly ash contains mainly Si, Al and Fe (both
in crystalline and amorphous form) and has compositional characteristics similar to
zeolites, which also contain minor elements such as Ca, Na, K and Ti. Fly ash is usually
composed of hollow aluminosilicate microspheres (senosphere). These spherical
particles are the result of solidification and cooling of gases during the combustion
process under high temperature and pressure. Also, the content of some thermal power
plant ashes can play an important role. Coal and coal by-products are reported to be
significantly enriched with trace metals and have been proposed as a promising source
of rare earth elements (REEs). NTE in lignite coals is known to be weakly correlated
with the organic fraction of the coal. The recovery of valuable elements from these ash
waste streams is well aligned with the "Waste to Value" concept and enhances the
sustainability of current disposal practices. Coal resources and related wastes in our
country offer an important opportunity when evaluated in terms of REE.
Within the scope of this thesis, Konya Şeker San. (Manisa/Soma), the recovery of rare
earth elements from Soma Thermal Power Plant fly ash sample was obtained by using
ore beneficiation methods. In the study of physical beneficiation experiments,
Mozzley table and centrifugal separators (MGS and Knelson) were used for separation
based on specific gravity difference. In physicochemical beneficiation experiments,
carbon removal experiments were carried out using Denver flotation cell. In chemical
beneficiation experiments, direct acid leaching and alkaline heat treatment+acid
leaching experiments were carried out.
According to the fly ash sieve analysis test results, the d80 size was found to be 105
microns. Basic oxide analysis showed that fly ash sample was mainly composed of
SiO2, CaO, Al2O3 and Fe2O3 compounds. In addition, ICP-MS analysis showed that
the total REE content of the fly ash sample was 197 g/t according to the ashing process
performed according to ASTM D6357 standard.
As a result of the beneficiation experiment using Mozzley table, the highest ∑REE
content was obtained in the light product with 238 g/t and 74.9% yield. From this
result, it is understood that REE moves with light materials with low density. As a
result of MGS experiments, it is seen that ∑REE is concentrated in the light product
with a content of 242 g/t. As a result of the Knelson experiment, a 2.2 wt% heavy
product was recovered with an REE recovery efficiency of 2.9% and REE content of
308 g/t. However, Mozzley table, MGS and Knelson beneficiation experiments
showed that there was no effective separation due to the very low content and yields.
After the physical enrichment experiments, physicochemical enrichment experiments
were carried out. Within the scope of flotation experiments, experiments were carried
out using emulsified kerosene 1500 g/t and 2500 g/t prepared with Span80 and Tween
20, keeping parameters such as mixing speed 1000 rpm, natural pH 13.10 constant. In
addition, experiments were carried out using 250 g/t MIBC, ısooctanol to examine the
effect of frother selection on flotation efficiency. In flotation experiments using
kerosene emulsified with Tween20, the highest NTE content was obtained when
MIBC was used as a frother with 89% REE recovery and 226 g/t REE content in the
sink product. It is understood that the use of frother together with kerosene has a
positive effect on flotation efficiency.
The effect of acid type, concentration (1 mol/L, 2 mol/L and 3 mol/L) and temperature
(20, 50, 90 ⁰C) parameters in direct acid leaching and alkaline pretreatment+acid
leaching experiments were investigated. In direct acid leaching experiments, leaching
time was selected as 2 hours, solid:liquid ratio as 1:10, and stirring speed as 400 rpm.
The acid types to be used in the experiment were HCl, H2SO4 and HNO3, acid
concentrations were 0 mol/L, 1 mol/L, 2 mol/L and 3 mol/L, different acid leaching
temperatures (20°C, 50°C, 90°C) were tested.
Alkaline heat treatment is applied to degrade the aluminosilicate structure to release
the REE-containing phases. As a result of the NaOH heat treatment of the fly ash
sample, it was observed that the Al203 and SiO2 phases reacted with the sodium
structure and the formation of cancrinite occurred. When the XRD analyses of the
products entering and leaving the alkali heat treatment were compared, it was seen that
especially the glassy phase was disrupted and the expected form was formed as a result
of alkali heat treatment, which is a pyrometallurgical process.
The alkali heat treatment experiment was carried out at 400 °C for 2 hours using a 1:1
ratio of NaOH:fly ash. In acid leaching experiments applied to alkali heat treatment
products, leaching time was 2 hours, stirring speed was 400 rpm and the solid:liquid
ratio was 1:10, while the acids used in direct acid leaching were used at similar
concentrations and leaching temperatures. As a result of acid leaching experiments
applied to the fly ash sample after alkali heat treatment, the highest ∑NTE dissolution efficiency of 94.7% was achieved at 3 mol/L HCl acid concentration and 20 ⁰C
leaching temperature. The NTE content in the solid residue was determined as 114 g/t.
After the determination of the most suitable experimental conditions as a result of
alkali heat treatment + acid leaching, 2 hours was determined as the most suitable
leaching time in the experiments carried out to determine the leaching time.
For the recovery of NTE from fly ash, a preliminary alkaline heat treatment followed
by acid leaching can be recommended instead of direct acid leaching.