Alüminyum siyah curuflarındaki alüminyumun ve bileşiklerinin hidro ve pirometalurjik yöntemler ile geri kazanılması
Recovery of aluminium and its compounds with hydro and pyrometalurgical methods from aluminium black dross
Yazar: OSMAN HALİL ÇELİK
Danışman: PROF. DR. ONURALP YÜCEL
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Ülkemizde ikincil alüminyum üretimi gün geçtikçe artmaktadır. Bunun sonucu olarak da ikincil alüminyum ergitilmesi işlemi sonrasında, azot ve argon gazları yardımıyla curuf oluşumu ve temizlenmesi adımları sırasında alüminyum siyah curufu oluşumu da artmaktadır. Alüminyum siyah curufu içerisinde % 15 – 60 metalik alüminyum, tuz (NaCl, KCl, CaF2), alüminyum oksit ve diğer metal oksitler bulunmaktadır. Alüminyum siyah curufundan metalik alüminyum geri kazanılması sırasında tuzlu alüminyum curufu (curuf keki – metalik olmayan kısım) oluşmaktadır.  Bu curuf yapısı içerisinde % 5 – 10 tuz (NaCl, KCl, CaF2), % 10 – 20 metalik alüminyum, % 30 – 60 Al2O3 ve % 5 – 10 diğer metal oksit ve bileşikler bulunmaktadır. 
Dünya' nın birçok ülkesinde alüminyum tuzlu curufunun çevreye, berteraf edilmeden veya geri dönüşümü yapılmadan gömülmesi yasaktır. Konuyla ilgili sivil toplum örgütleri ve devlet kurumları tarafından yapılan baskılar sonucunda önemli yasalar çıkartılmıştır. Ayrıca bu atığın bertaraf edilmesi yerine işlenip birçok sektöre hammadde kaynağı olacağı farkedildiği için yüksek teknoloji sahibi ülkeler tarafından kurulmuş büyük geri dönüşüm şirketleri bulunmaktadır. 
Bu çalışmada geri dönüşüm belgesine sahip alüminyum siyah curufu geri dönüşümü yapan özel bir firmadan alınan 15 kg' lık alüminyum siyah curufunun boyut kontrolünün yapılması, ön işlemlerden geçirilmesi, içerisindeki tuzun, metalik alüminyumun ve alüminyum oksitin çözeltiye alınması amacıyla deneyler yapılmıştır. Metalik alüminyumun sodyum hidroksit liçine tabi tutularak çözeltiye alınmasının sağlanması ve alüminyum hidroksit olarak geri kazanılması, buradan da alüminyum oksit (% 99,85), alüminyum sülfat (% 99) üretimleri gerçekleştirilmesi üzerine çalışılmıştır. Geriye kalan yapı içerisinde bolca bulunan alüminyum oksit (% 78) yapısının eritiş işlemine tabi tutulup, su ile çözündürülüp, çözeltiye geçmesi sağlanmıştır. Ayrıca çıkan tüm sonuçlar atomik absorpsiyon spektrometre ile okunup, elde edilen katı yapıların ve çözeltilerin kimyasal analiz işlemleri yapılmış ve XRD sonuçları belirlenip incelenmiştir. 
Metalik olmayan kısım içerisinde bulunan tuzların (NaCl, KCl) ülkemiz şartlarında curuf giderimi sırasında, argon (Ar) gazı pahalı olduğu için azot (N2) gazının kullanılmasından kaynaklanan ve % 10 – 12 aralığında yapıda bulunan AlN yapısının giderilmesinin sağlanması için su ile liç deneyleri, deney grubunun başlangıcında yapılan deneylerdir. Tuzların gideriminin % 99 oranında sağlanırken AlN yapısının giderilmesi % 86,4 olarak sağlanmıştır. 
Metalik alüminyumun çözeltiye alınması için yapılan NaOH ile liç deneyleri iki set grubu halinde incelenmiştir. Birinci set grubu deneylerin NaOH konsantrasyonu ve süre incelenirken, ikinci set deneylerde ise NaOH konsantrayonu ve katı/sıvı oranları incelenmiştir. Metalik alüminyum çözeltiye alınma verimi yaklaşık % 100 olarak sağlanmıştır. 
Çözümlendirme işlemleri sonrasında kalan yapı içerisindeki alüminyum oksitin (% 78 Al2O3) çözeltiye alınması için yüksek sıcaklıklarda ( 300 – 700°C ) NaOH ile eritiş deneyleri yapılmış, elde edilen yapılar su içinde çözündürülüp, alüminyumun çözeltiye alınma verimi % 96,7 olarak belirlenmiştir.

Abstract:
Secondary aluminum production in our country is increasing day by day. As a result of this, formation of aluminum black dross (slag) also increases during the steps of dross formation and cleaning due to nitrogen and argon gases following secondary aluminum melting process.  Aluminum black dross includes high percentage of metallic aluminum (30% – 60%), salts (NaCl, KCl, CaF2), aluminum oxides (Al2O3) and other metal oxides. There are many small companies that are working on recycling aluminium black dross in our country. They produce metallic aluminium with this recycling process. During the recovery of metallic aluminum from aluminum black dross, aluminum salt slag (slag cake - non-metallic residue) is generated. The non-metallic residue structure contains 5%- 10% salt (NaCl, KCl, CaF2), 10%-20% metallic aluminum, 30%-60% Al2O3 and 5%-10% other metal oxides (FeO, MgO, SiO2, TiO2, Cr2O3) with other compounds like nitride (AlN), carbide (AlC3), sulfide (Al2S3), phosphide (AlP).
Non-metallic residues that is formed from melting of aluminium black dross are so dangerous for environment. It is caused mainly by AlN. AlN in the non-metallic residue reacts with ungerground water also moisture too. After AlN reacts with underground water NH3 gas is formed. After that pH increases above 9. So, Al2O3 which is protective layer on metallic aluminium is also started to dissolve in NH3 solution because of the pH. Metallic aluminium reacts with water and with this reaction H2 gas, which can be exploded when it is reacts with flame, is formed. PH3 (AlP), CH4 (AlC3), H2S (Al2S3), HCN can be also formed if the pressure is 5 bars and temperature is 150°C underground.
It is prohibited to bury the aluminum salt slag in the ground without being disposed or recycled in many countries of the world. Major laws have been enacted regarding the subject, as a result of pressures exerted by civil society organizations and government agencies. Besides, large recycling companies founded by the countries with a high technology are available as it is realized that this waste would be treated as raw material source for many industries as metallurgy, ceramic, chemical, concrete etc. instead of disposing. Berzelius Umwelt – Servise AG (B.U.S) is a one of the biggest recycling factories in the world also is the biggest one in Germany. The company recycle all aluminium black dross also non-metallic residue. All the harmful, dangerous gasses for health are refined by active carbon filters. The company also gain all the explosive gasses like H2 and CH4 as a heating source. Aluminium ceramic fiber is produced for a last product in the company. Berzelius Umwelt's process is a close loop. They only give water to environment as a waste. RVA is French based company that are working on non-metallic residues. RVA has 3 different type of products which are produced from non-metallic residue names aluminium granules, salts and Valoxy that is used in secondary steel production with adding CaO and CaCO3 as a synthetic flux and unclean oxide raw material in ceramic industry. Befesa Escorias Salinas SA is another big company that works on all kind of aluminium wastes. Company is separated 2 companies for the different aluminium wastes in Spain. They also sell the recycling systems that recycle aluminium black dross and aluminium salt slags (non-metallic residue).    
In this study, some experiments were performed for the dimensional control, pre-treatment, getting salt, metallic aluminum and aluminum oxide into the solution of 15 kg aluminum black slag obtained from a private company which recycles aluminum black dross with the recycling certificate. 
It was studied in order to include metallic aluminum into the solution by being subjected to sodium hydroxide leach and recycle as aluminum hydroxide and then perform the production of aluminum oxide (99,85%), sulphate  (99%). It is provided that aluminum oxide structure (78%) found plenty in the remaining structure to be subjected to the melting process, dissolved into water and transferred into solution. In addition, reading all the results by atomic absorption spectrometer, analysis of the solutions obtained after the experiments, chemical analyses of the resulting solid structures and solutions and XRD results have been specified.
Leaching with water experiments performed in order to ensure elimination of A1N structure located in the structure at the rate of 3 – 15 % arising out of the use of nitrogen (N2) gas as argon gas (Ar ) is five times expensive during the removal of dross under the conditions of our country and because of  the salts (NaCl, KCl, CaF2) contained in NMR (non-metallic residue) are of the experiments which are performed at the start of the experiment group. Water leaching experiments are done for removing salts and aluminium nitride. Temperature (25°C, 80°C), stirring speed (500 RPM), 1/5 solid/liquid rate are investigated while water leaching experiments. Removing of salts is provided nearly same at 25°C and 80°C at a rate of 99%, while the removal of AIN structure is provided at 25°C at a rate of 42,48, at 80°C at a rate of 86.4.
Leaching experiments performed with NaOH to include metallic aluminum into solution was examined in two sets of groups. NaOH concentration (0,5 – 0,7 – 0,9 – 1,0 – 1,2 – 1,5 M) and time (15, 30, 45, 60, 90 minutes) was analyzed at the first set of groups while NaOH concentration (0,7 – 0,9 – 1,0 – 1,2 – 1,5) and solid/ liquid ratio (1/5, 1/10, 1/15) was analyzed at the second set experiments. It is determined that solid/liquid rate is not a effective parameter to produce sodium aluminate solution. Efficiency of including metallic aluminum into the solution is determined to be 99 % (1,5 NaOH M concentration, 60 minutes and 1/5 solid/liquid rate)  approximately. 0,25 gram was taken for all the NaOH leaching experiments. All the experiments are done at room temperature (25°C). 
Melting (fusion) experiments were performed with NaOH at high temperatures (300, 400, 500, 600, 700, 750 °C) to include  aluminum oxide (% 78 Al2O3) in the structure of the remaining after dissolving process into the solution and after dissolving the resulting structures in water, efficiency of including aluminum into the solution is determined to be 96,7%. 0,25 gram sample was taken for the experiments. Sample/Solid NaOH rate is 1/2 and time is set one hour for all the partial melting experiments. Iron crucibles are used in the partial metlting experiments. Iron also reacts with NaOH. But, Iron oxide is precipitated about 2,5 pH. Sodium aluminate solution' s, which is produced after partial melting experiment with water leaching, pH is 12 – 12,5. That is why it is not important to use iron crucibles that don't pollute the sodium aluminate solition.
Sodium aluminate solutions, which are produced from NaOH leaching and NaOH partial melting experiments, are integrated to produce aluminium hydroxide with pH adjusting. Diluted sulfuric acid (Merck) is used to produce aluminium hydroxide. pH is adjusted from 12 – 12,5 to 9 – 9,5. After aluminium hydroxide precipitated, aluminium oxide is produced from Al(OH)3 in calcination furnace at 1100°C. Aluminium sulfate is also produced from Al(OH)3 with sulfuric acid leaching. All three product's quality is determined with XRD and AAS analysis and compared with similar products in market.