Atık çözeltilerden solvent ekstraksiyon yöntemi ile bakır, nikel ve çinko kazanımı
Copper, nickel and zinc recovery from wastewater solutions with  solvent extraction method
Yazar: ALİCAN ESENBOĞA
Danışman: PROF. DR. SERVET İBRAHİM TİMUR
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Bölümü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2014
Konu: Metalurji Mühendisliği = Metallurgical Engineering
Dizin: Ağır metal giderimi = Heavy metal removal ; Endüstriyel atık su = Industrial waste water ; Metal ekstraksiyonları = Metal extractions ; Çözücü özütlemesi = Solvent extraction

Özet:
Kimyasal kullanımının yoğun olduğu endüstrilerde oluşan atık çözeltilerde çeşitli metal iyonları bulunmaktadır. Deşarj edilebilir atıksuların metal konsantrasyonları çevre yasaları tarafından belirlenen değerlerin altında olmak zorundadır. Bu nedenle işletmeler, prosesleri sırasında oluşan atıksuları deşarj etmeden önce arıtma prosesinden geçirmek durumundalardır. Proseslerdeki öncelikli hedef atıksu oluşumunu minimuma indirmek olsa da özellikle hidrometalurjik proseslerde bunu sağlamak bir hayli zordur. Bu nedenle  işletmeler atıksuların kompozisyonuna göre metal iyonlarını bertaraf etme veya metalleri geri kazanma yollarına başvurmaktadırlar. Endüstride uygulanan bir çok arıtma veya geri kazanım yöntemi bulunmaktadır. Özellikle ekonomik anlamda değer taşıyan metaller içeren atıksulardan metal geri kazanımı günümüz şartlarında proseslerin verimliliği açısından zorunlu hale gelmektedir. İşletmeler sahip oldukları atıksuyun metal konsantrasyonuna, oluşan atıksu miktarına göre proseslerine maksimum katma değer katacak geri kazanım yöntemini seçerek proseslerine adapte etmektedirler.
Solvent ekstraksiyon yöntemi sadece bir geri kazanım yöntemi olmamakla birlikte, sulu çözeltilerde bir arada bulunan birden fazla metali geri kazanmak için uygun ve etkili bir yöntemdir. 
Bu çalışmada altın rafineri atıksuyu olan bakır, nikel ve çinko iyonları içeren bir çözelti kullanılmıştır. Atıksu çözeltisi 11,3 g/L Cu2+, 3,33 g/L Zn2+ ve 0,39 g/L Ni2+ iyonları içermektedir. Metallerin geri kazanım prosesinde,  öncelikle bakırın ekstraksiyonu ardından da nikel ve çinko için ekstraksiyonları yapılmıştır.
Ekstraksiyon deneylerinde; yapılan literartür araştırması ve ön deneyler sonucunda yükleme süresi, karıştırma hızı, organik konsantrasyonu sabit tutulmuştur. Bakır ekstraksiyon deneylerinde sadece LIX 84-I kullanılmış ve A/O oranı, çözelti pH'ı ve yükleme adımı kademe sayısı yapılan deneyler sonucunda optimize edilmiştir. 11,3 g/L içeren bakır içeren pH deperi 3 olan çözeltide A/O oranı 1 iken, , 20 dakika süreli 3 adım sonucunda çözeltide bulunan bakır iyonlarınının %98,6'sı organik faza geçerek rafinatta 0,16 g/L bakır kaldığı tespit edilmiştir.
CYANEX 301 organik ekstraktantı ile yapılan yükleme deneyleri pH değeri 1,2 ve A/O oranı 1 iken çinko için %99,8 nikel  için %68,6 verimle gerçekleştirilmiştir. Sıyırma performansı yükleme performansı kadar iyi olmayan yüklü CYANEX 301 organik ekstraktantı oda sıcaklığında yapılan 3 M sülfürik asit ile yapılan sıyırma işleminde nikel sıyrılamamış, çinko ise 6,98 oranında sıyrılmıştır. Bu aşamada asit konsantrasyonu ve sıcaklık artırılarak 50 °C sıcaklıkta 6 M H2SO4 ile yapılan sıyırma işlemlerinde tek adımda maksimum nikel için %6,95 çinko için %49 sıyırma verimlerine ulaşılmıştır.
CYANEX 272 organik ekstraktantı ile yapılan çinko yükleme deneylerinde pH yükseldikçe üçüncü faz oluşumu görülmüştür. Bu nedenle ulaşılabilen en yüksek yükleme verimi pH 1,5 iken %30 olarak tespit edilmiştir.
CYANEX 272 organik ekstraktantının farklı oranlarda nötralize edilerek Na-CYANEX 272 tuzunun oluşturulmasıyla yapılan yükleme deneylerinde %97,1 verimle nikel, %99,9 verimle çinko yüklendiği görülmüştür.
Bakır yüklendikten sonra  yapılan iki aşamalı çöktürme deneyleriyle çözeltiden nikel %99,84 oranında çinko %99,99  oranında uzaklaştırılmıştır.

Abstract:
The wastewater of chemical-intensive industries contains various of metal ions. To discharge these wastewaters, metal ion concentrations of them have to be lower than specified limits due to the environmental policies. As a consequence, the enterprises have to execute wastewater treatment before discharging them. The main aim in here is to minimize the wastewater that has been produced. However aspecially in the fields like hydrometallurgy it is not very likely to achieve that. For that reason the enterprises choose to apply metal removal or metal recovery methods to their produced wastewaters. There are several metal removal and recovery methods at the industury. Metal recovery is becoming an obligation due to the economic values of the metals in these waters. The enterprises select the most suitable method to gain the maximum economic benefit due to the amount of the wastewater that has been produced and its metal concentration.
In order to select the correct wastewater treatment, the characteristics of the wastewater must be specified. The metal ion concentrations, wastewater type (acidic or basic), acid concentration, volume of the wastewater procuced per day are the most important parameters that have to be taken under consideration during the process installation. Chemical precipitation, ion exchange, adsorption, membrane filtration(reverse osmosis, ultrafiltration, nanofiltration), electrochemical techniques (electrolysis, electrocoagulation, electrodialysis) and solvent extraction are the most common and effective wastewater treatment techniques that have been used in various industries.   
Solvent extraction method is not only a recycling method but also a very effective technic to recover the metals from the aqueous solutions that contains several of them simultaneously. The process contains two basic steps. First step is the one that the metal ions in the aqueous phase transfer to the organic phase which is called extraction. Second step is the reverse step of the extraction step which is called stripping. The metal ions in the organic phase transfer to the aquoeus phase with the exchange of H+ ions in the aquoues phase. Complete reaction is shown in the equation 1 for both steps. 
Mn (s) + nRH (org) ⇔ MRn (org) + nH+ (s)	(1)
There are two important components in a solvent extraction system. First one is the aqueous solution which contains metal ions, takes part in the system as the aqueous Second component is the organic extractant, that takes part in the process as organic phase. In order to select the accurate organic extractant for the process some important properties of the organic extractant has to be evaluated. Desired properties for an organic extractant are; low cost, low solubility in the aqueous phase, high chemical stability, non toxic and non-flammable, mixable with the diluents, high stripping performance, high metal extraction capacity, good extraction kinetics. In this process the LIX 84-I organic extractant was chosen for copper extraction, CYANEX 272 and CYANEX 301 were chosen for nickel and zinc. All of the extractants were suitable in acidic solutions.
In this thesis, gold refinery wastewater that contains copper, nickel and zinc in the chloride and nitrate media has been used.. In consequence of  gold refining process the solution were strongly acidic (pH below 0). In order to adapt the pH for metal extraction firstly caustic solution has been added and pH adjusted to 1.  After the pH arrangement the metal ion concentrations were analyzed and the copper, zinc and nickel were 11.3 g/L , 3.33 g/L , 0.39 g/L respectively.
At the metal recovery process firstly the copper ions have been extracted from the wastewater since the copper ions can be extracted with LIX 84-I, the organic extractant that has been chosen for copper extraction, from acidic solutions at low pH values.
In the extraction tests, parameters such as ; extraction time, stirring speed, extractant concentration were set constant due to the results of literature research results and the preliminary tests. Copper extraction test were carried out in order to optimize initial pH, A/O ratio, extraction step number with the organic extractant LIX 84-I.
In the pH optimization tests, the influence of the initial pH of the solution between the values 1.5-3.5 were not significant. The maximum pH that obtained was 3.5 because of the buffering effect of the solution. A/O ratio test were carried out between 0.25 – 4 . Optimum A/O ratio that has been chosen was 1.
From the solution that contains 11.3 g/L copper ions; after 3 steps extraction of 20 minutes with 0.4 M LIX 84-I concentration at pH 3, %98.6 of the copper ions extracted. The raffinate concentration that determined were 0.16 g/L. 
As a result of copper extraction and stripping tests, the raffinate became available for nickel and zinc extraction and the stripping solution was suitable for copper electrowinning or copper sulphate salt production. The impurities in the stripping solution were 0.008 g/L nickel, 0.188 g/L zinc.
LIX 84-I organic extractant has good extraction performance for nickel and zinc too. However the extraction of nickel and zinc with this extractant can only be performed in high pH values between 5-9. Because of the metal hydroxide formation in the solution at these pH values, the LIX 84-I were not used for nickel and zinc extraction. CYANEX 301 and CYANEX 272 were suitable for this part of the process since both of the extractants are extracting nickel and zinc at low pH values.
In the extraction tests that have been performed with the CYANEX 301 extractant, the maximum efficiency that has been obtained with the optimum conditions, 20% vol. CYANEX 301 concentration , pH 1.2, A/O 1, were 99.8 % for zinc and %68,6 for nickel. Stripping performance of this extractant were relatively low compared to its extraction performance. With 3 M sulphuric acid concentration at A/O rate of 1, nickel stripping was not established and the efficiency for zinc was 6.98 %. To overcome this situation the acid concentration and temperature increased to 6 M and 50 °C. The stripping efficiency increased to 6.95 % for nickel and 49 % for zinc at single step. In order to achieve better stripping performance for CYANEX 301, to use hydrochloric acid as stripping solution were advised in the literature. However the aim of this thesis were to prepare metal sulphate solutions that are suitable for metal electrowinning or metal sulphate production, hence the stripping tests were performed only with sulphuric acid.
CYANEX 272 organic extractant selected for its beneficient performance of zinc extraction at acidic solutions. The extraction experiments were taken between pH 1.5-3. CYANEX 272 extraction experiments third phase formation and crud formation have seen between the pH 2-3. The maximum extraction yield that have been achieved was 30 % for zinc at initial pH of 1.5 while nickel extraction were not determined.
There were some examples of sodium salt prereparation of the organic extractants. This sodium salts of the extractans have some influence on extraction and stripping performances in zinc and nickel extraction.  In order to prepare the sodium salt of the CYANEX 272 the pure organic extractant were treated with caustic solution before the extraction step. in the literature CYANEX 272 organic extractant neutralized at different ratios (20% - 40%) with NaOH solution to generate sodium salt of CYANEX 272. With the increase of the neutralization ratio, the extraction yield of zinc and nickel were significantly improved. With the 20 % neutralization ratio the extraction of nickel and zinc were 8.9 % and 93.3 % respectively. 40 % neutralization ratio improved the co-extraction of nickel. The extraction yield that have been reached were 97.1 % nickel, 99.9 % zinc.
Precipitation test were carried out in order to create an alternative method for nickel and zinc recovery by producing nickel and zinc hydroxides. The precipitaion process included two steps. The first step the pH of solution were set at 7.5 and given enough time to reach equilibrium. After the solution got stable solid/liquid phase seperation have implemented by filtration. After filtration the solid dried for a while and added to the solution again. The pH of the solution set at 8 and the same solid/liquid seperation were performed. After the second step 99.84 % of nickel and % 99.99 of zinc removal have been achieved.