Galvaniz küllerinden klor giderilmesi

Abstract

Bu çalışmada galvaniz küllerindeki klorun giderilmesi amacıyla pirometalurjik ve hidrometalurjik yöntemler denenmiştir. Üç grup deneyden birinci grupta, her hangi bir ön işlem görmemiş malzeme kullanılırken, diğer gruplarda öğütülmüş ve metalik kısmı ayrılmış malzeme kullanılmıştır. Deney sonuçları aşağıda özetlenmiştir. Pirometalurjik Çalışmalar 1. Grup Deneyler: Elektrik dirençli bir tüp fırınında, çeşitli sıcaklıklar ve reaksiyon sürelerinde, hava üflenerek gerçekleştirilen deneylerin sonuçları, malzemenin çok miktarda metalik çinko içermesi sebebiyle sapmalar göstermiştir. Bu sapmaların minimuma indirilmesi, metalik kısmın klor gidermeden önce ayrılmasını gerekli kılmaktadır. Böylece klor giderme randımanı yükselmekte ve çinko kayıpları azalmaktadır. 2. Grup Deneyler: Metalik çinkosu eleme yolu ile ayrılmış galvaniz külleriyle birinci grup deneylere ben zer şekilde yapılan çalışmalar sonucu optimum klor giderme şartları 1000 C ve 240 dak. olarak tespit edilmiştir. Bu işlemle küllerin klor içeriği %4,972'den %0,029'a kadar düşürülmüştür. Sabit yataklı tüp fırında elde edilen optimum şartlara uygun olarak, döner fırında (3 dev/dak) yapılan deneylere aynı klor içeriği %:,022'ye kadar düşürülmüştür. Hidrometalurjik Çalışmalar: 3. Grup Deneyler: Hidrometalurjik yolla klor gidermede, sıcaklık, Na~C0" miktarı gibi çeşitli parametreler incelendiğinde, optimum klor giderme şartlarının 80 C da %20 pulp oranında, stokiometrik miktarda Na"C0" ilavesin de, 180 dak. süreyle çözümlendirme olduğu belirlenmiştir. Bu şartlarda galvaniz küllerindeki klor %4,972'den %0,338 e.düşürülmüştür.

Zinc can be recovered from various types of scrap and final products are slab zinc, zinc dust, zinc alloy, zinc oxide, zinc sulfate, zinc chloride, zinc ammonium chloride and lithopone. It is possible to classify zinc scrap according to various processes utilizing zinc metal as follows: -Galvanizers ' dross -Die castings -Skimmings or ashes -Sal ammoniac sikmmings -Chemical resudes -Flue dusts -Die casting skimmings -Leaching residues -Lead slag -Other metallic scrap This study deals with dechlorination of galvanizing ash for recovering of zinc by electrowining. As known, zinc ash contains chloride as a main impurity. Because of the chloride content, the ashes may not be suited for a treatment by a direct leach with sulphuric acid since in that case the chloride will enter the resulting sulphate solution. Chlorides will not be tolerated in a subsequent electrowining of the zinc metal. It is known that even a very small amount of chloride in the sulphate electrolyte is extremely damaging to the electrolysis. Presence of the chloride ion in the sulphate electrolyte causes the corroding of the lead anode. The zinc ash is formed when metallic zinc in a galvanizing bath is oxidized on the surface of the bath. The oxidized material floats on the top of the bath and is usually removed by the ladles. This zinc ash is a mixture of crude zinc oxide and varying quantities of entrained metallic zinc. Besides these, there will also be various contiminantes of other metals (i.e. iron, lead etc.) and especially chloride VI compounds from the use of chloride fluxes in the galvanizing process. In this study zinc ash, obtained from a galvanizing plant, is chemically analysed and composition of the zinc ash is given as follows : Zn(Metallic) 54.89% Zn(oxide) 25.58% Zn(Chloride) 2.53% Zn(total) 83.00% CI 2.89% Fe 1.46% Pb 0.49% Particle size distribution of the zinc ash is carried out by screening. For this purpose, 100 g of sample is screened by using ASTM.E 11-81 standart sieves. The results are shown below : Sieve Number % Weight 28 24.778 35 8.294 48 8.055 65 3.395 100 3.025 150 12.223 200 9.795 270 10.496 325 7.495 -325 12.442 For different particle size, chloride content is obtained as follows: Sieve Number %C1 in +150 4.074 -150+200 4.546 -200+270 4.997 -270+325 5.015 -325 5.025 To decrease the chloride content of the zinc ash three different types of experiments were performed. Non-treated original zinc ash is used in the first group experiments. Here, 5 g(T0,001) of zinc Vll ash is put into the alsint boat and heated to different temperatures at different times. During heating, a pump is used to supply air to the system. The resuls obtained from the first group experiments can be summarized as follows : %cı ' %cı : %C1 %C1 %C1 at 600°C at 700°C at 800°C at 900°C ". at 1000°C 0.5 h 0.745 0.800 0.757 0.403 0.256 1.0 h 0.634 0.538 0.219 0.350 0.239 2.0 h 0.481 0.627 0.157 0.045 0.260 3.0 h 0.503 0.226 0.458 0.079 0.555 In the second group experiments, the zinc ash, containing zinc oxide and appreciable amount of metallic zinc, was milled before mechanical screening tests. It is determined that the fraction left on a 100 mesh sieve number is readly smelted. -100 mesh (-0.149 mm) fraction which can not be smelted is chemically analysed. The chemical _ composition of the fraction -100 mesh is given as follows. Zn(metallic) 15.600% Zn(oxide) 48.659% Zn(chloride) 4.421% Zn(total) 68.680% CI 4.972% Fe 1.471% Pb 0.517% Similar to the first group experiments, 5 g of s sample, the fraction -100 mesh, is put in the alsint boat and heated to different temperatures at different times. Air blowing has been supplied by the pump which has 2.5 1/min. of blowing capacity. The results are obtained as follows : %C1 %ci %ci %ci %ci at 600°C at 700°C at 800°C at 900°C at 1000°C 0.5 h 0.990 0.424 0.241 0.105 0.039 1.0 h 0.923 0.386 0.259 0.098 0.036 2.0 h 0.893 0.357 0.225 0.036 0.025 3.0 h 0.775 0.317 0.287 0.055 0.029 4.0 h 0.687 0.304 0.152 0.061 0.029 Vlll The third group experiments involve three main operations ; a) Milling and metallic seperation of zinc, b) Washing the fraction -100 mesh with water and addition of soda ash. to remove chloride, c) Heating the washed zinc ash in a tubular furnace to decrease the chloride content. The washing of zinc ash is performed in a glass leaching reactor under different temperatures, pulp ratios, durations and different quantities of soda ash. In this step, the effects of temperature, time, quantities of soda ash, pulp ratios on the chloride removing-yield are investigated by various experiments. Optimum leaching conditions are obtained by maintaining the leaching temperature at about 80 C, pulp ratio at 20%, the leaching time at 4 hours, and stochiometric soda ash addition. Chloride content of zinc ash decreased to 0.346% from 4.997% by washing the zinc ash under optimum leaching conditions. However, optimum leaching conditions are obtained from the laboratory experiments, chloride content of zinc ash did not decline to the permeable level to recover the zinc by electrolysis. Because of the left chloride content after the washing of zinc ash, should be treated before electrowining. For this reason, alsint boat containing 5g+0,001 of milled and washed samples are heated under air blowing at different temperatures and times. The results are Riven as follows : Finally, 1000 g + 0.1 of milled and screened zinc ash are charged into a rotary furnace at about 900 C and 1000 C respectively for 4 hours and the samples are taken out the furnace twice an hour. The results IX were obtained as follows %C1 %C1 Some important results obtained from this study can be summarized as follows: 1- The results obtained from the first group experiments have shown some deviations because of the metallic zinc content in zinc ash. To reduce the zinc loss, during dechlorination of zinc ash, screening should be performed. At the end of the screening metallic part of the zinc ash can be melted directly. 2- Appliying the pyrometallurgical method, the optimum conditions in dechlorination of zinc as which does not include the metallic part are obtained at the temperatures of 1000 C and 240 minutes of a reaction time by air blowing to the system. This operation can be performed in a rotary furnace and it makes continous chloride removing possible. So that, chloride content can be decreased to 0.029% from 4.972% level. 3- X-ray analysis of the material under -100 mesh, after milling and screening operations, showed that the chloride content is in theform of ZnCl_, Zn0.ZnCl".nH"0 and PbCl~. These compounds can be converted in to the gase phase according to their high vapour pressure at convenient temperatures, so that chloride removing can be possible. But ZnCl" has higroscopic characteristic and it may plug the filter. In that case, working under oxidising conditions prevents ZnCl_, PbCl" vapourisation and makes Cl" vapourisation possiDle. In this study, air blowing is applied to the furnace and Cl" Vapourisation occures. But in industrial applications, rurnaces are usually heated with coal, fuel-oil or natural gase. This makes ZnCl", PbCl" vapourisation possible. By this way, it is necessary to use a filter system to hold metall-chlorides. 4- Experiments showed that chloride content of the waste product can be reduced by using Na«CO" solutions so this can be an alternative method to pyrometallurgical chloride removing. Na^CO- amount in the solution is sufficient to bind chloride in the solid. Chloride content of the waste product can be decreased to 0.338% from 4,972% levels under experimental conditions shown below. If this method is compared with direct pyro.- metallürgical chloride removing, chloride content of the solid is more higher than the alternative method. This is because of the binding of chloride in the original wastes with Zn and Pb as oxi-chloride and not being affected by Na~C0" leaching. 5- It is possible to decrease the chloride content of the product taken from Na"C0« leaching to 0.022% levels by applying a pyrometallurgical method under experimental conditions shown below : Temperatures : 1000°C Duration : 240 min. (air blown) By this way it is shown that pyrometallurgical chloride removing is more effective than Na^C0" leaching. Although pyrometallurgical chloride removing is more advantage, the main drowback of this method can be arranged as follows : - Corrosive gase formation, - The gase can not be released to the atmosphore directly due to its chloride content. 6- Final product incudes approximately 78.6% Zn, 1.7% Fe, 0,52% Pb, 0.03% Ni and 0.022% CI. This product can be charged into a system in which zinc is recovered either pyrometallurgically or hydro- metal lurgically. xi BÖLÜM 1. GİRİŞ VE AMAÇ Sülfürlü ve oksitli tip cevherlerden pirometalur- jik veya hidrometalur jik yolla üretilen rafine çinko, saf halde çoğunlukla galvanizleme tekniklerinde kulla nılmaktadır flj. Türkiye bazında sanayide kullanılan toplam 45.000 ton çinkonun yaklaşık %50'si galvaniz ve çinko kaplama işlemlerinde sarf edilmektedir [2j. Günümüzde üretilen metallerin hammaddelerden ka zanılması gittikçe önem kazanmaktadır. Bunun nedeni birincil hammaddelerin miktarlarının ve içerdikleri metal tenörlerinin sürekli azalmasıdır. Bu yaklaşım kaplama işlemlerinde kullanılan çinko için oldukça önem lidir. Sıcak daldırma yolu ile yapılan galvanizleme işlemi genellikle açık sistemlerde sürekli veya süreksiz şekilde uygulanmaktadır. Bu prosedür sırasında ergimiş çinkonun oksijene karşı yüksek afinitesi ve kullanılan flaksların kimyasal bileşimleri dolayısıyla bu işlemde önemli ölçüde artıklar oluşur. Edinilen teknik tecrübelere göre örneğin Kanada için galvanizlemede kullanılan çinkonun %26'sı artık şeklin de ortaya çıkmaktadır [3 J. Teknikte galvaniz külü olarak adlandırılan bu artık ürün oksit, klorür, oksi klorür ve metalik halde ortalama %80-85 çinko içermek tedir [4J. Uygulamada büyük miktarlarda oluşan bu ara üründen çinkonun geri kazanılması vazgeçilmez bir gerek liliktir. Genellikle galvaniz küllerinin işlenmesi söz konu su üründen çinkonun, metalik, ZnO veya ZnCl" şeklinde kazanılmasıyla yapılmaktadır. Ancak genel uygulama -2- küllerden çinkonun metalik halde kazanılması yönünde dir. Küllerin oluşmasındaki şartlar gereği bu küller de önemli miktarda klorun varlığı kaçınılmazdır. Söz konusu küllerde ZnCl", ZnO.ZnCl".nH"0 veya PbCl" şek linde bağlı klor elektrolitik çinko üretimini güçleş tirmektedir. Galvaniz küllerine uygulanacak çinko üretim yönteminden evvel klor içeriğinin asgari sınır lara kadar düşürülmesi gereklidir. Bu tez çalışmasında bir galvaniz tesisinden alınan galvaniz küllerinden klorun çeşitli metalurjik işlemler le giderilmesine çalışılmıştır. Amaç söz konusu küller deki klor içeriğinin elektroliz yoluyla metalik çinko üretimini bozmayacak seviyelere indirilmesidir.