Düşük miktarda altın içeren bizmut-kalay atığından  altın geri kazanımı
Recovery of gold from bismuth-tin scrap
Yazar: RUKİYE ATAY
Danışman: DR. ÖĞR. ÜYESİ MEHMET ŞEREF SÖNMEZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Metalurji ve Malzeme Mühendisliği Ana Bilim Dalı / Üretim Metalurjisi ve Teknolojileri Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Metalurji Mühendisliği = Metallurgical Engineering

Özet:
Altın eski çağlardan beri insanlar için önemli olmuş ve bu yüzden de çok yüksek miktarlarda kullanılmıştır. Bu yüksek talebin karşılanabilmesi için dünyada çok büyük miktarlarda altın üretimi yapılmakta ve üretim sırasında çeşitli oranlarda altın içeren atıklar oluşmaktadır.
Değerli metal özellikle altın üretimi yapan fabrikalarda çıkan atık da değerli olduğu için altının geri kazanımı önemlidir. Firmalar tesis içinde kendi imkânlarıyla (ergitme ve kül etme) bu atıklardan altını geri kazanmaktadır. Ancak, düşük miktarda altın içeren elektroform, cila tozları, lavabo suları, havalandırma tozları, arıtma su çamuru gibi karmaşık yapıda olan ramatlarda altının geri kazanılmasında bazı teknik problemler çıkmakta, çevre kirliliğine sebep olmakta ve yüksek verimle altının eldesi mümkün olamamaktadır.
Bizmut-Kalay-Altın içeren elektroform ramatının atık olarak karmaşık bir yapıda olması altın içeriğinin belirlenebilmesi için uygun numune alınmasını olanaksız hale getirmektedir. Bu sorunu giderebilmek ve analiz yapılmaya uygun numune almayı sağlayabilmek amacıyla ramat parçalarına ön işlemler uygulanmış; üç boyutlu karıştırıcıda 1 saat karıştırılarak  kül homojen hale getirilmiştir. Daha sonra altın kral suyu (3HCl + HNO3) ile liç edilmiş, altının çözeltiye geçmesi sağlanmıştır. Çözeltiye geçen altın, sodyumbisülfit kullanarak kimyasal çöktürme ile kral suyunda bulunan altın geri kazanılmıştır. Yapılan tüm deneylerde sıcaklık, süre, karıştırma hızı ve süresi, kimyasal çöktürücü kullanımı gibi parametreler üzerinde optimum şartlar belirlenmiştir. Belirlenen optimum şartlarda; kral suyundan altın sodyumbisülfit kullanarak çöktürülmüştür. Çöktürülen altın çamuru kurutulmuş sertlik değeri ölçülmüştür. Mikroyapısı incelenmek üzere krom regia kullanarak dağlanmıştır.
Bu çalışmanın amacı; ülkemizde altın geri kazanımı sırasında çevresel faktörler hiçe sayılarak ve ilkel metotlar kullanılarak, altın kaybı pahasına uygulanan yöntemlere alternatif bir proses geliştirmek ve optimizasyonunu sağlamaktır. Çalışmada karmaşık yapısı dolayısıyla geri kazanım işleminin zor olduğu elektroform ramatından altının çevre dostu bir şekilde ve yüksek verimle elde edilmesi amaçlanmaktadır.

Abstract:
Gold has been important for humans therefore, it has been used at enormous amount in jewellery since ancient times. In order to be able to satisfy this continuously high demand, large amount of jewel has been produced and during the production process, wastes containing different ratios of gold are formed. 
Gold jewelry design and production in the world is constantly being renewed and developing. In recent years, attention has been drawn to the use of gold jewelry and the decrease in purchase. The reason is that the gold prices are rising and the different values begin to take place. As a solution, jewelry makers have taken action to withdraw this situation and have turned to more modern, everyday life and simple models in gold jewelry designs. They also produced lightweight gold jewelery and presented it to the market at light prices.
One of the most important uses of gold is its use for ornamental purposes, including  jewelry which accounts for its largest industrial use. In use for jewelry, gold is  alloyed with other metals to increase its hardness , as pure gold is rather soft and  is also extremely malleable. The gold content in jewelry alloys is generally designated by a karat system. The system expresses the weighted fractions of gold in 24ths , thus an 18 kt alloy would contain 18/24 + or 75 wt % gold a 14 kt gold would contain 1U/2U or 58.33 wt % gold. The alloying metals in karat gold are silver, copper, zinc, nickel and sometimes small amounts of platinum and or palladium. The scrap karat gold coming into the Refinery is of mixed karatage and is primarily of the Au - Ag _ Cu combination with small amounts of zinc and nickel. Platinum and Palladium is sometimes present in very small to trace amounts. The gold ranges in content from 30 to 70 percent and the silver from 3 to 13 percent. The analytical techniques described in this paper will be limited to the analysis of gold and silver with the major emphasis on the Fire Assay technique. The analytical scheme for the analysis of materials containing large amounts of platinum and palladium is a subject which should be covered in another full paper, and could not be adequately described in the time alloted.
Naturally occurring gold is never pure. Hydrothermal solutions leach other elements as well as gold from the rocks through which the solutions pass. Some of these elements are present in trace quantities only; the proportions of others such as silver and tellurium may be significant and materially effect fineness. Gold forms natural alloys with silver, copper, mercury and tellurium; less commonly with titanium, bismuth, palladium, lead and zinc. Varieties in primary ores include cuproaurite (copper gold), porpezite (palladium gold) and bismuthaurite (bismuth gold). Whilst these minerals are seldom found in alluvial detritus, their presence in a weathering zone may help unravel the geological history of an area under review.
Gold has a characteristic metallic yellow colour, but can be black or ruby when finely divided. In commercial operations mixing gold with other metals also changes its colour:
•blue ± gold with iron
•green ± gold with a higher silver content than copper
•pink (or rose) ± 50% gold, 45% copper, and 5% silver
•white ± gold with nickel, zinc, copper, and tin; manganese-nickel is often
used because it bleaches gold
•yellow ± 50% gold, 25% silver, and 25% copper.
The principal natural alloys of gold are native gold, electrum, amalgum and tellurides.
Jewellery production  is  the  main use,  of gold  accounting  for more than  80%  of the  total  yearly market  for the  metal.  In  small jewellery workshops,  were the jewellery  is  measured,  finished,  cleaned  and  polished,  the  waste is  collected and than  ~ansferred to  founders  for the  final  treatment.  This  procedure  leads to  poor recovery, mainly due to the lack of  chemical and morphological  knowledge of  the  constituents of  the waste.
Waste from precious metals, especially those that produce gold, is also precious, so recovery is important. Firms are recovering gold from these wastes on their own facilities (melting and ashing). However, there are some technical problems in recovering gold in complicated structures such as electroforms containing low amounts of gold, polishing powders, basin waters, ventilation powders, refining water muds, causing environmental pollution and avoiding high yields of gold.
Jewellery  workshops  generate  three  different  kind  of  waste:  "handwashing  waste",  "jewellery  polishing waste" and "floor sweepings waste"
"Handwashing waste"  is  generated by the  rubbish  coming  from  handwashing of operators  and  clothes  for  laboratory  cleaning;  it  is  characterized  by  an  organic  matrix  in  which  gold  particles  are  segregated.  Accounting for 40.7  %  of the  total  waste  from  craft workshops, an  average  gold grade  of 2.89  %  has been  found.  It  contains  some  other  components,  such  as  soap  and  exhausted  coffee powder, that make its benefication  difficult.
"Jewellery  polishing  waste"  is  generated  when  the  artefacts  are  cleaned  and  polished  using  bristles  of  different  hardness running over their  surfaces;  it is  characterized by a  mixture of plastic  and metal bristles, abrasive  paste  and  metal dust,  mainly composed  of gold alloys. It  accounts  for 26%  of the  total  waste.  Its  gold content is  5.34 %. 
The  "floor  sweepings  waste"  contains the  product  of the  floor  sweeping.  It  accounts  for  33%  of the  total  waste. Its gold content is  1.20 %.
The complex structure of bismuth-tin-containing electroform ramate as waste makes it impossible to take appropriate samples in order to determine the gold content. In order to be able to solve this problem and to obtain samples suitable for analysis, pretreatments were applied to the slab pile; the ash was homogenized by stirring in a three-dimensional mixer for 1 hour. Then the gold was leached with aqua-regia (3HCl + HNO3) and the gold was passed through the solution. The gold passing through the solution was recovered by chemical precipitation. All experiments were carried out at room temperature and optimum conditions were determined on parameters such as temperature, time, mixing time and rate, use of chemical precipitator. Under optimum conditions, gold was precipitated from aqua regia by using sodiumbisulfite. The precipitated gold slush was dried in stove and melted. Then it was bakalited for grinding and polishing to examine microstructure. It was applied microhardness test. The specimen was etched by chrome regia for metallography.
The purpose of this study is; the development of an alternative process to the methods applied at the expense of gold loss and the optimization by using primitive methods and ignoring the environmental factors during the recovery of gold in our country. It is aimed at achieving environmentally friendly and high efficiency of gold from the electroform ram, which is difficult to recycle due to its complicated structure in operation.