Gold is an economically and industrially important metal with a wide range of uses. This noble metal is indispensable in jewelry. It is also useful in technological applications due to good physical properties, such as good electrical conductivity, formability, stability, and corrosion resistance. Because gold has a high and relatively stable value, it has also very important monetary significance. Given the fact that the gold on Earth is in limited quantities and that Earth’s reserves are slowly depleting, the recycling of gold is becoming increasingly important.
There are several known methods of dissolving gold. The dissolution in sodium (NaCN) and potassium (KCN) cyanide are the most important in the industry. However, since cyanides are dangerous and harmful to the environment, we will focus on the use of aqua regia in the bachelor's thesis. Refining is an important process in the processing and recycling of gold. For that purpose, Miller and Wohlwill methods are used.
In the practical part of the bachelor's thesis, we recycled gold from 58 used mobile phones using aqua regia. The thesis involved disassembling mobile phones and sorting parts that contained gold. We separated gold from the mentioned parts using a mixture of hydrochloric acid and hydrogen peroxide. Gold was filtered and dissolved in aqua regia. Gold was then eliminated from the solution using sodium metabisulfite and pure zinc. The sediments were melted in an electric resistance chamber furnace. The metal particle was then analyzed by XRF analysis and differential scanning calorimetry.
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