Investigation of refining gold scrap with quartation process

Gold was the first metal used by humanity on earth, because of the original color, being native in nature and good resistance to atmospheric corrosion. Besides having excellent chemical properties of pure gold, the lattice structure also makes this metal superplastic. For example, 1 km wire can be wiredrawn by using 1 g gold through the properties of elasticity. Gold is a precious metal used for jewelry, coinage and other arts throughout recorded history. A gold standard was often impressed by a monetary policy within and between nations, but gold coins ceased to be minted as a circulating currency in the 1930s. Except for use as bullion and gold ornaments, it began to be used especially in circuit boards of electronic devices, as conductors for joining small electronic components after 1970. Copper is used for this purpose, but it corrodes faster than gold. Therefore, the use of copper as a metal conductor in the short-lived electronic card has been completely replaced by gold. Gold is also used in infraredshielding, colored-glass production, gold leafing, and tooth restoration. Certain gold salts are still used as anti-inflammatories in medicine. Until the early 20th century, gold production was 50,000 tons. The remaining 250,000 tons were carried through the main bulk production quantities of cyanide-added methods Gold is a metal that mankind has produced more than 10000 years. Initial production method is sorting-melting, but in the form of visible native gold was exhausted in nature, especially human beings has continued producing gold ore by a simple method of preparation of the river bed. finer dimensional gold is produced by amalgamation method when these resources are exhausted in the field. . It is available in gold stocks enough for centuries to humanity to be used for technical purposes or jewelry in the world. However, due to respond in a 100% recycling metal recycling has application. The main area of the gold are in the jewelry industry, gold alloys with copper or silver to add the welding ability on the mechanical properties. After this process, jewelry items are made by using different techniques. Jewelry is damaged while using and become a scrap. Other important sources of scrap are corrupted circuit boards in electronic devices. The jewelry and circuit cards in electronic devices should be recycled, before using in industry, purity of gold must be minimum 99,9% and maximum 99,99% in commercial terms. There are many methods for refining of gold scrap. The cheapest and convenient method is quartation method, also aqua regia extraction, electrolytic refining (Wohlwill, etc.), Miller process can be used instead of quartation. Gold alloys, which contain more than 25% of gold, process for obtaining pure gold by dissolving in nitric acid. In this study, one of the most classical methods for refining of scrap gold, which is quartation process is experimentally analyzed. For this purpose, pure gold, silver, and copper were obtained from a market, was alloyed in a gold refinery, İstanbul Kuyumcukent. Different results are obtained from the dissolution of alloys with nitric acid at room temperature. Before experiments, 2 g samples of quartation alloys which have different size of surface area as 1 cm2, 2 cm2, 3 cm2, 4 cm2 and 5 cm2 with different amounts of gold, silver and copper is melted with a torch in a pot and molded. In the experiments, binary and ternary alloys are used. In these alloys, the percentage of copper and silver is changed between ranges from 15% to 85%. The effects of amounts and type of metals in the alloy, surface area and the amount of acid are discussed by using ternary alloys to optimize the result. In the experiments, increasing the amount of silver becomes difficult to dissolve on the purpose of refining at the room temperature and fixed amount of nitric acid with ternary alloys. In Au-Ag-Cu alloys, dissolution rate decreases significantly when the quantity of silver is more than 15 %. The reason of decrease is detected as an increasing beta phase in the Cu-Ag binary phase diagram. Instead of silver, the dissolution rate is increasing with the usage of copper more than 15 %. It is observed that the resolution of alloy takes more time when the amount of copper is increased in the ternary alloy. Therefore, binary quartation alloys were examined as a second case. In this case of searches and practically experiences show that for a full resolution of gold, the alloy must contain 25% or less. Research of binary alloy results that silver has a better solution performance than copper. For instance, sample alloy, which contains 25 % Au- 75 % Ag, fully dissolves in 10 minutes by 12.5 g nitric acid per gram alloy. However, if the alloy involves 25% Au- 75 % Cu, it consumes 15 g nitric acid per gram alloy for full dissolution in 10 minutes. As expected, copper should resolve faster than silver because of copper is more active metal than silver. On the other hand, silver has more efficient dissolution performance than copper because silver and copper behave in nitric acid as Ag1+ and Cu2+, respectively. In the other case of experiments, the effect of sample surface area to dissolution rate is analyzed with binary alloys. These experiments which completed in optimum circumstances, by using 25, 2% Au- 74,8% Ag and 25,3% Au- 74,7% Cu binary alloys which are aproximetaly 2-2,1 g with 1 cm2, 2 cm2, 3 cm2, 4 cm2 ve 5 cm2 sufrace areas, shows that dissolution rate of the copper-gold alloy is 0.095 g/cm2.min, the silver-gold alloy is 0.108 g/cm2.min. Results show that silver-gold binary alloy dissolves 14% faster than copper-gold binary alloy. Practically, to obtain more than 99.9 percent purified gold with quartation method alloying and dissolving steps are repeatedly applied. As a result of this study, pure gold is obtained successfully in one time at optimum situations. For instance, sample alloy, which contains 15%Au- 85% Ag, fully dissolves in 10 minutes by 12.5 g nitric acid per gram alloy and resulted with 99.97% pure gold powder.