Recovery of Metallic Values in Smart Cards

Today, smart cards which include a small microchip are very widely used in our daily lives. The chief among these is credit cards. In addition, gift shopping card, phone card, sim card, hotel room card involves great proportions. They generally include many precious metals in their body, including noble metals, and semi-noble metals; predominantly gold, silver, copper, etc. The aim of this experimental work is to recover the metals from the smart cards by hydrometallurgical processes namely acidic leaching (HNO 3 and Aqua Regia) followed by precipitation and cementation. Three different types of smart cards; credit cards supplied from different banks, telephone cards produced for Turk Telekom, and sim cards from three different mobile service providers, are used in the experimental work. As a result of this study, almost all copper, silver,


RDMS.000878. 16(1).2021
region, the hologram on the card, picture, relief, etc. are defined by the ISO-7816 standard [8,9]. Smart cards are divided into three groups depending on the memory; memory only, security logic memory, and memory with its own processor. Additionally, they can be investigated as two groups, according to their connection type; contact and contactless.
Today, smart cards have a big area of usage. According to the data of the Interbank Card Center (BKM), as of the end of June 2021, 79.8 million credit cards, 141.5 million debit cards and 50 million prepaid cards are used in Turkey [10]. In addition, according to the research of We Are Social, the number of mobile phone users in Turkey has reached 59 million. Of these, 77 percent, or 45 million, use smartphones. Thus, it can be said that the number of SIM cards in use is around 59 million [11]. Also, the amount of phone cards, meal cards, etc., such as Sodexho and Ticket is nearly the same as others. As of December 2017, there were 20.5 billion credit, debit, and prepaid cards in circulation worldwide including global generalpurpose cards [12]. With consumers worried about touching surfaces during the coronavirus pandemic, the use of mobile payments and contactless credit or debit cards has significantly increased in this term [13]. The aim of this experimental work is to recover the metals from the smart cards by using the similar processes which have used in the recycling of WEEE's.

Material and Method
Three different types of smart cards; credit cards supplied from different banks, telephone cards produced for Turk Telekom, and sim cards from three different mobile service providers, are used in the experimental work. Every smart card is analyzed by wet and dry analysis methods to obtain their precious metal contents. Chemical analyses of the smart cards are shown in the Table 1. Chips are taken from the smart cards by a specially designed apparatus and weighted. After chips are dismantled from the smart cards, they were hold in hot water for 30 minutes to separate plastic part and chip. Weights of the raw smart card, taken part (chip and plastic body) and chip only are given in Table 2 and photographs of smart cards and chips are shown in Figure 1. Recycling of the plastic residue, from which the chip is removed is not a subject of this research.  Smart cards contain more than one metal (Au, Ag, Cu, Ni, and Zn) which exist all together. Their similar physical and chemical properties make it hard to separate them individually. At first step; silver, copper, and nickel are taken by HNO 3 leaching. After that, copper and silver are separated by cementation. Silver is precipitated by copper powder from that solution. Afterwards copper is separated by zinc powder. Residue from HNO 3 leaching is treated with aqua regia. Aqua regia is the only aqueous mixture which dissolves gold. Gold is precipitated from the acidic solution selectively. The most known chemicals for gold precipitation from acidic solutions are ferrous sulphate, sodium nitrite, sulphur dioxide, and sulphides [14]. Sodium metabisulphide is chosen as the precipitation agent. The practice of gold precipitation by sodium metabisulphide was developed in 1916 at the Nipissing mill to replace aluminum precipitation [15,16]. Flow sheet that has been applied on the experiments is given in Figure 2.

Nitric acid leaching and cementation experiments
In the nitric acid dissolution experiments five different solutions (1-5%) are prepared and shredded chips are boiled for 30 minutes in that solutions separately. As a result, silver, copper, nickel, and zinc in the chip dissolve completely. After that, these metals are separated selectively by precipitation methods. Metallic ion concentrations after HNO 3 leaching are given in Table 3.

Aqua regia leaching and gold precipitation experiments
Aqua regia (a mixture of acids containing 3 units of HCl and 1 unit of HNO 3 ) is a highly oxidizing acid in which gold dissolves easily. HNO 3 leach residue is leached in 5% aqua regia solution and all of the metallic parts in chip dissolve after 15 minutes of reaction time. Results are given in Table 4. One of the most known chemicals for gold precipitation is the sodium metabisulphide. Precipitation reaction with sodium metabisulphide is given below: 2 AuCl 3 + 3 Na 2 SO 3 + 3 H 2 O → 2 Au + 6 HCl + 3 Na 2 SO 4 1M sodium metabisulphide solution is added to the aqua regia solution after dissolution and stirred at 600-800rpm for 15 minutes. At the end It was found that gold is fully precipitated.

Conclusion
It can be seen from the experiments conducted in this work, silver and copper can be separated from nitric acid solutions by cementation successfully. Gold is precipitated by sodium metabisulphide from aqua regia solution with more than 90% for all the smart card types. Nickel in the solution can also be