Gold, silver, bronze, nickel, zinc and other metals present in various electronic appliances and computer equipment, which end up as waste, can be fully recovered. According to Luis Henrique Mendes da Silva and Maria do Carmo da Silva Hespanhol, professors in the Graduate Program in Agricultural Chemistry at the Universidade Federal de Viçosa, “it is possible to recover 100% of these metals using aqueous two-phase systems (SABs), an economically feasible and efficient method which does not jeopardize health or the environment.” The recovery of metals prevents new elements from being taken from nature, reduces contamination by inappropriate disposal of this waste and brings economic gains by allowing already extracted resources to be back to the production cycle.
Professors Silva and Hespanhol estimate that the removal of metals from nature by industry cause a very strong environmental impact. Within 30 to 40 years, various sources are expected to be depleted, while these minerals will be scattered in the environment, as components of some products. Therefore, it is a strategic challenge the creation of simple and cheap recovery methods that do not endanger the health of those who will handle with them. The SABs meet all these requirements.
With over twelve years of experience with the application of these systems, the researchers explain that the SABs can be used to extract various materials. However, the most interesting results were obtained in the purification of metals. The aqueous two-phase system is mostly composed of water mixed with small amounts of inorganic salt and polymer. The researchers explain that “you can take a glass of water, add salt and polymer, which is a white powder, and shake. The system becomes turbid as milk. After 20 to 30 seconds, the system is separated into two phases. With the addition of an extract into the system, the gold ion extracted remains completely on the top, while the other metals stay on the bottom”.
In practice, SABs are applied as follows: first, the metal plate must be ground in a mill. Then, it is treated with hydrochloric acid, which dissolves this plate and forms a colored liquid, which is almost 90% water. The addition of salt and the polymer is enough to separate the system into two phases. Pure gold goes to the polymer-rich phase and the other elements, such as copper, iron and nickel, stay in the salt-rich phase. For those metals that were on the bottom, it is only required the preparation of another aqueous biphasic system for each of them and change the polymer and salt. Thus, all the metals can be purified very efficiently.
The researchers claim that, besides its high accuracy in the extraction of metals, the method is easy to apply: “The operator does not need to be a chemist or an expert in any area. After a 30-minute training, anyone can operate it without risks because it is not toxic.” Unlike other extraction methods, the aqueous two-phase system causes no harm to health. The professors assert that hexane and water, for example, can be used to extract gold, but it would require the manipulation of a highly toxic solvent and special trained personnel.
The easy application of aqueous two-phase system allows making the best use of the electronic waste available, wherever it may be: “An Indian, a Chinese or an American could make it. Energy and resources have already been spent to take these products to where they are. It is not economically feasible to concentrate all these materials in one single place for processing them. It is interesting to recover these metals in the place where the products are.”
The literature indicates that, when using SABs, everything that happens in a beaker, in a laboratory, can happen on a large scale. Since 2011, professors Silva and Hespanhol have been developing a project in partnership with Vale, a global mining company, involving this metal purifying method. The company is requiring the patents of the application of this system. “They know that this is a highly strategic research, and they will perform second-order mining, by extracting metal from products. We envision that this technology will be absorbed by the Vale company”, researchers concluded.
Besides the environmental and economic benefits of the method, the professors pointed out their personal concern on the social gains that the application of this research can provide: “We would be very pleased to see this technology used by people in need because it would promote a significant change in the relationship of economic forces, and would be an opportunity for socially unfavored people. Imagine garbage collectors in Baghdad, Aracaju, Piauí, or anywhere else, with access to electronic waste, who could obtain valuable metals by just using simple containers to implement the two-phase aqueous system! For us, as scientists and human beings, it would bring great joy. But we know that hard research work is necessary to make it become reality. “