Gold is used in electronic boards. Photo: Internet

Currently, the amount of e-waste collected is still too small - more than 10,000 tons compared to more than 90,000 tons of e-waste that Vietnamese people generate every year. Most of the collection and dismantling is not in accordance with regulations and only focuses on recovering materials that are easy to recover and recycle such as some metals, the rest is destroyed or goes to solid waste landfills. The waste contains some precious metals, such as gold, copper, palladium, etc., so if there is an effective recycling technology solution, it will bring economic value and protect the environment.

Dr. Trieu Quoc An, Faculty of Food and Environmental Engineering, Nguyen Tat Thanh University, said that there have been a number of researches on electronic waste treatment technology in the country for recycling and metal recovery. However, the process of recovering precious metals, especially gold, is still limited. Current technologies are mainly based on hydrometallurgy (the process of recovering metals by low-temperature reduction reactions in a chemical solvent less than 100°C) or heat treatment (using a furnace at high temperature). However, to dissolve gold, these technologies often use many different chemicals (cyanide, thiosulfate, halide, ...) with high oxidizing and toxic properties, capable of creating secondary waste sources, and the recovery efficiency is not high (about 90-95%).

Face with that fact, Dr. An and his colleagues have researched a solution to recover gold directly without having to go through many stages and without using many chemicals. Specifically, the team performed gold extraction directly from electronic boards using a mixture of persulfate (S2O8²-)/hydroxy peroxide (H2O2).

Gold is coated on the electronic board surface through a layer of iron/nickel/aluminum alloy (Fe-Ni-Al) which will be removed thanks to the strong oxidizing properties of the persulfate (S2O8²-)/hydroxy peroxide ( H2O2). Base metals, such as Fe, Ni, Al, Cu will be partially dissolved, except for gold and thanks to that the gold layer is released from the surface of the electronic board.

According to Dr. An, this process does not need to go through pre-treatment steps, such as cutting and grinding into powder like processes used such as heat treatment and hydrometallurgy. In addition, the chemicals used are not highly toxic and pollute the environment, the recovery efficiency is up to 98%, the gold purity is over 95%. The components in the solution after the extraction process can be converted or recycled into other valuable products.

Dr An added that, in the current hydrometallurgical process, the dissolution of metals in electronic waste, especially from printed circuit boards, forms solutions in which basic metal ions are (copper, iron, lead, nickel...) much higher concentration of gold ions. In this method, adsorbents are often used to separate gold ions III (the oxidation state of gold), after which the gold ions are further reduced to recover gold.

Therefore, the group also studied the use of Zirconia oxide (ZrO2) adsorbent surface modified with thioctic acid in the separation of gold (III) ions. The results show that the material has the ability to selectively separate gold (III) ions from the solution after dissolving the metals from the electronic board. In addition, ZrO2 can also be used to adsorb Pladium Pd(II) ions, without affecting the particle size and morphology of the obtained materials. According to Dr. An, using ZrO2 adsorbent surface modified with thioctic acid can be applied in the hydrometallurgical process to separate metals, saving costs and limiting secondary wastes because the material can reuse.

Currently, the technology of gold extraction and gold ion separation (III) using ZrO2 adsorbent material has been completed by the research team in the laboratory and wishes to cooperate with enterprises wishing to deploy the technology in the extraction of precious metals from e-waste sources.

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