Hold onto that old newspaper, it could be worth its weight in gold. That鈥檚 the message from Japanese scientists who say that newsprint is a vital ingredient in a new process for recovering gold and other precious metals from industrial waste metal solutions. The treated paper can hold its weight in gold, they say.
Old electronic consumer devices such as computers, televisions and mobile phones are an important source of precious metals, which are used in their manufacture. But recovering the metals isn鈥檛 easy and usually requires large quantities of chemicals that are known to damage the environment.
Now a team of Japanese chemists says it can do a similar job using inexpensive and renewable materials.
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Katsutoshi Inoue and colleagues at in Japan, crushed and washed old newspapers and then combined the pulp with a chlorine compound.
The chlorinated paper was then treated with (DMA) and formaldehyde to form what they call a DMA-paper gel. Finally, this is dried to powder form.
Strong liquor
Inoue鈥檚 team tested the DMA-paper gel鈥檚 ability to bind to, or adsorb, metal using a standard industrial sample consisting of a liquor produced by dissolving old metallic components in hydrochloric acid.
The liquor contains the common metals copper, zinc and iron, each in concentrations ranging from 190 to 840 parts per thousand. However, it also contains 250 parts per million of gold and 11 to 16 parts per million of platinum and palladium.
The gel turned out to be highly selective in the metals it adsorbed. It took up over 90% of the gold, platinum and palladium, but almost negligible quantities of copper, zinc and iron.
The waste paper is a crucial part of the gel鈥檚 structure: the amorphous nature of the cellulose within the paper allows chemicals to penetrate easily into its matrix and leads to a high carrying capacity 鈥� one kilogram of gel can hold 906 grams of gold.
Slow but sure
鈥淎nd you can use the gel again after the metal [is removed],鈥� says Chaitanya Raj Adhikari, a member of Inoue鈥檚 team. Adhikari says it is as yet unclear exactly why the DMA-paper gel is so selective for precious metals. 鈥淎lthough amine groups in DMA are known to favour precious metals,鈥� he says.
鈥淥ur gel is prepared from inexpensive, renewable resources and it has high selectivity and capacity for precious metals,鈥� says Adhikari. 鈥淭hose properties make it a wonderful adsorbent.鈥�
Jianmin Yu at in Yunnan province, China, agrees that the DMA-paper gel gives impressive yields, but says it takes at least five hours to adsorb the precious metals, a significant disadvantage that may limit its industrial use. 鈥淭he adsorbing kinetics are very slow,鈥� he says.
Journal reference: (DOI: 10.1021/es800155x)
