Simple and cost-effective extraction of rare earth precious metals from industrial waste


Researchers from Kanazawa University recovered palladium and metal from industrial waste, which helps reduce pollution and reduce demand from depleting natural resources.

Many rare metals are in scarce supply, but demand for use in electronics, medical instrument and other purposes is growing. As waste, these metals pollute the environment and harm human health. It would be better if we recycled the metals from waste for reuse. Unfortunately, conventional recycling methods are a combination of complex, expensive, toxic, wasteful and ultimately inefficient.

In an upcoming study in Journal of Chemical Engineering, researchers from the University of Kanazawa report a major improvement in the recovery of silver and palladium ions from acidic waste. Recovery of the metals is in the form of elemental, metallic direct – simply burn the extracted material and collect the remaining metal after further heating.

The researchers modified ultrasound particles of cellulose, a abundant and non-toxic biopolymer, to adsorb silver and palladium ions at room temperature. The adsorption was almost complete at acidic pH by acid densities of about 1 to 13 percent depending on size. These are reasonable test situations.

“The adsorbent selectively purchased the soft silver cations and palladium,” explained lead author Foni Biswas. “Of the 11 competing metals we tested, only copper and lead cups were advertised, but we easily removed them.”

The peak of metal ion was fast – e.g., an hour for silver. The highest adsorption usually requires many hours with other techniques.

“Intraparticle proliferation did not inhibit adsorption, an endothermic, spontaneous chemical process,” explains lead author Hiroshi Hasegawa. “The maximum potential of a metal field – eg, 11 mmol / g for silver – is much higher than previously reported in research.”

After extraction, the researchers simply added the cellulose granules to obtain element silver or palladium powder. After burning at a higher temperature the powder turned into bullets. Cyanide or other toxic agents were not required. Spectroscopic studies showed that the last metal particles were in metallic rather than oxide form.

“We removed almost all silver and palladium from real industrial waste samples,” says lead author Biswas. “By obtaining pure and elemental metals we went as smoothly as we did in our experiments. ”

Palladium and silver are precious metals but natural supply is increasingly limited. Future needs will require the recycling of the metals we already have in a practical way. The research reported here is an important development to avoid supply and circulation problems that will only grow in the coming years.

Fact: “Selective recovery of silver and palladium from acidic waste solutions using cellulose with dithiocarbamate action” by Foni B. Biswas,
Ismail MM Rahman, Keisuke Nakakubo, Koki Yunoshita, Masaru Endo, Kanji Nagai, Asami S. Mashio, Tsuyoshi Taniguchi, Tatsuya Nishimura, Katsuhiro Maeda and Hiroshi Hasegawa, 5 October 2020, Journal of Chemical Engineering.
DOI: 10.1016 / j.cej.2020.127225