Find gold from technology waste

Scientists have published the results of the study 'recovering' gold in technology waste unexpectedly. Every 1 ton of garbage smartphone, people will get about 350 grams of gold.

There are many methods for extracting gold such as precipitation, ion exchange, solvent extraction. But these methods must use toxic chemicals and the residues after the gold has been separated are toxic wastes.

Scientists are constantly searching for ways to separate gold from other materials most effectively, safely and least polluted.

Gold . everywhere

But why do we have to find another method of collecting gold besides mining gold ore? The answer is that this rare metal is actually everywhere around us.The most potential "gold mine" today is e-waste, especially laptops, smartphones and digital cameras.

Every 1 ton of garbage smartphone, people will get about 350 grams of gold.

Thanks to its high electrical conductivity and antioxidant, corrosion resistance in different environments, gold is not only used for jewelry but also for making circuit boards, ICs and connectors. electronic device.

Connectors made of gold will transfer digital data faster and more accurately than other metals. For computers, gold is used in electronic circuits to form a central processor (CPU), the computer's brain.

According to the United Nations Environment Commissioner in 2014, 1 gold is collected for every 41 smartphones. Particularly, an iPhone contains about 0.034 grams of gold and 0.34 grams of silver. Federico Magalini, e-waste expert and executive director of UK e-waste Sofies recycling company, once gave a surprising number: the amount of gold in a ton of smartphones is 70 times more than the one. Ordinary gold mine.

In an interview with The Verge, Magalini said that the average gold content in any ton of material is 0.5g. This number for gold mines is much higher, "every 1 ton of digging material can filter 5-6 grams of gold".

Although the amount of gold in a phone is not worth it, but with 1 ton of smartphones, we will get about 350 grams of gold, which is 70 times higher than the average in the gold mine, according to Magalini. "So we think that separating gold from e-waste is more efficient (mining) because the concentration of gold is very high," Magalini said.

There is another huge "gold mine" but the recall is not simple: the vast ocean. According to the US Department of Commerce's National Oceanic and Atmospheric Administration, a study has estimated that every 100 million tons of seawater in the Atlantic and North Pacific contain one gram of gold.

Big Think page estimates an estimated 20 million tons of gold in the ocean. Even according to a report published in the journal Environmental Science & Technology in October 2017, every year 1.8 million USD worth of gold passed through the sewer system in Switzerland.

The reason may be because Switzerland has many gold refineries. However, according to the Washington Post, scientists believe that the amount of gold mixed in waste water is not high enough to deserve investment to recover them.

Gold absorbing foam

One of the new methods of gold splitting and shows the potential is to use a special "sponge" (like a dishwasher) to "absorb" gold in a liquid environment.

According to research published in the Journal of the American Chemical Society on November 3, this method is arguably the most effective so far to separate gold from liquids. Recall the story of the amount of gold found in underground sewage in Switzerland to see how useful this method can be.

The researchers first made a frame made of metal-organic compounds, consisting of iron ions connected by a "skeleton" of 1,3,5-benzenetricarboxylate compound, then wrapped this frame. into a polymer layer called PDA . The main layer of this shirt will help to summarize the "stray" gold molecules in the solution that need to "treat gold".

Big Think page describes this tool as a sponge for washing dishes, but it does not absorb soap or water, but absorbs and holds gold. Exciting future: dip the 'sponge' (purple) into a yellowish solution to "collect" precious metal easily.

"Golden suction sponge".

This method is said to be more effective than similar products before. The researchers said that when immersed in the solution, each gram of this special sponge will absorb 1 gram of gold. Especially, it can "catch" 99% of the gold in any solution within just 2 minutes.

After being filled with gold, the sponge will be decomposed with hydrochloric acid to obtain the final result: gold.

The researchers tested this method in many different practical situations, including the recovery of gold in electronic waste, one of the most practical applications.

In their experiments, the researchers separated the metal components of copper, nickel and gold in the computer processor and mixed it with some chemicals to form a liquid solution.

The problem here is how this special "sponge" absorbs only gold in the solution that contains these three different metals. The amazing thing is that the experimental results show that "sponge" can get 95% of the amount of gold in the solution above.

Because of the "fame" of the gold-containing sewage in Switzerland, the team also applied its work there, eventually obtaining 99% of the gold and this waste water. Experimental results with seawater also obtained 99% of the gold contained in the test sample.

Big Think commented that these positive results show the potential of "sponge gold" method for waste water, which has many different substances and no filter can only retain gold and " give away "other impurities.

"Mining" right in the city

It would be wasteful if not taking advantage of the metal in electronic waste. In fact, urban mining trend has appeared , ie "mining in the city" , or rather, investing in the exploitation of metals from local waste.

BBC recognizes that urban mining can become a "big business" and takes the example of a specialized metal separator from the University of New South Wales (UNSW) by a professor led by Veena Sahajwalla. blame.

In an interview with the BBC in August, Sahajwalla is confident the facility will start making profits within the next 2-3 years."Metal separation from e-waste has both economic, social and environmental benefits," said the professor, implying that urban mining also creates jobs for local workers.

A study jointly conducted by Tsinghua University (China) and Macquarie University (Australia) showed that the cost of exploiting metal from electronic waste was 13 times lower than mining, according to BBC data. lead again.

"Therefore, metal extraction from e-waste has the potential to become a lucrative business," commented Professor John Mathews (Macquarie University).

The need for urban mining is very large, so the amount of electronic waste generated each year is increasing. According to data from the International Telecommunication Union - a United Nations agency, an estimated 45 million tons of e-waste is thrown away in 2016, and this figure is expected to increase to 50 million tons by 2021. .

There is another benefit to urban mining when it is possible to reuse metals from electronic waste, which means reducing the need to exploit them in the wild, thereby avoiding resource depletion.