Far Eastern Federal University scientists developed a method to extract gold from coal ash. They found out that on average, each ton of combustible stones waste burnt in Far East region power stations and boilers contains about 2.5 grams of gold, and it is considered as average performance according to the industry standards. Also there are platinum group metals and other valuable components in the waste. Technologies of "all you need" extraction from the processed coal can be converted to non-waste facilities of of ash dumps recycling.
Coal ash has been being regarded as a "gold mine" by science for decades. However, there are very few factories processing waste that occupies vast areas and pollute the environment in Russia. The reason is the complexity of technologies and investors distrust of them, who are not very encouraged by an alchemy bordering idea to extract precious metals from waste. But in the years ahead, the situation could change. At last this is a belief of a group of scientists of the Engineering School of the Far Eastern Federal University. Technologies of valuable components extraction from a variety of anthropogenic waste are intensively developing, and who knows for how long they still remain in the shadow of the traditional ways of ore deposits exploitation.
However, before moving to the story of the "coal Klondike", we recall that all projects of extracting revenue from waste are originally aimed on environment protection. Ash and slags resulting from coal combustion are such waste from which is necessary to protec territories. Ash slags are of the IV danger class, that is not very dangerous but still violate the ecosystem. Ash dumps (this is repositories of coal enterprises waste) occupy large areas, withdrawing much land from agriculture, contaminate soil by nmetal oxides including heavy ones, and produce much dust. Fighting it is possible but expensive, and, as a rule, the owners of ash dumps have no time to do this.
For example, there are 30 million tons of ashes and slags stockpiled on an area of about 150 hectares in Vladivostok - about the same territory had been occupied by one of the world's largest Olympic complex "Luzhniki" before its reconstruction.
Almost every big Russian city also has coal-fired powers, and, consequently, their ash «stadiums». There are hundreds of those all over the country.
Team of FEFU solves two issues in its study: to get rid of this waste and to make its processing cost-effective.
"As the amount of ash slags is huge, the large-capacity processing is required - Andrei Taskin, the deputy project manager, chief specialist FEFU department of the industrial cooperation development, explains. - Technically, its not a problem to recycle it in building and road construction materials -, but difficulties with distribution and logistics of such products will appear in case of large-scale production. In addition, as the economic efficiency of such production is so low that it is never within investors interests. But if you extract the valuable components of the waste first, it will become advantageous to deal with it. For example, ash contains more than 2 grams of gold per ton. It is considered average performance, by the standards of modern gold mining. The problem is only that the gold and other valuable components are difficult to extract".
According to the scientist, the environment friendly technologies of valuable components extraction from the ash slags hadnt existed until recently. The methods that had been known previously, did not solve the primary problem of waste disposal. A big "man-made tail" still remained after its application, and it had to be processed. But now they managed to mix, as they say, business with pleasure.
"We have developed more or less optimal technology - Andrei Taskin says. - It is similar to the extraction of valuable components from the ore deposits, but, of course, with its own features. Milestones: fractional separation, crushing of raw materials and comprehensive extraction of necessary elements by a combination of gravitational, electromagnetic, vibratory, sonication impact and flotation. Then the concentrate we get is exposed to chemical treatment by widely used non-toxic chemicals. A "pure tail", which remains, - is transformed into construction materials. Sand and unburned carbon are separated as well, and the first one goes to construction, the second one returns to power stations as fuel. Some other useful components also can be removed from the ash slags. But the main economic effect is achieved by gold and platinum group metals extraction. The residue also has a positive effect on the attractiveness of the project, but with longer terms for investments return".
Andrei Taskin says, the true gold is contained in the ash dumps. Scientists can bring it to the state of the ingot or transfer the concentrate with a high content of precious metal to the refining processing. Currently, studies of samples taken from the Primorye ash disposal plants are being conducted in the laboratory. The findings will help to accurately assess the "gold mineralization" of particular coal wastes (from particular sources). The project will last for two years.
The authors of the technology are not ready to say when a really functioning ash processing plant will appear. While the technology is more or less clear, the path of administrative and financial issues solution is not completely understood.
"The complexity, for example, may arise in case energy workers refuse to transmit coal waste of their enterprises for recycling, - Andrei Taskin says. - Energy workers are often not ready to transfer the waste for recycling for free of charge or for a little money. Overestimation of the initial price of ashes stags unambiguously reduces the investment attractiveness of the project.
At the level of the municipal administration, a problem of allocation of land for construction will arise with a high probability, as the bank may refuse to give a loan on reasonable terms, and so on".
However, developers have found industrial partners interested in introducing the new Russian technology of complex processing of industrial wastes. Production plant will be created for sure, but it hasnt been decided yet what scale it woud have. It might be a small experimental plot, or a large plant that will enable new high-tech jobs, improving the ecological situation in the whole region.
FEFU project "Development of physical and chemical principles of technology and basic technological solutions for extracting the fine gold and platinum group metals from industrial waste of energy enterprises" is supported by FTP "Research and development 2014-2020".