Money doesn't grow on trees, but gold can. An international team of scientists has found a way to grow and harvest gold from crops. A gold-mining technology called phytomining uses plants to extract particles of the precious metal from soil.
Some plants have a natural ability to absorb through root system and accumulate metals such as nickel, cadmium and zinc in leaves and shoots. For years, scientists have been looking for ways to use such plants, called supersinks, to remove pollutants from the environment.
But nothing is known about gold superaccumulators, since this metal is practically insoluble in water, and therefore plants have no natural way to absorb its particles through their roots.
"In some chemical conditions Gold solubility can be artificially increased,” says Chris Anderson, an environmental geochemistry and phytomining specialist at Massey University in New Zealand.
Getting gold
Fifteen years ago, Chris Anderson first demonstrated to the public that the mustard plant was capable of absorbing gold from chemically prepared soil containing particles of this metal.
The technique works something like this: Find a fast-growing plant with a lot of above-ground foliage, such as mustard, sunflower or tobacco. Plant the crop in soil containing gold. Nice place there may be waste heaps or dumps surrounding old gold mines. Conventional methods cannot ensure 100 percent extraction of gold from minerals, and therefore some volumes of the metal end up in waste. When the plant reaches its maximum height, treat the soil with a chemical that dissolves the gold. The plant absorbs gold-containing water from the soil, and in the process of “breathing” water appears from tiny pores on the surface of the leaves, and precious metal accumulates in biomass. All that remains is to harvest.
However, putting the gold into the crop is the easy part of the job. Getting it from the plant proves much more challenging, Anderson explains.
“Gold behaves differently in plant material,” says the scientist. If a plant is burned, then some amount of metal will remain in the ashes, and some of it will disappear altogether. Ash treatment is also a major challenge and requires the use of large volumes of concentrated acids, which are dangerous to transport. 
Gold, which can be found in plants, is in the form of nanoparticles and is therefore of great value to the chemical industry, which uses gold nanoparticles as a catalyst for chemical reactions.
Golden Harvest
Phytomining will never replace gold traditional sources, says the scientist. “The value of this technology is the potential for revitalizing contaminated land in gold mining areas,” adds Chris.
The chemicals used to dissolve gold cause plants to absorb other contaminants from the soil, such as mercury, arsenic and copper, which are common elements found in mine waste and dangerous for people and the environment.
"If we can make a profit by extracting gold from crops while restoring soils, that would be a significant achievement," Anderson says. IN given time he is working with researchers in Indonesia to create environmentally friendly technology for small firms using manual labor in gold mining, which will reduce mercury pollution as a result of the activity.
However, some scientists say the environmental risks associated with gold farming itself may be too great. Indeed, to dissolve gold particles in the soil, it is necessary to use cyanide and thiocyanate - the same dangerous chemicals, used by mining companies to extract gold from stones. Independent agronomists are confident that the process itself can create environmental problems.
Money doesn't grow on trees - but gold might. An international team of researchers has found a way to grow and harvest gold from plants.
This technique uses plants to extract precious metal particles from the soil. Some plants have the natural ability to absorb metals such as nickel, cadmium and zinc through their roots and accumulate in their leaves and shoots. For years, scientists have been exploring the possibility of using these plants, called hyperaccumulators, to clean up chemical pollutants.
But there are no gold hyperaccumulators known to science because gold does not dissolve in water, and plants have no natural way to extract gold particles through their root systems.
However, geochemist Chris Anderson from Massey University in New Zealand states: "Under certain chemical conditions, gold solubility can be enhanced."
15 years ago, Anderson first demonstrated that mustard plants were able to absorb gold from chemically prepared soil containing metal particles.
This technology works something like this: You find fast growing plant with a large volume of above-ground leafy matter, such as mustard, sunflower or tobacco. Plant it on soil containing gold. A good place is waste rock dumps near old gold mines. Traditional gold mining is unable to extract 100 percent of the gold from the surrounding rock, so some remains in waste. Once the crop is up, treat the soil with a chemical agent that makes the gold soluble. As moisture evaporates from the leaves of the plant, it will draw gold-rich water from the soil and concentrate it in its green mass. Then harvest.
As Anderson explains, placing the gold into the plant is the easiest part of the job. It is much more difficult to remove it back later.
“Gold behaves differently inside a plant,” he says. If the plant is burned, some of the gold will remain combined with the ashes, and some will simply disappear. Handling the remaining ashes is also difficult because it requires huge amount strong acid which may be dangerous to transport.
Extraction of precious metal using plants will never replace traditional methods gold mining According to Anderson, "The value of this technique lies in the restoration of sites contaminated by metal mining."
The chemicals that make gold soluble also cause plants to release other contaminants, such as mercury, arsenic and copper - substances that are common in mine waste sites and can pose a risk to people and the environment.
“If we can make a profit by mining gold and restoring the soil at the same time, that will be good deed" says Anderson, who is currently working with a team of researchers in Indonesia to create a sustainable system for small-scale gold miners to reduce mercury pollution from their operations.
However, some scientists point out that the environmental risk associated with the cultivation of gold-bearing plants is also not too low - the medicine in in this case not much better than the disease itself. The fact is that to dissolve gold particles in water, the same chemicals are used that mining companies use to extract gold from mineral rock - and these are cyanide and thiocyanate.
It is not uncommon for a person to pick up a stone and seem to see gold in it. How can you tell if it is gold or not? If the stone has yellow grains visible to the eye, then this is easy to check. Use a needle to scratch the yellow grains. If it's gold, it will scratch like metal. Lead can be scratched for clarity, and gold will be scratched in the same way. Pyrite will crumble. But mica crumbles into flakes. If you press such a scale with your fingernail on something hard, it will simply crush into dust. Pyrite will crumble when struck. A grain of gold will behave like metal and will simply flatten. But this is visible gold. If it is not visible, but your sixth sense tells you - There is gold in this stone.
Then we start scouring the Internet and reading a lot about aqua regia and other complicated things. chemical processes. However, everything is much simpler and less dangerous for your health and the health of others. Before you pick up acid and mercury, remember what you will do after the acid eats your lungs and the mercury accumulates in your limb and you will never be able to lift it again. In order to check whether there is gold in a stone or not, it is enough to have a regular tincture of iodine on hand. Unpleasant smell. It's tolerable. Kitchen hood to help you. Where to start? You need to crush the stone in a mortar. Just grind it into powder. Pour the powder into a jar with a lid. Test jars are very convenient for these purposes. Fill the powder with tincture of iodine from the first aid kit. Not with acid and mercury, but with ordinary iodine tincture. Stir thoroughly. We close the lid, otherwise the smell in the rooms is like in a hospital. After the sediment has settled, lower a strip of filter paper (just cut it off paper towel strip) into the solution without touching the precipitate. Took it out and dried it. Then they dipped it again and dried it. Do this several times. Dry the strip and set it on fire. Naturally, in compliance with fire safety rules. If gold is present in the stone, then the ash remaining after burning the strip of paper is colored purple color. You can see what the color purple looks like in Yandex where there is a good color scale.
So I recommend this particular method for determining the presence of gold in stones. Absolutely safe except for burning the strip.
Naturally, the method of washing crushed ore is more interesting, but this is only provided that it contains visible gold. The ore is crushed in a mortar made from an ordinary gas cylinder. The cylinder, with certain safety measures, is cut to half and the ore is crushed in it using a round steel bar. Then the resulting powder is washed.
If there is fine gold in the ore, we use the same iodine to collect it, but only in the solid state. Solid (crystalline) iodine is easier to obtain than acids. It is much easier to work with and does not get dirty environment. And this is a matter of extraction, i.e. production Not the topic of today's article.
Where the bronze cliffs hung
Above the greens mountain river,
A geologist in a checkered shirt stood up
And he swung his pickaxe at the rocks.
V. Soloukhin
Our planet is great and rich. Walled up in its depths countless treasures- oil and coal, gold and diamonds, copper and rare metals. At the cost of enormous amounts of time and labor, humanity over the thousands of years of its existence has managed to extract only a small fraction of underground wealth from the earth. In all countries of the world, a large army of exploration geologists is examining, tapping, and feeling the Earth, trying to find new deposits of minerals. The experience of many generations and first-class technology, the erudition of great scientists and complex instruments - everything is put at the service of searching for earthly treasures. And yet these searches are rarely crowned with success. Nature jealously guards its secrets, yielding only to the most inquisitive and persistent.
Since ancient times, signs have been passed down from generation to generation indicating the emergence of gold-bearing veins and oil, copper ores and coal to the surface. The idea of using plants to search for minerals has long been conceived. In vintage folk beliefs it speaks of herbs and trees capable of detecting various deposits. For example, it was believed that rowan, buckthorn and hazel growing nearby hide gems, and the intertwined roots of pine, spruce and fir indicate gold placers beneath them. Of course, these legends remained a beautiful dream, and that's all.
Geologists have resorted to the help of plants only in recent decades, when scientifically based connections were found between certain plants and deposits of certain minerals. Thus, in Australia and China, with the help of plants that select soils with a high copper content for growth, deposits of copper ore were discovered, and in America, deposits of silver were found using the same method.
For recent years In our country, scientists have conducted thorough studies of the vegetation settling in areas where metal-bearing ores are located. The conclusions that scientists came to were truly amazing. The connection between the plant, the soil and the subsoil turned out to be so close that appearance or chemical composition For some plants, it was possible to judge what ores lie in the place where they grow. After all, the plant is not at all indifferent to what species is under the soil on which it grew. Groundwater gradually dissolves metals to one degree or another and, seeping upward into the soil, is absorbed by plants. Therefore, grass and trees growing above copper deposits will drink copper water, and above nickel deposits - nickel water. Whatever substances are hidden in the earth - beryllium or tantalum, lithium or niobium, thorium or molybdenum, water will dissolve their smallest particles and bring them to the surface of the earth; the plants will drink these waters, and microscopic amounts of beryllium or tantalum, lithium or niobium, thorium or molybdenum will be deposited in every blade of grass, in every leaf. Even if metals lie deep under the soil, at a depth of twenty or thirty meters, plants will sensitively respond to their presence by accumulating these substances in their organs. In order to determine how much and what metals a plant has accumulated, it is burned and the ash is studied. chemical methods. It happens that over large deposits of some ore, this metal accumulates in a plant a hundred times more than in the same plant growing in another area. Most metals are always accumulated by plants in very small quantities. The living organism of the plant needs them, and without them the plant gets sick. However, strong solutions of the same metals act as poison on many plants. Therefore, in areas of metal ore deposits, almost all vegetation dies. Only those trees and herbs remain that can withstand the accumulation of large quantities of any metal in their bodies. Thus, in these areas thickets of certain plants that are capable of drinking appear. metal water. They indicate the places where you need to look for minerals.
For example, large quantities Some plants from the legume family, such as Sophora and commonweed, are able to accumulate molybdenum in their bodies. Larch needles and wild rosemary leaves easily tolerate large amounts of manganese and niobium. Neither deposits of strontium or barium, willow and birch leaves accumulate these metals thirty to forty times more than normal. Thorium is deposited in the leaves of aspen, bird cherry and fir.
In the Altai Mountains, where copper ore has long been mined, you can often find a perennial herbaceous plant with narrow bluish leaves, above which rises an indistinct cloud of numerous pale pink flowers. This is downloading Patren. Sometimes kachim forms large thickets that stretch in wide stripes for several tens of kilometers. It turned out that in most cases copper ore lies just under the kachima thickets. Therefore, geologists, before starting underground work, draw up maps of the distribution of kachim and use the maps to determine the locations of supposed copper deposits. The powerful, woody, twisted cachima root goes deep into the ground. It penetrates through the soil and through cracks in the underlying rock reaches groundwater in which copper is dissolved. Copper water rises up to the bluish leaves and light flowers. From June to August, the kachima thickets appear from an airplane as a pink lace, draped by nature over the scorched steppe rocky slopes. On aerial photographs, this lace will be indicated by a clear stripe, indicating the places where copper ore occurs.
In the east of our country, dense thickets over deposits of rare metals that contain beryllium are formed by Stellera dwarf. Steller - very graceful plant with straight thin stems, densely dressed with bright green oval leaves pressed to the stem. The stem is crowned with a bright light crimson head, consisting of two dozen small tubular flowers; the outside of the tube is crimson, and the tip of the rim is white. Just like the kachim, this extremely elegant and tender plant a powerful root has developed underground, penetrating with its branches deep into cracks in hard rock and sucking up water with beryllium dissolved in it. 
Steller perfectly withstands the beryllium “menu”. Wide stripes of its continuous thickets indicate on aerial photographs the location of underground deposits of rare metals.
Everyone knows what enormous technical significance uranium has. Many countries around the world are searching for this radioactive element. And here plants help geologists. If the uranium content in the ash of burnt branches of bushes and trees is high, it means that uranium can be found in this area. Junipers are especially good at collecting uranium. Their powerful, long roots manage to penetrate to great depths during the two to three hundred years of life of each individual. Even if the uranium deposits are not rich, the juniper will accumulate quite a lot of uranium in its branches. Even better indicates the presence of uranium, the well-known berry bush blueberry. If this plant drinks uranium waters, its oblong fruits acquire a wide variety of colors. irregular shape, and sometimes even turn from dark blue to white or greenish. Pink fireweed, growing on uranium deposits, can give the plant a range of colors - from white to bright purple. For example, fireweed flowers of eight different shades were collected near uranium mines in Alaska.
As a rule, uranium is accompanied by sulfur and selenium. Therefore, plants that accumulate these substances are also taken into account as an indicator of possible uranium deposits. If geologists know plants well, they will always distinguish selenium astragalus from all others. And where there is selenium, there may be uranium.
In some areas of the Karakum Desert, sulfur deposits emerge close to the surface. The soil is so saturated with sulfur that, except for one type of lichen, nothing grows there. But lichens form large bald patches, clearly visible from an airplane.
Almost no vegetation grows in desert gold deposits. But wormwood and harelips feel excellent here. These plants accumulate such quantities of gold in their bodies that they can rightfully be called golden.
It is interesting that some plants living above ore deposits change their appearance in one way or another. Therefore, geologists in search of minerals must pay attention to the ugly shapes of trees and grasses. For example, where a large nickel deposit was discovered, nickel waters influenced herbaceous plants that “their own mother will not recognize them.” The well-known furry lumbago with large flower completely changed here. Above the nickel deposits, you can collect a bouquet of lumbago with flowers of the most varied colors - white, blue, and indigo. In addition, you can find here individuals whose petals seem to be torn into narrow ribbons or have none at all. Only bare, uncovered stamens stick out at the top of the stem.
The hairy breast has changed even more noticeably. This perennial resembles a small aster. Its small yellow baskets rise like a shield above a woolly white-felt stem framed by numerous oblong leaves. But nickel, which from the beginning of life penetrated into all her organs, did its dirty work - the baby was unrecognizable. Smallest yellow flowers, which should have been collected into an inflorescence, scattered throughout the stem and hidden in the axils of the leaves. The leaves and stems also lost their shape and color. Every plant is a freak; one more unusual than the other. Ugly individuals of the hairy breast are so confined to deposits of nickel ores that, having encountered these forms somewhere in large quantities, geologists begin to carefully examine this area and almost always find nickel there.
It has also been noted that hollyhock flowers with abnormally dissected narrow petals may indicate deposits of copper or molybdenum.
Rocky slopes in Armenia blaze with tongues of fire in spring. The poppy is in bloom, coloring the foothills in festive red. The poppy petals with a large black spot at the base are wide, almost kidney-shaped. However, the poppy that grows in some areas is not similar to its relatives. Its petals are dissected into lobes in a way that is observed in most individuals growing in these areas. What's the matter? The fact is that deposits of lead and zinc are hidden in the ground here. These metals, constantly absorbed by the plant, changed the entire course of its development, and as a result, the shape of the petals also changed.
And the petals of poppies growing on copper-molybdenum deposits can be completely black, with a narrow red border - this is how they grow black spot. In other individuals, the spots on the petals become long and narrow, forming a kind of black cross in the center of the flower, or, conversely, move to the outer edge of the petal. In general, these poppies look so unusual that they immediately catch the eye of even an unobservant person. And for geologists they are a godsend!
Sometimes, with an increased content of metals in the soil, plants take on an unusual dwarf form. When cold wormwood grows over a lithium deposit, it appears undersized with its twisted stem and small, abnormally bluish leaves. Plants that absorb large amounts of boron also do not grow upward, but take on a form spread out on the ground, which differs sharply from the usual appearance of this plant. The gumweed that drinks lead water also grows small and stocky, and its leaves and stems become dark red, while its flowers become small and inconspicuous.
However, the opposite also happens. For example, in some areas of our country you can find giant aspens. The leaves of these tall, thick-trunked aspens are several times larger than usual. Can you imagine an aspen leaf thirty centimeters long? Giant leaves on equally gigantic petioles flutter like flags. Maybe these extraordinary trees drink “living” water? In a way, yes. They drink water saturated with thorium - here, under the soil, lies a deposit of rare metals.
Narrow rivers flow through the cold lands of Yakutia, among marshy swamps and open larch forests, flowing into deep rivers.
Summer is short and stormy in the Arctic. The ice floes, colliding, float along the spring waters of the rivers, and already on their banks low thickets of rhododendrons are covered with a purple-pink foam of small flowers, blueberries are blooming tender leaves, wild rosemary smells intoxicating. Above all this spring splendor from dawn to dusk there is a tedious ringing of mosquitoes. Somewhere here, among the larches, under a dense lichen carpet, the richest diamond deposits lie deep in the ground. Diamonds are interspersed with small raisins in the rock containing coal. This type of rock with diamonds is called a kimberlite pipe. How to look for it, this kimberlite pipe, if it is hidden by nature under seven locks? Only occasional outcrops of kimberlite on the surface help geologists discover diamond deposits. Either a powerful landslide will expose ancient layers of the earth, or a long-ago earthquake or volcanic eruption. True, in recent years new technologies have come to the aid of geologists. smart appliances, allowing one to “see” underground, but they cannot accurately indicate the locations of natural treasure troves. Is it possible to use vegetation as assistants, scientists wondered. It turned out it was possible. It was noticed that directly above the kimberlite pipes both trees and shrubs look much better than their counterparts growing on limestone. This is understandable. In rocks that include diamonds, in addition to coal, apatites containing phosphorus, mica containing potassium, and various rare metals necessary for the plant body were found. All these elements, in greater or lesser quantities, are dissolved by groundwater, which then penetrates the soil. Therefore, plants that are lucky enough to grow above diamond deposits feed much better than trees and shrubs growing on skinny limestone. That is why above the diamond deposits the larch is taller and thicker, the alder is curly, and the blueberry thickets are thicker. Where one hundred frail larches grew on limestone or a swamp, two hundred healthy ones grew on kimberlite pipes. If you rise above these places by plane, you can see denser and lush thickets among the larch forests - exactly in those places where kimberlite pipes lie. But in such an important matter as the search for diamonds, the human eye is not trusted. Much more objective is the eye of the camera, dispassionately looking down at the ground. On the film, the camera carefully marks with dark spots on the gray background of light forests areas of denser and higher forest, and therefore, places where you need to look for diamonds.
No, it is not an easy task to search for minerals. And, of course, one cannot completely trust the testimony of trees and herbs alone. However, plants, like real scouts, have more than once helped geologists in search of underground treasures.
Money doesn't grow on trees, but gold can. An international team of scientists has found a way to grow and harvest gold from crops. A gold-mining technology called phytomining uses plants to extract particles of the precious metal from soil.
Some plants have the natural ability to absorb metals such as nickel, cadmium and zinc through their roots and accumulate in their leaves and shoots. For years, scientists have been looking for ways to use such plants, called supersinks, to remove pollutants from the environment.
But nothing is known about gold superaccumulators, since this metal is practically insoluble in water, and therefore plants have no natural way to absorb its particles through their roots.
“Under some chemical conditions, gold solubility can be artificially increased,” says Chris Anderson, an environmental geochemistry and phytomining specialist at Massey University in New Zealand.
Getting gold
Fifteen years ago, Chris Anderson first demonstrated to the public that the mustard plant was capable of absorbing gold from chemically prepared soil containing particles of this metal.
The technique works something like this: Find a fast-growing plant with a lot of above-ground foliage, such as mustard, sunflower or tobacco. Plant the crop in soil containing gold. A good place might be waste piles or dumps surrounding old gold mines. Conventional methods cannot ensure 100 percent extraction of gold from minerals, and therefore some volumes of the metal end up in waste. When the plant reaches its maximum height, treat the soil with a chemical that dissolves the gold. The plant absorbs gold-containing water from the soil, during the process of “breathing” water emerges from tiny pores on the surface of the leaves, and the precious metal accumulates in the biomass. All that remains is to harvest.
However, putting the gold into the crop is the easy part of the job. Getting it from the plant proves much more challenging, Anderson explains.
“Gold behaves differently in plant material,” says the scientist. If a plant is burned, then some amount of metal will remain in the ashes, and some of it will disappear altogether. Ash handling is also a major challenge and requires the use of large volumes concentrated acids which are dangerous to transport.
Gold, which can be found in plants, is in the form of nanoparticles and is therefore of great value to the chemical industry, which uses gold nanoparticles as a catalyst for chemical reactions.
Golden Harvest
Phytomining for gold will never replace traditional sources, the scientist says. “The value of this technology is the potential for revitalizing contaminated land in gold mining areas,” adds Chris.
The chemicals used to dissolve gold cause plants to absorb other contaminants from the soil, such as mercury, arsenic and copper, which are common elements found in mine waste that pose a risk to people and the environment.
"If we can make a profit by extracting gold from crops while restoring soils, that would be a significant achievement," Anderson says. He is currently working with researchers in Indonesia to develop environmentally friendly technology for small manual gold mining firms to reduce mercury pollution from their operations.
However, some scientists say the environmental risks associated with gold farming itself may be too great. After all, to dissolve gold particles in the soil, it is necessary to use cyanide and thiocyanate - the same dangerous chemicals used by mining companies to extract gold from stones. Independent agronomists are confident that the process itself can create environmental problems.