How much gold is in sea salt. Seawater amalgamation for gold recovery
In the second half of the 19th century, gold was first discovered in seawater. True, in such minute quantities that the conversations that had begun about extracting gold from the ocean quickly died out.
Scientists soon discovered that certain heavy metal compounds could precipitate gold from solutions. Iron sulfide, pyrite, “assimilated” the yellow metal especially intensively.
That's when they tried towing bags of ore behind the stern of the ships. Upon returning from the voyage, an increased gold content was found in the pyrite.
In 1902, the famous Swedish scientist Svante Arrhenius determined the total amount of gold in the World Ocean. According to his calculations, it turned out to be 8 billion tons. Today we know that Arrhenius's data is greatly exaggerated, but there is no exact data yet.
Disputes about the average gold content of seawater flare up again from time to time. Scientists have different estimates of the content of this metal in sea water. Moreover, there are discrepancies of several orders of magnitude.
Developed and mastered in last years The neutron activation method for fine analysis of the composition of liquids made it possible to conduct interesting research. Employees of the research vessel "Mikhail Lomonosov" conducted research in exactly this way.
Cruising the tropical zones of the Atlantic Ocean, they made 89 samples of sea water for gold, taken from a variety of points and at different depths, even from a depth of more than five kilometers.
They are precipitated with special reagents, and the sediment is placed in a nuclear reactor. Irradiated there by a stream of neutrons, the elements begin to emit gamma rays - they give a “voice”. Based on the characteristics of this induced radiation, the gold content of the sample can be determined.
According to Mikhail Lomonosov, the average concentration of precious metal in sea water is significantly higher than previously established. Some samples contained almost a thousand times more gold than could be expected.
This convincingly confirms the previously stated assumption that the gold content varies very significantly in different places and at different depths. Until now, the very existence of zones with high gold concentrations has been questioned.
Scientists have not yet undertaken to explain the reasons for such anomalies. You can, of course, remember that in areas of gold deposits, groundwater contains hundreds of times more gold than in other places.
The data of “Mikhail Lomonosov,” in the words of Academician A.P. Vinogradov, can again “excite passions in connection with gold in sea water.” The researchers themselves believe that large and systematic work is needed, which is not only of natural scientific interest, but may also have practical significance. Reliable identification of zones of increased gold concentrations, the reasons for their formation and the conditions for sustainable existence may once again raise the question of extracting gold from sea water.
Uranium, gold, lithium - billions of tons of valuable raw materials are dissolved in salt water. Previously, the process of extracting useful substances from water was extremely labor-intensive. Now researchers are going to finally extract this treasure from the depths of the sea.
16 05 2016
14:18
The oceans store approximately four billion tons of uranium and tens of thousands of kilograms of gold.
The sea is a gold mine. At least if you know where to look. Typically, one liter of seawater contains only a few billionths of a gram of gold. But recently, researchers from Germany and Iceland discovered a boiling gold-bearing spring: on the Icelandic Reykjanes Peninsula. There, the concentration of gold is half a million times higher than in ordinary seawater.
Not only this one a precious metal, but other valuable substances are also dissolved in huge quantities in sea water. About four billion tons of uranium rest in the sea. This is enough to satisfy humanity's energy needs for 10,000 years. Or, for example, lithium: This rare earth chemical element is used for batteries in tablets or smartphones. More and more countries are investing in exploring how the oceans can be used as a new source of resources. But you need to understand that catching raw materials from water is far from a trivial task.
In Germany, the Helmholtz Center for Ocean Research (Geomar) in Kiel was involved in the discovery of gold deposits in hot springs in Iceland. “The concentrations measured are fairly consistent with significant gold deposits,” says Mark Hannington, head of Geomar's marine exploration working group.
The team believes that the geothermal reservoirs of the Reykjanes Peninsula contain at least 10,000 kg of gold. Researchers suggest that gold dissolved in seawater and circulating in underground rock crevices must have accumulated over the course of long periods, before it left the underground reservoir and then flowed out through the wells in very high concentrations.
Golden microbes
“This gold can appear in liquids in the form of fine gold nanoparticles,” suggests Dieter Garbe-Schönberg from the University of Kiel. So-called nano gold is in demand in many areas of technology. Its special surface properties can, for example, provide more efficient control of chemical reactions in catalysts.
But how can such finely ground gold be extracted from water, and even so that this process is inexpensive, simple and environmentally friendly? Young researchers from the University of Heidelberg and from the German Cancer Research Center had a brilliant idea. In order to force gold to precipitate from solution, they use the properties of specially adapted bacteria.
Delftia acidovorans is the name of a microbe that only grows in gold mines. This microorganism has adapted to the environment; it separates the precious metal even from solutions with a relatively low concentration of gold. The researchers identified the necessary genes and inserted them into the microbe E. coli, which is distributed throughout the world.
This allowed them to re-extract the precious metal from gold-bearing solutions, such as those produced by extracting gold from electronic scrap. The researchers have applied for a patent on these biotechnological processes because they have already demonstrated high competitiveness compared to classical chemical gold processing. This discovery could also revolutionize the extraction of gold from the sea.
Billions of tons of uranium
The United States, meanwhile, is promoting a major research program to mine uranium from the oceans. The vast dissolved reserves in water come from natural minerals that have been washed out to sea through weathering and other erosive processes. However: uranium is not easy to fish out of water. Back in the 1980s, Japanese scientists experimented with materials that specifically captured and bound uranium from seawater.
The Americans are trying to make this method more effective. The research consortium wants to literally fish for uranium. In the journal Industrial and Chemical Engineering Research, materials and a description of the method itself were presented to the public for the first time. This method will likely be able to reduce the cost of extracting uranium from the sea by three to four times, while increasing the volume of extracted raw materials.
“To secure the future of nuclear power, we need to find an economically viable and reliable source of fuel production,” explains Philip Britt, program director at the US Department of Energy. The method is primarily being developed at two government research institutes, Oak Ridge National Laboratory in Tennessee and Pacific Northwest National Laboratory in Richland.
Long threads (cords) of polyethylene fibers serve as “fishing rods (catchers) for uranium”. Thin but stable fibers are specially treated so that in the process some of their molecules are converted into amidoxime. This organic compound, consisting of carbon and nitrogen, is a “bait” for uranium dissolved in water, since it preferentially creates compounds with this substance.
Impact on environment
In order to “catch” uranium, the cords simply need to be placed in the sea, preferably in that area of \u200b\u200bwater masses where there is a current and mixing occurs. After a few weeks, the uranium-bearing cords can be removed. They are placed in an acid bath, where the uranium is released as uranyl. The compound can be easily extracted from solution and can then be easily enriched and processed into uranium. The uranium “fishing rod” survives this procedure without problems and, according to the researchers, can be reused directly back into the ocean.
How much uranium can be extracted from the sea in this way has already been demonstrated by tests at three different locations on the US West Coast, Florida and the coast of Massachusetts. After 49 days in seawater, the cords recovered and bound about six grams of uranium per kilogram of absorbent material. Japanese researchers were once able to achieve a result of two grams of uranium per kilogram of absorbent material. And at the same time, the Japanese plastic cords had to remain in the water for 60 days.
"Understanding how the absorbent material works in natural conditions in seawater," says Gary Gill, deputy director of the Pacific Northwest National Laboratory. Because in addition to extracting uranium as much as possible, it must be ensured that the method does not have a negative impact on the environment. "But we have already found that most These absorbent materials are non-toxic,” says Gill.
The team has been working on improving the method for five years. It all started with computer modeling. The program checked which chemical groups selectively captured and bound uranium. This was followed by thermodynamic and kinetic studies that determined how quickly uranium from water binds to a particular absorbent substance and where the equilibrium of this reaction is. The entire process only works when more uranium is bound than is dissolved.
Lithium for batteries
The Chinese Academy of Sciences and the Japan Atomic Energy Agency (JAAE) were also involved in the project. At the Rokkasho Fusion Institute, which is part of the Japan Atomic Energy Agency, Japanese researchers continue to study technical ways to extract strategically important raw materials from seawater.
These substances include lithium, a metal that is one of the rare earth chemical elements. It is needed primarily for the manufacture of compact lithium-ion batteries, which are now common in tablets, digital cameras and mobile phones, and are also used for efficient energy storage in electric cars.
While the world's known, accessible lithium deposits are estimated at about 50 million tons, scientists suspect that 230 billion tons of lithium may be dissolved in ocean waters. However, the raw material is found only as a trace element. About 150,000 liters of seawater barely contain even 30 grams of lithium.
But Tsuyoshi Hoshino from the Rokkasho Synthesis Institute is not at all embarrassed by this. A scientist has just presented to the public a method by which the desired metal can be filtered out of water, even if it is present there in very small quantities. This method does not require additional energy use, because it is supplied by the electrically charged lithium particles themselves.
In the filter, which consists of a thin glass-ceramic membrane that has lithium ion conductivity, charged particles move from negative side to the positive side, thus producing electrical voltage. “Microporous ceramics allow only electrically charged lithium particles dissolved in seawater to pass through,” explains the researcher. In a 72-hour test, the filter achieved a recovery rate of about seven percent.
Researchers know this is just the beginning. Experts from the UK Energy Research Center suggest that in 2030, it will be possible to obtain commercial quantities of raw materials from the sea using these methods, provided that the prices of gold, uranium or lithium remain high enough.
Sylvia von der Weiden.
Despite the fact that seawater contains gold in microscopic quantities (4 mg/ton), mining it will soon be profitable. In fact, if we look at how the amount of human waste is growing, it becomes obvious that their complete processing into finished products is difficult. At the same time, the use of waste disposal products for the extraction of gold and other metals appears to be beneficial.
American researcher Henry Ball more than 30 years ago established that seawater contains gold in the form of iodide. Gold iodide (AuI) solid citric- yellow color with a density of 8.25 g/cm3. Decomposes into elements when heated to 177°C or under the influence of water. Reduced by sulfur dioxide or carbon monoxide to gold. Adds ammonia. It is obtained directly from elements at 100°C, by the reduction of Au2Cl6 or H with a KI solution, and by the action of hydroiodic acid on gold (III) oxide.
As a result of his research, Ball proposed extracting gold from seawater using quicklime. According to his calculations, only 1 ton of lime is required for 4.5 thousand tons of water. The principle of operation of the Balla installation was simple. At high tide, sea water enters the pool, where it is mixed with lime milk. After a certain period of time, having already been “spent” , through a drain pipe it is discharged back into the sea. The remaining sediment at the bottom is pumped into a settling tank, from where it is transported to the processing site for gold extraction.
Kirov engineer Russian V.I. proposed an even cheaper and waste-free method of extracting gold. To extract gold, he suggests using ash from thermal power plants instead of quicklime. Fly ash from thermal power plants contains at least 10% quicklime, so processing 4.5 thousand tons of sea water will require approximately 10 tons of ash. Currently, ash dumps from thermal power plants amount to more than 10 billion tons. Fly ash is used very poorly.
To implement this method, multimillion-dollar investments are required in the construction of a concrete dam, as well as the laying of pipes to drain the treated water into the sea.
A simple calculation shows that using this method is a thousand times less expensive than other methods of extracting gold from water. In addition, already at present, this method will easily pay for itself within a year. Even assuming a 20% recovery of gold from sea water. In the case of incidental extraction of rare, noble and trace metals from sea water, the payback time will be reduced several times.
The most difficult thing about this method is choosing the location for constructing a flooded pool.
The ideal location should be located close to water currents, with regular ebbs and flows, the shore should be made of hard rock (for example, granite, limestone, etc.), away from populated areas, near railway tracks.
Compliance with these requirements will reduce the cost of constructing a pool.
The total amount of gold in the waters of the World Ocean is estimated at 25-27 million tons. This is extremely high. Over the entire period of time, humanity has produced about 150 thousand tons.
There are 10 10 tons of various substances dissolved in the World Ocean, all of which are known in the earth’s crust. The Gulf Stream alone transports 3 million tons of various salts per second. In the distant past, they received from the sea in approximately the same way as today - evaporation. Using sophisticated technology, sodium, potassium, chlorine, magnesium, calcium, bromine, and lithium are extracted.
Getting gold
For a long time, man dreamed of extracting gold from sea water. And it seemed so real that Germany was going to pay for reparations for the First World War with “sea” gold. This was done by Nobel Prize laureate F. Haber. However, despite the fact that the ship was well equipped, and the expedition was well subsidized and prepared, nothing came of it: all the gold extracted from sea water was valued at $0.0001, that is, only 0.09 milligrams were obtained from 15 tons of water .
Soviet scientist A. Davankov on the ship "Mikhail Lomonosov" obtained a milligram of gold using an ion exchange column from 500 tons of water. This, of course, is not enough, but there are a lot of ships, so it’s a matter of installing replaceable traps. Natural sorbents - sludge - have already done a similar job. In the bottom sediments of the Red Sea, silt contains 5 grams of gold per ton of sediment. Apparently, over 10 million tons of gold are dissolved in the world's oceans. This is already significant. However, this is not all gold that came from the continents. Thus, the fresh waters of some rivers contain up to 16 clarke of gold. Where is it? In the silts of coastal sediments? If so, then such deposits can be discovered.
The gold content of ocean water is estimated differently: according to S. Arrenis (1902), gold contains 6 milligrams per ton, according to G. Putnam (1953) 0.03-44, and according to 1974 data 0.04-3.4 micrograms per liter The state of the metal has been established in: suspensions of microparticles, colloids, complex ions AuCI 2 and AuCI 4, organogold compounds.
How did they try to extract gold? There are many ways: bags of pyrite were towed behind the ship; seven grams of leaded zinc filings were washed with 550 liters of water and obtained 0.6 milligrams of gold and 1.1 milligrams of silver; used as an absorbent were zeolites, permutites, coke, slag, cement clinker, charcoal, peat, wood flour, sulfite cellulose, glass powder, lead sulfide, colloidal sulfur, metallic mercury, magnesium hydroxide (In 1925, 5 milligrams of gold from 2 tons of water), ion exchange resins (A. Davankov, 1956). However, gold continues to interest people. In sea water, for 11 main ions (CI -, SO 2\4, HCO 3 -, CO 2\3-, Br -, F -, H 2 BO 3-, Na +, Ca 2+, K +) there are 99 .99 percent. Naturally, this information is quite approximate. In fact, sea water is a complex complex of ionic and colloidal solutions, mineral suspensions, gases, organic residues, etc. In addition, the composition of seawater is affected by industrial waste. Thus, the lead content has increased 10 times over the past half century. Special areas appeared - “oases of metals”.
Mining of other metals
In 1948, the Swedish ship Albatross discovered bottom sources of hot metal-bearing brines in the Red Sea. Detailed work carried out on the Discovery vessel in 1966 identified three large depressions more than 2 kilometers deep, where brines with temperatures up to 56 ° C and a salt concentration of 26 percent were encountered.
In a 200-meter-thick layer in the Atlantis II, Chain and Discovery depressions, the contents of iron, manganese, zinc, lead, copper, gold, silver, indium, cobalt, cadmium, arsenic, and mercury are tens of thousands of times higher. High concentrations of sulfides were found in the sediments at the bottom of the depressions. These sediments are underlain by barren carbonate rocks, under which basalts occur. The deposition of ores began 13 thousand years ago. It has been established that since 1964, brine levels have been increasing. So, in 1973 it reached 62° C.
Ore-bearing silts have already been estimated in cubic meters, in tons and in dollars, but practical use of this unusual type of deposit is apparently far away. In an area of over 2 million square kilometers, metal-bearing sediments associated with fault zones and underwater volcanoes have also been established. Their practical significance is still unclear.
According to the most optimistic estimates, uranium reserves on land are about 5 million tons (excluding CIS countries), and the World Ocean contains 4 billion tons of this element.
The search for sorbents for some metals yielded unexpected results: titanium hydroxide sorbs chromium (accumulation coefficient 1 million), vanadium (100 thousand), manganese, iron, copper, nickel (10-100 thousand). Copper is sorbed on ion exchangers, and in A. Davankov’s experiments, silver is sorbed (2.5 milligrams per 200 grams of sorbent). Sorbents of molybdenum, cesium, thorium, radium, and ruthenium have already been tested.
It turned out that the polyethylene sorbent precipitates 9/10 of the initial amount of indium in 20 days, and chitosan (a component of the shell of crustaceans and the cover of arthropods) sorbs zinc, copper, cadmium, lead and other metals. It is interesting that nature itself suggests the method of technology: kelp concentrates iodine and aluminum; radiolarians – strontium; – nickel; lobsters and mussels – cobalt; octopuses – copper; jellyfish – zinc, tin and lead; holothurians – vanadium; some types of tunicates - tantalum and niobium. In ascidians (tunicate litter) the concentration of vanadium is 10 10 (the metal is part of the pigment). Japan refused to import vanadium as it began to obtain it from the sea, using sea squirts.
Scientists from many countries have studied the genesis and topography of the distribution of gold in sea water, and have sought methods for its extraction.
Gold was discovered in various types of seaweed and in marine sediments (at a depth of 89-198.6 m), in coastal waters, in geysers in Arkansas (USA) and in sea water. Gold content by different definitions ranged from 3 to 200 mg/t. Silver was also discovered there.
Gold content in sea water and methods of its extraction
According to geochemists, one liter of sea water contains 0.000004 milligrams of dissolved gold, one cubic kilometer contains 0.004 tons, and the entire volume of the World Ocean contains more than 6 million tons.
Gold can be extracted by filtering seawater through adsorbents (fine coal, cellulose compounds, pyrite, sulfide ores, rags soaked in reagents) and then burning or dissolving them.
- precipitation by chemical methods;
- electrolysis;
- sorption by ion exchange resins;
- placed in a special container;
- ion flotation through special networks;
- soaked in reagents.
Associated extraction of gold from sea placers
Of practical interest is the associated extraction of gold from titanium-zirconium coastal marine placers. The value and economic significance of coastal placers are determined not only by large reserves of ore minerals, but also by the possibility of complex use of raw materials.
A study of seven samples of sand from titanomagnetite sea placers in Primorye revealed an increased gold content. In addition to the main components (ilmenite, magnetite, rutile and zircon), garnet, staurolite, kyanite, kyanite, sillimanite, etc. can be extracted. The content of ilmenite in various deposits ranges from 0.6 to 19%, titanomagnetite from 1 to 28%.
The bulk of gold (95%) is concentrated in the -0.3 + + 0.1 mm class. No associated gold was found. Gold is mostly thin-plate, scaly, isometric in plan, oval, elongated, less often - irregular in shape, completely rounded, heavily abraded, deeply altered by corrosion processes. Laboratory experiments have established that gold can be extracted using jigging machines, although the mass of one piece of gold (scale) from a sea placer is five times less than the mass of gold of the same size from a river placer. Gold recovery by jigging was 84% from river placers and 67% from sea placers. When cleaning the tailings, gold recovery increases to 88%.
When studying the sands of one of the titanium-zirconium deposits of marine origin in the central region of Russia, it was found that free gold contained 29%, associated with other minerals - 71%. The mineralogical analysis established that the gold is very fine and dusty, the grain size ranges from 0.05 to 0.25 mm (the predominant grain size is -0.12 + 0.05 mm). The shape of gold grains is lumpy-angular and lamellar. The gold is mostly yellow with only a small amount of greenish-yellow. The surface of most large gold grains is altered by corrosion, some of them are covered with a thin film of iron hydroxides, and some grains are rounded. The purity of gold, as determined by the largest slightly corroded crystal, is about 890.
The processing of titanium-zirconium sands in semi-industrial conditions was carried out according to a scheme including screening, disintegration, mechanical scrubbing, desliming and flotation. Selection of collective flotation concentrate and finishing of final concentrates was carried out by a combination of magnetic and electrical separations with flotation and gravity processes on a concentration table. The highest concentration of gold was observed in rutile concentrate and middling products from the electro-separation of non-magnetic and magnetic fractions.
A noticeable concentration of gold is also observed in zircon concentrate. However, the extraction of gold in these products is low, and the bulk of it is lost in quartz sands, according to the portal fishingby.com. The recovery of gold into the collective flotation concentrate is 22% of the original or 75% of the gold found in the sands in free form.
Experience in industrial installations
On the sands of one of the placers of the Baltic Sea, the Moscow Mining Institute (MGI) conducted research using an installation mounted on board a dredger to determine the influence of sea waves on the enrichment process. Hydrocyclones, jet concentrators and a belt friction separator were installed on board the dredger. Two concentrators worked in the main operation to produce tailings and rough concentrates, which were cleaned at the third concentrator.
According to the scheme, a rough concentrate is obtained containing 45-60% of the heavy fraction and an extraction of useful minerals of 81%. The test results fully confirmed the data obtained during the enrichment of sea sands at an onshore installation.
To refine the rough concentrate in laboratory conditions, a scheme has been developed using gravity, magnetic and electrical separation with preliminary roasting of the zircon-rutile product. Subsequently, in laboratory conditions, a scheme for obtaining a gravity concentrate with a heavy mineral content of about 80-85% was developed. The scheme included the main concentration of sands on jet concentrators and four re-cleanings of the concentrate.
The development of rich underwater deposits will require less capital investment than the development of continental deposits.
