Often there is a need to clean gold from other metals contained in the alloy or in scrap. When gold is obtained by cyanidation, the dissolution of the ore in a solution of potassium cyanide, in the final product, gold also often turns out to be mixed with silver and copper.
If it is necessary to make high-grade gold out of low-grade gold, the same task arises - to purify the precious metal from accompanying impurities. Classic way, which allows you to simply clean, dissolve gold in aqua regia.
Dissolution of gold
Homemade mix
Aqua regia, or Aqua Regia, is a mixture of concentrated nitric and hydrochloric acids in a ratio of 1:3 by volume and approximately 1:2 by weight. More specifically, 65-68% by weight nitric acid (HNO3) and 32-35% hydrochloric acid (HCl). Such a strange name for this mixture was given by alchemists: only this "vodka" had the ability to dissolve the "king of metals" - gold (the very word "vodka" in the Russian scientific language meant chemical "water" - a liquid reagent; behind a strong alcoholic drink this term was fixed much later).
As a result of the reaction of metallic gold with aqua regia, a complex compound is formed - chloroauric acid, or hydrogen tetrachloraurate. In this case, the following reaction occurs:
Au + HNO3 + 4 HCl = HAuCl4 + NO + 2 H2O.
Based on this chemical equation and the density of aqua regia, it turns out that at least 5 ml of the reagent is needed to dissolve 1 gram of gold. In this case, in fact, gold dissolves only in hydrochloric acid. Neither nitrogen nor oxygen is present in chloroauric acid. Nitric acid acts only as an oxidizing agent, catalyzing the entry of gold into the reaction. In this regard, the dissolution process is best done as follows.
First of all, if we are dealing with scrap containing gold, we need to remove ferromagnetic particles using a magnet. After that, the gold can be purified as much as possible from impurities with the help of other acids, primarily pure nitric acid. Only then can the gold dissolution process begin.
First you need to measure 3.75 ml of hydrochloric acid for each gram of gold-bearing metal and fill it with only her. If at the same time a more or less noticeable reaction begins, it means that some impurities have already begun to dissolve. It is necessary to wait for the end of the process, drain the solution and fill the metal with a new portion of hydrochloric acid. Now you need to start heating the container with the reagent, gradually adding nitric acid at the rate of 1.25 ml per 1 gram of metal.
The main thing is not to overdo it with nitric acid, since when gold is precipitated from solution, it will be necessary to get rid of it most consistently. As soon as all the metal is dissolved, you should immediately stop adding it to the solution. Moreover, not all of the original substance will necessarily dissolve: silver, unlike gold, is passivated in aqua regia due to the formation of a dense chloride film on the surface. After the dissolution is over, keep the solution heated for about half an hour.
Filtration of the solution
Now it's time to filter the solution. While the filter can be used quite coarse, finer cleaning will occur later.
The resulting precipitate
It should be understood that aqua regia itself is a rather unstable substance: hydrochloric and nitric acids react with each other. Initially transparent, it soon turns into an orange-brown shade of nitrogen oxides, and then completely loses its oxidizing properties. In this case, the following reactions take place:
HNO3 + 3HCl = 2Cl + NOCl + 2H2O
In addition, both acids simply evaporate. In this regard, it is advisable to keep the solution at this stage for about a day, as this will facilitate the further process of evaporating nitric acid.
When evaporating, add to the solution a small amount of sulfuric acid, not more than 50 ml per liter. This will help precipitate residual lead and silver chloride (which, although sparingly soluble, may be present in small amounts in solution). In addition, the evaporation process will go faster.
Heating is done slowly and carefully. The solution is evaporated to the consistency of syrup (no more!). It is impossible to bring to a boil, since in this case it is impossible to exclude the precipitation of gold in the form of a metal precipitate already at this stage.
Then we add hydrochloric acid to the solution to the original volume and again evaporate to a syrupy state. The process is repeated three times. Following this, the liquid is diluted 2 times cold water and left in the cold for a day. In this case, the remains of silver chloride should precipitate: it dissolves only in concentrated hydrochloric acid, and the better, the higher the temperature. Accordingly, as the concentration and temperature decrease, AgCl precipitates. Now filtering is being carried out “in full”: there should not be any turbidity in the solution.
Royal vodka is a composition of concentrated hydrochloric and nitric acids in a ratio of 1:3 by volume. This synthesis has the strongest oxidizing power, dissolving even gold. But why is it called that? It's simple, aqua regia is able to dissolve the "king of metals", that is, gold, and vodka from pet water. In the writings of Albert the Great, this substance was referred to as "aqua secunda" secondary vodka, later other alchemists in their writings called it "aqua regia (regis)".
History of aqua regia
The turning point in the development of chemistry was the 13th century, when alchemists discovered strong mineral acids capable of dissolving many water-insoluble substances. Before that, the world only knew about acetic acid known since ancient times. The newly discovered acids turned out to be a million times stronger, which brought alchemy to a new frontier, because it became possible to produce many chemical processes and reactions. So soon nitric acid was discovered, called "aqua fortis" - strong water, corroding everything that came into contact with it, with the exception of gold, all the metals known at that time. Three centuries later, hydrogen chloride (hydrochloric acid) was discovered.In 1597, the alchemist Andreas Libavia first described the preparation of aqua regia by mixing a concentrate of nitric and hydrochloric acid. Prior to this, there were attempts to obtain alkahest by dry distilling mixtures of saltpeter, ammonia, blue vitriol and alum in a glass vessel and covering with a lid or cap. This method was described in the XIV century by the alchemist Pseudo-Geber, but it was very painstaking and complex, moreover, such a mixture could cope with silver, but gold was beyond his control. And in the 16th century, a universal solvent was nevertheless found and the invention of "aqua regia" contributed to the development of technical chemistry and the improvement of assay analysis.
What acids does aqua regia consist of?
As for the composition of aqua regia, it turned out that the chemical mixture of hydrochloric and nitric acid, when interacting with its components, enhances its abilities several times. The mixture turned out to be so strong that gold dissolves in it, and even platinum at a ratio of 1: 4 (hydrochloric acid, when reacting with nitric acid, releases chlorine, while the solution turns green, and particles of free chlorine attack gold).The interaction formula looks like this:
Nitric acid oxidizes hydrochloric acid
HNO3 + 3HCl = NOCl + Cl2 + 2H2O.
During this process, two active substances appear: nitrosyl chloride and chlorine, which are able to dissolve gold:
Au + NOCl2 + Cl2 = AuCl3 + NO.
Gold chloride instantly attaches an HCl molecule to itself, and tetrachloroauric acid is formed, also popularly known as “chlorine gold”: AuCl3 + HCl = H (AuCl4).
The preparation of aqua regia at home should take place in compliance with all safety measures and in a well-ventilated area.
To prepare aqua regia, you need to acquire two main ingredients: concentrated hydrochloric acid and nitric acid.
We also strongly recommend using only glass test tubes (with marks) and a glass rod to evenly stir the "explosive mixture". Original cast is a mixture of two acids in a 1:3 ratio. Mix using only one test tube, do not measure acids in other containers, this way you minimize the chance of spilling acid.
Now you need to discuss separately those components that you will encounter in the manufacture of aqua regia.
Nitric acid
Monobasic acid, sensitive to light, has a very pungent suffocating odor. Nitric acid under strong light will decompose into nitric oxide and water. In this regard, one of the strongest acids is stored in a dark or opaque container. A concentrated solution of nitric acid does not dissolve aluminum and iron, so you can safely store it in a metal container.
I would like to note that nitric acid is a very strong electrolyte (like most acids) and an oxidizing agent. Highly interesting fact, is that nitric acid (like ozone) can be formed in the atmosphere during strong flashes of lightning. The composition of atmospheric air consists of 78% nitrogen, which reacts with atmospheric oxygen. This reaction produces nitric oxide (NO). Subsequently, with further oxidation in the open air, nitric oxide is converted into nitrogen dioxide (NO2, or as it is also called brown gas). When atmospheric moisture reacts with nitrogen dioxide, nitric acid is produced. The concentration in such cases is minimal, and it is not at all dangerous for people, animals and nature.
Hydrochloric acid
The second component of aqua regia is hydrochloric acid. This acid is colorless, in the open air emits steam in the form of "smoke", a very caustic liquid (hydrochloric acid of technical importance may have a yellowish tint due to the presence of iron and chlorine impurities in it).
When it comes to the physical properties of hydrochloric acid, here it is necessary to note its strong side when all metals (which are in the series of voltages up to hydrogen) are dissolved (H2 is released and chloride salts are formed). It is necessary to be very careful when using this acid, to carry out work or experiments in the open air or in a well-ventilated area, since the acid has a very pungent odor and strongly irritates the mucous membranes of the upper respiratory tract of the human body.
Hydrochloric acid is produced by dissolving hydrogen chloride gas in ordinary water(H2O). In turn, hydrogen chloride can be obtained by reacting sodium chloride with highly concentrated sulfuric acid.
The use of aqua regia
Many Soviet and post-Soviet families knew the composition of aqua regia by heart. People use it to dissolve gold at home, in order to extract pure gold from microcircuits, transistors, watches and other unnecessary devices that contain a small amount of gold in their composition.The main aspect of the successful completion of your planned chemical experiment with aqua regia is safety. Use funds personal protection, follow the safety rules, be extremely vigilant and attentive, your life and health will be at stake.
Video about aqua regia
What is royal vodka? No that's not elite drink, as one might think. Aqua regia is a mixture of certain concentrated acids in a certain proportion. Classic recipe aqua regia is as follows: one-fourth hydrochloric acid (formula HCl) and three-quarters nitric acid (formula HNO3). Such a drink is unlikely to benefit human body. But he is able to dissolve gold and platinum. And not only them.
Most metals are completely soluble in aqua regia. But not a single acid, which is part of the composition, is individually capable of this. Due to the complex reaction between nitric and hydrochloric acid, the power to dissolve metals is born. She is not subject to tantalum, iridium and rhodium. In appearance, aqua regia is just a yellow liquid with a sharp bad smell.
How did aqua regia come into being and why was it called that?
Royal vodka appeared thanks to the tireless attempts of alchemists to create a kind of philosopher's stone that would turn everything into gold. Gold for the people of that time was royal, royal metal. Accordingly, the liquid that was able to dissolve this precious metal was called the king of water. But in Russian, the name of this acid was interpreted differently, like aqua regia.
For the first time the recipe for vodka was found in the treatise of the alchemist Pseudo-Geber. True, the recipe is somewhat different from the modern one. At that time, alchemists received aqua regia from a mixture of copper sulphate, ammonia, alum and saltpeter. The ingredients were mixed in a jar with a glass lid.
In later years, in the thirteenth century, another recipe for royal vodka was found. This recipe is attributed to Bonaventure, who mixed ammonia with nitric acid. The same alchemist found that silver dissolves in nitric acid - this is good way separate silver from gold. Bonaventure was the first to use the name aqua regia.
The recipe for vodka, which includes concentrated hydrochloric and nitric acids, appeared at the end of the sixteenth century. Described it by Andreas Libavius in his Alchemy. Libavia attached great importance to aqua regia, seeing in it a universal solvent (one of the most difficult tasks of alchemy). Since the sixteenth century, aqua regia has actively helped mankind in increasing knowledge about various substances and chemical reactions between them. Royal water has also contributed to the development of assay analysis.
Interesting case happened during World War II. In Nazi Germany, the Nobel Prize was banned. Therefore, two German physicists (Max von Laue and James Frank) decided to keep their gold medals at the Niels Bohr Institute (Denmark). When Denmark was occupied, one of the Institute's chemists dissolved gold medals in vodka. The jar of solution stood throughout the war among hundreds of other different solutions. After the end of the war, the same chemist separated the gold back from the solution and gave it to the Swedish Academy of Sciences and the Nobel Foundation. From the received gold, new medals were made and given to James Frank and Max von Laue.
Properties of aqua regia
A mixture of hydrochloric and nitric acid forms highly active products (chlorine dioxide, nitrogen and nitrosyl chloride). Royal vodka is one of the strongest oxidizers. It should be noted that this vodka is prepared immediately before use. After all, over time, it breaks down into gaseous products. Gold dissolves in vodka at a rate of approximately 10 µm/min.
The use of royal water
The main and professional use of royal water is its use as a reagent, due to which metal chloride is obtained. Some use this reagent to extract gold from old radio components. And also, with the help of royal water, you can easily crack padlocks.
The main thing is not to forget that royal water can only be used for the first time after its manufacture.
It is also worth analyzing in detail those acids that are part of aqua regia.
Nitric acid
light sensitive acid. When illuminated, it will decompose into oxide and water. Therefore, nitric acid is kept in a dark cabinet or in an opaque container. And also HNO3 itself does not dissolve iron, so it can be safely stored in an iron container. Nitric acid is one of the strongest electrolytes and oxidizers.
Known cases of formation of HNO3 in the atmosphere. When lightning strikes, nitrogen in the atmosphere reacts with oxygen to form nitric oxide. Subsequently, this nitric oxide reacts with moisture in the air to form nitric acid in small concentrations.
Hydrochloric acid
Colorless acid, with a pungent odor, very caustic, emits a light vapor in the open air. HCl dissolves many metals. You have to be very careful when using this reagent. You can work with it only in a room that is actively ventilated. After all, the steam emitted by this acid can irritate the mucous membranes of the respiratory tract.
How to prepare royal water
To cook it yourself aqua regia you will need:
- concentrated HCl, HNO3;
- glass test tube;
- glass rod.
- First of all, you must accurately measure the right number of reagents. We remind you that you need to mix three parts of hydrochloric acid with one part of nitric acid. Do not think to measure the amount of liquid by eye. The slightest inaccuracy will lead to the fact that the reagent will be weak in efficiency. It is best to take a glass test tube with divisions by which you will navigate.
- Try to use minimal amount utensils. And also try to transfer reagents from one tube to another as little as possible. Beware of spilling them.
- We advise you to first pour hydrochloric acid into the test tube, and then add nitric acid to it. This is done so that when you pour a smaller amount of liquid into large quantity liquids, reduce splashing. Pour in the acid carefully, in a thin stream. Do not bring a test tube of acid close to your face so as not to accidentally inhale the fumes.
- When you have mixed all the reagents, gently stir the mixture with a glass rod. You need to mix thoroughly so that all the reagents react with each other, and not just delaminate. Under no circumstances should the test tube be shaken. If you did everything right, then the liquid you mixed will be yellow at first, and after half an hour it will darken to orange.
At all stages don't forget to be careful!
Video
From the video you will learn what royal vodka is.
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Ordinary people who are not related to chemistry do not always know what Royal Vodka is. Often it is confused with the usual alcoholic drink. In fact, aqua regia is a mixture of concentrated acids, which is used to dissolve any metals, including precious ones.
The composition of aqua regia includes hydrochloric acid (one volume) and nitric acid (three volumes). Sometimes sulfuric acid is added. This solution has many recipes. In the Middle Ages, aqua regia was prepared by distilling a mixture of saltpeter, blue vitriol and alum with the addition of ammonia.
Today is the most popular recipe includes a combination of nitric and hydrochloric acids. The peculiarity of such a solution is that it doubles and triples its oxidizing properties.
Separately, none of the acids that make up its composition can dissolve metals.
It is often used to dissolve rare earth and precious metals in the aqua regia industry. The chemistry of such metals has its own specific features: the dissolution process is carried out in stages. First, nitric acid oxidizes hydrochloric acid.
During this reaction, chlorine and nitrosyl chloride are formed, which, in turn, can also platinum. The reaction produces tetrachloroauric acid, colloquially known as "chlorine gold", from which it is easy to obtain metallic gold.
The resulting acid, which includes gold in its composition, dissolves well in water. Its crystals are light yellow.
The solution therefore turns yellowish. When heated, the composition decomposes with the release of hydrochloric acid and gold chloride, which has a reddish-brown color.
With continued heating, all gold compounds decompose with the release of metallic gold. When platinum is dissolved in aqua regia, chloroplatinic acid is obtained. When the solution is evaporated, it is released in the form of red-brown crystals of the composition.
Often, mining people want to learn how to make aqua regia on their own. Such a highly oxidizing solution is not sold ready-made. To extract precious metals, it can be prepared on your own.
Aqua regia can be obtained by mixing one part of nitric acid and 3 parts of hydrochloric acid. It is necessary to strictly adhere to the proportions so that the reaction is strong.
Nitric and hydrochloric acid If this is not done, then the solution will not dissolve precious metals due to the weakness of the reaction. Do not mix reagents by eye, as this will not achieve proper accuracy.
When preparing such a solution, you should:
- use protective equipment for hands and eyes;
- measuring tube, which will help to accurately establish the proportions;
- hood to remove toxic fumes of acids;
- a specially prepared platform on the working table, which will provide protection against the spillage of hazardous acids and chemical burns.
The preparation of aqua regia must be carried out in compliance with strict proportions. Only in this case will it be possible to obtain a composition that will dissolve gold and platinum. How to cook aqua regia in stages, will be described below.
Stages of preparation of aqua regia
- First, hydrochloric acid must be poured into a chemical vessel with risks, since it needs more than nitric acid to prepare aqua regia. When mixing reagents in hydrochloric acid, nitric acid must be poured. This will avoid unnecessary splashing of components and therefore chemical burns.
- After that, nitric acid is added. It must be poured in a thin stream to avoid the appearance of dangerous splashes. Do not lean towards the test tube, as acid vapors are dangerous if they enter the Airways, or in the eyes. Pour in the reagents at arm's length from the face.
- The resulting composition of acids should be mixed with a stick very carefully. You can not shake the solution very strongly, as it is very dangerous. Royal vodka will be ready when the sediment falls to the bottom of the container in which it is located.
At first, its color will be yellow, like hydrochloric acid. Within an hour, the solution will change color to dark orange. This will be proof that the reaction went right.
"Balm Bolotov" is used as a prophylactic agent that improves immunity, helps to reduce the risk various diseases prevents stroke and heart attack. "Bolotov's Balm" contributes to the overall rejuvenation of the body. Helps with diseases of the gastrointestinal tract, heartburn, herpes, hemorrhoids, cancer and AIDS.
Royal vodka should be consumed immediately after sleep, because. it neutralizes harmful substances that accumulate in the human body during sleep. After taking it, you will feel refreshed.
Royal vodka Bolotov ("Balm of Bolotov") should be used:
1.
To stimulate the formation of gastric juice enzymes (pepsins).
2.
To normalize the reduced secretion of gastric juice.
3.
To normalize the zero acidity of gastric juice.
4.
To thin the blood in the circulatory system.
5.
For neutralization high content blood sugar and cleansing of blood vessels from salts of fatty acids.
6.
For rejuvenation of the body, due to an increase in the percentage of young cells.
7.
For splitting old and diseased cells, cells of pathogenic organisms.
8.
To normalize the body when it is alkalized due to the predominant intake of food herbal products, which have a high alkalinity and are harmful.
9.
For the treatment of heartburn, gastritis, stomach ulcers, hemorrhoids, herpes and others.
10.
To normalize the work of the entire gastrointestinal tract.
11.
To increase the body's immunity (when creating mucopolysaccharides).
12.
For splitting of plaques in vessels.
13.
To prevent stroke, heart attack, arrhythmia, with atherosclerosis of blood vessels.
14.
To normalize a non-closing and weakened pylorus 12 of the duodenum.
15.
To neutralize free radicals.
This unique drink participates in the breakdown of cells damaged by nitrates, radionuclides, free radicals, carcinogens, and various poisons of heavy metal salts. It breaks down all types of cancer cells whose protoplasm is weakened by the intake of the amino acid TRYPTOFAN.
Preparation: You need to take 3 liter jar and fill it with clean water, leaving room in the jar for the following ingredients, which must be added and mixed thoroughly in the following sequence: 300 ml grape vinegar(6% concentration), 3-6 teaspoons of sulfuric acid (98%), 3-6 teaspoons of hydrochloric acid (36%), 12 tablets of nitroglycerin.
Attention: Follow the sequence of adding the ingredients of aqua regia and thoroughly stir the resulting solution after adding each component.
Reception: Take 1 teaspoon to 2 tablespoons 3-4 times daily before meals or as part of any beverage immediately after meals, such as tea or coffee. Between doses it is better not to drink. You also need to drink a drink immediately after sleep.
The maximum dosage is 2 tbsp. spoons 4 times a day.
