Barium sulfate is an inorganic substance with the chemical formula BaSO4. It is a white powder, odorless, insoluble in water. Its whiteness and opacity, as well as high density determine the main areas of application.
Barium refers to alkaline earth metals. The last named so because, according to Mendeleev, their compounds form insoluble land mass and oxides "are earthy look." Barium is naturally found in the form of a barite mineral, which is barium sulfate with various impurities.
It was first discovered by the Swedish chemists Scheele and Gan in 1774 as part of the so-called heavy spar. Hence arose the name of the mineral (from the Greek "Baris." - heavy), and then the metal itself, when in 1808, he was isolated in pure form by Humphry Davy.
Since BaSO4 - a salt of sulfuric acid, its physical properties are determined partly by the metal which is soft, chemically active and silver-white. Natural barite is colorless (sometimes white) and transparent. Chemically pure BaSO4 has a color from white to pale yellow, it is non-flammable, with a melting point of 1580 ° C.
What is the mass of barium sulfate? Its molar mass is 233.43 g / mol. He has an unusually high specific gravity - from 4.25 to 4.50 g / cm 3. Because water-insolubility, high density makes it ideal as an excipient aqueous drilling fluids.
BaSO4 - This is one of the most sparingly soluble compounds in water. It can be obtained from two highly soluble salts. Take an aqueous solution of sodium sulfate - Na2 SO4. Its molecule in water dissociates into three ions: two Na + and one SO4 2- .
Take also an aqueous solution of barium chloride - BaCl2. a molecule which dissociates into three ions: one Ba 2+ and two Cl -.
BaCl2 → Ba 2+ + 2Cl -
Mix an aqueous solution of sulfate and a mixture containing chloride. Barium sulfate is formed as a result of combining into one molecule two ions with the same in magnitude and opposite in sign charge.
Below you can see the complete equation of this reaction (the so-called molecular).
The result is an insoluble precipitate of barium sulfate.
In practice, the raw material for obtaining marketable barium sulfate, intended for use in drilling fluids in the drilling of oil and gas wells, is, as a rule, mineral barite.
The term “primary” barite refers to commercial products that include raw material (obtained from mines and quarries), as well as simple enrichment products by methods such as washing, sedimentation, separation in heavy media, flotation. Most of the raw barite requires bringing it to the minimum purity and density. The mineral that is used as a filler is crushed and sieved to a uniform size so that at least 97% of its particles have a size of up to 75 microns, and no more than 30% are less than 6 microns. Primary barite should also be sufficiently dense so that its specific weight is 4.2 g / cm 3 or higher, but at the same time soft enough so as not to damage the bearings.
Receiving a chemically pure product
Mineral barite is often contaminated with various impurities, mainly iron oxides, which dye it in different colors. It is processed by the carbothermic method (heating with coke). The result is barium sulphide.
BaSO4 + 4 С → BaS + 4 СО
The latter, unlike sulfate, is soluble in water and readily reacts with oxygen, halogens and acids.
Sulfuric acid is used to obtain a high purity product. Barium sulphate, formed by this process, is often called blanfix, which in French means “white fixed”. It is often found in consumer products, such as paints.
Under laboratory conditions, barium sulfate is formed by combining barium ions and sulfate ions in the solution (see above). Since the sulphate salt is the least toxic barium because of its insolubility, waste, containing other salts, sometimes treated with sodium sulfate to bind the entire barium, which is sufficiently toxic.
From sulfate to hydroxide and back
Historically, barite has been used to produce barium hydroxide Ba (OH)2. necessary when refining sugar. It is generally a very interesting and widely used compound in the industry. It is readily soluble in water, forms a solution known as barite water. It is convenient to use to bind sulfate ions in various compositions by the formation of insoluble BaSO4 .
We saw above that when heated in the presence of coke from sulphate it is easy to obtain water-soluble barium sulphide - BaS. The latter, in contact with hot water, forms hydroxide.
Barium hydroxide and sodium sulfate, taken in solutions when mixed will give an insoluble precipitate is barium sulphate and caustic soda.
It turns out that natural barium sulphate (barite) industrial method is first converted into barium hydroxide, and then used to produce the same cleaning sulfate at different salt systems by sulfate ions. Similarly, the reaction will take place when cleaning from SO ions.4 2 - solution of copper sulfate. If we make the mixture "+ barium hydroxide, copper sulphate", the result is a copper hydroxide and the insoluble barium sulfate.
Even in the reaction with sulfuric acid itself, its sulphate ions will be completely bound by barium.
Use in drilling mud
Around 80% of global production of barium sulfate, purified and ground barite is consumed as a component of drilling fluids when creating oil and gas wells. The addition of it increases the density of the fluid injected into the well, with the aim of better resistance to high formation pressure and to prevent breakouts.
When the well is drilled, the bit goes through a different formation, each of which has its own characteristics. The greater the depth, the greater the percentage of barite must be present in the structure of the solution. An additional advantage is that the barium sulfate - nonmagnetic substance, so it does not interfere with holding of various downhole measurements via electronic devices.
Paint and paper industry
Most synthetic BaSO4 Used as a component of white pigment for paints. So, Blanfix mixed with titanium dioxide (TiO2 ) sold as white oil paint used in painting.
BaSO combination4 and ZnS (zinc sulfide) produces an inorganic pigment called lithopone. It is used as a coating for certain grades of photographic paper.
More recently, barium sulfate has been used to lighten paper designed for inkjet printers.
Application in the chemical industry and non-ferrous metallurgy
In the production of polypropylene and polystyrene BaSO4 used as a filler in a proportion of up to 70%. It has the effect of increasing the resistance of plastics to acids and alkalis, and also gives them opacity.
It is also used to produce other barium compounds, in particular its carbonate, which is used to make LED glass for television and computer screens (historically in cathode-ray tubes).
Molds used in metal casting often coat barium with sulphate to prevent adhesion to the molten metal. This is done in the manufacture of anode copper plates. They are cast into copper molds coated with a layer of barium sulfate. When liquid copper hardens in the form of a finished anode plate, it can be easily removed from the mold.
Since barium compounds emit green light when burning, the salts of this substance often use pyrotechnic formulas. Although nitrate and chlorate are more common than sulfate, the latter is widely used as a component of pyrotechnic stroboscopes.
Barium sulfate is a radiopaque agent used to diagnose certain medical problems. Since such substances are opaque to X-rays (block them as a result of their high density), the areas of the body in which they are localized appear as white patches on the X-ray film. This creates the necessary distinction between one (diagnosable) organ and other (surrounding it) tissues. The contrast will help the doctor see any special conditions that may exist in this organ or part of the body.
Barium sulfate is taken by mouth or rectally with an enema. In the first case, it makes the esophagus, stomach, or small intestine opaque to X-rays. Thus, they can be photographed. If the substance is injected with an enema, the colon or intestine can be seen and fixed by X-rays.
The dose of barium sulfate will be different for different patients, it all depends on the type of test. The drug is available in the form of special medical barium suspension or tablets. Different tests that require contrast and X-ray equipment require different amounts of suspension (in some cases, it is necessary to take the drug in tablet form). Contrast should be used only under the direct supervision of a physician.