Barium sulfate is an inorganic substance with the chemical formula BaSO4. It is a white odorless powder, insoluble in water. Its whiteness and opacity, as well as high density determine the main applications.
Barium refers to alkaline earth metals. The latter are named so because, according to DI Mendeleyev, their compounds form an insoluble mass of earth, and the oxides "have an earthy appearance." Barium in nature is contained in the form of a barite mineral, which is barium sulfate with various impurities.
It was first discovered by the Swedish chemists Sheele and Ghana in 1774 as part of the so-called heavy spar. Hence the name of the mineral (from the Greek "baris" - heavy), and then of the metal itself, when in 1808 he was singled out in pure form by Gemfri Devi.
Since BaSO4 Is a salt of sulfuric acid, its physical properties are partly determined by the metal itself, which is soft, chemically active and silvery-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 sulphate? Its molar mass is 233.43 g / mol. It has an unusually high specific gravity - from 4.25 to 4.50 g / cm 3. Considering the insolubility in water, high density makes it irreplaceable as a filler of aqueous drilling fluids.
BaSO4 Is one of the most difficultly soluble in water compounds. It can be obtained from two highly soluble salts. We take an aqueous solution of sodium sulfate-Na2 SO4. Its molecule in water dissociates into three ions: two Na + and one SO4 2- .
We also take an aqueous solution of barium chloride-BaCl2. molecule of which dissociates into three ions: one Ba 2+ and two Cl -.
BaCl2 → Ba 2+ + 2Cl -
Mix the aqueous solution of sulphate and the mixture containing chloride. Barium sulfate is formed as a result of the combination of two ions in one molecule with the same charge and opposite in sign.
Below you can see the complete equation of this reaction (the so-called molecular).
As a result, an insoluble precipitate of barium sulphate is formed.
In practice, the raw material for the production of commodity barium sulphate, intended for use in drilling fluids when drilling oil and gas wells, is, as a rule, mineral barite.
The term "primary" barite refers to a commodity product that includes raw material (obtained from mines and quarries), as well as products of simple enrichment 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 ground and sieved to a uniform size so that at least 97% of its particles have a size of up to 75 μm and not more than 30% are less than 6 μm. The primary barite must also be sufficiently dense to have a specific gravity of 4.2 g / cm 3 or higher, but it is soft enough not to damage the bearings.
Preparation of a chemically pure product
Mineral barite is often contaminated with various impurities, mainly iron oxides, staining it in different colors. It is processed by carbothermic method (heating with coke). The result is barium sulphide.
BaSO4 + 4 C → BaS + 4 CO
The latter, unlike sulphate, is soluble in water and easily reacts with oxygen, halogens and acids.
To produce a high purity product, sulfuric acid is used. Barium sulphate, formed by such a process, is often called the blanfix, which in French means "white fixed." It is often found in consumer products, such as paints.
In the laboratory, barium sulphate is formed by combining in the solution of barium ions and sulfate ions (see above). Since sulfate is the least toxic barium salt because of its insolubility, waste containing other salts of it is sometimes treated with sodium sulfate to bind all of the barium being sufficiently toxic.
From sulphate to hydroxide and back
Historically barite was used to produce barium hydroxide Ba (OH)2. necessary for the refining of sugar. This is generally a very interesting and widely used industry connection. It is highly soluble in water, forms a solution known as barite water. It is convenient to use it to bind sulfate ions in various compositions by forming insoluble BaSO4 .
We have seen above that when heated in the presence of coke from sulfate, it is easy to obtain a water-soluble barium sulfide-BaS. The latter forms hydroxide when it interacts with hot water.
Barium hydroxide and sodium sulfate taken in solutions, when mixed, will give an insoluble precipitate of barium sulphate and sodium hydroxide.
It turns out that the natural barium sulfate (barite) is firstly converted into barium hydroxide by industrial process, and then serves to obtain the same sulfate in the purification of various salt systems from sulfate ions. Similarly, the reaction will also take place in the purification of SO ions4 2-solution of copper sulphate. If you make a mixture of "barium hydroxide + copper sulfate", then the result is copper hydroxide and insoluble barium sulfate.
Even in reaction with the sulfuric acid itself, its sulfate ions will be completely bound by barium.
Use in drilling fluids
About 80% of the world production of barium sulphate, refined and ground barite, is consumed as a component of drilling fluids in the creation of oil and gas wells. Adding it increases the density of the fluid pumped into the well, in order to better resist high reservoir pressure and prevent breakouts.
When the well is drilled, the bit passes through various formations, each of which has its own characteristics. The greater the depth, the greater the percentage of barite should be present in the structure of the solution. An additional advantage is that barium sulfate is a non-magnetic substance, so it does not interfere with carrying out various measurements in the well with the help of electronic devices.
Paint and varnish and paper industry
Most of the synthetic BaSO4 It is used as a component of white pigment for paints. Thus, blanfix in a mixture with titanium dioxide (TiO2 ) is sold as a white oil paint, used in painting.
The combination of BaSO4 and ZnS (zinc sulphide) gives an inorganic pigment, which is called a lithopone. It is used as a coating for certain types of photographic paper.
More recently, barium sulfate has been used to lighten paper intended for inkjet printers.
Application in the chemical industry and non-ferrous metallurgy
In the production of polypropylene and polystyrene BaSO4 is used as a filler in a proportion up to 70%. It has the effect of increasing the resistance of plastics to acids and alkalis, and also imparts opacity to them.
It is also used for the production of other barium compounds, in particular its carbonate, which is used to manufacture LED glass for television and computer screens (historically in cathode ray tubes).
Forms used in casting metals are often coated with barium sulfate to prevent adhesion to the molten metal. This is the case when manufacturing anode copper plates. They are cast into copper ingots covered with a layer of barium sulfate. When liquid copper solidifies as a finished anode plate, it can be easily removed from the mold.
Since barium compounds emit green light during combustion, the salts of this substance are often used in 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 an X-ray contrast 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 regions of the body in which they are localized appear as white patches on the X-ray film. This creates the necessary difference between one (diagnosed) organ and other (surrounding) tissues. Contrast will help the doctor see any special conditions that may exist in this organ or part of the body.
Barium sulfate is taken through the 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 with 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 as a special medical barium suspension or in tablets. Different tests that require contrast and X-ray equipment require a different amount of suspension (in some cases, the drug should be taken in tablet form). Contrast substance should be used only under the direct supervision of a physician.