Mercury compounds. Overview, description

Mercury compounds are used as a means of protecting plants from mildew (downy mildew), as well as from mold, putrefaction.

Mercury Chloride (I) Hg2Cl2 (calomel) is a heavy white powder without taste, odorless, insoluble in water, slowly decomposes into light. It reacts with ammonium hydroxide, forming free mercury in the form of a fine black powder. Kalomel is used as a laxative, diuretic, antiseptic. In the industry it is used for the production of Bengal lights and artistic porcelain. In scientific laboratories, a calomel electrode is often used.

Mercuric iodide (I) Hg2I2 – a light yellow powder that darkens in light as a result of decomposition and evolution of finely dispersed mercury – is used as an antiseptic and a medicine.

Mercury Nitrate (I) Hg2 (NO3) 2 forms colorless crystals soluble in very dilute nitric acid; It is used as a caustic substance and antiseptic, as well as for blackening brass.

Mercuric sulphate (I) Hg2SO4 is a light yellow powder that becomes gray in the light. It is poorly soluble in water. It is used in the technology of batteries and electrolytic cells.

Mercuric chloride (II) HgCl2 (mercuric chloride or mercuric chloride) is obtained as a colorless crystal or a white powder that is noticeably volatile at 100 ° C and completely evaporates at 300 ° C. It is soluble in water and forms acidic solutions as a result of hydrolysis and weak Ionization. Sulem is highly poisonous, is an effective antiseptic and mordant and is used to disinfect clothes. Her aqueous solutions of 1: 1000 or 1: 5000 are used for disinfection and washing of wounds and treatment of skin diseases. In industry, sulem is used for the preservation of wood and anatomical specimens, as well as for embalming, disinfecting, tanning, dyeing wood, in electroplating and depolarizing dry batteries and for many other purposes.

Iodide mercury (II) HgI2 – bright red poisonous powder – used as a mordant and a medicine.

Mercury Nitrate (II) Hg (NO3) 2 is a white crystalline, water soluble powder used in medicine, in the manufacture of felt hats, for the synthesis of fulminate mercury (rattling mercury) Hg (CNO) 2, the initiating explosive for detonator capsules and capsules – igniters in shells, grenades and torpedoes.

Mercury (II) thiocyanate Hg (CNS) 2 – a white odorless powder, when heated, increases many times in volume, which is used to demonstrate the experience of “Pharaoh’s snake”; The compound in powder and in vapors is poisonous. Mercury forms many complex compounds. For example, an alkaline solution of potassium tetraiodomercurate K2 [HgI4] (Nessler’s reagent) is used to quantify ammonia, in the presence of which a brown precipitate of NH2Hg2I3 is formed. This method allows one to detect up to 10-8 fractions of ammonia in water.

Mercury amidochloride HgNH2Cl (white amorphous powder) is obtained by adding ammonium hydroxide to mercuric chloride (II); When heated, it does not melt, but evaporates in the mode of low-red heating. This compound is used to treat skin rashes and irritations (white mercury ointment).

Properties of mercury and its application

Mercury (Hg) is a chemical element of group II of the periodic system of elements. Mendeleev University; Atomic number 80, relative atomic mass 200.59. Mercury under normal conditions is a shiny, silver-white heavy liquid metal. Its specific gravity at 20 ° C is 13.54616 g / cm3; The melting point is -38.89 ° C, boiling point 357.25 ° C. When it freezes (-38.89 ° C), it becomes hard and easily liable to forging.

Even under normal conditions, mercury has an increased saturated vapor pressure and evaporates at a fairly high rate, which increases with increasing temperature. This leads to the creation of a mercury atmosphere that is dangerous to living organisms. For example, at 24 ° C, atmospheric air saturated with mercury vapor may contain about 18 mg / m3; This level is 1800 times higher than the maximum allowable concentration (maximum permissible concentration) of mercury in the air of the working area and 60,000 times the MPC in the ambient air. Mercury can evaporate through layers of water and other liquids.

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When exposed to mercury vapor voltaic arc, electric spark and X-rays, phenomena of luminescence, fluorescence and phosphorescence are observed. In a vacuum tube between mercury electrodes in electrical discharges, a luminescence is obtained, rich in ultraviolet rays, which is used in engineering when designing mercury lamps. Another remarkable property of mercury is due to the fact that when metals are dissolved in it, amalgams are formed-metal systems, one of which is mercury. They do not differ from conventional alloys, although with excess mercury they are semi-liquid mixtures. The compounds resulting from amalgamation readily decompose below their melting point with the release of excess mercury, which has found wide application in the extraction of gold and silver from ores. Metals wetted by mercury are subject to amalgamation. Steels alloyed with carbon, silicon, chromium, nickel, molybdenum and niobium are not amalgamated.

Mercury – is very aggressive with respect to various construction materials, which leads to corrosion and destruction of production facilities and vehicles. So, in the 1970s. The problem of the contamination of airplanes, in the design of which mercury got into, causing liquid metal embrittlement of aluminum alloys, was quite actual. The aircraft were sent for major repairs and even decommissioned.

In compounds, mercury exhibits an oxidation state of +2 and +1. In the special literature, Hg (ll) or Hg (l) is usually indicated in such cases. With high ionization potential, high positive oxidation potential, mercury is a relatively chemically stable element.
This determines its ability to recover to the metal from various compounds and explains the frequent occurrences of mercury in nature in the native state.

In air, mercury is not oxidized at room temperature. When heated to temperatures close to the boiling point (300-350 ° C), it combines with air oxygen to form a red oxide of divalent mercury HgO, which upon further heating (up to 400 ° C and higher) again decomposes into mercury and oxygen. Yellow mercury oxide HgO is obtained by adding alkalis to an aqueous solution of the salt Hg (ll). There is also mercury oxide of black color (Hg2O), unstable compound, in which the oxidation state is +1. In hydrochloric and dilute sulfuric acids and in alkalis, mercury does not dissolve. But it dissolves easily in nitric acid and in royal vodka, and when heated in concentrated sulfuric acid. Metal mercury can dissolve in organic solvents, as well as in water, especially in the absence of free oxygen. Its solubility in water also depends on the pH of the solution. Minimal solubility is observed at pH 8, with increasing acidity or alkalinity of water it increases. In the presence of oxygen, mercury in water is oxidized to the ionic form of Hg2 + (creating concentrations of up to 40 μg / l).

Mercury reacts with halogens (chlorine, iodine, fluorine, bromine), sulfur, selenium, phosphorus and other non-metals. Of practical importance are iodine mercury HgJ, mercury chloride (calomel) Hg2Cl2 and chlorine mercury (mercuric chloride) HgCl2. When mercury reacts with sulfur, mercury sulphide HgS is formed, the most common in nature is its compound, in the form of which almost all of the mercury is extracted. It is known in three modifications: red (identical to the mineral cinnabar), black (black mercury sulphide, or metacinnabarite) and – p-cinnabar (in natural conditions it is not found). Other mercury compounds include mercury mercury Hg (ONC) 2, nitrate Hg (NO3) 2, sulfate (HgSO4) and sulfite (HgSO3), mercury red and yellow iodide, etc.

There is a large number of mercury-containing organic compounds in which metal atoms are bound to carbon atoms. The chemical bond between carbon and mercury is very stable. It is not destroyed by water, weak acids, or bases. From the standpoint of danger to living organisms (that is, from toxicology – the science of poisons), the most toxic of organometallic compounds of mercury are short-chain alkyl mercury compounds, primarily methylmercury.
Mercury is widely used in the manufacture of scientific instruments (barometers, thermometers, manometers, vacuum pumps, normal elements, polarographs, capillary electrometers, etc.), mercury lamps, switches, rectifiers; As a liquid cathode in the production of caustic alkali and chlorine by electrolysis, as a catalyst in the synthesis of acetic acid, in metallurgy for amalgamation of gold and silver, in the manufacture of explosives; In medicine (calomel, mercuric organic compounds, etc.), as a pigment (cinnabar), in agriculture (organic compounds of mercury) as a seed dressing and herbicide, as well as as a component of the paint of sea-going ships (to combat fouling by their organisms ). Mercury and its compounds are toxic, so working with them requires taking the necessary precautions.

Mercury has always found wide application in various spheres of practical, scientific and cultural activities of man. By the early 1980’s. It was known for over a thousand different areas of its application. Here are the main ones, in which mercury and its compounds are used to some extent and now:

– chemical industry – production of chlorine and caustic, acetaldehyde, chlorovinyl, polyurethanes, organomercury pesticides, paints;
– Electrotechnical industry – manufacture of various lamps, relays, dry batteries, switches, rectifiers, ignitrons, etc .;
– radio engineering industry and instrument making – production of instrumentation (thermometers, barometers, manometers, polarographs, electrometers), radio and television equipment;
– medicine and pharmaceutical industry – manufacturing of eye and skin ointments, substances of bactericidal action, production of vitamin B, making dental fillings (amalgams of silver and copper);
– Agriculture (pesticides, antiseptics);
– mechanical engineering and vacuum technology – the production of vacuum pumps, etc .;
– military business – the production of detonators, guided missiles;
– metallurgy – production of ultrapure metals, precise casting, amalgamation of precious metals;
– mining (rattling mercury);
– laboratory practice and analytical chemistry.

In the energy sector, mercury was used as a working fluid in powerful industrial-type binary installations, where mercury steam turbines were used to generate electricity at the first stages, as well as in nuclear reactors for heat removal. Elemental mercury is used in the processes of separation of lithium isotopes. Mercury is sometimes alloyed with other metals. Its small additives increase the hardness of the lead alloy with alkaline earth metals. It was even used for soldering. Mercury cyanide was used in the production of antiseptic soap.

Ways of water softening

In natural waters there is a very large number of different chemical compounds. In the process of natural circulation, natural waters, being in contact with air and rocks of the earth’s crust, are enriched with the substances contained in them. In addition, in these waters are the products of vital activity of animals and plants. In a number of water sources, water is additionally contaminated with waste from human production activities. The direct use of natural waters for industrial and domestic needs is in most cases unacceptable. The requirements for the quality of water consumed in industry are determined by the specific conditions of various technological processes. For example, many manufactures (textile, leather) can not use hard water, i.e. Containing salts of calcium and magnesium. The name of water hardness arose from the fact that washing tissues in water with a high concentration of Ca and Mg ions makes the fibers brittle, inelastic, as if rigid. This is due to the formation on the fibers of calcium and magnesium salts of fatty acids that are part of soap, as well as carbonate salts.

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A particularly high demand for consumed water makes heat-and-power production.

The presence of a significant amount of hardness salts in water makes water unsuitable for many technical purposes. With prolonged feeding of steam boilers with hard water, their walls are gradually covered with a dense crust of scale. Such a crust can cause blistering and cracks, both in boiling pipes and on the walls of the boiler itself.

Therefore, the chemical control of Ca2 + and Mg2 + ions is very important for conducting the water-chemical regime of operation of heat and power equipment.

Water has universal properties, due to which it is used as raw material, chemical reagent, solvent, heat and coolant, in some cases as a catalyst. For example, hydrogen is obtained from water, used in the production of alcohols, aniline, detergents, and the like. Water serves as a reagent for the production of acids, alkalis and bases, various organic products – alcohols, acetic aldehyde, phenol, in hydration and hydrolysis reactions. Water is used as a solvent for solid, liquid and gaseous substances. As a coolant and coolant, water is used for exo – and endothermic processes. Hot water and steam have significant advantages over other heat carriers: high heat capacity and thermal stability, easy temperature control depending on pressure, etc.

In order to save water, so-called recycled water is used, i.e. Repeatedly used and returned to the production cycle. To save water as heat and coolant, it is replaced by air.

Natural waters are divided into atmospheric, surface and underground.
Atmospheric water – rain and snow sediments – is characterized by a small content of impurities in the form of dissolved gases. In this water, dissolved salts are almost completely absent.

Surface waters – rivers, lakes and seas – are distinguished by a diverse composition of impurities, containing gases, salts, bases, acids. The greatest content of mineral impurities in sea water (salinity is more than 10 g / kg).

Underground waters – well, key, artesian – are characterized by different composition of dissolved salts, which depends on the composition and (coagulation) of individual particles and the formation of sediment.

Softening and desalting of water are the main processes of water treatment, which consist in removal of salts of calcium, magnesium and other metals. There are physical, physical-chemical and chemical methods of softening water.
Physical methods – thermal (boiling), distillation and freezing. Thermally, salts of temporary hardness are removed. Distilled water, which does not contain salts, is obtained by distillation in special distillation units. It is necessary for the preparation of chemically pure reagents, drugs, in laboratory practice, etc. Freezing is based on the difference in the crystallization temperatures of water and impurities.

Physicochemical methods are electrochemical, based on the use of electrodialysis, electroosmosis, electrocoagulation, and ion-exchange (ion-exchange) methods, which have become widespread.

Ion exchange methods are based on the removal of calcium and magnesium ions from the water by means of ion exchangers (hardly soluble solids) capable of exchanging their ions for ions contained in water. Distinguish the processes of cation and anion exchange, respectively, ion exchangers are called cation exchangers and anion exchangers.

Of electrochemical methods of considerable interest is the electrocoagulation. Its essence consists in obtaining electrochemically aluminum hydroxide, which possesses high sorption ability in relation to harmful impurities. The process is carried out in electrolyzers. The advantages of electrocautery include: high sorption capacity of electrochemical Al (OH) 3, the possibility of mechanization and automation of the process, small dimensions of treatment facilities.

The chemical method of softening water consists in treating it with solutions of certain chemical compounds in order to bind Ca2 +, Mg2 + ions and others into insoluble and easily removable compounds.

Properties of mercury

Mercury (Hg) is a chemical element of Group II of the Periodic Table of Elements. Mendeleev University; Atomic number 80, relative atomic mass 200.59; The composition of natural mercury includes 7 stable isotopes with mass numbers: 196 (prevalence 0.146%), 198 (10.02%), 199 (16.84%), 200 (23.13%), 201 (13.22%) , 202 (29.80%) and 204 (6.85%). Natural mercury is characterized by a relatively stable isotopic ratio. Nevertheless, radioactive isotopes are present in small amounts in it. More than 20 short-lived isotopes were artificially obtained, of which 203Hg (half-life period of 46.6 days) and 197Hg (64.1 hours) are of practical importance (labels in medicine, in analytics, in technological processes). Mercury under normal conditions is a shiny, silver-white heavy liquid metal. Its specific gravity at 20 ° C is 13.54616 g / cm3; Melting point = -38.89C, boiling point 357.25C. When it freezes (-38.89 ° C), it becomes hard and easily liable to forging.

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Even under normal conditions, mercury has an increased saturated vapor pressure and evaporates at a fairly high rate, which increases with increasing temperature. This leads to the creation of a mercury atmosphere that is dangerous to living organisms. For example, at 24 ° C, atmospheric air saturated with mercury vapor may contain about 18 mg / m3; This level is 1800 times higher than the maximum allowable concentration (maximum permissible concentration) of mercury in the air of the working area and 60,000 times the MPC in the ambient air. Mercury can evaporate through layers of water and other liquids. In addition to noble gases, mercury is the only element that forms vapors that are monatomic at room temperature (Hgo). Under normal conditions, the solubility of mercury vapors in water free of air is about 20 μg / l.

When exposed to mercury vapor voltaic arc, electric spark and X-rays, phenomena of luminescence, fluorescence and phosphorescence are observed. In a vacuum tube between mercury electrodes in electrical discharges, a luminescence is obtained, rich in ultraviolet rays, which is used in engineering when designing mercury lamps. The same phenomenon formed the basis of the spectral method for determining small amounts of mercury in various objects. Mercury is characterized by a very low specific heat. This property was used in mercury vapor steam installations. Another remarkable property of mercury is due to the fact that when metals are dissolved in it, amalgams are formed-metal systems, one of which is mercury. They do not differ from conventional alloys, although with excess mercury they are semi-liquid mixtures. The compounds resulting from amalgamation readily decompose below their melting point with the release of excess mercury, which has found wide application in the extraction of gold and silver from ores. Metals wetted by mercury are subject to amalgamation. Steels alloyed with carbon, silicon, chromium, nickel, molybdenum and niobium are not amalgamated.

In compounds, mercury exhibits an oxidation state of +2 and +1. In the special literature, Hg (II) or Hg (I) is usually indicated in such cases. With high ionization potential, high positive oxidation potential, mercury is a relatively chemically stable element. This determines its ability to recover to the metal from various compounds and explains the frequent occurrences of mercury in nature in the native state. Usually native mercury contains small amounts of other metals, including gold and silver, that is, in fact, is an amalgam. Mercury minerals are known in which noble and other metal contents are very high (mercury silver, mercury gold, mercury palladium, mercury lead, gold amalgam, etc.). Mercury is very aggressive with respect to various structural materials, which leads to corrosion and destruction of production facilities and vehicles. So, in the 1970s. The problem of the contamination of airplanes, in the design of which mercury got into, causing liquid metal embrittlement of aluminum alloys, was quite actual. The aircraft were sent for major repairs and even decommissioned.

In air, mercury is not oxidized at room temperature. When heated to temperatures close to the boiling point (300-350 ° C), it combines with the oxygen of the air, forming a red oxide of divalent mercury HgO, which upon further heating (up to 400 ° C and higher) again decomposes into mercury and oxygen. Yellow mercury oxide HgO is obtained by adding alkalis to an aqueous solution of the Hg (II) salt. There is also mercury oxide of black color (Hg2O), unstable compound, in which the oxidation state is +1. In hydrochloric and dilute sulfuric acids and in alkalis, mercury does not dissolve. But it dissolves easily in nitric acid and in royal vodka, and when heated in concentrated sulfuric acid. Metal mercury can dissolve in organic solvents, as well as in water, especially in the absence of free oxygen. Its solubility in water also depends on the pH of the solution. Minimal solubility is observed at pH 8, with increasing acidity or alkalinity of water it increases. In the presence of oxygen, mercury in water is oxidized to the ionic form of Hg2 + (creating concentrations of up to 40 μg / l).

The prevalence of mercury in nature

Mercury is a rare element. Its average content in the earth’s crust and main types of rocks is estimated at 0.03-0.09 mg / kg, ie, 1 kg of rock contains 0.03-0.09 mg of mercury, or 0.000003-0, 000009% of the total mass (by comparison, one mercury lamp, depending on the design, may contain from 20 to 560 mg of mercury, or from 0.01 to 0.50% by weight). The mass of mercury, concentrated in the surface layer of the earth’s crust with a capacity of 1 km, is 100,000,000,000 tons (one hundred billion tons), of which only 0,02% are in its own deposits. The remaining part of mercury exists in a state of extreme dispersion, mainly in rocks (41.1 million tons of mercury is dispersed in the waters of the World Ocean, which determines a low average concentration of mercury in its waters – 0.03 μg / l). It is this scattered mercury that creates a natural geochemical background, on which mercury contamination is imposed due to human activities and leading to the formation of technogenic pollution zones in the environment.

More than 100 mercury and mercury-containing minerals are known. The main mineral, which determines the industrial significance of mercury deposits, is cinnabar. Native mercury, metacinnabarite, livestone and mercury-containing faded ores have a sharply subordinate value and are extracted along with cinnabar.

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In total, about 5000 mercury deposits, ore sites and ore occurrences, which have been given an independent name, have been discovered in the world; Of these, about 500 have been developed at different times. But in the history of the mercury industry, the vast majority of mercury (more than 80%) was obtained from 8 deposits: Almaden (Spain), Idrija (Slovenia), Monte Amiata (Italy), Huancavelica (Peru), New Almaden and New Idrija (USA), Nikitovka (Ukraine), Khaidarkan (Kyrgyzstan).

In the industry, two versions of the technology for its extraction from ores are used to produce metallic mercury: oxidation-distillation firing with the release of mercury from the gas phase, and a combined process involving preliminary enrichment and subsequent pyrometallurgical processing of the concentrate. According to experts, about 700,000 tons of mercury were produced by man, a significant part of which is scattered on the earth’s surface. The amount of mercury that has entered the habitat during other types of human activity (when mining various minerals, smelting metals, producing cement, burning fossil fuels, etc.) is also great.

Mercury concentrates not only in mercury minerals, ores and their enclosing rocks. According to the Clark-Vernadsky law on the universal dispersion of chemical elements, in some quantities, mercury is found in all objects and components of the environment, including meteorites and lunar soil samples. In high concentrations, mercury is found in the ores of many other minerals (polymetallic, copper, iron, etc.). The accumulation of mercury in bauxites, some clays, combustible shales, limestones and dolomites, in coals, natural gas, oil.

Modern data indicate a high content of mercury in the mantle (the second from the surface, after the earth’s crust, the Earth’s shell), as a result of its degassing, as well as the natural process of evaporation of mercury from the earth’s crust (rocks, soils, waters), there is a phenomenon called “Mercury respiration of the Earth.” These processes go on constantly, but are activated by volcanic eruptions, earthquakes, geothermal phenomena, etc. The supply of mercury to the environment as a result of the mercury respiration of the Earth (natural emission) is about 3000 tons per year. The supply of mercury to the atmosphere caused by human industrial activity (man-made emissions) is estimated at 3600-4500 tons per year.

Distribution and migration of mercury in the environment are carried out in the form of a cycle of two types. First, a global cycle involving the circulation of mercury vapor in the atmosphere (from land-based sources to the World Ocean and vice versa). Secondly, the local circulation, based on the processes of methylation of inorganic mercury, coming mainly from technogenic sources. Many stages of the local circulation are not yet sufficiently clear, but it is believed that it involves circulation in the habitat of dimethylmercury. It is with the second type of circulation that formation of dangerous situations from environmental positions is most often connected.
Entering the environment from natural and man-made sources, mercury and its compounds undergo various transformations in it. Inorganic forms of mercury undergo transformation as a result of oxidation-reduction processes. The mercury vapor is oxidized in water in the presence of oxygen by inorganic divalent mercury, to which the organic substances present in the aqueous medium, which are particularly numerous in the contamination zones, contribute significantly. In turn, ionic mercury, entering or forming in water, is capable of forming complex compounds with organic matter. Along with oxidation of mercury vapors, the formation of Hg2 + can occur when mercury-organic compounds are destroyed.

The background levels of mercury in natural soils depend on their type, but in most cases they are in the range 0.01-0.1 mg / kg. The lower limits are characteristic of sandy soils, the upper ones for soils rich in organic matter. The contents exceeding these values ​​are related to the influence of pollution. In contaminated zones, mercury levels, especially in the upper horizons of soils, increase tens of times, sometimes even thousands of times. In soils, mercury is actively accumulated by humus, clay particles, it can migrate down the soil profile and enter groundwater, be absorbed by vegetation, including agricultural, and also be released as fumes and dust into the atmosphere. If the soils are heavily soiled, mercury concentrations in the air can reach dangerous levels for humans.

In surface waters, mercury migrates in two main phase states – in water solution (dissolved forms) and in suspension (suspended forms). In turn, in a solution of water it can be in the form of a divalent ion, mercury hydroxide, complex compounds (with chlorine, organic matter, etc.). Among the Hg (II) compounds, we already know about this, a special role belongs to the organochlorine compounds in terms of their ecological and toxicological significance. The most important accumulators of mercury, especially in conditions of pollution, are suspended matter and bottom sediments of water objects. The highest concentrations of mercury are characterized by man-made muds actively accumulating in rivers and reservoirs, where industrial wastewater enters. Mercury levels in them reach 100-300 mg / kg and more (against a background of up to 0.1 mg / kg). There are cases when the amount of mercury, supplied with sewage and accumulated in such mud, was tens and hundreds of tons. The normal functioning of such rivers and reservoirs, their practical use is possible only with the removal of contaminated sediments.