Metallic mercury

Exists as the (Hg —Hg) ion. Other polymercury cations, e.g. Hgj (Hg plus AsFj), Hg4 etc., are also known. All positive oxidation state compounds of Hg are readily reduced to the metal, mercury chlorides... 

In presence of hydrochloric acid, tin(II) in aqueous solution (1) is precipitated by hydrogen sulphide as brown SnS, and (2) will reduce mercury(II) chloride first to mercury(I) chloride (white precipitate) and then to metallic mercury. 

Mercuric chloride test. Add mercuric chloride solution to formic acid or a solution of formate and w arm. A white precipitate of mercurous chloride, insoluble in dil. HCl, is produced. Sometimes the reduction proceeds as far as metallic mercury, which appears as a grey precipitate. 

It is one of four metals — mercury, cesium, and rubidium — which can be liquid near room temperature and, thus, can be used in high-temperature thermometers. It has one of the longest liquid ranges of any metal and has a low vapor pressure even at high temperatures. 

Propyn-l-ol Alkali metals, mercury(II) sulfate, oxidizing materials, phosphorus pentoxide, sulfuric acid... 

Other recovery methods have been used (10). These include leaching ores and concentrates using sodium sulfide [1313-82-2] and sodium hydroxide [1310-73-2] and subsequentiy precipitating with aluminum [7429-90-3], or by electrolysis (11). In another process, the mercury in the ore is dissolved by a sodium hypochlorite [7681-52-9] solution, the mercury-laden solution is then passed through activated carbon [7440-44-0] to absorb the mercury, and the activated carbon heated to produce mercury metal. Mercury can be extracted from cinnabar by electrooxidation (12,13). 

Secondary. Scrap material, industrial and municipal wastes, and sludges containing mercury are treated in much the same manner as ores to recover mercury. Scrap products are first broken down to Hberate metallic mercury or its compounds. Heating in retorts vaporizes the mercury, which upon cooling condenses to high purity mercury metal. Industrial and municipal sludges and wastes may be treated chemically before roasting. 

Mercury from these accumulated wastes is generally best recovered by total degradation in stills, where metallic mercury is condensed and collected. The recovery costs are amply compensated by the value of the metal recovered. Moreover, disposal problems are either eliminated or severely diminished. 

Most inorganic mercury compounds have very low vapor pressures, and generally do not contribute to high mercury vapor readings. MetaUic mercury is the most potent and troublesome in this respect. Organic mercurials also contribute to mercury vapor readings, possibly by virtue of the presence of extremely small amounts of metallic mercury present as an impurity. 

Another method of removing mercury compounds from aqueous solution is to treat them with water-soluble reducing agents, thus hberating metallic mercury (26). The use of formaldehyde (qv) at a pH of 10—12 also is recommended. 

When an aqueous effluent stream containing organomercurials cannot be recycled, it may be treated with chlorine to convert the organomercury to inorganic mercury. The inorganic compounds thus formed are reduced to metallic mercury with sodium borohydride. The mercury metal is drained from the reactor, and the aqueous solution discarded. The process utilising sodium borohydride is known as the Ventron process (27). 

This equipment is used for the capture of Particulate Matter (PM), including particulate matter less than or equal to 10 micrometers ( m) in aerodynamic diameter (PMk, particulate matter less than or equal to 2.5 m in aerodynamic diameter (PMj 5), and hazardous air pollutants (HAPs) that are in particulate form, such as most metals (mercury is the notable exception, as a significant portion of emissions are in the form of elemental vapor). 

The mechanistic sequence as outlined for quinolizidine-10-c/has metallic mercury as the reduced species. Mercurous acetate is the form in which the mercury eventually appears. It has been shown (76) that under the standard operating conditions, mercuric acetate will oxidize metallic mercury to the... 

The isolation of mercury is comparatively straightforward. The most primitive method consisted simply of heating cinnabar in a fire of brushwood. The latter acted as fuel and condenser, and metallic mercury collected in the ashes. Modem techniques are of course less crude than this but the basic principle is much the same. After being crushed and concentrated by... 

The halides are the most familiar compounds of mercury(I) and all contain the Hg2 + ion (see below). Hg2p2 is obtained by treating Hg2C03 (itself precipitated by NaHC03 from aqueous Hg2(N03)2 which in turn is obtained by the action of dil HNO3 on an excess of metallic mercury) with aqueous HF. It dissolves in water... 

Calomel, derived from the Greek words icaX6-g (beautiful) and fXsXaf (black), seems an odd name for a white solid. It might arise from the colour of the material obtained when Hg2Cl2 is treated with ammonia this is a product of variable composition (see below) which owes its colour to the presence of metallic mercury. Other more fanciful derivations are listed in the Oxford English Dictionary 2, 41 (1970). 

There have been numerous reports of possible allergic reactions to mercury and mercury salts and to the mercury, silver and copper in dental amalgam as well as to amalgam corrosion products Studies of the release of mercury by amalgams into distilled water, saline and artificial saliva tend to be conflicting and contradictory but, overall, the data indicate that mercury release drops with time due to film formation and is less than the acceptable daily intake for mercury in food . Further, while metallic mercury can sensitise, sensitisation of patients to mercury by dental amalgam appears to be a rare occurrence. Nevertheless, there is a growing trend to develop polymer-based posterior restorative materials in order to eliminate the use of mercury in dentistry. 

Insolubility in water and other common solvents. No metals dissolve in water electrons cannot go into solution, and cations cannot dissolve by themselves. The only liquid metal, mercury, dissolves many metals, forming solutions called amalgams. An Ag-Sn-Hg amalgam is used in filling teeth. 

In the first cell the net reaction is the production of metallic mercury and gaseous oxygen through electrolysis of aqueous mercuric nitrate ... 

The mercuric sulfide may be saved and converted to metallic mercury or mercuric chloride by the usual procedures. 

We return now to the mercuro-de-diazoniation. Nesmeyanov s school continued the work on metallo-de-diazoniations from 1929 to 1953 (see summary by Nesmeyanov, 1972). A major discovery was made at the very beginning, namely the influence of copper powder (Nesmeyanov, 1929 b Nesmeyanov and Kahn, 1929). With this addition metallic mercury was not required instead the double salt of the diazonium chloride and mercuric chloride was used. The copper reacts stoichiometrically as an electron donor. Therefore, either arylmercuric chlorides (Scheme 10-87) or diarylmercury compounds (Scheme 10-88) can be obtained. These reactions are called Nesmeyanov reactions. Specific examples are the syntheses of di-2-naphthyl-... 

For liquid electrode metals (mercury, gallium) the determination of the surface tension can be applied. From changes of the surface tension as a function of dissolved adsorbable species the surface coverage... 

In this final section, the global cycles of two metals, mercury and copper, are reviewed. These metals were chosen because their geochemical cycles have been studied extensively, and their chemical reactions exemplify the full gamut of reactions described earlier. In addition, the chemical forms of the two metals are sufficiently different from one another that they behave differently with respect to dominant... 

There are several environmentally significant mercury species. In the lithosphere, mercury is present primarily in the +II oxidation state as the very insoluble mineral cirmabar (HgS), as a minor constituent in other sulfide ores, bound to the surfaces of other minerals such as oxides, or bound to organic matter. In soil, biological reduction apparently is primarily responsible for the formation of mercury metal, which can then be volatilized. Metallic mercury is also thought to be the primary form emitted in high-temperature industrial processes. The insolubility of cinnabar probably limits the direct mobilization of mercury where this mineral occurs, but oxidation of the sulfide in oxygenated water can allow mercury to become available and participate in other reactions, including bacterial transformations. 

Alkali-metal-mercury compounds decompose rapidly in O2 or moisture and must be prepared in melt atmospheres or under vacuum. To prepare NaHg, NaHg2 and Na,Hg2, known amounts of Hg and Na are flushed with N2. The reaction is exothermic, and mixing is carried out slowly, homogeneity being achieved by shaking. An excess of Na or Hg is necessary for crystal formation. ... 

The reaction between Hg(II) and olefins has been examined from several angles and work prior to 1950 has been summarised by Chatt . Several types of complex and product are formed, depending on the olefin, which involve no change in the oxidation state of the mercury atom. Propenyl ethers have long been known to produce the corresponding glycol plus metallic mercury but no kinetics are available . 

Experience shows that in the deposition of a number of metals (mercury, silver, lead, cadmium, and others), the rate of the initial reaction is high, and the associated polarization is low (not over 20 mV). For other metals (particularly of the iron group), high values of polarization are found. The strong inhibition of cathodic metal deposition that is found in the presence of a number of organic substances (and which was described in Section 14.3) is also observed at mercury electrodes (i.e., it can be also associated with the initial step of the process). 

Silver and gold, which are corrosion resistant in many solutions, are rather efficient catalysts for the cathodic reduction of oxygen and certain other reactions. Some sp-metals (mercury, tin, zinc) exhibit interesting catalytic properties for the cathodic reduction of CO2. Copper might be a very interesting material for a number of electrochemical reactions, but so far has not been examined thoroughly. 

The Alclad alloys have been developed to overcome this shortcoming. Alclad consists of a pure aluminum layer metallurgically bonded to a core alloy. The corrosion resistance of aluminum and its alloys tends to be very sensitive to trace contamination. Very small amounts of metallic mercury, heavy-metal ions, or chloride ions can frequently cause rapid failure under conditions which otherwise would be fully acceptable. When alloy steels do not give adequate corrosion protection—particularly from sulfidic attack—steel with an aluminized surface coating can be used. 

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