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硫黄の環境化学

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かって知り合いの先生が某大学の入試問題で硫黄の化学を穴埋め問題で出したが、受験生や予備校からは単なる記憶問題と猛反発を食った。それに比べ天下のT大の問題は考えさせるものが多いというのである。
 
しかしながら硫黄Sの示す化学種の多さには驚嘆に値するものがあるのである。出題者は工夫は少なかったがそれを狙ったのであろう。
 
inchem.org/documents/ehc/ehc/ehc019
 
Hydrogen sulfide is a colourless gas with a characteristic odour
    that is soluble in various liquids including water, alcohol, ether,
    and solutions of amines, alkali carbonates, and bicarbonates
. It can
    undergo a number of oxidation reactions to yield principal products
    consisting of sulfur dioxide, sulfuric acid, or elemental sulfur.
    Reaction rates and oxidation products depend on the nature of the
    oxidizing agent
.

        The methylene blue colorimetric method has acceptable specificity,
    accuracy, and sensitivity for hydrogen sulfide determinations, and is
    generally recognized as a standard analytical procedure. It has been
    used successfully, in automatic continuous monitoring, but
    sophisticated maintenance facilities and highly trained technicians
    are required for this method. Gas chromatography coupled with flame
    photometric detection is an alternative method for hydrogen sulfide
    determination, either as a laboratory method or for continuous
    monitoring in stationary field settings.

        Most of the direct-reading methods of hydrogen sulfide
    determination in the occupational environment are susceptible to
    various forms of interference. However, methods employing chemical
    detector tubes appear to be useful in occupational settings, where
    hazardous levels of hydrogen sulfide can occur. Under these
    conditions, reliability and accuracy compensate for a certain lack of
    specificity.

Sources of hydrogen sulfide

        Hydrogen sulfide is one of the principal compounds involved in the
    natural cycle of sulfur in the environment. It occurs in volcanic
    gases and is produced by bacterial action during the decay of both
    plant and animal protein. It can also be produced by bacteria through
    the direct reduction of sulfate. Significant concentrations of
    hydrogen sulfide occur in some natural gas fields and in geothermally
    active areas.

        Hydrogen sulfide can be formed whenever elemental sulfur or
    certain sulfur-containing compounds come into contact with organic
    materials at high temperatures. In industry, it is usually produced as
    an undesirable by-product, though it is an important reagent or
    intermediate in some processes. Hydrogen sulfide occurs as a
    by-product in: the production of coke from sulfur-containing coal, the
    refining of sulfur-containing crude oils, the production of carbon
    disulfide, the manufacture of viscose rayon, and in the Kraft process
    for producing wood pulp.

Sのサイクルは窒素サイクル同様、火山、バクテリア、動物、植物の多種多様な様相を示す。工業活動による酸性雨も考慮せねばなるまい。
 
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Sources Associated with Human Activity

        There are various circumstances under which naturally occurring
    hydrogen sulfide is released by human activity. For example, hydrogen
    sulfide occurring in association with natural gas and/or crude oil
    deposits in some areas may be released during extraction and drilling
    operations. The sulfur content of crude oils ranges from 0 to 5% and
    some natural gas deposits have been reported to comprise up to 42%

hydrogen sulfide (Espach, 1950). Coals can contain sulfur levels of up
    to 80 g/kg and, occasionally, conditions arise in which hydrogen
    sulfide is formed within such deposits. Thus, special precautions must
    be taken in some mining operations as well as in the drilling and
    extraction of natural gas and crude oils with significant sulfur
    content.

        Hydrogen sulfide can also be released by activities surrounding
    the development and use of geothermal resources. At the Cerro Prieto
    geothermal power generating plant in Baja California, Mexico, for
    example, hydrogen sulfide levels are sufficiently high to necessitate
    special ventilation to protect electrical systems, and alarms for the
    protection of personnel (Mercado, 1975).

        During industrial operations, hydrogen sulfide can be formed
    whenever elemental sulfur or certain sulfur-containing compounds come
    into contact with organic materials at high temperatures. It is
    usually produced as an undesirable by-product, though it is also used
    as an important reagent or desirable intermediate compound in some
    industrial processes such as the manufacture of sulfides, sodium
    hydrosulfide, and various organic sulfur compounds. Examples of
    processes in which hydrogen sulfide occurs as a by-product include the
    production of coke from sulfur-containing coal, the production of
    carbon disulfide, the manufacture of viscose rayon in the Kraft
    process for producing wood pulp (Macaluso, 1969) and sulfur extraction
    by the Frasch process.

        In refining sulfur-containing crude oils, about 80%-90% of the
    divalent sulfur compounds of hydrogen and carbon are converted to
    hydrogen sulfide. Both the hydrogen sulfide produced and that
    occurring in other industrial, geothermal, or natural gas streams can
    be recovered by one of a number of processes that can be classified as
    either absorption-desorption processes or processes involving
    oxidation to oxides or to elemental sulfur. The bulk of hydrogen
    sulfide recovered in industrial processes is used to produce elemental
    sulfur or sulfuric acid (Macaluso, 1969).

        Large quantities of hydrogen sulfide are used in the production of
    heavy water, which is employed as a moderator in some nuclear power
    reactors. The process is based on enrichment of the deuterium content
    of water by hydrogen sulfide in a gas/liquid ion exchange system,
    followed by separation of heavy water and water by fractional
    distillation (McGraw-Hill Encyclopedia of Science and Technology,
    1960).

        In the tanning industry, hydrogen sulfide is produced in the
    process by which hair or wool is removed from the hides. This
    typically involves deliming by adding ammonium chloride or ammonium
    sulfate followed by pickling with sulfuric acid, and takes place in
    large rotating drums. The gases evolved, including hydrogen sulfide,

    are released from the drums on opening the hatches either to add
    chemicals or to unload the treated hides, and also from the waste
    waters (ILO, 1971).

        As in the natural environment, hydrogen sulfide can be generated
    by bacterial action in industrial or community settings in malodorous
    and sometimes dangerous amounts.

        In some countries, such as India and Sri Lanka, hydrogen sulfide
    is produced in the process by which coconut fibres are separated from
    the husk. This procedure involves the decomposition of the husks in
    shallow ponds. The hydrogen sulfide is produced as a result of
    microbiological decay processes.

 

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