Hazardous Materials
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chlorination A chemical reaction that involves the addition of chlorine to a substance; the treatment of contaminated drinking water to kill the micro- organisms that cause dysentery, cholera, typhoid, hepatitis, and other diseases
,., 1 burn when exposed to an atmosphere of h f Elements orher rhan hydr~ge;.:i~~d copper, arsenic, antimony, phosphorus c 10tine.
For exa mple exposure of fme y I . . d 'and Sul fur ro chlori1;e causes rhem ro burn with mean escence. ·
Ss(/) Sulfur
Cu(s) + Clz(g) - CuClz(s) Chlorine Copper( !!) chloride
Copp~r
2As(s) + Arsenic
2Sb(s) + Antimony
Pis) + Phosphorus
+ IOClz(g) Chlorine
3Clz(g) Chlorine
3Clz(g) Chlorine
6Clz(g) Chlorine
2AsCl3(s) Arsenic trichloridc
2SbCl3(s) Antimony trichloride
4PC13(/) Phosphorus 1richloride
2S2Clz(/) + Disulfur dichloride Sulfur tetrachloride
In these instances the chlorine acts as an oxidizing agent. Chlorine als~ supports the combustion of certain organic co_mpounds. These reac.
tions occur slowly unless the mixture of the compound_ and chlo~me is e~posed to light, For instance a mixture of elemental chlorine and gasoline vapor ts essennally unreacrive in the dark, but when the mixture is exposed ro light, the reaction occurs instantaneously. In such reactions, the light acts catalytically.
When chlorine atoms are incorporated into a compound, the associated chemical phenomenon is referred to as the chlorination of the compound. This term is also used to describe the treatment of drinking water and wastewater with elemental chlorine and chlorine-containing oxidizing agents. When used in this fashion, chlorine acts as a micro- bicide by killing undesirable microorganisms.
In the United States, there are nearly 60,000 municipal water treatment facilities that provide drinking water ro over 260 million people. The use of chlorine for treating drink- ing water saves millions of lives annually from waterborne diseases like cholera and dys- entery. Notwithstanding this fact, we noted in Section 7.1-I that chlorine is not a totally effective microbicide, because it does not effectively destroy the Cryptosporidium parvum bacterium.
When it is dissolved in water, chlorine reacts to form hypochlorous acid, which is even more powerful than chlorine as an oxidizing agent.
Clz(g) + HzO(/) ---> HCIO(aq) + HCl(aq) Chlori ne Water Hypochlorous acid Hydrochloric acid
During the chlorination of drinking water and wastewater, it is the presence of hypochlo· rous acid that aids in making chlorine an effective microbicide.
7.3-E WORKPLACE REGULATIONS INVOLVING CHLORINE When the use of elemental chlorine is necessary in the workplace, OSHA requires employ- ers to provide thelf workers with respiratory protective gear. When employees are exposed to a relattvely small amo~nt of chlorine, they should wear goggles and impermeable gloves, and whenever possible, their activities should be conducted within a fume hood, When wmking ~n bulk chlorine storage systems, however, employees should wear fully encapsulanng swts ~nd ~se self-~ontained breathing apparatus.
'.o avoid or mm1m1ze the ill effects associated with exposure to chlorine, osBA requires employers to limit employee exposure in th k I aximum chlo· . . . . e wor p ace to a m h 11 rme concentrat10n m air no greater than 1 part ·11· d an 8- 01
kd per m1 10n, average over
wor ay.
248 Chapter 7 Chemistry of Some Common Elements
FIGURE 7.13 When carriers transport any amount of chlorine in a rail tankcar, DOT requires them to post POISON GAS placards on each of its sides and to mark CHLORINE and INHALATION HAZARD on two opposing sides. DOT also requires them to display the identification number 1017 on each side. In this instance, the carrier chose to display 1017 across the center area of the POISON GAS placards. HOKX 7718 is the reporting mark and number of Occidental Chemical Corporation, Dallas, Texas . At the time this tank was photographed, DOT did not require the MARINE POLLUTANT marking to appear on two opposing sides. (Courtesy of the Chlorine Institute, Arlington, Virginia and Andrew Johnson, iMed Design, Inc., Reno, Nevada .)
7.3-F TRANSPORTING CHLORINE Chlorine is transported as a liquefied compressed gas in steel cylinders, ton-containers, cargo tanks, and rail tankcars at 84 psi (580 kPa) at 70°F (21 °C). The ton-container is a welded tank having a maximum loaded mass of 3700 pounds (1680 kg).
When shippers intend to transport chlorine, DOT requires them to identify it on the accompanying shipping paper as follows:
UN1017, Chlorine, 2.3, (5.1), (8) (Marine Pollutant) (Poison - Inhalation Hazard, Zone B)
The rail tankcar in Figure 7.13 is an example of a type of bulk packaging used to trans- port chlorine. DOT requires carriers to display POISON GAS placards and MARINE POLLUTANT on the tankcar. DOT also requires them to display the identification number lOl7 on orange panels, across the center area of the POISON GAS placards, or on white ~quare-on-point diamonds, and to mark the expression INHALATION HAZARD on the ulk packaging. One means of complying with these DOT requirements is noted below:
Chapter 7 Chemistry of Some Common Elements 249
When chlodne is u,n,ported in b"lk by highway oe rail, DOT ,~ display its name on two opposing sides of the tankcar or cargo tank used fes carriers . . d. 1 p or sl.. · to When it is transported by rail, DOT requtres earners to isp _ay OISON GAs '11P11tent on squares having a white background and black border (Section 6.6-D). Placari
The DOT-approved tanks and cylinders used for transporting chi . equipped with fusible plugs designed to melt in the temperature range of 1Ss°r1ne a (70 to 74°C). The plugs are located on th~ valve just _below t_h~ valve sea:o 16s:; exposed to the temperatures routinely associated with fire cond1t1ons the · Whe
d h • ' rneit- n these plugs permits chlorine to be slowly release to t e environment and p 1ng of reven vessels from rupturing. ts the DOT also regulates the constru~tio': and fabri~ation of ra_il tan½cars _and tank t
used to transport chlorine. To maintain the confined chlorine pnmanly in th ~Ucks state, DOT requires a minimum of 4 inches (10 cm) of insulation about them. Ae liquid in Section 3 7-A thermally insulated tankcars constructed to DOT specificat· s noted · ' Ions h been designed to allow external heat to be slowly transferred to the contents Und ave normal conditions of transport. When exposed to heat, however, these tanks lo erht~e . . set e mtegnty and rupture. tr
7.3-G RESPONDING TO INCIDENTS INVOLVING A RELEASE OF CHLORINE
Because elemental chlorine poses an inhalation health hazard, emergency responders not be too wary when they encounter chlorine during transpo_rtation incidents. In zi~~- after two freight trains collided in Graniteville, South Carolina, a pressurized tank ' ruptured and released more than 9200 gallons (35 m3) of liquid chlorine into the envir~:'. ment. This sole incident caused the deaths of nine people, the hospitalization of more tha 250 individuals, and the evacuation of more than 5400 people.5 n
When emergency responders are called to a scene at which chlorine tanks or con- tainers have ruptured or could potentially rupture, it is vital to acknowledge the toxic- ity hazard associated with elemental chlorine. Because inhaling chlorine may be fatal, the use of fully encapsulated suits and self-contained breathing apparatus is absolutely essential.
The responsibilities of a first-on-the-scene team responding to a large spill of chlorine begin with the immediate isolation and evacuation of all unauthorized persons to a dis- tance that relates to the amount of chlorine that has been or could potentially be released into the environment. As initial guidance, 6 DOT recommends the isolation of unauthor- ized persons 3000 feet (1000 m) in all directions when a release of chlorine from a rail tankcar, highway tank truck, or trailer is involved; 1250 feet (400 m) from multipl: ton cylinders; and 800 feet (250 m) from multiple small cylinders or a single ton cylinder. As additional protection during a large spill of chlorine, DOT also recommends the evacua- tion of unauthorized persons to a distance ranging from 0.5 mile (0.8 km) to 7+ miles (11 + km) during day and nighttime hours, respectively, from the same transport vessels. The latter distances are selected by consideration of the prevailing wind speed [low ( <6 mph, or <10 km/hr), moderate (6-12 mph, or 10-20 km/hr), or high (>12 mph, or 20 km/hr)]for the relevant type of transport vessel. .
Emergency responders must also identify those who have been exposed to chJrni f~om leaks ?r ruptured con~a_i~ers. Th~se ~ndividuals should be moved downwind t: k~~t air where, 1f necessary, artificial respiration can be supplied. They should ~J~o skin warm with blankets and provided with immediate first-aid attention. To nu01nuze
' ·1rnenr, 5David van Sickle, "Acute health effects after exposure to chlorine gas released after a train derai Amer. J. Emerg. Med., Vol. 27 (2009), pp. 1-7. 35). 6 R . . · 2012), P· Table 3, Emergency esponse Guidebook (Washington, DC: U.S. Department of Transportation,
250 Chapter 7 Chemistry of Some Common Elements
ns Persons exposed to chlorine should remove their clothing and shower thoroughly. bur , · · f " fo prevent the impairment O _v1S1on, they should irrigate their eyes with flowing water for a proidmately 30 minutes._ Fmally, they sho~ld be transported to an emergency medical P ·t·ty fo r follow-up examinat10ns by physicians
fuOI • An emergen~y response team may be required to examine the physical condition of
a chlorine container or r~il tankcar. Unruptured vessels should be cooled with water as he ream members pmpoint the specific spots from which chlorine is leaking or could t orenrially leak . Becau~e containers and transport vessels contain liquid chlorine, it is ~ften the liquid that dnps fro~ valves, fittings, or openings. Liquid chlorine is substan- . lly more concentrated than Its gas, and when unconfined it readily evaporates. One
ua · 'd hi · ' volume of hqm c . orme evaporates into approximately 460 volumes of gas. Conse- uently, the immediate area surrounding a chlorine leak becomes a highly toxic envi-
q · h' d nment wit 111 secon s. ro Locating a chlo~ine leak_ is not always a simple matter, especially when the gas has been escaping from its container or transport vessel for some time and the atmosphere is heavily laden with chlorine. One method of detecting a chlorine leak is based on the chemical reaction between chlorine and ammonia. These two substances react to form ammonium chloride and ammonium hypochlorite, each of which is a white solid.
Ammonia Chlorine Water Ammonium chloride Ammonium hypochlorite
The method consists of tying a rag soaked with household ammonia to a broomstick and rhen passing the stick along the surface of the chlorine container or tank. Ammonia vapor- izes from the liquid and reacts with the chlorine at the point from which it is escaping. At this location, a white cloud drifts into the air. By observing the cloud's formation, the source of the leak is easily identified. This simple procedure is ineffective when the sur- rounding atmosphere is heavily laden with chlorine, because under these conditions, the ammonium compounds are produced virtually throughout the area.
When chlorine is leaking from a tank or container, the exit points must be closed or sealed. When sealing an opening is impossible or impractical, an attempt should be made to prevent the further escape of liquid chlorine into the environment. This can sometimes be accomplished by rolling the vessel so that the opening points upward. Although chlo- rine gas continues to escape from the opening, the more concentrated liquid remains con- fined within the vessel.
When emergency responders arrive at the scene of an incident involving the release of chlorine, specialized equipment should be available for their immediate use. An essential item is a kit that contains a clamping device to seal a leak at the fusible plug and a patching device to seal a leak in the cylinder sidewall. They are components of the so-called Chlorine Institute Emergency Kit "A, " which is available from several com- mercial outlets. 7 There are also "B " and "C" kits for use on ton cylinders and tanks, respectively. . To improve the speed and effectiveness of a response action at an emergency involv- ing the release of chlorine the Chlorine Institute formalized an action known as the Chlorine Emergency Plan, ~r CHLOREP. Under this plan, the United States and Canada are divided into regional sectors in which specially trained teams are located. In the event of an emergency involving the release of chlorine, or when CHEMTREC (Section 1.12) is contacted, the caller is put into immediate contact with the closest CHLOREP team, which then oversees the handling of the incident. ,:;:;--_ s~e Chlori~e Institute is a trade association consisting primarily of compa~y repr~sentatives interes_r:d in the lnei~rod_uct1on, distribution, and use o f chlorine and o~her subst~n~e~ associated with the chlor-alkali industry,
offices are loca ted at 1300 Wilson Boulevard, Arlington, Virginia 22209.
Chlorine Emergency Plan (CHLOREP) An action plan for aiding emergency responders during incidents involving the release of chlorine during transportation mishaps or at user locations
Chapter 7 Chemistry of Some Common Elements 251
Convention on Certain Conventional Weapons An interna- tional treaty that aims to restrict or prohibit the use of certain con- ventional weapons dur- ing warfare, including those containing incen- diary agents
White phosphorus
/!\ PC------~P
TABLE 7.9 MM1411Mii:41hM::ii,IMl·i\4M~ RED PHOSPHORUS
WHITE PHOSPHORUS (AMORPHOUS)
Melting point 111'F {44'C) 1 094 'F {590'C) at 43 (4400 kPa) atrn
Boiling point 535'F {280'C) 781 'F {416'C) {sublirn ates) Specific gravity at 68'F {20'C) 1.82 2.34
Vapor density (air - 1) 4.42 4.77
Autoignition point 86'F {30'C) (spontaneous S00'F (260°() i nition in dry air) g
7 .4 PHOSPHORUS Elemental phosphorus has several allotropes, two of which are especially import white phosphorus and red phospho~us. :Vhite ~hosphorus is the un~table form of the:~'. ment at room conditions. On standmg, 1t acquires a yellow coloration due to the pa . 1 conversion of the white allotrope to the more stable red allotrope. For this reason, phosphorus is also called yellow phosphorus.
The physical properties of white and red phosphorus are provided in Table 7.9. Their properties are so strikingly different that we discuss them here separately. Both are used to manufacture important chemical products such as special alloys (e.g., phosphor bronze) rodenticides, fireworks, matches, phosphoric acid, and metallic phosphides. In the past' both were also used as the active agent in incendiary bombs. When dropped from militar; aircraft, these bombs set fires to objects or caused burn injuries to persons through the action of flames and heat. The composition of some incendiary bombs containing red phosphorus was 50% of the incendiary mixture.
White phosphorus has also been used in incendiary bombs to illuminate the battle- field during nighttime. However, the addition of white phosphorus in munitions is now regarded as an unwarranted wartime practice, because flaming droplets from exploded ordnance can become embedded beneath skin and seriously burn civilians.
White phosphorus has also been used in tracer, smoke, and signaling systems. The mixture of tetraphosphorus hexoxide and tetraphosphorus decoxide produced by the combustion of white phosphorus possesses the best obscuring power of any known smoke-producing material.
In 1983, many of the world's civilized countries agreed to ban the use of incendiary weapons during certain warfare operations by acceptance of the Convention on Certain Conventional Weapons. Known formally as the Convention on Prohibitions or Restric- tions of the Use of Certain Conventional Weapons Which May Be Deemed to Be Exces- sively Injurious or to Have Indiscriminate Effects, it prohibits the use of incendiary weapons against civilian populations and restricts their use against military targets located within a concentration of civilians, but it does not restrict the use of incendiary bombs in illumination, tracer, smoke, or signaling systems.
Although the United States is a signatory to the Convention, it has not ratified the non use of incendiary weapons on military targets located in civilian-populated areas. _In 2005, during the U.S.-led assault on Fallujah, Iraq, incendiary munitions containing white phosphorus were used to flush enemy troops from covered positions.
7 .4-A PRODUCTION AND PROPERTIES OF WHITE PHOSPHORUS White_ phosphor~s is a waxy, translucent solid at ambient conditions. Each of its_ m~;; cules 1s tetratom1c and has the tetrahedral shape like that shown in the left margin- these reasons, the chemical formula of white phosphorus is P4 •
252 Chapter 7 Chemistry of Some Common Elements
White phosphorus is industrially prep d b h • k in an electric furnace Th • _are Y eating calcium phosphate rock with sand
and co e b . 1 Th e principal components of sand and coke are silicon diox-ide and car on, respecnve y. e production of white phosphorus is denoted as follows: 2Ca3(P04)2(s) + 6Si02(s) + IOC(s) -, 6CaSiO3(s) + I0CO(g) + P4(g)
cn1ciulll phosphalt.! Silicon dioxide Carbon Calcium silicate Carbon monox ide Phosphorus
The phos~horuf.Japors are vented from the furnace and condensed under water to pro- duce a white so 1 . . ..
Because rhe autoigrutwn t~mperature of white phosphorus is on] 86°F (30°C), white h sphorus spontaneously 1grutes when e d · Th · · y · p o xpose to air. e auto1grut1on temperature 1s so I that body heat can serve as an ig 't• T . . • • ow . . ru ton source. 10 reduce or ehmmate the nsk of 1ts taneous combust10n white phos h · d · spon . ' P orus 1s store under water or a blanket of rutrogen.
White phosphorus is often _said to possess the offensive odor of a mixture of garlic and rotten fish, but this comparison is misleading. This specific odor is more likely associ- ated with the presence of phosphine (Section 9.6-B), a toxic gas slowly produced by the reaction between phosphorus and cold water.
P4(s) + 6H2O(/) - 3H3PO2(aq) + PH3(g) Phosphorus Water Hypophosphorous ac id Phosphine The combustion of white phosphorus produces two oxides, tetraphosphorus hexox-
ide and tetra phosphorus decox1de, as follows:
P4(s) + 3O2(g) - P4O6(s) Phosphorns Oxygen Tetraphosphorus hexoxide P4(s) + 5O2(g) - P4O1o(s) Phosphorus Oxygen Tetraphosphorus dt:coxidt:
As implied by these equations, tetraphosphorus hexoxide and tetraphosphorus decoxide are the products of incomplete and complete combustion, respectively. Both are white compounds. Consequently, when white phosphorus burns, billows of dense white, chok- ing smoke are produced. This luminous dense smoke accounts for the use of white phos- phorus as a component of military smoke and signaling systems.
Although spontaneous combustion is the principal hazard associated with white phosphorus, its vapor also is highly poisonous. Prolonged exposure to phosphorus vapor causes phossy jaw, or phosphorus necrosis, which in the worst instances causes disinte- gration of the jawbone. In addition, white phosphorus burns the skin and produces wounds that are extremely painful and slow to heal. For this reason, users must always handle white phosphorus with gloves.
7.4-8 TRANSPORTING WHITE PHOSPHORUS When shippers offer solid or molten white phosphorus for transportation in bulk, DOT requires them to enter the relevant shipping description shown in Table 7.10 on the accom- panying shipping paper. When the element is molten, HOT markings must be displayed.
DOT requires carriers to display the relevant identification number-1381 or 2447- on orange panels or across the center area of SPONTANEOUSLY COMBUSTIBLE plac- ards or white square-on-point diamonds. For example, any of the following may be used 10 display the identification number 1381 on bulk packaging: 1381 1· ~
phossy jaw (phospho- rus necrosis) The disfiguring affliction caused by overexposure to phosphorus vapor
Chapter 7 Chemistry of Some Common Elements 253
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Red phosphorus
TABLE 7.10 -wm.;;,1.;.;a;;.;;;.;,;;.140@11, osphorus WHITE PHOSPHORUS
White phosphorus, solid
White phosphorus, molten
SHIPPING DESCRIPTION
UN1381, Phosphorus, white, dry, 4.2, (G.i) PG I (Marine Pollutant) (Poison) '
HOT, UN2447, Phosphorus, white, molten 4 2 (6.1 ), PG I (Marine Pollutant) (Poison) ' · '
When white phosphorus is transported in bulk by highway or rail, DOT requir to display a name such as PHOSPHORUS, WHITE, DRY or PHOSPHORUS e~arriers MOLTEN on two opposing sides of the transport vehicle used for shipment.' All l-il'fc, labeling, marking, and placarding requirements apply. Other
7 .4-C RESPONDING TO INCIDENTS INVOLVING A RELEASE OF WHITE PHOSPHORUS
White phosphorus generally is burning when first-on-the-scene responders arrive scene involving its release. Although the fire can be effectively extinguished with w:t a experts advise firefighters to avoid its use due to the formation of toxic phosphine. lnst/~r, they recommend the use of dry sand, because it can blanket the element, prevent rei~'. tion, and minimize the potential exposure to phosphine.
When small quantities of white phosphorus are burning, it is best to segregate them from nearby combustible materials. This may not be a simple matter, because phosphorus melts at a relatively low temperature and flows as it burns into nearby low areas. For this reason, appropriate action should be taken by constructing dams or dikes.
Firefighters responding to incidents involving elemental phosphorus should wear pro• tective gear and use self-contained breathing apparatus. They should be particularly cau· tious to avoid inhaling the fumes from a phosphorus fire. Fumes contain particulates of the phosphorus oxides, which when inhaled, can seriously irritate the nose, mouth, throat, and lungs.
7 .4-D RED PHOSPHORUS The red allotrope of phosphorus is a dark red solid whose molecules consist of long chains of p4 tetrahedra, each having an undefined length. The following example shows only three interlinked tetrahedra, but this number is generally much larger .
. (t)._.(t)._.(/). p p p
Due toitS The chemical formula of red phosphorus is usually denoted as either P or Po:i• d) phos· undefined structure, red phosphorus is also known as amorphous (unstructur~C) ill an phorus. It is produced industrially by heating white phosphorus at 482°F (2SO iron container from which air has been excluded. . al reac·
When compared to white phosphorus, the red allotrope is sluggish in che!lll~ored in tivity. Small quantities are not spontaneously combustible. They generally are 5
closed containers without an overlying layer of water or nitrogen. bustible, Bulk quantities of red phosphorus, however, are spontaneously corn ide, 'f~e
forming a mixture of tetraphosphorus hexoxide and tetraphosphorus deco"
254 Chapter 7 Chemistry of Some Common Elements
II trope combines spontaneously with atmospheric oxygen, but the combustion red 3. occurs very slowly. When it is stored in bulk the accumulated heat of com-
act10 h b . f th · ' · · f d re . n triggers t e urnmg O e entire mass. For this reason, bulk quantities o re bustl0 h rus are rarely stored. ph0iedo phosphorus is nonpoisonous, but like the white allotrope, it reacts with water to
Phosphine. /orJll
4.E TRANSPORTING RED PHOSPHORUS 7· hippers intend to transport red phosphorus, DOT requires them to identify it on Whenc~mpanying shipping paper as follows: the ac
UN1338, Phosphorus, amorphous, 4.1, PG III
\'(/hen red phosphorus is transported in bulk by highway or rail, DOT requires carriers to display the name PHO~PHORUS (AMORPH_OUS) on_two opposing sides of t~e trans- port vehicle used for shipment. All other labeling, markmg, and placarding reqwrements apply.
7.4-F RESPONDING TO INCIDENTS INVOLVING A RELEASE OF RED PHOSPHORUS Bulk quantities of red phosphorus are unlikely to be encountered, but containers holding small quantities have been involved in fires. These fires can be extinguished by the appli- cation of dry sand, foam, or dry chemicals, but not water. Because phosphine is produced when water is applied to burning red phosphorus, the use of dry sand is advised for fire exringuishment.
7.5 SULFUR Elemental sulfur occurs naturally, particularly in countries bordering the Gulf of Mexico and in Japan, Mexico, and Italy. Sulfur also occurs in minerals and ores too numerous to mention, in which it is combined with metals and other nonmetals. Sulfur accounts for 0.06% by mass of all the elements found on Earth.
7.5-A PRODUCTION AND PROPERTIES OF SULFUR Most of the world's supply of elemental sulfur comes from natural deposits of the element frequently called brimstone. These deposits are often located near hot springs and volca- noes. To isolate the sulfur from them, hot water under pressure is pumped into the subter- ranean brimstone-bearing deposits, whereupon the sulfur melts and is brought to the surface by an airlift. Brimstone often has an offensive odor because it contains hydrogen sulfide, a toxic gas having the odor of rotten eggs (Section 10.13-A). Their containers and tanks must be handled with special care, as the gas can evolve and accumulate in the vent spaces above the liquid.
By contrast, pure sulfur is an odorless solid. When it is heated at atmospheric ii~essure, it vaporizes, but the vapor ~an be condensed on~ cold s~r~ace, produci_ng a
Is e dust called flowers of sulfur. It 1s used as a commercial fung1c1de and acancide ect1on 7.5-B). f T?e solid state of sulfur occurs in numerous allotropic forms, the two most common
~I which are orthorhombic sulfur and monoclinic sulfur. Orthorhombic sulfur is the sta- phe a_llotrope of solid sulfur at ambient conditions. It is a yellow, crystalline solid whose te YSrca! properties are noted in Table 7.11. When orthorhombic sulfur is maintained at a Pa~Perature between 205 and 235°F (96 and 113°C), it changes into a mass of long trans- ailoent needles composed of monoclinic sulfur. Because monoclinic sulfur is not the stable
trop · I e, 11 s owly changes back into the orthorhombic form.
Sulfur, solid
Sulfur, liquid
flowers of sulfur The finely divided powder of elemental sulfur
Chapter 7 Chemistry of Some Common Elements 255
TABLE 7.11 Physical Properties of Elemental Sulfur (Orthorhombic)
Melting point 248°F (120°()
Boiling point 832°F (445°C)
Specific gravity at 68°F (20°C) 2.07
Vapor density (air= 1) 8.9
Vapor pressure at 475°F (246°C) 10 mmHg
Flashpoint 405°F (207°C)
Autoignition point 450°F (232°C)
Lower flammable limit (as dust)• 0.002 lb/ft3 (35 g/m3)
Upper flammable limit (as dust)• 0.09 lb/ft3 (1400 g/m3) a The lower and upper flammable limits of sulfur dust vary with ,ts particle size and depth of drspersron.
Both solid allotropes exist as molecules having eight sulfur atoms bonded together in the puckered-ring arrangement shown below:
Molten sulfur has a highly complex molecular arrangement. Chemists denote it as s where x is a relatively small but undefined number. The chemical formula of sulfur vap;; at its boiling point is also represented as Ss, but when the vapor is further heated, the cyclic arrangement breaks down, and the sulfur molecules assume the formula S,. To avoid ambiguity, S8 is denoted in this text as the formula of liquid and solid sulfur, a~dS, is represented as the formula of gaseous sulfur. -
When elemental sulfur is exposed to an ignition source, it first melts and the liquid sulfur burns with a blue flame before it vaporizes. The combustion produces sulfur diox- ide, a poisonous gas having a suffocating, choking odor (Section 10.12).
Sg({) + 802(g) - 8S02(g) Sul fur Oxygen Sulfur dioxide
Elemental sulfur also combines with most metals. For example, when a mixture of mercury and iron is heated, the elements unite to form mercury(II) sulfide and iron(II) sulfide, respectively.
8Hg(l) + Sg(/) - 8HgS(s) Mercury Sulfur Mercury(U) su lfide
8Fe(s) + Sg(/) - 8FeS(s) Iron Sulfur lron(U) sulfide
Elemental sulfur is likely to spontaneously ignite under the following conditions: . ·xrure is When flowers of sulfur are dispersed into air a potentially explosive mi . •ry
d d Th . . . . . , . electf!CI pro uce . e spontaneous 1gmt1on of this rruxture is triggered by the sta~ic dust generated by the movement of the sulfur particles within the air. The potential for_ ah the explosion may be markedly reduced by electrically grounding the vessel in whic sulfur is confined.
2 56 Chapter 7 Chemistry of Some Common Elements
FIGURE 7.14 _El_emental sulfur is a constituent of many industrial and domestic products including gunpowder, matches, insect1c1des, ferti lizers, and vulcanized rubber. When the sulfur burns, it is converted into the toxic gas sulfur dioxide.
Elemental sulfur reacts with many oxidizing agents. When the mixture is activated, the resulting heat of reaction is likely to cause the ignition of the residual sulfur. Conse- quently, all mixtures of elemental sulfur and oxidizing agents pose the risk of fire and ex- plosion. Every effort should be employed to keep sulfur and oxidizing agents segregated.
7.5-B COMMERCIAL USES OF SULFUR Sulfur is one of the world's most important raw materials. There is hardly a segment of the chemical industry that does not use elemental sulfur or one of its compounds in manufac- turing or production processes. Approximately 80% of the elemental sulfur produced in the United States is used as a raw material for the manufacture of sulfuric acid (Section 8.7). As Figure 7.14 illustrates, sulfur is also used to produce vulcanized rubber products (Section 14.11-A), fertilizers, dyes and other chemical substances, drugs and other pharmaceuticals, black gunpowder, fireworks, pesticides, and matches.
Elemental sulfur is used as a fungicide (for killing fungi) and an acaricide (for killing mites and ticks). For agricultural use, it is commercially available as a dust, paste, and wettable powder. The dust is applied undiluted, but the paste and wettable powder for- mulations may contain pulverized clay, which deposit and stick to the surfaces of leaves. They kill by direct contact.
Sulfur is also used as a raw material by the chemical industry to produce other chem- ical products. For example, elemental sulfur is united with carbon and fluorine to produce carbon disulfide (Section 13.10) and sulfur hexafluoride, respectively: 1 Carbon disulfide is produced when sulfur vapor is passed over very hot carbon in the
absence of air. The presence of air is avoided to reduce or prevent the likelihood that carbon disulfide will ignite.
C(s) + S2(g) Carbon Sulfur
CS2(g) Carbon disulfide
Chapter 7 Chemistry of Some Common Elements 257 I
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TABLE 7.12
SULFUR
Sulfur, elemental, solid
Sulfur, elemental, molten
Shipping Descriptions of Sulfur
SHIPPING DESCRIPTION
NA 1350, Sulfur, 9, PG Ill
NA2448, Sulfur, molten, 9, PG 111
or UN2448, Sulfur, molten, 4. 1, PG 111
<J(%jj l
Sulfur hexafluoride is the predominant product formed when sulfur comb· fluorine. tnes With
S8(s) + 24F2(g) ---> 8SF5(g) Sulfur Fluorine Sulfur hexafluoride
It is used as an insulator in high-voltage electrical equipment.
7 .5-C TRANSPORTING SULFUR When shippers offer sulfur for transportation, DOT requires them to identify the relev entry in Table 7.12 on the accompanying shipping paper. DOT regulates the transponatio:n; s~ for domestic and international transportation as a class 9 and a flammable solid, res~. t1vely. For domestic transportation, DOT notes at 49 C.F.R. §172.102.30 that shippers are ?-ot subject to its labeling requirements if the sulfur is transported in nonbulk packaging, or if 1t is formed in a specific shape like prills, granules, pellets, pastilles, or flakes.
At 49 C.F.R. §172.102.30, DOT also notes that the CLASS 9 placard is not required on bulk packaging when molten sulfur is transported domestically, as long as the packag- ing is marked with the identification number 2448 on orange panels, white square-on- point diamonds, or HOT markings. At 49 C.F.R. § 172.325, DOT also requires the packaging to be marked with the expression MOLTEN SULFUR.
~-2448 1~~ When molten sulfur is transported internationally in bulk packaging, DOT requires its carriers to display FLAMMABLE SOLID placards on the packaging. DOT also requires the HOT marking and the expression MOLTEN SULFUR to be displayed on the packag· ing. Alternatively, the identification number may be displayed across the center of the FLAMMABLE SOLID placard, but the HOT marking and the expression MOLTEN SULFUR are still displayed on the packaging.
7.5-D RESPONDING TO INCIDENTS INVOLVING A RELEASE OF SULFUR The following practices should be implemented at fire scenes involving burning sulfur:
Firefighters may effectively extinguish sulfur fires by applying water to rbe!Tl :~:i fog. The fog not only removes heat from the fire scene, but it also avoids the pote buildup of steam that could cause the hot material to splatter.
258 Chapter 7 Chemistry of Some Common Elements
TABLE 7.13 Physical Properties of Graphite and Diamond
GRAPHITE DIAMOND
~eltin9 point 6606-6687'F (3652-3697'() 6422'F (3550'C)
soilin9 point 7592' F (4200'C) 8726'F (4830'C) ·re gravity at 68'F (20'C) 2.20-2.35 3.52 speCI I
0.4 density (air= 1) vapor flashpoint >200'F (>93' C)
ition point 1346'F (730°C)
1 To avoid inhaling toxic levels of sulfur dioxide, firefighters responding to incidents involving burning sulfur must wear fully encapsulating suits with self-contained breathing apparatus. . .
1 Because sulfur readily melts under fire conditions and flows into lower adiacent eas where it can ignite secondary fires, firefighters must take appropriate action to
:;gregate the molten material from combustible materials by constructing dams or dikes. 1 When firefighters respond to transport incidents involving molten brimstone, they
must understand that hydrogen sulfide may evolve and accumulate in the vent spaces of the transport vessels. Inhalation of the gas may be deadly.
7.6 CARBON Elemental carbon occurs naturally as its two primary allotropes, graphite and diamond. 8
It also occurs in soot, coal, coke, charcoal, and carbon black. In these two primary allo- tropes, the elemental carbon is represented by its chemical symbol, C.
The natural abundance of carbon is only 0.08% by mass on Earth, yet carbon ranks much higher in terms of importance, because it is a constituent of the compounds needed by all living organisms for survival.
7.6-A COMMON ALLOTROPES OF CARBON Neither diamond nor graphite is generally considered hazardous. Each possesses substan- tially different physical properties, some of which are compared in Table 7.13. Graphite (the "lead" of pencils) is a black material that feels slippery, but diamond can be cut and polished to a crystalline, transparent luster. Although graphite is one of the softest known substances, diamond is the hardest substance found in nature.
'There are several other carbon allotopes whose properties are not discussed in this text. In 1962, a one-atom- thICk sheer of carbon called graphene was first isolated from graphite. Its structure resembles a densely packed hexagonal honeycomb of carbon atoms. It is regarded as a distinct allotrope of carbon because it possesses a set of unique properties, even different from those of graphite.
In 1985, the carbon allotrope having 60 carbon atoms per molecule (C6ol was discovered by vaporizing graphite with a laser. It is called buckminsterfullerene. The name is derived from the observation that its hollow soccer-ball-shaped molecules resemble rhe celebrared geodesic domes designed by American architect and engi'. nee, R. Buckminster Fuller. Each c60 molecule is colloquially called a "buckeyball. " Its symmetry consists of 32 IOterlocking rings (20 hexagons and 12 pentagons) . This geometrical shape is called a truncated icosahedron. d. \0 1991, the carbon allotrope called a carbon nanotube was discovered. Ir takes the physical form of cylin- T~ca carbon molecules with at least one end typically capped with a hemisphere of the buckeyball structure. n, e ~ame 15 derived from irs size, because the diameter of a nanotube is of the order of a few nanometers but ,,:;
1 e sev~ral_millimeters in length. A carbon nanotube exhibits extraordinary strength and is currently finding
u ness in diverse areas including food, cosmetics, electronics, and medicine.
Graphite
Chapter 7 Chemistry of Some Common Elements 259
FIGURE 7. 15 The struc- tures of two carbon allo- tropes, diamond and graphite. In the graphite structure shown in (a), planar hexagonal rings covalently bond to one another in successive sheets. In the diamond structure shown in (b), each carbon atom is covalently bonded to four other carbon atoms in a tetrahedral arrangement.
't::=::=-- ~--_y+;;~ : 4fW_:;:s-r : I I I I I I q i- I 1-o-l II :=ell I I 1- 1 I I I II_.__ ___ I
I I I I 11~ 1 I I I I I I I I
/--4-_/ :
(a)
I I I
(b)
The physical properties of graphite and diamond are linked with the structure f substances. In the graphite structure shown in Figure 7.15(a), each carbon atom is~ 0 the to other carbon atoms in planar hexagonal rings joined to one another in succon~ed sheets. In the diamond structure shown in Figure 7.15(b), each carbon atom is syrn:siv_e cally bonded to four other carbon atoms in a tetrahedral arrangement. etn-
The diamond structure is produced in nature when carbon-containing materials subjected to a pressure of approximately 0.8 million pounds per square inch (5.6 milt kPa) within the hot mantle of Earth, over 75 miles (120 km) below its surface. The hig~~s° gem-quality diamonds are discovered in ancient volcanic pipes in a greenish rock, kimber'. lite, in South Africa, Canada, Arkansas, Siberia, and elsewhere.
For decades, scientists and engineers have attempted to produce diamonds in labora- tories by replicating Nature's process. Limited success was initially experienced. The dia- monds produced were small and useful only as low-grade industrial diamonds. They were too dark in color to be suitable for gemstones. Today, however, significant advances in producing gemstone-quality diamonds have been made by passing carbon vapor over diamond seeds inside a vacuum chamber at an approximate temperature of 2000'F (1093°C). Using this technique, the ability to produce 10-carat diamonds has been mas- tered.9 By comparison, the largest polished (faceted) natural diamond is the Golden Jubi- lee Diamond, which weighs 545.67 carats (109.13 g). It is among the crown jewels of the royal family of Thailand.
At moderate temperatures and pressures, graphite is the stable allotrope of carbon. On Earth's surface, diamond converts into graphite at an imperceptibly slow rate. How- ever, when diamond is heated to approximately 3583°F (1700°C) in the absence of air, it rapidly converts into graphite.
c(diamond) - C(graphite)
Although graphite and diamond are stable substances at the conditions experienced on Earth's surface, both burn in air. The products of their incomplete and complete com· bustion are carbon monoxide and carbon dioxide, respectively.
7 .6 -B COMMERCIAL USES OF DIAMOND AND GRAPHITE Diamond companies advertise that a diamond is "a girl's best friend," the supre7; token of love and affection. In many parts of the world, a woman's acceptance 0
2 20121, pP· 9Lauren K. Wolf and Carmen Drahl, "Carbon Goes Deep," Chem. Eng. News, Vol. 90 (March 1 ' 54-58.
260 Chapter 7 Chemistry of Some Common Elements
Jllscone-quali~y ~-amon! fro~ her fiance serves as a formal sign of their betrothal. Jllscone-quahty 1~mon s pn~arily serve in this exalted role because their dazzling
:rkle is so appeal'.ng. !ndustn~I dia_monds have more mund~ne uses in saw blades ~ed co cut marble, m wire-drawing dies, and in drill bits, grinding wheels, and hack-
v blades. sa' Graphite a~d diamond undergo phase changes from solid to liquid carbon at exceptionally hig~ tempe:at_ures. F~r example, Table 7.13 shows that diamond melts ar 6422°F (3550 C). This is the highest melting point of any element that occurs
03rura11Y• . Graphite and diamond also possess an important anomalous property when com- ared with other nonmetals: They are extraordinarily good conductors of heat. If you are
iortunate enough to own _a 5-carat diamond, hold it to the tip of your tongue. The dia- ond feels cold, because it conducts the heat from your tongue. Diamond possesses the
~ghest thermal ~onductivit~ of ~II s~bstances. The properoes of ~raph1te give nse to many industrial applications, of which the fol-
lowing are representative:
1 Graphite is molded into crucibles that are used to hold molten steel and other high- melting metals.
1 Graphite is used to line the walls of furnaces and other vessels where high-tempera- ture operations are conducted. The graphite protects the underlying metal from melt- ing or softening.
1 The nose and leading edges of aircraft wings generally are coated with graphite to protect the underlying metal from the heat of friction generated when the aircraft travels at high speeds through the air.
I Graphite-based dry powder is an effective fire extinguishing agent on class D fires, because the carbon conducts heat away from the burning metal.
Carbon in the form of coke (Section 7.6-E) is also used in the chemical and metallur- ~cal industries as a reducing agent. This chemical property is put to use at foundries dur- ing the production of iron and other metals from their naturally occurring ores.
7.6-C COAL Almost without exception, all fossil fuels found in nature can be traced to the giant plants rhac grew during the carboniferous age. Three hundred million years ago, plants grew much more luxuriantly than they do today. During this period, the dominant plants were rreeferns, which grew 30 feet (9.1 m) in height with crowns of large, feathery fronds. As Earth evolved over the subsequent millennia, the remains of the ferns and other plants ultimately were buried at great depths below the planet's surface, where intense tempera- ture and pressure compacted, hardened, and chemically altered them into fossil fuels: coal, natural gas (Section 12.5), and crude oil (Section 12.13-A). This conversion process is called the carbonization of vegetable matter. carbonization • The
Coal is a readily combustible black rock whose composition consists of a mixture process of converting of ca b • d I • d f an organic compound h r onaceous material and organic and inorganic compoun s. t is extracte rom into carbon or a carbon- t e earth by surface mining as well as from seams that exist in deep, underground containing residue, natural deposits. In the United States, coal is abundant far more than either natural gas typically conducted or crude petroleum. Natural sources of coal occur primarily in West Virginia, Pennsyl- under intense tempera- ;ania, Kentucky, and Wyoming. They are also plentiful in areas outside the United ture and pressure tar,es , especially Australia India and China. On the international scale, China is coal Any black or
coa 's . ' ' rnaior consumer. brownish combustible In thCeoal _is largely mined to operate factories and power plants that genera_te_ ele_ctricity. rock that formed natu-U d I h I rally by the partial ated. T n1te States, coal is used as the fuel at 4~0 power p ants w ere e ectnc1ty is gene:- decomposition of plant rn he worldwide burning of coal at coal-fired power plants accounts for approx1- life at increased pres-
ately 24% of the carbon dioxide found in the atmosphere (Figure 5.6). Coal and other sure and temperature Chapter 7 Chemistry of Some Common Elements 261
1,
I I
black lung disease (pneumonoconiosis) • The lung disease caused by long-term inhalation of coal-mine dust
Federal Coal Mine Health and Safety Act of 1969 • The federal statute that empowers the Mine Safety and Health Administration within the U.S. Depart- ment of Interior to reg- ulate health and safety conditions within coal mines
rank (grade) Any class or type of coal dis- tinguished by its carbon content and density
fossil fuels are nonrenewable natural resources; once used, only their ash d products remain. As we continue to advance into the twenty-first century .0 ther b EPA regulations could trigger a decline in the use of coal for energy prod~ct' e 11't'tPaq \ more likely that coal will remain the United States' primary fuel source for el;on;_ Yet, it~ eration until 2035.10 ctr1city&en~
An underground coal mine itself poses a potentia~y haz~rdous environment. Fi methane seeps from the coal seams into the surrounding environment where it po arnrnable of fire and explosion (Section 12.5-A). In addition, the atmosphere of a coal mises the risk laden with coal dust. When the dust is inhaled over long periods, it causes resp·ne 0 ften is ea_ses including black lung disease, or pneumonoconiosis. These miners have l;atory dis. with coal dust, the presence of which severely restricts the exchange of oxygen be: coated lungs and the blood. Their lungs ultimately become scarred, and they experienc een the sema, chronic bronchitis, shortness of breath, disability, and premature death The e~Phy. effec - . · ere 1s nve treatment or cure for those who have contracted black lung disease. no
To limit the amount of coal dust that workers could potentially inhale within . regulations promulgated pursuant to the Federal Coal Mine Health and Safety~ rtune, 1969, or Coal Act, require mine operators to reduce coal-mine dust within active ct oi areas to less than 2 mg/m3 of air. Although this regulation produced a decline t0~ number of workers who now contract black lung disease, approximately 1000 Amenr· 1 e
k til ' wor ers s l contract the disease annually. The hazards of coal dust are not limited to its potential health hazards. It is also
readily combustible material. Coal dust ignites readily when exposed to heat, sparks 0 ~
other ignition sources. When dispersed in air, its lower flammable limit is greater than 0.05 oz/ft3 (>50 g/m3). Precaution always needs to be exercised by the generators and users of coal dust to prevent its ignition.
7 .6-D RANKS OF COAL Coal occurs naturally in several forms, each differentiated from the others by its rank, or grade. The ranks of coal are determined by the extent to which carbonization has occurred. Six major ranks of coal are recognized: peat, lignite, subbituminous, bitumi- nous, semianthracite, and anthracite. As we read from left to right in this list, each rank is progressively older and denser than those before it. Lignite and anthracite, for example, have specific gravities of 1.29 and 1.4 7, respectively. Given this wide range, these are sometimes referred to as soft coal and hard coal, respectively.
Some representative information about the individual ranks of coal is provided in Table 7.14. Each rank is characterized by its heat content and carbon content. The carbon occurs both as the element and in the form of numerous compounds that become locked within the complex structure of coal. The compounds that are volatile evolve from co_al as it is crushed and pulverized; they burn when their vapors are exposed to an igniu~n source. Before they ignite, however, a sufficient energy of activation generally mus~ provided to first vaporize and release them from the inner structure of coal. The evo1v\ fl bl h. 1 . . d evo ve heat serves to produce more amma e vapor, w 1ch subsequent y 1gmtes an . the heat. In this fashion, coal fires are self-sustaining until the flammable compounds in coal have been entirely exhausted. h ,oal
Table 7 .14 shows that sulfurous compounds also are components of coal. W en burns, sulfur dioxide is produced. rnains,
After the flammable components of coal have burned, a solid residue or ash r~uJII, This ash consists of a mixture of the oxides of arsenic, barium, beryllium, boron, ca
10u.s. Energy Information Administration, Today in Energy (March 9, 2012).
262 Chapter 7 Chemistry of Some Common Elements
d
rABLE 7.14 Some Properties of the Different Ranks of Coal
HEAT CONTENT CARBON CONTENT SULFUR CON TNT E
RAllli<0F COAL Btu/lb kJ/kg (%) (%)
5500-8800 13,800-20,500 25-35 0.5-3 peat
7000 16,300 25-35 0.5-3 Lignite Bituminous
7300-10,000 17,000-23,250 45-86 0.8-5.0
subbiturninous 9000 20,960 35-45 0.6-1.8
sernianthracite 11,500-14,000 26, 700-32,500
cite 14,000-14,500 32,500-34,000 40 0.4-1.9 Anthra
hromium, iron, mercury, thorium, uranium, zinc, and other elements. Although compo- c enrs of this mixture were formerly ejected as fly ash into the atmosphere from the smoke- nracks of coal-fired plants, today's environmental regulations require its capture using ~r-pollution-control equipment. However, there are no federal regulations that address the uJrirnate fate of the flyash generated during the burning of coal. Most of it ends up in stor- age near the plants in huge piles, reservoirs, or impoundments.
7,6-E CHEMICAL PRODUCTS OBTAINED FROM COAL A mixture of volatile gases evolves when coal is heated in the absence of air within a simple closed assembly like that shown in Figure 7.16. The mixture is called coal gas. It consists of ammonia, carbon monoxide, hydrogen sulfide, hydrogen cyanide, and meth- ane, none of which condenses when exposed to the temperature of a cold water bath. Although coal gas once was used to heat and illuminate homes and other buildings, its use is now obsolete.
Coal Gaseous hydrocarbons, ammonia, etc.
(coal gas)
Benzene, toluene, phenol, etc.
(coal tar)
~:~UR~i7"16 In this laboratory demonstration. coal is strongly heated in the absence of air. In this manner. two sour ma e or combust ible mixtures are isolated: coal gas and coal tar. When coal is exposed to an ignition ~ chemical components of t hese mixtures ignite and burn .
flyash The mixtu~e of ultralight, fine particles generated during the combustion of coal
coal gas The flamma- ble and toxic mixture of gases and vapors produced when coal is strongly heated in the absence of air
coal tar The con- densed black, viscous liquid produced by heating coal in the absence of air
distillation • A physical process in wh ich a sub- stance or group of substances is separated from a mixture by heat- ing the mixture to a specified temperature or range of tempera- tures, thereby convert- ing one or more components into a vapor that is subse- quently condensed and collected
Coal gas
Chapter 7 Chemistry of Some Common Elements 263
I
I
I I
Coal tar
Creosote oil
Coal tar pitch
The heating of coal also produces a viscous liquid called coal tar, a corn . uct used for waterproofing when sealing roofing or pavements and coating rnercia] Prod pipelines. It is also used as a binder during the construction of carbon electl!nddergrouh ·
d . roesf ••d pro uct10n of elemental aluminum. or th Coal tar may be subjected to a separation process called distillation d . e · · h • . , ur1ng 1ht 1s eated within specified temperature randgeshto vap
1 ~nze its components ~hich
t ese components are subsequently condense , t e resu ting materials ar · "'hen tar distillates. Although the latter term is loosely defined, three distillatee caUed to,
1 · d . sa~ • mze commercially: recog.
The "light" oil is so named because it is a mixture of compounds like be tion 12.11-A) and toluene (Section 1~.11-~), ""'.hose densit~es are less than ~~:ne (Sec. of water; hence, it floats on water. Light 011 boils near 392 F (200°C). density The "middle" oil boils between 392 and approximate_ly 518°F (200 and 2?0•c . a raw material from which the chemical industry obtains naphthalene (Secti {" It is A), phenol (Section 13.2-1), and cresols (Section 13.2-J). on 2-12. The "heavy" oil boils between 518 and 662°F (270 and 350°C). It cont . h . d b . a1ns a t racene and other polynuclear aromatic hy rocar ons (Sect10n 12.12-E). A n-
mercially important product produced from heavy coal tar distillate is ere corn. ·1 · 1· · ·d I d ·1 d · 050te 01 , a viscous 1qu1d w1 e y use to preserve ra1 roa cross ties and utility 1 . d d h l · · · bl f 1 · · po es against ecay an to cut asp a t so 1t 1s smta e or app 1cat10n as a road d
f. q roo mg tar.
The viscous residue remaining after coal tar is heated to 662°F (350°C) is called coal tar pitch. Products made from this residue are used chiefly as sealants and roofing- and road- paving compounds.
The solid residue that remains when coal and coal tar pitch are heated in the absence of air is called coke. The heating process is conducted in industrial ovens known as bee- hives. Coke is the form of carbon used by metallurgists to reduce the ores of arsenic, tin, copper, iron, zinc, phosphorus, and other elements. It is also used in the steel industry for reducing the iron oxide in iron ore in blast furnaces.
C(s) + FeO(s) -- Fe(s) + CO(g ) Carbon Iron(II) oxide Iron Carbon monoxide
This chemical process is called smelting. A unique form of coke called petroleum coke is similarly produced when the residues from heating certain crude oil fractions (Section 12.14) are thermally treated.
7.6-F CHARCOAL AND CARBON BLACK Charcoal results when wood, animal bones, nut shells, corn cobs, or peach pits are heated in the absence of air. Most individuals first experience charcoal briquettes when they_fuel the backyard barbeque, but considerable quantities of carbon are also used industrially for "adsorbing" undesirable substances from products destined for commercial us~ Adsorption refers to the surface retention of solid, liquid, or gaseous molecules an should not be confused with the term absorption, a process involving the physical pene- tration of one substance into the bulk of another one. Charcoal is highly porous bee}~\: it retains the skeletal cellular structure of the material from which it was made .. for porosity gives charcoal a very large surface area per unit weight, and forms the basis its effectiveness as an adsorbing agent.
90 o•C)
Charcoal may also be heated in the absence of air at 1472 to 1652°F (S~O t~ en as ro produce activated charcoal, or activated carbon. This material often is c os
264 Chapter 7 Chemistry of Some Common Elements
~?£ .;:::i::tr:rmiS 9 t Rn?! :r:w'E:::¥ - -;;- -~ ,,- bing medium, because its average internal surface area is 284,000 ft
2 ~oz
3o ad;'itg). Medic~! per~on~el use activated charcoal as an antidote for the quick (929 t of potential po1sonmg caused by the consumption of certain drugs and p~s- rre_ac!lle~t is also used industrially as an adsorbing agent to purify atmospheric _emis- ric1d:f~orn exhaust stacks by re~u~ing or eliminating the concentration of un~esira?le s10° es On a smaller scale, 1t 1s used in gas mask canisters and cigarette filter ups
ic gas • ro" h sarne purpose. . . . for t;hen coal tar is burned m a furnace with a limited amount of air, a finely divided
f carbon called carbon black is produced. The soot that forms during petroleum form_o ,ornposed primarily of carbon black. Different grades are available commercially fires is e distinguished primarily by their particle size. They are used as components of a rbat ~:r of consumer products including inks, paints, plastics, and tires, belts, and other n~:sion-resistant rubber products. Carbon black is an ideal component in these products ~ue to its high surface-area-to-volume ratio.
7.6-G CONSUMER PRODUCT REGULATIONS INVOLVING CHARCOAL To inforrn the public that carbon monoxide is produced when charcoal burns, CPSC requires charcoal manufacturers to affix the label shown in Figure 7.17 to charcoal pack- aging. In addition to the written warning, the label contains a pictograph of a grill situ- ated inside a tent, home, and vehicle. These drawings are enclosed in a circle with an X through it. They serve to convey the message that burning charcoal in enclosed areas should be avoided, because deadly concentrations of carbon monoxide could accumulate and kill the occupants.
7.6-H TRANSPORTING CARBON-BASED PRODUCTS When shippers intend to transport coal tar distillates, DOT requires them to identify the distillates on the accompanying shipping paper as shown in Table 7.15. All other labeling, marking, and placarding requirements apply.
When shippers offer hot coal tar pitch for transportation in a kettle or other bulk container as an elevated-temperature material, DOT requires them to display the HOT marking on both sides and ends of the container.
DOT also regulates the transportation of coal dust, charcoal, activated carbon, coke, and carbon black. DOT requires shippers who offer these products for transportation to identify it as shown in Table 7.15 on the accompanying shipping paper. For domestic transportation, DOT allows the use of other appropriate shipping names. All other label- mg, marking, and placarding requirements apply.
aWARNING CARBON MONOXIDE HAZARD Burning charcoa l inside ca n ki ll you. It gives off carbon m onoxide, w hich has no odor.
NEVER bu rn charcoa l inside hom es, vehicles o r tents.
FIGURE 7 17 . and back ·a At 16 C.F. R. § _1 500. 14(b)(6), _c PSC requires charcoal manufacturers to affix this label to the front and use i P nels_ of bags holding charcoal briquettes and other forms of charcoal that are intended for retail sale
n cooking or heating.
coal tar distillate • Any fraction obtained by distilling coal tar
creosote oil An oily liquid obtained from the distillation of coal tar coal tar pitch The residue remaining after coal is heated to approximately 662°F (350"C) in the absence of air coke The final residue remaining after coal or coal tar pitch is heated in the absence of air
smelting A chemical process used to isolate an element from its naturally occurring ore by reacting the ore with coke
charcoal The residue remaining after wood, animal bones, nut shells, corn cobs, or peach pits are heated in the absence of air
adsorption A physical phenomenon character- ized by the adherence or occlusion of atoms, ions, or molecules of a gas or liquid to the surface of another substance
activated charcoal (activated carbon) • The amorphous form of carbon characterized by a high absorptivity for certain gases and vapors
carbon black The finely divided form of carbon produced when coal tar burns in a fur- nace with limited air
Chapter 7 Chemistry of Some Common El ements 265
11
I TABLE 7.15
Shipping Descriptions of Carbon-Based Che . Products lllical
CARBON-BASED PRODUCT
Activated carbon Carbon black
Charcoal Coal dust
Coal gas
Coal tar distillates
Coal tar pitch
Coke
SHIPPING DESCRIPTION
UN1362, Carbon, activated, 4.2, PG 111 UN1361, Carbon (carbon black), 4.2, PG 11 or UN1361, Carbon (carbon black), 4.2, PG Ill UN1361, Charcoal, 4.2, PG Ill
UN1361, Carbon (coal dust), 4.2, PG 11
UN 1023, Coal gas, compressed, 2.3 (2.1)
UN! 136, Coal tar distillates, flammable, 3, PG 11 or UN! 136, Coal tar distillates, flammable, 3, PG 111 UN3257, Elevated-temperature liquid, n.o.s., 9, PG
111 or UN3258, Elevated-temperature solid, n.o.s., 9, PG 111 or UN1999, Tars, liquid, 3, PG II
or UN1999, Tars, liquid, 3, PG Ill
UN1361, Carbon (coke), 4.2, PG II
or UN1361, Carbon (coke), 4.2, PG Ill
7 .6-1 RESPONDING TO INCIDENTS INVOLVING A RELEASE OF COAL
Most fires involving coal may be effectively extinguished with water. When bulk quantities of coal are burning, it is essential to use a deluging volume of water for the following reasons:
When fires are extinguished only on the surfaces of coal, combustion continues within the interior of the reserve. Because the liberated heat cannot easily dissipate, the tern· perature of the entire bulk increases, and the coal erupts into flame once again. When water contacts coal, coke, or charcoal, the mixture may chemically react to form carbon monoxide and hydrogen. This is the "water gas" previously no~ed ID Section 7.2-C. When water gas ignites with in the confinement of a coal IU1ne, it serves to rekindle coal fires.
7 .6-J UNCONTROLLED COAL FIRES Uncontrolled coal fires typically are confined to natural coal beds and abandoned coa~ mines. They represent potentially destructive phenomena, not only because they co;;:s a valuable natural resource, but because they transform landscapes and generat: ro· of toxic air pollutants-the constituents of coal gas and coal tar. In essence, coal fires pod·
·d h d. · h · d · surrou v1 et econ JtJons t at can cause environmental catastrophes. The resi ents in . haling ing communities can be swallowed into sinkholes or valleys or be sickened by in pollutants in the dominant atmosphere, perhaps fatally. '
266 Chapter 7 Chemistry of Some Common Elements
When coal fires exist in coal beds, the coal was probably ignited by means of light- . trikes or spontaneous combustion. A notable example of an uncontrolled fire in a ings . M . . N . 0
1 bed is Burning ount~m in ew South Wales, Australia. This fire has been burning ,oa 6000 years by some eSttmates and is credited as the oldest known ongoing coal fire. for I the United States, there are at least 112 documented out-of-control underground 0 d 1 . 11 6
·n abandone coa mmes, utmost have been burning "only" for decades. World- fires
I th th d f d · · ·
12 Th ·d however, ere are ousan s o ocumented fires in abandoned coal mines. ese wi e, l'k 1 · · · d h
. were most 1 e Y mitiate w en methane (natural gas) seeped from the coal, accumu-fires d' nf' d · · h di ·n the surroun mg co me envuonment and ignited· then the burrung met ane !ate . ' ' ' . died the burning of the coal. kin d d . 1 . · · · h h h Fires burn ownwar in coa mmes, acqumng oxygen from the air t at passes t roug the fissures in surrounding ro~k. Although attempts are sometimes made to e~tinguish them, most abandoned coal m~nes a_re ~early impossible to access. Beca_use entering them . highly dangerous undertaking, firefighters cannot deluge the fires with water. Further- is \e it is also impossible to starve the fires of oxygen, because the burning coal is exposed :i~o;t continuously to. new so~rc~s of air f~om the countless borehol_es d~iven into the
rking mines to provide vent1lat1on for miners. Consequently, the fires in abandoned WO , • coal mines are only rarely extinguished. Many quietly smolder from one generation into the next.
U I /Au ust2011) pp.60-65. 11 ristin Ohlson, "Earth on Fire," Discover u Y g World: A,Global Catastrophe," Int. J. Coal Geo/., Vol. 59 G. B. Stracher, editor, "Coal Fires Burnmg around the 120041, pp, 7-17.
Chapter 7 Chemistry of Some Common Elements 267