608 



UNITED STATES MINERAL RESOURCES 



Sulfur recovered 

 from hydrocarbc 



Figure 68. — Production of sulfur contained in pyrites, recovered from petroleum and natural gas, and recovered from base- 

 metal ores, United States, 1&00-70. Data from U.S. Bureau of Mines. 



may (1) combine with hydrogen and be expelled 

 into the atmosphere as hydrogen sulfide gas, (2) 

 combine with oxygen and be expelled as sulfur diox- 

 ide gas (the two gases can react and produce ele- 

 mental sulfur), or (3) combine with metals and 

 form metallic sulfides. 



Exposure to atmospheric oxygen breaks down 

 most sulfide minerals to relatively soluble sulfate 

 minerals. Ground and surface waters leach the sul- 

 fate minerals and carry their salts to the sea, where 

 the sulfate ion has accumulated in a concentration of 

 2,650 ppm. 



Where restricted arms of the sea spread over con- 

 tinents during periods of aridity, sea water evapo- 

 rates and becomes increasingly saline, resulting in 

 successive precipitation of calcium carbonate as 

 limestone, calcium sulfate as gypsum, and sodium 

 chloride as common salt. Owing to seasonal and 

 longer range climatic variations, alternating layers 

 of the different evaporites may precipitate. Vast 

 amounts of calcium sulfate as gypsum have been 

 withdrawn from the sea in the course of geologic 

 times (Borchertand Muir, 1964). 



THE ORGANIC CYCLE 



Sulfur is an essential constituent of certain pro- 

 teins and fats needed by plants and animals ; plants 



utilize it as sulfate ions from soils, ground water, or 

 sea water. Animals obtain their sulfur from water 

 or by consuming plants or other animals. Upon death 

 and decay, the reduced sulfur is released ; on land it 

 enters soils or humic compounds or is emitted into 

 the atmosphere; in seas, it reenters the sea water. 

 The cycle is balanced in the sea, but on the land, 

 sulfur is lost both to the atmosphere and to the sea 

 through the leaching of soil and humins by surface 

 waters. 



Bacteria use sulfur compounds in metabolism; 

 some bacteria reduce sulfates, others oxidize sulfides 

 either to sulfates or to elemental sulfur, and still 

 others oxidize elemental sulfur (Davis, 1967). In 

 aerated environments the bacterial sulfur cycle tends 

 to be complete and balanced, but in anaerobic en- 

 vironments the reactions result in only reduction of 

 sulfate ions. The reduction of sulfate is accomplished 

 largely by one species, Desulfovibrio desulfricans, an 

 anaerobe found in stagnant marsh waters, tidal fiats, 

 oxygen-deficient bottom waters of seas and oceans 

 and in ground water, oil field brines, and petroleum, 

 to depths as great as 5,000 feet below land surfaces. 

 This anaerobe is limited to environments having 

 temperatures less than 165°F. 



Desulfovibrio uses dead organic matter, be it 



