Gypsum formation

Gypsum-treated muds have proved useful for drilling anhydride and gypsum, especially where these formations are interbedded with salt and shale. The treatment consists of conditioning the base mud with plaster (commercial calcium sulfate) before the anhydride or gypsum formation is penetrated. By... 

Ritsema, C. J. and J, E. Groennenberg. 1993. Pyrite oxidation, carbonate weathering, and gypsum formation in a drained potential acid sulfate soil. Soil Sci. Am. J. 57 968-976. 

The action of magnesium sulfate is associated with a migration of hydroxide ions towards the surface to produce insoluble brucite, and a migration of sulfate ions inwards to form gypsum. The calcium needed for gypsum formation is supplied first by the decomposition of calcium hydroxide and subsequently by decalcification of the C-S-H phase. Eventrrally, a double surface layer is formed consisting of an external layer of brucite, followed by a layer of gypsum. 

Concerning gypsum, BeUmann et al have discussed the influence of sulfate concentration and pH value of solution on the gypsum formation in detail P2. They indicate that portlandite will react to gyp>sum at a minimal sulfate concentration of approximately 1400 mg/1 (pH=12.45). With rising pH, higher concentrations of sulfate ions are needed for the reaction to proceed. Between pH values of 1245 and 12.7, the sulfate concentration slowly increases, whereas it rises dramatically from that level on. In solutions in which sodium ions are the counterpart of the hydroxide ions, the precipitation of gypsum can take place until pH values of approximately 129. Beyond that mark, a further increase of the sulfate concentration is unable to lead to the formation of gypsum I52. ... 

The key difference between the brine process and seawater process is the precipitation step. In the latter process (Fig. 6) the seawater is first softened by a dding small amounts of lime to remove bicarbonate and sulfates, present as MgSO. Bicarbonate must be removed prior to the precipitation step to prevent formation of insoluble calcium carbonate. Removal of sulfates prevents formation of gypsum, CaS02 2H20. Once formed, calcium carbonate and gypsum cannot be separated from the product. 

The sodium formate process is comprised of six steps (/) the manufacture of sodium formate from carbon monoxide and sodium hydroxide, (2) manufacture of sodium oxalate by thermal dehydrogenation of sodium formate at 360°C, (J) manufacture of calcium oxalate (slurry), (4) recovery of sodium hydroxide, (5) decomposition of calcium oxalate where gypsum is produced as a by-product, and (6) purification of cmde oxahc acid. This process is no longer economical in the leading industrial countries. UBE Industries (Japan), for instance, once employed this process, but has been operating the newest diaLkyl oxalate process since 1978. The sodium formate process is, however, still used in China. 

Sulfur constitutes about 0.052 wt % of the earth s cmst. The forms in which it is ordinarily found include elemental or native sulfur in unconsohdated volcanic rocks, in anhydrite over salt-dome stmctures, and in bedded anhydrite or gypsum evaporate basin formations combined sulfur in metal sulfide ores and mineral sulfates hydrogen sulfide in natural gas organic sulfur compounds in petroleum and tar sands and a combination of both pyritic and organic sulfur compounds in coal (qv). 

Backfill containing a large proportion of bentonite has a tendency to change its volume with variations in water content of the surrounding soil. This can lead to formation of hollow cavities in the backfill with a considerable decrease in the current delivery. A standard backfill consists of a mixture of 75% gypsum, 20% bentonite and 5% sodium sulfate. The specific resistivity of this backfill is initially 0.5 to 0.6 m and can rise with increased leaching to 1.5 m. 

Salts are sometimes added to drilling muds to obtain certain desired mud characteristics. They can also enter the drilling fluid through contamination by addition of makeup water, formation-fluid inflow, and drilled formations such as salt domes, gypsum or anhydride formations. In freshwater systems, if salt contamination reaches undesirable levels, the following methods should be considered for control. 

The amount of hardness present in natural surface and groundwaters depends to a large extent on the action of dissolved carbon dioxide in rainwater on the watershed s geological formations (such as limestone, dolomite, gypsum, or magnesite). The dissolved hardness levels remain relatively low because of the sparingly soluble nature of the salts formed. Typically, MU water sources initially contain anywhere from 5... 

Hydration is the incorporation of water mole-cule(s) into a mineral, which results in a structural as well as chemical change. This can drastically weaken the stability of a mineral, and make it very susceptible to other forms of chemical weathering. For example, hydration of anhydrite results in the formation of gypsum ... 

Important metallic ore deposits include Besshi (Kieslager)-type (strata-bound cupriferous pyritic deposits), strata-bound Mn-Fe-type, skam-type, Kuroko-type and vein-type. Dominant non-metallic deposits are limestone, clay, native sulfur, zeolite, silica and gypsum deposits. The deposits are divisible into three groups, based on their ages of formation Carboniferous-Jurassic, Cretaceous-Paleogene and Tertiary-present. 

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