Iron, precipitation

Foulants enter a cooling system with makeup water, airborne contamination, process leaks, and corrosion. Most potential foulants enter with makeup water as particulate matter, such as clay, sdt, and iron oxides. Insoluble aluminum and iron hydroxides enter a system from makeup water pretreatment operations. Some well waters contain high levels of soluble ferrous iron that is later oxidized to ferric iron by dissolved oxygen in the recirculating cooling water. Because it is insoluble, the ferric iron precipitates. The steel corrosion process is also a source of ferrous iron and, consequendy, contributes to fouling. 

Iron Precipitation. Rich sulfide ore or Hquated antimony sulfide (cmde antimony) is reduced to metal by iron precipitation. This process, consisting essentially of heating molten antimony sulfide ia cmcibles with slightly more than the theoretical amount of fine iron scrap, depends on the abihty of iron to displace antimony from molten antimony sulfide. Sodium sulfate and carbon are added to produce sodium sulfide, or salt is added to form a light fusible matte with iron sulfide and to faciHtate separation of the metal. Because the metal so formed contains considerable iron and some sulfur, a second fusion with some Hquated antimony sulfide and salt foHows for purification. 

Eisen-erz, n. iron ore. -fallung, /. iron precipitation. -finger, m. iron trap, farbe, /. iron color. 

A further problem is FW line iron deposits, which may be produced where soluble iron is present. The iron precipitates as a result of heat and the presence of trace amounts of oxygen. The reactions under these circumstances include the following ... 

Although the sulfur so formed can be further oxidized by the bacteria, the presence of surface coatings of sulfur and iron precipitation products on chalcopyrite are implicated for... 

The dominating reason behind the problems is clogging of the wells mainly caused by iron precipitation. For this reason the research on ATES is focused on how to collect geological, hydrogeological and hydrochemical data in a proper way in order to design functional systems and wells. 

As it can be seen from Table 5, the hydrolyzate properties were similar in the case of both acids. The only difference was observed for absorbable iron content (Table 6). When phosphoric acid was used, the concentration of absorbable iron was much lower (30.5 mgFe/kg) than it was when sulphuric acid was applied (86.3 mgFe/kg). However, the decrease of absorbable iron was lower than it should be, considering the stochiometry. The amount of phosphoric acid used was about 20 times higher than that, required for complete iron precipitation in form of FeP04. However, further addition of phosphoric acid (2 % process 5, Table 6) results in very effective decrease of absorbable iron content (2.5 mgFe/kg). 

Figure 8.7 Simplified model of nicotiniamine (NA) function in plant cells. Iron is transported across the plasma membrane by the Strategy I or Strategy II uptake systems. Once inside the cell, NA is the default chelator of iron to avoid precipitation and catalysis of radical oxygen species. The iron is then donated to proteins, iron-sulfur clusters and haem, while ferritin and iron precipitation are only present during iron excess. (From Hell and Stephan, 2003. With kind permission of Springer Science and Business Media.)...

Other special features used in the pilot wetland are floating mats and similar installations to assist the sedimentation of iron precipitates to which arsenic is mainly bound. They can be seen in Figure 6. They have proved to significantly increase the effectiveness of iron and arsenic removal by keeping the pond size to a minimum. This is essential under the conditions already described in the Introduction, namely limited space available at most of the sites. 

Figure 5. Aeration cascade between the mine adit and the inflow to the pilot wetland. The dark stain from iron precipitates is clearly visible.

The formation of hydroxyl precipitate prevents from the transfer of electron especially between oxygen and the mineral surface. As a result of all these processes, EIS represents passivation characteristic. And the corrosive potential moves towards negatively, the surface resistance increases, and the corrosive current decreases. The formation of surface hydroxyl iron precipitates makes the pyrite surface very hydrophilic. 

Karathanasis, A.D. Thompson, Y.L. (1995) Mineralogy of iron precipitates in a constructed acid mine drainage wetland. Soil Sci. Soc. Am. J. 59 1773-1781... 

ISOTEC catalysts prevent iron precipitation and iron fixation to soil, thus increasing the mobility of process reagents. 

If iron is present, the dry residue is subjected for several weeks to sunlight which renders the iron insoluble in acetic acid, after which acetic acid dissolves the calcium and magnesium carbonates which are separated by dilute sulphuric acid, precipitating calcium and dissolving magnesia. The residue from acetic acid treatment consists of clay, silicious matter and iron. The clay and iron are dissolved by marine acid (hydrochloric) and the iron precipitated by caustic alkali (phlogisticated alkali) and the clay by alkali carbonate. The silicious matter may be identified by its complete solution with effervescence under the blowpipe with mineral alkali (sodium carbonate). 

Improved raw material utilization via hot acid leaching and iron precipitation as previously described... 

Pentachlorophenol, a widely used wood preservative, is considered to be moderately biorefractory with a biodegradation rate constant of 3 x 1012 L/ cell/hr, a log of 5.01, and a vapor pressure of 1.1 x 10-4 mmHg at 20°C. Watts et al. (1990) carried out completely mixed batch tests by treating penta-chlorophenol-contaminated soils with Fenton s reagent. Mineralization of pentachlorophenol (PCP) was studied in commercially available silica sand and two natural soils by removal of parent compound and total organic carbon with corresponding stoichiometric recovery of chloride. The soluble iron concentration decreased over the first 3 hr of treatment, and the concentration remained relatively constant thereafter. A possible mechanism for iron precipitation was proposed as follows ... 

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