Iron, carbon precipitation

Iron carbonate, precipitated. See Iron oxide brown... 

Synonyms Burnt sienna Burn umber Iron carbonate, precipitated Iron subcarbonate Pigment brown 7... 

Localized pre-boiler scale and corrosion debris deposits. Combination of New phosphate, iron, copper, and silica deposition Old re-deposited debris Transport of Fe, Cu, Ni, Zn, Cr oxides to HP boiler section, leading to deposition, fouling, and possible tube failures Transport of minerals and debris including malachite, ammonium carbamate, basic ferric ammonium carbonate Precipitation in FW line of phosphates, iron, and silicates... 

Above the eutectic temperature in the iron-FcsC system (1130°C)12, growth of large graphite plates and flakes occurs from the liquid phase. Carbon precipitates in the form of highly ordered graphite crystals from molten iron supersaturated with carbon. The Raman spectrum for chlorination at 1200°C is shown in Fig. 2c. A very strong and narrow... 

Carbonate precipitation, in hazardous waste management, 25 821 Carbonates, 6 304-305 9 806 chemical properties, 6 306-310 economic aspects, 6 312 health and safety factors, 6 312 iron, 14 533... 

F.J. Derbyshire, A.E.B. Presland, D.L. Trimm, Graphite formation by the dissolution-precipitation of carbon in cobait, nickel and iron, Carbon, 13 (1975) 111-113. 

Pour 50 cc. of concentrated sulfuric acid slowly into about 1 liter of water in an evaporating dish and add 50 g. of iron nails or turnings. When the action becomes slow heat the dish until the acid is practically all neutralized, as indicated by the fact that evolution of hydrogen ceases. Filter from the undissolved iron, carbon, silicon, and other residues, using a folded filter, and evaporate to crystallization. If the solution oxidizes appreciably in the operation additional iron and acid must be added to effect reduction. Oxidation will be indicated by a change in color from bottle green to a yellowish shade of green, or by the formation of a rusty precipitate. 

The resulting Soln. C is a predominantly NaCl solution similar to terrestrial seawater (Soln. D, Table 5.3). Had we chosen a concentration factor of 600-fold, the agreement would have been even better. In any case, the concentration factor is arbitrary. The point is that simple processes, starting with a dilute Fe-Mg-HC03-rich solution formed by reaction of water with ultra-mafic and mafic rocks, evaporation, and carbonate precipitation, converted the solution into an Earth-like seawater NaCl brine. The Na/Mg ratio of solution C is 9.9, while terrestrial seawater has a Na/Mg ratio of 8.8 (Soln. 5.3D). Note also the similar pH values (8.03 and 8.05, Table 5.3). This solution did not (cannot) evolve into an alkali soda-lake composition as some have hypothesized or assumed for Mars (e.g., Kempe and Kazmierczak 1997 Morse and Marion 1999) because the mass of hypothesized soluble iron and magnesium and the low solubility of their respective carbonate minerals are sufficient to precipitate most of the initial soluble bicarbonate/carbonate ions. 

The combination of the sulfate reduction reaction, and reactions primarily with iron and manganese oxide minerals can lead to significant calcium carbonate precipitation. This type of net process can be represented schematically as ... 

Reaction 6.16 results in the pH of the waters, in the absence of carbonate precipitation, being buffered at higher pH values (e.g., Ben-Yaakov, 1973). It is, therefore, reasonable to expect that the effectiveness of sulfate reduction in producing carbonate dissolution or precipitation may depend in part on the availability of reactive iron. This conclusion has been demonstrated in a study of the pore water geochemistry of aluminosilicate and carbonate-rich sediments from Kaneohe Bay, Hawaii. The aluminosilicate sediments contain abundant pyrite whereas the pyrite content of the carbonate sediments in this bay is low. Pore waters collected from the aluminosilicate sediments have higher pH values than those collected from the carbonate-rich sediments. This observation is a result of the pH values in the pore waters of the aluminosilicate sediments being buffered at... 

Commercial zinc sulphate invariably contains a small amount of iron as an impurity. Since FeS04-7H20 crystallizes isomor-phously with ZnS04-7H20 a preparation of the latter cannot be freed of the former by recrystallization. By addition of chlorine, or its equivalent, to the solution of zinc sulphate, the iron is oxidized to ferric salt the ferric salt hydrolyzes somewhat, and, if the acid produced by the hydrolysis is neutralized as fast as formed, the hydrolysis proceeds to completion and all the iron is precipitated as Fe(OH)3. In this case, the reagent used to bring about the exact neutrality of the solution is a suspension of basic zinc carbonate. (Compare the similar procedure for removing traces of iron in the preparation of strontium chloride, Preparation 21.)... 

Carbonate iron sediments are formed when iron is precipitated in the presence of dissolved carbonic acid or as a result of interaction of the primary sediments with organic matter in the course of diagenesis. The determination of the stability of primary iron carbonates with respect to iron oxides and hydroxides was made on the basis of using the functional dependence of and on pH, calculated by the method of Garrels and Christ (1968) for the system carbonate-water. According to this dependence, in conditions of FeCOj in equilibrium with water the value of partial pressure of carbon dioxide decreases in proportion to increasing pH. 

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