Iron, refining residues

The usual extraction procedure is to roast the crushed ore, or vanadium residue, with NaCl or Na2C03 at 850°C. This produces sodium vanadate, NaV03, which is leached out with water. Acidification with sulfuric acid to pH 2-3 precipitates red cake , a polyvanadate which, on fusing at 700°C, gives a black, technical grade vanadium pentoxide. Reduction is then necessary to obtain the metal, but, since about 80% of vanadium produced is used as an additive to steel, it is usual to effect the reduction in an electric furnace in the presence of iron or iron ore to produce ferrovanadium, which can then be used without further refinement. Carbon was formerly used as the reductant, but it is difficult to avoid the formation of an intractable carbide, and so it has been superseded by aluminium or, more commonly, ferrosilicon (p. 330) in which case lime is also added to remove the silica as a slag of calcium silicate. If pure vanadium metal is required it can... 

FERROSEP A magnetic process for removing iron contaminants from petroleum residues before desulfurization. Developed by Nippon Oil Company and Nippon Petroleum Refining... 

The first studies indicated that the second iron atom also had a tyrosine residue attached to it. Later refinement of the structure showed that it is actually pentacoordinale, but the argument remains the same. 

Other factors indicated m the data of Tables 1 and 2 include Pour Point—defined as the lowest temperature at which the material will pour and a function of the composition of the oil in terms of waxiness and bitumen content Salt Content—which is not confined to sodium chloride, but usually is interpreted in terms of NaCl Salt is undesirable because of the tendency to obstruct fluid flow, to accumulate as an undesirable constituent of residual oils and asphalts, and a tendency of certain salt compounds to decompose when heated, causing corrosion of refining equipment Metals Content—heavy metals, such as vanadium, nickel, and iron, tend to accumulate in the heavier gas oil and residuum fractions where the metals may interfere with refining operations, particularly by poisoning catalysts. The heavy metals also contribute to the formation of deposits on heated surfaces in furnaces and boiler fireboxes, leading to permanent failure of equrpment, interference with heat-transfer efficiency, and increased maintenance. 

McCallum, S. A., and Pardi, A. (2003). Refined solution structure of the iron-responsive element RNA using residual dipolar couplings. J. Mol. Biol. 326, 1037—1050. 

Stainless steel vessels or stainless-steel-lined vessels are recommended to prevent the formation of color complexes, especially if moisture or residual fatty acids are present in a carbon steel tank. Since glycerine is hygroscopic, care should be taken to exclude moisture from the refined glycerine storage tank. Glycerine subjected to heat should not be stored in vessels containing copper or tin, as copper or iron salts will catalyze oxidation of glycerine under those conditions (23). 

The caliche is worked for refined nitrate on the places of production in about one hundred and fifty factories. The ground is broken by blasting, and the big blocks are broken into smaller ones by means of crowbars, and the lumps of caliche are separated from the rocky over-layer by hand. The caliche is crushed into 2-in. lumps, placed in long iron tanks heated with steam coils, and is there boiled with water. The earthy residue is left on a false bottom about 1 ft. from the real bottom of the tank, while the mother liquors, containing the NaNOs in solution, are run into the next tank. The extraction of the caliche is carried out systematically. The tank containing nearly exhausted caliche is treated with fresh water, while the liquor from this tank is run through a 9-in. pipe into the second tank, where it meets with a partly extracted caliche. From this, still... 

Interestingly, even at that time, a series of five histidine residues was postulated to constitute the potential iron-binding site, in that they are also conserved in other lipoxygenases, although site-specific mutagenesis studies indicated that three of these could be mutated individually in 5-LO without loss of either oxygenase or LTA4 synthetase activity (112,113). This proposal has now been refined and it is believed that the nonheme iron is bound permanently by and... 

---