Iron in water

Figure 5.4 EfTect of temperature on corrosion of iron in water containing dissolved oxygen. (Courtesy of McGraw-Hill Inc., Corrosion, Causes and Prevention, by F. Speller, p. 168, McGraw-Hill, 1951)...

McPeak, John F. and Harold L. Aronovitch, Iron in Water and Processes for its Removal, Hungerford and Terry Inc., Clayton, N.J., 1983. 

It should be emphasised that potential-pH diagrams can also be constructed from experimental E -I curves, where E is the polarised potential and / the current. These diagrams, which are of more direct practical significance than the equilibrium potential-pH equilibrium diagrams constructed from thermodynamic data, show how a metal in a natural environment (e.g. iron in water of given chloride ion concentration) may give rise... 

The mathematical model may not closely fit the data. For example. Figure 1 shows calibration data for the determination of iron in water by atomic absorption spectrometry (AAS). At low concentrations the curve is first- order, at high concentrations it is approximately second- order. Neither model adequately fits the whole range. Figure 2 shows the effects of blindly fitting inappropriate mathematical models to such data. In this case, a manually plotted curve would be better than either a first- or second-order model. 

Calibration data for determination of iron in water by AAS (Reprinted with permission from D. G. Mitchell and J. S. Garden Talanta, 1982, 29, 921-929.)... 

We suggest using a new parameter, the minimum reportable concentration, defined as the concentration whose confidence band just includes zero (5.). This parameter is obtained by reducing the value of signal Yo, figure 4, until the band around predicted concentration, Xo, just touches zero. For example, for the determination of iron in water by AAS, (data given in Table III) the detection limit, defined as the concentration at which the... 

Table III. Determination of Maximum Concentration of Iron in Water by AAS...

Confidence bands are direct precision data, and the maximum reportable concentration can be defined as the maximum concentration at which the method yields adequate precision ( ) (excluding measurements near the minimum reportable concentration, where poor precision is unavoidable). Table III shows RCB for the determination of iron in water by AAS. The analyst may consider a RCB of say, 15% to be adequate. The maximum reportable concentration would be 15 pg/ml from a single, weighted least-squares curve, and 20 pg/ml by the multiple-curve method. Samples containing > 20 pg/ml should be diluted to 1-10 pg/ml and analyzed using standards containing 0.05 - 15 pg/mL. (Note that it is always better to include a standard above the maximum desired concentration. The precision of this standard measurement will be poor, but poor data at this level are better than none.)... 

Analytical model, assumptions and practical implications, 52-57 Analytical performance, correlation chromatography, 108 Analytical process, steps of, 7 Aroclors, isomer-specific analysis of, application of SIMCA, 195-232 Atomic absorption spectrometry, determination of iron in water, 116... 

The reaction produces hydroxyl ions which react directly with the Fe ions to produce an oxide precipitate. The combined anodic and cathodic reactions form the corrosion cell, the electrochemical potential of which lies between the single potential of the two half reactions. This mixed potential is termed the corrosion potential, corr> and for corrosion to proceed beyond the equilibrium state, the corrosion potential must be more positive than the equilibrium single potential of iron. For iron in water at pH 7 and with [Fe j = 10" M, for example, the potential of the anodic reaction is. 

Information about the corrosion of boiler piles comes from analysis of scale samples and also from laboratory experiments. Smith and McEaney (1979) used XRD and SEM to follow the initial stages in the development of scale on gray, cast iron in water at 50 °C. At first, the corrosion product was a mixture of magnetite and green rust. Whether lepidocrocite formed depended on the level of oxygen in the system. 

Meng, X. Korfiatis, G.P. Jing, C. Christodou-latos, C. (2001) Redox transformations of arsenic and iron in water treatment sludge during aging and TCLP extraction. Environ. Sci. Tedin. 35 3476-3481... 

Bang, S., Johnson, M.D., Korfiatis, G.P. and Meng, X. (2005a) Chemical reactions between arsenic and zero-valent iron in water. Water Research, 39(5), 763-70. 

Pohl, P. and B. Prusisz. 2006. Redox speciation of iron in waters by resin-based column chromatography. Trends Anal. Chem. 25 909-916. 

Hydrogen peroxide was detected during the corrosion of metals The view that acids are required for corrosion to occur was dispelled by the observation of rusting of iron in water and oxygen... 

The principle of the cathodic protection may be elucidated for the case of carbon steel. The Pourbaix diagram for iron in water consisting of the plot E (potential) vs pH is shown in Figure 1.68. The regions of passivity, immunity and corrosion are seen in the figure. 

Figure 1.68 E-pH diagram for iron in water. (Reproduced from Corrosion for Science and Engineering, Tretheway and Chamberlain, Copyright Pearson Education Ltd)...

In the discussion of E the vs pH diagram for iron in water depicted in Figure 1.70, we noted that, with application of high positive potentials, the system moves into a region of passivity and results in a reduced corrosion rate. The passive film formed should be coherent and insulating to withstand corrosion and mechanical breakdown. Upon formation of the passive state the corrosion rate is reduced. Thus by polarization and applying more positive potentials than corrosion potentials the metal attains passivity and is protected. This is the principle of anodic protection. It is necessary that the potential of passivation be maintained at all times, since deviations outside the range would result in severe corrosion. 

While a number of deckboard incubations of seawater samples show an increase in Fe(II) on irradiation [98,136,151], only a few studies have examined the change in iron speciation in situ as a function of time of day. Waite and Szymczak [152] measured the concentration of iron in waters overlying a coral reef on One Tree Island on Australia s Great Barrier Reef and observed... 

Migration of iron in waters is regulated chiefly by the amount of atmo-... 

EXAMPLE 26-6 Suppose that five different analysts (i = 5) A, B, C, D, E reported triplicate results (J — 3) in parts per million for iron in water. We wish to determine whether the values of the means differ among analysts. 

Electrochemical Aspects The half-reactions responsible for the corrosion of iron in water are, for oxidation,... 

One other use of LIBS for quantitative analysis is that involving colloidal and particulate iron in water and the sequential use of two lasers. A custom coaxial sample flow apparatus was used to control the atmosphere of laser-induced plasma and thus determine iron concentrations as low as 16 ng ml. both in an Fe(OH) colloidal suspension and in boiler water sampled from a thermal power plant. The ensuing method took only 100 s to apply, even with an accumulation of 2000 pulses [173]. 

Fig 1. Maximum solubility of aluminum and iron in water at various pH values. Adapted from the article by Ganrot (53), and based on data summarized by Baes and Mesmer (7). 

When the total concentration of iron in water is 0.3 mg/L or greater, the iron will cause the water to have an unpleasant taste and redden in color—this may result in the staining of plumbing fixtures and clothes, and accumulations of iron deposits in the... 

The thiocyanate method has been used for determining iron in waters [139,140], in organic materials [141], nickel and its salts [142], non-ferrous metals [143], titanium tetrachloride [144], and alkalis [8]. 

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