Ferric hydroxide precipitation

Addition of sufficient base to give a > 3 to a ferric solution immediately leads to precipitation of a poorly ordered, amorphous, red-brown ferric hydroxide precipitate. This synthetic precipitate resembles the mineral ferrihydrite, and also shows some similarity to the iron oxyhydroxide core of ferritin (see Chapter 6). Ferrihydrite can be considered as the least stable but most reactive form of iron(III), the group name for amorphous phases with large specific surface areas (>340 m2 /g). We will discuss the transformation of ferrihydrite into other more-crystalline products such as goethite and haematite shortly, but we begin with some remarks concerning the biological distribution and structure of ferrihydrite (Jambor and Dutrizac, 1998). 

Plutonium Pu co-precipitated with ferric hydroxide, precipitate dissolved in acid Anion exchange chromatography - [903,904]... 

As the pyrite dissolves by oxidation, calcite is consumed and ferric hydroxide precipitates (Fig. 31.4) according to the reaction,... 

As the first step in the coprecipitation process, ferric hydroxide precipitates either from the effect of the changing pH on the solubility of ferric iron,... 

Figure 12. Possible isotope fractionation steps during anaerobic photosynthetic Fe(II) oxidation (APIO). It is assumed that the process of oxidation proceeds through an oxidation step, where Fe(II),q is converted to soluble Fe(III) in close proximity to the cell, followed by precipitation as ferric oxides/hydroxides. As in DIR (Fig. 5), the most likely step in which the measured Fe isotope fractionations are envisioned to occur is during oxidation, where isotopic exchange is postulated to occur between pools of Fe(II) and Fe(III) (Aj). As discussed in the text and in Croal et al. (2004), however, it is also possible that significant Fe isotope fractionation occurs between Fe(III), and the ferrihydrite precipitate (Aj) in this case the overall isotopic fractionation measured between Fe(II), and the ferrihydrite precipitate would reflect the sum of A and Aj, assuming the proportion of Fe(III) is small (see text for discussion). Isotopic exchange may also occur between Fe(II),q and the ferric hydroxide precipitate (Aj), although this is considered unlikely.

Next we explore using the 5 Fe value of the ferric oxide/oxyhydroxide precipitate as a proxy for 5pe(ni)aq, which allows Equation (21) to be used to calculate the Ape(ni)-Fe(n) fractionation from the measured 5 Fe values for the ferric precipitate and Fe(II)aq. This approach is valid when the molar proportion of Fe(III)3q is very small. However, if there is a significant Fe isotope fractionation between Fe(III)3q and ferric hydroxide precipitate, this must be taken into account. As discussed in the previous chapter (Chapter 10A Beard and Johnson 2004), at low... 

Radioactivity of uranium can be measured by alpha counters. The metal is digested in nitric acid. Alpha activity is measured by a counting instrument, such as an alpha scintillation counter or gas-flow proportional counter. Uranium may be separated from the other radioactive substances by radiochemical methods. The metal or its compound(s) is first dissolved. Uranium is coprecipitated with ferric hydroxide. Precipitate is dissolved in an acid and the solution passed through an anion exchange column. Uranium is eluted with dilute hydrochloric acid. The solution is evaporated to near dryness. Uranium is converted to its nitrate and alpha activity is counted. Alternatively, uranium is separated and electrodeposited onto a stainless steel disk and alpha particles counted by alpha pulse height analysis using a silicon surface barrier detector, a semiconductor particle-type detector. 

Other sugars and polyols also complex with iron. Fructose is the most effective, but sorbitol, glucose, galactose, lactose, sucrose, pentoses and tetroses can also keep hydrolyzed ferric salts in solution. An excess of sugar must always be present in order to prevent ferric hydroxide precipitate. There appears to be a competition between the OH- and sugar hydroxyls for the Fe3+. 

In 1900 Sir William Crookes prepared a solution containing a uranium salt and a small amount of a ferric salt. When he added to this an excess of a solution containing ammonium hydroxide and ammonium carbonate, he found that the resulting ferric hydroxide precipitate was intensely radioactive. After studying the radioactive properties of the substance which precipitates with the iron, he said, For the sake of lucidity the new body must have a name. Until it is more tractable I will call it provisionally UrX—the unknown substance in uranium (30). It is now known as uranium Xi. H. N. McCoy and W. H. Ross, B. B. Boltwood, and R. B. Moore and H. Schlundt found independently that there are two uraniums, uranium 1 and uranium 2 (12, 48, 81, 108, 109, 110). 

Liu, R., Qu, J., Xia, S. et al. (2007a) Silicate hindering in situ formed ferric hydroxide precipitation inhibiting arsenic removal from water. Environmental Engineering Science, 24(5), 707-15. 

Why is it necessary to use scavenge techniques for the removal of barium (by barium chromate) and plutonium (by ferric hydroxide precipitation) ... 

Illite purified 7.6 0.25 gram used because of large bulk volume. Ferric hydroxide precipitated with NH3 and dried at 50 °C. 4... 

When a solution of potassium ferro-dinitroso thiosulphate, KFe(N0)2S203.H20, is boiled, sulphur dioxide is expelled, and ferric hydroxide precipitated. Upon concentrating the clear solution obtained by filtering, crystals of potassium ferro-heptanitroso sulphide are obtained.5... 

The sodium salt,1 NaFe(N0)2S203.2H20, is obtained in a similar manner to the preceding salt. It yields either laminated or needle-shaped crystals, which are glistening black in appearance. They are appreciably more soluble in water than those of the potassium salt, and yield a deep brown solution. The salt is fairly stable below 0° C., but above that temperature continuously evolves nitric oxide. When its aqueous solution is boiled, sulphur dioxide is expelled and ferric hydroxide precipitated. Upon concentrating the clear solution obtained by filtering, crystals of sodium ferro-heptanitroso sulphide, NaFe4(N0)7S3.H20, separate out.2... 

Mineral saturation indices for melanterite and amorphous iron hydroxide agree quite well with field occurrences of the same minerals. Jarosite, however, appears to be supersaturated for nearly all of the samples regardless of the presence or absence of the mineral in these streams. Field observations indicate that jarosite precipitation occurs in the microenvironment of bacterial colonies where the chemical conditions may be quite different from the bulk solution. These considerations lead us to suggest that there is a kinetic barrier which hinders jarosite precipitation but does not hinder ferric hydroxide precipitation and that this barrier is overcome by the surfaces of bacterial colonies (both iron-oxidizers and unidentified nonoxidizers ). ... 

Ferric salts (chloride or sulfate) are also used as coagulants in water treatment plants [50], and the resulting ferric hydroxide precipitates constitute a major portion of the clarifier sludge or WTR. In principle, the DMP is capable of selectively recovering... 

The ferric hydroxide precipitate obtained is dissolved with nitric acid and is made to about 7 M nitric acid solution. This is poured on an an ion-exchange resin column (3 (j> x 40 cm) in order to adsorb plutonium. The effluent from the column is almost neutralized and americium is extracted with 30 % dibutylphosphate-dodecane solution keeping the volume ratio of organic to aqueous phases 1 2. Americium is back-extracted with 1 M nitric acid. About 15 g of plutonium and 160 mg americium were recovered from about 200 1 of the aqueous waste from the plutonium laboratory. 

In the case of El about 50 of the ionic iron was in the ferrous valence, and 50 in the ferric state after U weeks. While with FS at pH 6.2, ferric hydroxide precipitates occurred without ascorbate within one week. The presence of ascorbate inhibited... 

Within the area of interest in the stability diagrams, ferric hydroxide precipitation is possible at lower oxidation potentials than manganic manganese oxides at any given pH. Similarly, at a fixed Eh ferric hydrox-... 

FeClj was added to background solution without pH adjustment at three concentrations. The ferric chloride addition resulted in a pH decrease. Final pH values were between 7 at 25 mgL and 3 at 100 mgL". This leads to the formation of ferric hydroxide precipitates, as described by Lo and Waite (1998). The size and charge of these precipitates depends on the dosage and the equilibrium pH, which is determined by the strongly acidic FeCl.s. 

As the membrane pores become smaller, the standard blocking law is no longer valid (Figure 6.55B). The cake filtration model remains valid, which indicates prevention of the ferric hydroxide precipitates from entering pores and subsequent internal deposition. Membrane pore radii were tabulated in Table 6.1 as 2,6, 4.8, and 9.1 nm for the 10, 30 and 100 kDa membranes, respectively. Lo and Waite (1998) reported iron hydroxide precipitates to be as small as 10 nm. Nevertheless, complete blocking (pore blocking by the particulates) is not a valid mechanism. Possibly cake formation prevents pore blockage. 

Inorganic colloids (hematite, 75 nm) did not cause irreversible flux decline. Pretreatment of the solutions using ferric chloride not only prevented flux decline under criticalfouling conditions (high calcium concentration and IHSS HA), but also influenced rejection. The latter depends on the charge of the ferric hydroxide precipitates. Cation rejection increased when positive ferric hydroxide colloids were deposited on the membrane, which the organic rjection decreased. 

Figure 7.49A). When a deposit of solids accumulates on the membrane surface, as is expected during ferric chloride treatment, the thickness of the unstirred boundar) layer increases (see Figure 7.49B). This means the concentration of solutes at the membrane surface increases and the overall rejection decreases. However, if the solids deposit has a positive charge (which is the case for the ferric hydroxide precipitates) then an additional barrier is added to the membrane. Solutes now have to pass through a positively charged and a negatively charged barrier, and the overall rejection will increase for some compounds.

Iron control agents such as citric acid and organophosphorus compounds form iron complexes and prevent the formation of ferric hydroxide precipitate. 

Can you prevent (mask) ferric hydroxide precipitation by adding ligands known to complex the ferric ion ... 

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