Ferric hydroxide colloid

One of the earliest known chemical properties of ferric salts was their ready conversion to ferric hydroxide colloids in solutions. These solutions were intensively studied in the classic period of colloid chemistry, and their properties have been discussed in detail by Weiser (8). Since the focus of these studies was on colloid properties per se, precautions were taken to prepare pure colloids. Generally hydrolyzed solutions would be dialyzed extensively against distilled water to remove foreign ions. Even the purest preparations retained detectable concentrations of anions, consistent with a positive surface charge on the colloidal particles. 

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. 

It t as found that the flux decline, even at critical fouling conditions is completely avoided by addition of ferric chloride. For large dosages (100 mgL FeCh), an osmotic pressure builds up and this reduces flux reversibly. The positive ferric hydroxide colloids deposit on the membrane and their charge appears to govern rejection. Cation rejection increases considerably, while the rejection of organics decreases. This demonstrates that the deposit on a fouled membrane can change rejection characteristics. 

F. Esmadi, J. Simm, Sorption of cobalt(II) by amorphous ferric hydroxide . Colloids and Surfaces A Physicochemical and Engineering Aspects, 104 (2/3) (1995), pp. 265-270. 

In a study of the surface modification of poly(bisphenol A carbonate) by sul-fochromic acid, application of this approach to the Is/Ic intensity ratio led to a density of 4-10 sulphur atom cm, which was found unrealistic and lead to the conclusion that the polymer was attacked and that sulfate was incorporated over a certain depth. This pretreatment made the zeta potential of the material more negative. It increased the uptake of ferric hydroxide colloids in subsequent adsorption tests, which in turn made the zeta potential more positive. As a consequence the promotion of yeast cell adhesion by the ferric hydroxide treatment was less affected by drying. 

Very finely divided minerals may be difficult to purify by flotation since the particles may a ere to larger, undesired minerals—or vice versa, the fines may be an impurity to be removed. The latter is the case with Ii02 (anatase) impurity in kaolin clay [87]. In carrier flotation, a coarser, separable mineral is added that will selectively pick up the fines [88,89]. The added mineral may be in the form of a floe (ferric hydroxide), and the process is called adsorbing colloid flotation [90]. The fines may be aggregated to reduce their loss, as in the addition of oil to agglomerate coal fines [91]. 

Haywood and Riley [14] have described a spectrophotometric method for the determination of arsenic in seawater. Adsorption colloid flotation has been employed to separate phosphate and arsenate from seawater [15]. These two anions, in 500 ml filtered seawater, are brought to the surface in less than 5 min, by use of ferric hydroxide (added as 0.1 M FeC 2 ml) as collector, at pH 4, in the presence of sodium dodecyl sulfate [added as 0.05% ethanolic solution (4 ml)] and a stream of nitrogen (15 ml/minutes). The foam is then removed and phosphate and arsenate are determined spectrophotometrically [16]. Recoveries of arsenate and arsenite exceeding 90% were obtained by this procedure. 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

Uranium coprecipitated with aluminium phosphate, precipitate dissolved in nitric acid Adsorption onto colloidal ferric hydroxide... 

To the filtered seawater (500 ml about 1.5 xg U) is added 0.05 M ferric chloride (3 ml), the pH is adjusted to 6.7 0.1 and the uranium present as (U02(C03)3)4- is adsorbed on the colloidal ferric hydroxide which is floated to the surface as a stable froth by the addition of 0.05% ethanolic sodium dodecyl sulfate (2 ml) with an air-flow (about 10 ml min-1) through the mixture for 5 min. The froth is removed and dissolved in 12 M hydrochloric acid-16 M nitric acid (4 1) and the uranium is salted out with a solution of calcium nitrate containing EDTA, and determined spectrophotometrically at 555 nm by a modification of a Rhodamine B method. The average recovery of uranium is 82% co-adsorbed WO4- and M0O4- do not interfere. 

Crystallization of ferric hydroxide into spinel by adsorption onto colloidal magnetite. 

Fox, L.F. (1988) The solubility of colloidal ferric hydroxide and its relevance to iron concentrations in river water. Geochim. Cosmochim. Acta 52 771-777... 

Sugimoto, T., K Sakata, A. Muramatsu (1993) Formation mechanism of monodisperse pseudocubic a-Fe203 partides from condensed ferric hydroxide gel. J. Colloid Interface Sd. 159 372-382 Sugimoto, T. Khan, M.M. Muramatsu, A. Itoh, H. (1993) Formation mechanism of monodisperse peanut-type a-Fe203 particles from condensed ferric hydroxide gel. Colloids Surfaces A 79 233—247. 

If ferric hydroxide be prepared by the hydrolysis of ferric chloride the resulting colloid contains chlorine ions which can be replaced by more readily adsorbable picrate or eosinate ions leaving hydrochloric acid in solution. 

When water pH is <6, iron corrosion and the formation of corrosion products such as colloidal ferric hydroxide can result. Colloidal ferric hydroxide, however, is difficult to detect and difficult to remove through filtration. Fuel containing these particles appears bright and clear. Only about 1 micron in diameter, colloidal ferric hydroxide compounds can pass through fuel filters and deposit onto fuel system components. Further system corrosion can follow. 

Ferrous hydroxide can continue to react with water and oxygen to form colloidal ferric hydroxide ... 

Decarlo, E. H. Thomas, D. M. 1985. Removal of arsenic from geothermal fluids by adsorptive bubble flotation with colloidal ferric hydroxide. Environmental Science Technology, 19, 538-544. 

That the dissociation goes even farther is evident from the small bit of colloidal suspension of ferric hydroxide that is obtained by boiling a solution of FeCl3 (you can see the beam of scattered light even though the solution is perfectly clear). This results from the reaction... 

Vanadium pentoxide sols can be employed to bring about coagulation of positively charged colloids for example, ferric hydroxide and aluminium hydroxide. The amount necessary for the coagulation of a given quantity of the positive colloid is very small in comparison with the required quantities of arsenic trisulphide, antimony trisulphide, and other negative colloids. It appears, therefore, that the colloidal... 

Colloidal saccharated iron is sometimes used in place of ferric hydroxide as an antidote in arsenical poisoning, but its adsorptive capacity depends on the alkalinity of the medium.4 Thus a commercial preparation containing 0-75 per cent, of sodium hydroxide was found to adsorb 12-57 per cent, of arsenious oxide (reckoned on the amount of iron present) addition of alkali increased the adsorption until, with 1-28 per cent, of sodium hydroxide present, there was a maximum adsorption of 27 per cent. The addition of acid correspondingly diminished the adsorption. A gel of ferric magnesium hydroxide, if prepared without boiling, also adsorbs arsenic from sodium arsenite solutions.5... 

When a solution of ferric chloride is poured into a relatively large volume of boiling water, colloidal ferric hydruxide is furmed The ferric hydroxide sol does nol react with hydrogen sulfide nor with potassium hcxacyanoferralc(ll), and like all colloidal substances does nol pass readily through animal membranes or parchment. 

P roblem 3 How will you prepare the colloidal solutions of the following Arsenic sulphide, ferric hydroxide, gold, sulphur, silicic acid, carbon, iodine, mastic. (Meerut 2000)... 

Ferric hydroxide sol A colloidal solution of ferric hydroxide is obtained by adding a freshly prepared saturated solution of ferric chloride (2 or 3 ml) drop by drop to 500 ml of boiling distilled water. Ferric chloride hydrolyses to give a brown sol of ferric hydroxide sol. 

---