Colloidal solution of iron

Konradova V. 1968. The ultrastructure of the tracheal epithelium in rabbits following inhalation of aerosols of colloidal solutions of heavy metals. II. Signs of cell alteration in the epithelium after 8 hour inhalation of colloidal solutions of iron and silver. Folia Morphol (Praha) 16 265-271. 

The mixture is loaded out of the reactor into tank 16 to distil tetraethyllead. The tank should already be filled with ground sulfure and ferric iron chloride. Iron chloride reduces the alkalinity of the dross and improves its consistency due to the formation of the colloid solution of iron hydroxide ground sulfure is uniformly distributed through the dross, also improving its consistency and preventing clotting of lead particles. 

Colloidal solutions of iron in ether have been obtained 3 by allowing sparks to pass between iron wire clippings immersed in that liquid and connected up with an induction coil. 

The results obtained in studying colloidal forms of transport are less certain and not always reproducible. Therefore special experimental investigations of the stability of colloidal solutions of iron, silica, and mixtures of the two were conducted in conditions as close as possible to nature, in addition to summarizing and critically examining published data. 

Colloidal solutions of iron are fairly stable, are easily obtained in laboratory conditions, and play a large part in the migration of this element in the supergene zone (Strakhov, 1960). Compounds of trivalent iron, mainly the hydroxide, usually form colloidal solutions colloids are not typical of the more soluble compounds of divalent iron. 

Structure of colloids of iron hydroxide. Colloidal solutions of iron hydroxide usually are obtained experimentally by hydrolysis of a ferric chloride solution. The particles that are formed consist of molecules of Fe(OH)3, which constitute the insoluble nucleus—the main mass of the micelle. The number of molecules in the nucleus is not constant and may range from tens to 500. 

Obtaining colloids of iron hydroxide. Stable colloidal solutions of iron are obtained only under certain conditions, a slight change in which leads to coagulation. Thus, when a ferric chloride solution is neutralized by an alkali according to the reaction ... 

In laboratory conditions hydrolysis usually is carried out as follows a solution of FeClj is added drop by drop to distilled water heated to boiling, stirring constantly. The whole liquid quickly takes on the red-brown color characteristic of hydrous ferric oxide, but remains transparent. If the solution is allowed to cool, the color fades somewhat, as some of the Fe(OH)3 changes back into FeCl3. To prevent the reverse reaction, the solution is boiled for a few minutes to remove HCl with water vapor, or it is removed by dialysis. In this way one obtains stable colloidal solutions of iron hydroxide containing from 5 to 5000 mg/1 of iron. 

At room temperature colloidal solutions of iron hydroxide can be obtained only by way of prolonged dialysis (Glazman et al., 1958). And finally, experiments are known in which sols were obtained by peptization, by treating freshly precipitated, washed Fe(OH)3 sediment with ferric chloride while heating. A dilute solution with a certain amount of HCl acts on freshly precipitated Fe(OH)3 as ferric chloride does. The sols of Fe(OH)3 obtained by peptization are no different in structure from the sols obtained by hydrolysis. 

Fig. 48. Stability of colloidal solutions of iron hydroxide of various concentrations (mg/1) as a function of pH.

Carbon dioxide has no essential effect on the stability of iron hydroxide colloids toward the action of electrolytes. The coagulation thresholds (concentrations of MgS04) prove to be the same for colloidal solutions of iron saturated with carbon dioxide (- co, bar) as for solutions in the air. 

Fig. 52. Coagulation of mixed colloidal solutions of iron and silica. Environment A—slightly acid B—slightly alkaline. Concentration of recent waters indicated at right. / = total precipitation of iron and silica with formation of banded sediments // = same, with formation of mixed sediments /// = total precipitation of iron and partial of silica / F= total precipitation of iron, silica in solution V = incomplete precipitation of iron, silica in solution VI— no precipitation observed.

Thus regardless of their origin, colloidal solutions of iron could hardly have accomplished the transport of a substantial amount of ore material. Coagulation of ferric iron colloids, even those stabilized by colloidal silica, already had occurred to a substantial extent in near-shore zones or even in rivers, under the influence of a relatively small increase in concentration of electrolytes. 

If a neutral solution of iron(III) chloride is added to a freshly prepared, saturated solution of hydrogen sulphide, a bluish colouration appears first, followed by the precipitation of sulphur. The blue colour is due to a colloid solution of sulphur of extremely small particle size. This reaction can be used to test the freshness of hydrogen sulphide solutions. 

Obtaining colloids of silica. The main laboratory methods of obtaining colloidal solutions of silica are condensational and come down to hydrolysis of soluble salts. The difference between obtaining colloids of Fe(OH)3 and Si02 is in the properties of the solutions of the original salts an acid reaction for iron and alkaline for silica. 

Colloidal iron consists mainly of colloidal solutions of hydroxides and phosphates of Fe (Fe, " 7 ) and colloidal solutions of the enumerated organic compounds (Fe , ). Direct determination of colloidal iron in sea waters is difficult and usually dissolved iron means the sum of Fe j + Fe. , . 

Our experiments also established that the process of aging of freshly precipitated iron hydroxides does not proceed in the same way in sediments obtained from ionic and colloidal solutions of Fe. Whereas colloidal sediments remain X-ray-amorphous for a long time, sediments from ionic solutions relatively rapidly acquire a crystal structure which is most clearly manifested in alkaline, is less ordered in acid, and almost X-ray-amorphous in neutral environments. 

Fig. 53. Dependence of second moments of PMR lines on pH of the solution (a) and on the age (b) of iron hydroxides. I = precipitates from true solutions of FeClj, age 7 months 2 = precipitates from true solutions of FeCli, age 1 month 3 = precipitates from true solutions of FeCl, freshly prepared f = precipitates from colloidal solutions of FefOH), freshly prepared 5 = precipitates from true solutions of FeCl3, pH = 10-11 (Mel nik et al., 1973).

Ionic solutions of Fe, which are stable at very low pH values, could not have formed in the weathered layer. Thus no colloidal solutions of ferric iron could have appeared. 

When thermal volcanic waters react with aerated surface waters, the appearance of ferric iron colloids is quite permissible. However, there are no organic compounds of fulvic acid t)q)e in volcanic waters and only colloidal silica could act as a stabilizer. At the same time there often is sulfur in thermal solutions, the stable form of which in the presence of free oxygen is the S04 ion—the main coagulant of colloidal iron. For this reason the possibilities of colloidal transport of iron from volcanic sources to sedimentary basins are limited. A high COj content in the hydrosphere and atmosphere does not exert a stabilizing effect on Fe(OH)3 colloids. 

Atoms on the surface of a colloidal particle are bonded only to other atoms of the particle on and below the surface. These atoms interact with whatever comes in contact with the surface. Colloidal particles often adsorb ions or other charged particles, as well as gases and liquids. The process of adsorption involves adhesion of any such species onto the surfaces of particles. For example, a bright red sol (solid dispersed in liquid) is formed by mixing hot water with a concentrated aqueous solution of iron(III) chloride (Figure 14-19). 

Iron dextran injection (INFED, DEXFERRUM) is a colloidal solution of ferric oxyhydroxide com-plexed with polymerized dextran (molecular weight -ISO IcDa) that contains 50 mg/mL of elemental iron. It can be administered by either intravenous (preferred) or intramuscular injection. When given by deep intramuscular injection, it is gradually mobilized via the lymphatics and transported to reticuloendothelial cells the iron then is released from the dextran complex. Intravenous administration gives a more reliable response. Given intravenously in a dose of less than 500 mg, the iron dextran complex is cleared with a plasma tj of 6 hours. When I g or more is administered intravenously as total dose therapy, reticuloendothelial cell clearance is constant at 10-20 mg/h. This slow rate of clearance results in a brownish discoloration of the plasma for several days and an elevation of the serum iron for 1-2 weeks. 

A similar study was conducted by Dimitrijevi6 et al. with neutral solutions of a-Fe203. The yield of Fe was found to be very low. However, a large Fe yield was found after dissolution of the colloid by hydrochloric acid under an argon atmosphere. This showed that electrons donated by the free radicals penetrated deep into the colloidal particles to reduce iron to F, . Buxton et al. observol in a study on the reductive dissolution of colloidal Fe304 that Fe ions in this material are less readily released into the aqueous phase than reduced Fe ions. 

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