Iron hydroxide floccules

Regarding iron addition as described above, one important consideration is the removal of the iron ions (Fe or Fe ) in treated streams. These cation ions can easily be removed from treated water increasing the pH. This pH adjustment causes iron cation precipitation via the formation of iron hydroxide floccules. These floccules may entrap Ti02-suspended particles facilitating both iron cations and Ti02 removal from the treated water. 

The ferrous ions that dissolve from the anode combine with the hydroxide ions produced at the cathode to give an iron hydroxide precipitate. The active surface of ferrous hydroxide can absorb a number of organic compounds as well as heavy metals from the wastewater passing through the cell. The iron hydroxide and adsorbed substances are then removed by flocculation and filtration. The separation process was enhanced by the addition of a small quantity of an anionic polymer. 

Waste Treatment. Figure 2 outlines the current waste recovery and treatment processes, and proposed changes. Acid waste streams are sent through nitric acid and secondary plutonium recovery processes before being neutralized with potassium hydroxide and filtered. This stream and basic and laundry waste streams are sent to waste treatment. During waste treatment, the actinides in the aqueous waste are removed by three stages of hydroxide-iron carrier-flocculant precipitation. The filtrate solution is then evaporated to a solid with a spray dryer and the solids are cemented and sent to retrievable storage. 

Depending on whether dissolved oxygen is present or not, the products of precipitation by an iron salt are different. But in both cases, coprecipitation of iron hydroxide is required so that flocculation of FeS or S, (both of which are highly colloidal) can be controlled. 

The pH adjustment is most commonly achieved by calcium hydroxide (added as a slurry). Sodium-based reagents preclude the formation of gypsum but result in higher total dissolved-metals levels for the treated discharge water stream. The neutralization-precipitation stage is typically completed in a single process step, complemented with pre-aeration or direct aeration. Final clarification is achieved by flocculation and settling of the iron hydroxide precipitates. 

Esumi et al [68] used dispersions of a-alumina as well to study the interaction between anionic fluorocarbon and hydrocarbon surfactants. The anionic fluorocarbon surfactants used were LiFOS and NFIOO, the anionic hydrocarbon surfactants were SDS and LiDS, and the nonionic surfactant was NP7.5. Like the flocculation behavior of iron hydroxide, a low concentration of an anionic surfactant precipitates alumina. A further addition of a surfactant, different from the first one, forms mixed bilayers and redisperses alumina. Measurements of zeta potentials, the size of adlayers, and the amounts of adsorbed surfactants indicated that mixed bilayers consisting of anionic hydrocarbon-nonionic hydrocarbon surfactants or anionic fluorocarbon-nonionic hydrocarbon surfactants are formed preferentially to hydrocarbon-fluorocarbon surfactant bilayers. 

As the typical mechanical properties of flocculated systems are connected with the formation of coherent network structures, the concentration of the dispersed phase is evidently of great influence. If the concentration is low, flocculation will be the result of loss of stability. At higher concentrations, however, a gel or paste will be formed. In Table 3 data obtained by Freukblich are giyen, from which jt appears that an iron hydroxide sol is flocculated at a concentration of 0.5%, whereas at a concentration of 5% it sets to a thixotropic vide infra) gel. 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

Zrinyi, M. Kabai-Faix, M. Fuhor, S. Horkay, F. (1993) Sedimentation and gelation of flocculated iron (III) hydroxide sols. Langmuir 9 71-76... 

Inorganic Flocculating Agents. The inorganic flocculating agents are water-soluble salts of divalent or trivalent metals. For all practical purposes these metals are aluminum, iron, and calcium. The principal materials currently in use are aluminum sulfate, aluminum chloride hydroxide. 

Typically limit to 0.5 ppm total Fe maximum in the cooling water. Above this level, phosphonate can be used to control problems initiated by iron. However, if the total Fe rises to 3.0 ppm, adsorption of the phosphonate onto the iron takes place and a loss of inhibitor function can occur. Iron salts present a serious fouling risk in cooling systems. Dissolved iron quickly oxidizes (especially where chlorine, bromine, or other oxidizing biocides are used) and forms ferric oxide/hydroxide, which acts as a flocculant,... 

HC1, some of the iron oxides will generally dissolve quite easily. If the acid solution is then made alkaline, the iron converts to ferrous hydroxide [Fe(OH)3] and then precipitates as a brown, lightly flocculating sludge of hydrated ferric hydroxide [Fe(OH)2]. 

Coagulation processes in estuaries are affected by other factors such as clay composition, particle size, and concentration of dissolved organic matter, to mention a few. For example, early work has shown that metal hydroxides can flocculate from dis-solved/colloidal organic matter during the mixing of river-derived iron and seawater in the mixing zone of estuaries (Sholkovitz, 1976, 1978 Boyle et al, 1977 Mayer, 1982) (more details are provided on metal colloidal interactions in chapter 14). Surface sediments in... 

Wet Tests.—The presence of iron in solution may readily be detected by a considerable number of sensitive reactions. Thus ferrous iron gives a green precipitate of ferrous hydroxide upon addition of excess of ammonium hydroxide. With potassium ferricyanide and a trace of acid, a deep blue precipitate—Turnbull s blue—is obtained. With potassium ferrocyanide a white precipitate is obtained in the entire absence of any ferric salt. Ferric iron, on the other hand, is usually characterised by its deep yellow or brown colour. Addition of concentrated hydrochloric acid deepens the colour. With excess of ammonium hydroxide, brown flocculent ferric hydroxide is precipitated. With potassium ferrocyanide solution, a deep blue colour is obtained in acid solution, whilst with potassium ferricyanide there is no action. Potassium thiocyanate gives in acid solution a deep red colour, which is not d troyed by heat. Salicylic acid gives a violet colour, provided no free mineral acid is present. 

Chen, W. J., D. P. Lin, and 1. P. Hsu (1998). Contrihution of electrostatic interaction to the dynamic stability coefficient for coagulation-flocculation kinetics of beta-iron oxy-hydroxides in polyelectrolyte solutions. J. Chem. Eng. Japan. 31, 5, 722-733. 

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