Some structural characteristics of iron oxyhydrate obtained electrochemically

Abstract

Being technological processes, sorptton and copreclpitation are Important in chemical manufacturing plants. They also have an important bearing on the purification of natural water and mine water involving removal of organic and inorganic impurities by aluminum and iron oxyhydrates (hydroxides).At the Mining Institute, Siberian Branch, Academy of Sciences of the USSR comparative investigations have been performed on removal of finely dispersed organic and inorganic impurities by reagent coagulation and electrocoagulation. It has been experimentally established that iron hydroxide precipitates obtained electrochemically have very high adsorption properties. Table 1 gives an example of water purification; it will be seen that electrocoagulation treatment of water leads to more complete removal of both finely dispersed mechanical impurities and impurities of the salt type.The use of electrocoagulation in industry is so effective that in certain technological water preparation schemes for special technological purposes, distillation and the use of chemical reagents have been eliminated. However, the adsorption properties of the precipitates have been assessed largely from the difference between the initial and final impurity concentrations in the water;, the nature of the adsorption processes and the cause of the marked difference between the results of water processing by chemical and electrochemical procedures have therefore remained obscure.The sorption parameters of hydroxide precipitates depend primarily on their chemical nature and structure. A comparison of the structural properties of precipitates obtained by chemical and electrochemical procedures is therefore of considerable theoretical and practical Interest.Sorption systems involving hydroxide precipitates are extremely complex. On the one hand the indefinite structure of the precipitates at the moment of formation causes considerable difficulties in the investigation and consistent description of the phenomena occurring in these systems; on the other hand, in our opinion, in this indefiniteness we have a clue to the development of more effective inorganic sorbents.The structure of pure iron hydroxide precipitates obtained by chemical reactions has been fairly thoroughly investigated. For example, Glemser [1] assumes that the Fe203--H20 system may contain the four following modifications (forms): c~-FeOOH (goethite), ~-FeOOH, ~-FeOOH (lepidocrocite), and ferromagnetic 6-FeOOH. It is also known that the highest adsorptlvity is exhibited by hydroxide precipitates at the moment of their formation. Aging of precipitates, which is assumed to be a combination of sequential and independently parallel processes, depends on the aging time, the pH of the medium, the temperature, and, to a considerable degree, the presence of impurities which can retard or accelerate this process. Ryzhak et al., [2] showed that even freshly precipitated hydroxide, obtained by mixing 1 N solutions of FeC13 and NaOH, is already slightly crystallized after 10 min and consists predomi...

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