Study On The Technique Of Preparing High Purity Potassium Ferrate(Ⅵ) By Electrolytic Method

The literatures on hand in relation to the methods of preparing ferrate( VI) especially by electrolysis are summarized in this paper. We found it a key to pay attention to the facts of current efficiency as well as relative ferrate concentration and simplifying the procedure of precipitation and purification so as to raise the technique level of preparing ferrate(VI) by the method of electrolysis.As for the method of preparing solid potassium ferrate from electrolytic synthesis of sodium ferrate solution, it is compared that the effects of the main procession facts of electrolysis upon both the anodic current efficiency and the relative concentration of Na2FeO4. One method was put forward to obtain high concentration of Na2pe04 in the high concentration of alkaline by quick electrolyzing iron anode. One simplified method was put forward to obtain high pure solid K2FeO4 by the way of studying the dissolving-precipitating rule of potassium ferrate. In addition, the properties of chemistry and physics such as composition, crystal shape, constructure characteristics of the said solid K2FeO4 was characterized by using the methods of chemical analysis, atomic adsorb spectrum(AAS),scanning electron microscope(SEM), powders X-ray diffraction(XRD),infrared spectrum(IR),thermal gravity adsorb(TGA),diverse thermal adsorb(DTA).The main conclusions follow as below.( I ) In the procession of preparing Na2FeO4 by electrolyzing and oxidizing anodic iron in the high concentration solution of NaOH, the current efficiency is directly proportional to both of the temperature and the alkaline concentration of the anolyte ,and the growth rate of the Na2FeO4 concentration of anolyte is directly proportional to both of the electrolyzing speed and the alkaline concentration of anolyte., The drop of current efficiency caused by the passive film on the iron anode can be prevented if periodically replacing electrolyte. The method of obtaining high concentration of Na2FeO4 solution by quick electrolysis mainly contains four aspects:adoption of either a diaphragm or an ionic membrane electrolytic cell in which a thin anodic cell lying between the two cathodes,(2)using an iron anode that has larger specific surface area,(3)keeping suitable concentration of NaOH in the anodic cell,adoption of lower current density and higher electrolyzing speed.The practical technique parameters follow as below: the NaOH solution of 14-16mol/L,the temperature of 303-308K,the surface anodic current density of 300A/m2,the unit electrolyzing speed of efficiency larger than 6.0A/L. The anolyte of Na2FeO4 in the concentration range from 0.32-0.48mol/L can be obtained by electrolyzing the iron anode during the time of 5-6h with an average current efficiency of 35% (6h) -49. 6% (3h). When using the method of periodically renewing electrolyte,the average current efficiency is 47.3%(II) The solubility of K2FeO4 in the solution of NaOH is higher than that of the same concentration of KOH solution and both of them become low with the growth of the alkaline concentration. The solubility of K2FeO4 in the mixed solution of KOH and NaOH was influenced by both of common ions effect and salting-out effect and the influence of common ions effect is more heavy. The rate of methanol's reacting with K2FeO4 is proportional to the content of water in the solid K2FeO4.The stability of the potassium ferrate solution is far below the solid. The existence of little water can cause the decomposition of K2FeO4 as following the procession of dissolving ?decomposition -redissolving-redecomposition.The method of obtaining high pure solid K2FeO4 by one procedure of precipitation and purification contains three aspects:Adoption of higher concentration solutions of Na2FeO4 and KOH. Both of them are added to the reactor by way in turn at lower temperature to control the over-saturation of K2FeO4,Adoption of the lower reaction temperature as well as suitable reaction time, Removing alkaline be done before disposing water and impurity in the purification procedure of K2FeO4 cake. Th...