Research On The Technique Of The Direct Production Of Solid Potassium Ferrate By One-step Electrolysis

A new simple technique was presented for the direct production of solid potassium ferrate (K.2FeO4) by one-step electrolysis with high current efficiency and low cost in this thesis. An electrolysis cell was configured with two compartments separated by a membrane. The electrolyte was a concentrated solution of pure KOH. The anode was a material containing iron. A piece of nickel foam acted as the cathode. The solid K2FeO4 with the purity over 90wt% could be separated from the anolyte after electrolysis. The electrolyte could be successfully reused for further ferrate synthesis. No byproduct resulting pollution was produced in the process.Properly configuration of electrolyte cell and operating parameters were optimized to produce solid K2FeO4 rapidly. The effects of various operating parameters on the current efficiency of the ferrate production and the molar ratio of Fe(VI) to total Fe were studied systematically, such as electrolyte temperature, the kind and concentration of alkaline, ferrate stabilizer, apparent current density of anode etc. A feasible technique about the reuse of anolyte was discussed. The method was established removing water and alkaline from K2FeO4 separated from anolyte. The purification of the products were studied.The current efficiency increased obviously with rising electrolyte temperature. The effect of different solutes on the current efficiency of ferrate production varied apparently at different temperatures. For the solution of 16 M NaOH, the current efficiency increased and reached its maximum at 35 C, then decreased dramatically with increasing temperature, while the content of ferrate dropped remarkably and that of Fe(OH)3 increased. However, the case was not that at all for the solution of 16 M KOH. The current efficiency was so low at 25 C that no obvious solid K2FeO4 was observed. But it increased greatly with the increasing temperature higher than 35 C, while the molar ratio of Fe (VI) to total Fe in solid K2FeO4 decreased by only 2-5% and always retained a value over 0.9.The current efficiency did not change greatly with addition of complex ferrate stabilizer to anolyte at room temperature. When the temperature was higher than 45 C, the stabilizer could enhance the current efficiency by 15 percent approximately. The purity of solid K2FeO4 produced was higher with the addition of stabilizer than without it at all temperatures studied. The higher the concentration of KOH was, the higher the current efficiency was. The effect of concentration of KOH was slightly on purity of solid K2FeO4 and the molar ratio of Fe (VI) to total Fe in it. The current efficiency reached its maximum when the apparent anodic current density was at 50~70 A/m2. The purity of solid K2FeO4 and the molar ratio of Fe(VI) to total Fe dropped slightly with the increasing apparent anodic current density. Although a maximum of current efficiency appeared for ferrate formation with increasing concentration of KOH in mixed alkalinesolution of KOH and NaOH which was used as electrolyte, it was still lower than that in 16 M KOH. The purity of solid K2FeO4 and the molar ratio of Fe(VI) to total Fe both increased with concentration of KOH in mixed alkaline, but both of their maximums were lower than that of 16 M KOH. The solution of 16 M KOH was a more proper electrolyte than mixed alkaline of the same [OH"] whether current efficiency or purity of solid K2FeO4 was considered.The key to ensure the reuse of anolyte was removing ferric hydroxide from the anolyte which was produced by the decomposition of ferrate. It was indispensable to supply solid KOH to anolyte continually or in batches while operating for a long time. Solid K2FeO4 produced should be separated as quickly as possible from anolyte by filtration or centrifuge after electrolysis. It remained stable only by rapid removal of water and alkaline from it. Although methanol was considered to be the optimal reagent for the removal of alkaline, it was recommended strongly to use ethanol because of toxicity of methanol. The purity of solid K2FeO4 was...