【作者】 高杰；

【导师】 杨长春；

【作者基本信息】 郑州大学 ， 物理化学， 2004， 硕士

【摘要】 本论文提出一种一步电解法直接制备固体高铁酸钾的新工艺。用隔膜式电解槽，浓KOH溶液为电解液，泡沫镍为阴极，含铁电极为阳极。经一步电解可直接从阳极液中分离出纯度大于90wt％的固体高铁酸钾。生产过程中不产生任何污染环境的副产物，电解液可以循环使用，生产工艺比较简单，成本较低，电流效率较高。 通过筛选电解槽结构、隔膜材料、各工艺参数的组合，确定了快速电解制备固体K₂FeO₄的条件。比较系统研究了电解液温度、苛性碱的种类和浓度、稳定剂、阳极表观电流密度等工艺参数，对固体K₂FeO₄生成电流效率、纯度、其Fe（Ⅵ）／Fe（T）摩尔比等指标的影响。对阳极液循环使用的可行性，进行了初步探讨。确定了对从阳极液分离的K₂FeO₄滤饼的脱碱、脱水方法，及低含量固体K₂FeO₄的提纯方法。 升高温度对电流效率的提高非常显著，不同苛性碱阳极液受温度的影响差别较大。16 M NaOH电解液，随温度升高在35℃出现电流效率最大值，随后电流效率急剧下降。16 M KOH溶液则完全不同，25℃时几乎观察不到高铁酸钾固体的生成，电流效率极低，35℃以后电流效率则随着温度的升高明显增加。升高温度，由NaOH电解液所制备的Na₂FeO₄溶液中，Na₂FeO₄的浓度降低，Fe（OH）₃的含量增加。而由KOH电解液所制固体K₂FeO₄中的Fe（Ⅵ）／Fe（T）摩尔比，随温度的升高仅减小2～5％，且始终大于0.9。 室温下，阳极液中加入高铁酸盐复合稳定剂，对电流效率的影响不明显。温度高于45℃，稳定剂可以使电流效率增加15％左右。在所研究的温度范围内，阳极液加入稳定剂后所制固体K₂FeO₄的纯度，都要比不加稳定剂时的高。KOH电解液的浓度，对所制备固体K₂FeO₄的纯度及其Fe（Ⅵ），Fe（T）摩尔比的影响不大。电解液中KOH的浓度越高，电流效率也越高。在阳极表观电流密度为50～70A／m²时，固体K₂FeO₄的电流效率最高。 随着混合碱中KOH浓度的改变，电流效率有一最大值，但这一最大值仍不如16 mol／L的KOH溶液做电解液时电流效率高。随着混合碱中KOH浓度的增加，所生成固体K₂FeO₄的纯度及其Fe（Ⅵ）／Fe（T）摩尔比都在增加，但是二者的最大值仍不如16 mol／L的KOH溶液做电解液时高。无论从电流效率还是从产品的一步电解法直接制备固体高铁酸钾工艺研究纯度来考虑，16 mol几的KOH溶液都优于OH一浓度为16 mol/L的混合碱。 保证阳极液能够循环使用的关键是除去其中的低价铁杂质。当电解时间较长时，应间歇或连续地向阳极液补加KOH固体。电解结束后，阳极液中的固体KZFeO;应立即过滤或离心分离出来，并及时脱水脱碱方能稳定存在。用甲醇脱碱效果最好，但考虑到甲醇的毒性，最好选用乙醇做脱碱溶剂。从阳极液中分离出的固态电解产物，只经脱水、脱碱处理，不经任何纯化处理，丸FeO4的含量不少于gowt%，将所制产品利用重结晶进行提纯，可得纯度为97.6%的凡FeO4晶体。 SEM结果表明，电解前的铁电极表面状态比较均匀，电解8h后电极的表面变得凹凸不平，这种不均匀的表面导致电极电位变化，影响槽电压，进而影响电能效率。直接电解所制KZFeO4单晶的X一射线面探衍射仪测定结果表明，KZFeO4晶体属正交晶系，空间群为Pnma;固态KZFeo;中的Feo户具有轻微畸变的四面体结构。KZFeo;的结构单元中四个铁氧键的键长分别是1 .644（6）A，1.651（4）A，1.651（4）A，1.657（5）A。计算密度为De一2.loZMg/m3。 用SEM照片给出了高铁酸钾晶体的外形应为长而薄的板条状，而不是棒状或针状。KZFeO;的粉末XRD图谱显示，直接电解所制KZFeO4固体比复分解法所制KZFe认固体与JCPDS中的标准更接近。直接电解所制凡Fe04固体的优势生长晶面及其结晶度与化学法所制的KZFeO;固体有所不同，表现在部分衍射峰的出现和强度有所不同。更多还原

【Abstract】 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更多还原