| Ferrate (Ⅵ) has the properties of sterilization, oxidation, coagulation, absorption, and it is a kind of environment-friendly and multi-functional"green chemical reagent". Meanwhile, it has the prospect of application and development, especially in water treatment. The effects of operating conditions and ultrasound on the electrochemical oxidation process of iron to produce sodium ferrate were studied when using cast iron as anode in this thesis. Research works were primarily as follows:1. The effects of operating conditions on the production rate of ferrateThe effects of NaOH concentrations, current densities, temperatures and electrolytes on the production rate of ferrate were investigated when using cast iron as anode. It is found that:(1) The production rates of ferrate are faster at the beginning of electrochemical oxidation process and slower with increasing durations in the experimental conditions. For example, when the operating condition is T=40℃, j=50mA·cm-2 and in 14 mol·L-1NaOH solutions, r1=8.91 mmol·L-1·h-1 is observed at 15 minutes, and r1=3.15 mmol·L-1·h-1 is observed at 75 minutes, which is decreased by 64.6%.(2) The production rates of ferrate increase with increasing concentrations of NaOH solutions, current densities and temperatures. For example, when the duration of electrolysis is 30 minutes, the production rates of ferrate in 12 mol·L-1, 14 mol·L-1, 16 mol·L-1NaOH solutions are .80 mmol·L-1·h-1, 7.13 mmol·L-1·h-1, 7.80 mmol·L-1·h-1 respectively when T=40℃and j=50mA·cm-2. As far as the effects of current densities are concerned, the production rates of ferrate in 50 mA·cm-2,100 mA·cm-2,150 mA·cm-2 are 7.13 mmol·L-1·h-1, 12.33 mmol·L-1·h-1 and 16.02 mmol·L-1·h-1 respectively when T=40℃in 14 mol·L-1 solutions. Moreover, the production rates of ferrate in 30℃, 40℃and 50℃are 4.73 mmol·L-1·h-1,7.13 mmol·L-1·h-1 and 9.34 mmol·L-1·h-1 respectively when j=50mA·cm-2 in 14 mol·L-1 solutions.(3) The production rates for ferrate formation in NaOH solutions are faster than in KOH solutions under the same condition. For example, r1=7.13 mmol·L-1·h-1 is observed in NaOH solutions, but when in KOH solutions r1=2.42 mmol·L-1·h-1, which is decreased by 66.1%2. The effects of operating conditions on the instantaneous current efficiency during the electrochemical oxidation process of cast iron to produce ferrateThe effects of NaOH concentrations, current densities, temperatures and electrolytes were investigated on the instantaneous current efficiency of electrochemical oxidizing cast iron to ferrate. It is found that:(1) The instantaneous current efficiencies of electrochemical oxidizing cast iron to produce ferrate decrease with increasing durations in the operating conditions.(2) The instantaneous current efficiencies of the electrochemical oxidation process increase with increasing concentrations of NaOH solutions and temperatures, but decrease with increasing current densities.(3) The instantaneous current efficiencies of the electrochemical oxidation process in NaOH solutions are higher than in KOH solutions under the same condition. 3. The effects of ultrasound on the electrochemical oxidation process of cast iron to produce ferrateThe effects of ultrasound on the electrochemical oxidation process of cast iron to ferrate were studied when using cast iron as anode. It is found that:(1) The productions of ferrate and the instantaneous current efficiencies during the electrochemical oxidation process under sonicated condition are both more than under silent condition.(2) The ultrasound can influence the morphology of the electrode. It is due to the cavitation caused by the ultrasound, which can improve the mass transfer process between the electrode and the solution. On the other hand, the micro-stream generated by the collapse of bubbles can erode the surface of the electrode, renew the electrode interface and increase the reaction surface area, which results in the increment of the productions and instantaneous current efficiencies. |
PDF Full Text Request